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Research Article
Eco-friendly Flame-Retardant Cellulose Nanofibril Aerogels by Incorporating Sodium BicarbonateClick to copy article linkArticle link copied!
- Muhammad FarooqMuhammad FarooqSchool of Chemical Engineering, Department of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, FI-00076, Aalto, FinlandMore by Muhammad Farooq
- Mika H. SipponenMika H. SipponenSchool of Chemical Engineering, Department of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, FI-00076, Aalto, FinlandMore by Mika H. Sipponen
- Ari SeppäläAri SeppäläSchool of Engineering, Department of Mechanical Engineering, Thermodynamics and Combustion Technology, Aalto University, P.O. Box 16300, FI-00076, Aalto, FinlandMore by Ari Seppälä
- Monika Österberg*Monika Österberg*E-mail: [email protected]. Tel: +358505497218.School of Chemical Engineering, Department of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, FI-00076, Aalto, FinlandMore by Monika Österberg
Abstract
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Cellulose nanofiber (CNF) aerogels offer excellent thermal insulation properties, but high flammability restricts their application. In this study, CNF aerogels were prepared by incorporating sodium bicarbonate (SBC), which effectively improved the fire retardancy without compromising the thermal conductivity of the aerogels, which was only 28 mW m–1 K–1. The minimum burning velocity of flame-retardant aerogels was 0.20 cm s–1 at 40 wt % of SBC, which is significantly lower compared to 5.84 cm s–1 of pure CNF aerogels. At the threshold concentration of 20 wt % SBC, the flame-retardant aerogel demonstrated flameless pyrolysis along with enhanced char formation. SBC additionally provides control over the microporosity and morphology, due to the concentration-dependent formation of lamellar layers during the preparation of aerogels. Overall, this work describes an efficient method for preparing flame-retardant CNF aerogels that could lay the foundation for next-generation bio-based insulation materials.
Copyright © 2018 American Chemical Society
1. Introduction
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The development of next-generation bio-based insulation materials is driven by the current environmental strive for sustainability, eco-efficiency, and industrial ecology. (1−3) Within this realm, efficient utilization of renewable lignocellulose resources holds potential for the development of green products as alternatives to petroleum and mineral-based materials. (3,4) Cellulose nanofibrils (CNF) have gained renewed interest among the research community in the last two decades. (5) CNF aerogels offer impressive properties such as low thermal conductivity, (6) low thermal expansion, (7) high strength and elastic modulus, (8) biocompatibility, and sustainability. (9) However, flammability (10) is one of the main drawbacks of aerogels fabricated from CNF, which hinders their use in this application. To meet the strict safety requirements, a considerable improvement in the flame retardancy is mandatory without compromising the insulation properties and thermal and mechanical stabilities. (11) It is these properties in combination with their microstructure that make CNF aerogels competitive candidates as effective heat insulators for buildings, domestic appliances, refrigeration equipment, and the automotive sector. (12)
The majority of commercially available flame retardants used in thermal insulation are fossil oil-based, chemically modified organophosphorous, organonitrogen, and halogenated organic compounds. (13) Especially the latter are highly effective in suppressing flammability, but their harmful impact on the environment and the risk to human health have caused a decline in their acceptance in general and led to legislative restrictions on their use since 2004. (14,15) Therefore, it is necessary to employ green chemistry principles to develop new environmentally friendly flame-retardant materials.
Han et al. (16) produced flame-retardant aerogels by in situ synthesis of magnesium hydroxide nanoparticles in cellulose gelled in alkaline urea solution. Resulting aerogels exhibited self-extinguishing behavior within 40 s. However, these composite aerogels exhibited increased thermal conductivity from 56 to 81 mW m–1 K–1 upon higher loading of magnesium hydroxide nanoparticles. A similar approach has recently been adopted by He et al. (17) to prepare cellulose-based composite aerogels with improved flame retardancy by utilizing aluminum hydroxide nanoparticles. Wicklein et al. (18) impregnated a CNF suspension with graphene oxide and clay mineral sepiolite nanorods. Upon freeze-drying, strong anisotropic aerogels were produced, which resisted combustion and exhibited a low thermal conductivity of 15 mW m–1 K–1. Nonetheless, the required use of corrosive acids and oxidants challenges the large-scale production of graphene oxide. (19)
Li and Wang (12) coupled polymerization of dopamine and hydrolysis of organosilicon in CNF suspension followed by freeze-drying. The formed aerogels showed self-extinguishing characteristics, but at the trade-off of increased thermal conductivity values. By utilizing the layer-by-layer technique, Köklükaya et al. (20) deposited cationic chitosan, anionic poly(vinylphosphonic acid), and anionic montmorillonite clay on CNF aerogels. The aerogel coated with five quad layers demonstrated self-extinguishing behavior in a flame test, but the complex fabrication route is the major drawback of this concept. More recently, Yuan and Zhang (21) prepared composite aerogels by in situ formation of silica nanoparticles in cellulose gel. Supercritical CO2 drying was employed to obtain highly porous flame-retardant aerogels. However, the tetraethoxysilane precursor used in that study has been linked to kidney and nasal mucosa damage. (22,23)
In the present article, we present the preparation of flame-retardant aerogels by freeze-drying a colloidal suspension of CNF in the presence of sodium bicarbonate (SBC) at different concentrations. Our results show that thermal decomposition of sodium bicarbonate to nontoxic gases not only contributes beneficially to the flame-retardant properties, but also offers control over the microporosity of the resulting aerogel.
2. Experimental Section
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2.1. Materials
Sodium bicarbonate (SBC) was obtained from ICN Biomedicals Inc. (Ohio). Poly(vinyl alcohol) (PVA) of MW 22 kDa was acquired from Fluka Chemie AG. All chemicals were of analytical grade and used without further purification. Nanofibrillated cellulose was produced from hardwood kraft pulp. The pulp was thoroughly washed into sodium form to remove extra electrolytes and control the counterion form. (24) Fibrillation was performed using the microfluidization process with M-110P processor (Microfluidics, Newton, MA). The pulp was passed one time through chambers of diameters 400 and 200 μm and six times through chambers of diameters 400 and 100 μm at a pressure of 2000 bar. (8) The charge density of the pulp used for the preparation of CNF was 0.065 milliequiv g–1, and the ζ-potential value of the corresponding CNF suspension was −3 mV. (8)
2.2. Preparation of Aerogels
Flame-retardant CNF aerogels were prepared by the freeze-drying procedure. A schematic illustration of the fabrication procedure is presented in Figure 1. Suspensions of CNF 0.5% by weight were conditioned with sodium bicarbonate at four different weight percentages: 10, 20, 30, and 40% relative to the resulting dry content of the entire mixture. SBC was dispersed in CNF suspension using an IKA ULTRA-TURRAX disperser at 10 000 rpm for 10 min. The mixture was kept at 100 °C for 60 min and freeze-dried to form aerogels. During exploratory research, it was found that flame-retardant aerogels without heat treatment (100 °C for 60 min) demonstrate poor mechanical stability. However, the aerogel structure becomes mechanically stable after the heat treatment. Pure CNF aerogel was produced using the abovementioned procedure without the inclusion of sodium bicarbonate. Flame-retardant aerogel samples were coded according to their weight percentage SBC content as C-SB10, C-SB20, C-SB30, and C-SB40. Pure CNF was used to prepare the reference aerogel, marked as CNF.
Figure 1
Figure 1. Schematics of the flame-retardant aerogel fabrication procedure and proposed fibrillar structure at each stage.
2.3. Morphological Characterization
Structural analysis of CNF aerogels was performed using a JEOL JSM-7500FA analytical field emission scanning electron microscope. Aerogel surfaces and cross sections were sputter-coated with gold/palladium. A secondary electron detector was used for capturing images at 1.5 kV. Field emission scanning electron microscopy (FESEM) images were analyzed using the image analysis software FIJI ImageJ (Research Services Branch, NIH, Bethesda, Maryland). (25)
Cylindrical CNF aerogel samples of 10 mm diameter and 10 mm length were analyzed by X-ray microtomography (MicroCT). Tomographic radiographs were acquired with Bruker SkyScan 1272 (Kontich, Belgium) at a source voltage of 30 kV, a current of 212 μA, and a pixel size of 14.998 μm. Exposure time for each projection was set to 212 ms at a rotation step of 0.4°, along with frame averaging of 5. At least 550 projections, as a stack of 1024 × 1024 grayscale bitmap images, containing 16-bit unsigned data were recorded for each sample. A built-in SkyScan program NRecon (Bruker-MicroCT, Kontich, Belgium), which implements the Feldkamp algorithm, was employed for the reconstruction of topography projection images. Three-dimensional (3D) volume rendering and further image processing were performed using the ImageJ software. (25)
2.4. Image Analysis
A total of 300 grayscale MicroCT images for each CNF aerogel were stacked and cropped into 400 × 400 pixel square images in ImageJ. The cropped image stacks were subjected to image thresholding by Otsu’s method, (26) which produced a stack of binary images, in which fibril layers and void spaces correspond to white and black areas, respectively.
2.5. Porosity and Pore Size Measurement
The apparent porosity of the pure CNF and flame-retardant aerogels was determined by dividing the total number of void voxels by the sum of black and white voxels present in an image.
The mean apparent porosity of pure and flame-retardant CNF aerogels was calculated from the whole stack of 300-segmented two-dimensional (2D) images. Pore size distribution is a critical parameter of porous structures. Five segmented 2D binary images (slices) from the stack of 300 slices were randomly chosen and subjected to the default particle analyzer algorithm to determine the pore size distribution. To evaluate the length of the fibril layers, ridge detection (27) was utilized. The slope method was used at default parameters. Five random segmented 2D binary slices from the stack of 300 were randomly selected for the analysis and mean values were calculated. For comparison, the porosity of the aerogels was also determined by relating the experimental density of the obtained aerogels to the theoretical density of aerogels with 0–40 wt % of sodium bicarbonate. The dimensions used in the calculation of the experimental densities of cylindrical aerogels were 16 mm (height) and 12.3 mm (diameter).
(1)
2.6. Chemical Composition
The chemical structure of pure and modified CNF aerogels was analyzed by Fourier transform infrared (FTIR) spectroscopy (Nicolet 380 FTIR Spectrometer by Thermo Fisher Scientific) with 2 cm–1 resolution at room temperature. A total of 30 scans within the range of 400–4000 cm–1 were recorded for each sample. Spectra were adjusted by automatic baseline correction using the built-in OMNIC FTIR software and were normalized relative to the band at 1150 cm–1.
2.7. Thermal Characterization
The thermal properties of pure CNF and modified CNF aerogels were determined using a thermogravimetric analyzer (TA Instruments Q500). Samples were heated from 25 to 600 °C at a heating rate of 10 °C min–1 under nitrogen atmosphere at a flow rate of 20 mL min–1. Thermal conductivities (λ) were measured using a C-Therm thermal conductivity analyzer (C-Therm TCi) by a modified transient source plane technique. Cylindrical samples (diameter ∼ 25 mm, height ∼ 7 mm) of pure CNF and flame-retardant CNF aerogels at four different concentrations of SBC were prepared. Three samples of each aerogel (9 mg) were measured at 24 °C from the top and bottom surfaces.
2.8. Flammability Test
The flammability of pure and modified CNF aerogels was tested by igniting the aerogels using a butane burner in a horizontal configuration as described in UL-94 standard. Cylindrical aerogel samples of 1.3 cm × 6 cm were held in the horizontal position using metal clamps and ignited endwise. This horizontal flame test was repeated three times. The whole combustion process was recorded by a digital camera, and the combustion velocity was measured at 10 s.
2.9. Polymer and Moisture Absorption
Aerogel sections (1.5 cm) were soaked in 15 wt % aqueous poly(vinyl alcohol) (PVA) solution until saturation absorption. Absorption capacity was calculated as the ratio of weight increase to the initial weight. Moisture absorption was evaluated by exposing aerogel sections (1.5 cm) to 80% relative humidity for 48 h. Moisture uptake was determined from the weight gain relative to the weight of aerogels that were preconditioned at 50% relative humidity.
3. Results and Discussion
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3.1. Flame-Retarding Properties of SBC–CNF Aerogels
CNF aerogels were prepared using sodium bicarbonate as a green flame-retarding agent. The flame-retarding performance of pure and SBC-containing CNF aerogels was determined by a horizontal combustion test (Figure 2b). Pure CNF aerogels ignited extremely quickly and engulfed in flames in <1 s. The average combustion velocity of pure CNF aerogel was 5.84 cm s–1. In contrast, SBC–CNF aerogels exhibited a distinctly lower burning rate. Already 10 wt % of SBC (C-SB10) had a considerable flame-retarding effect compared to the pure CNF aerogel. The burning velocity of C-SB10 was 0.33 cm s–1 along with a self-extinguishing behavior after 5 s of initial burning. The slow, flameless combustion partially consumed the sample, leaving behind a partly preserved aerogel and a charred residue. At higher concentrations of SBC, the flame-retardant aerogels (C-SB20, C-SB30, and C-SB40) self-extinguished as the flame source was removed. A further decrease in the combustion velocity was also observed; however, after 10 s of burning, the combustion velocity did not change notably among C-SB20, C-SB30, and C-SB40 samples. Combustion velocity data and the burning behavior revealed that the aerogel at 20 wt % SBC shows optimum flame-retarding properties in terms of self-extinguishing behavior and pyrolysis (Figure 2c). Overall, the incorporation of SBC efficiently circumvents the flammability of CNF aerogels, which was probably due to the release of carbon dioxide and water upon heat-induced decomposition. To further confirm this hypothesis, the physical, chemical, and thermal properties of the aerogels were determined more in detail.
Figure 2
Figure 2. Horizontal flame test of pure CNF aerogel and flame-retardant CNF aerogels containing 10–40 wt % sodium bicarbonate. (a) Combustion velocities determined from the videos recorded during the flame test. Still images of the aerogels (b) before combustion and (c) after 10 s combustion, except for pure CNF where the still image is taken after 2 s of combustion.
3.2. Morphology and Chemical Structure of the Aerogels
Porosity is an important feature of an aerogel structure since it determines the effective volume of air in the matrix. X-ray MicroCT and image processing were used to evaluate the apparent porosity values. X-ray MicroCT has a limited spatial resolution, which hinders its ability to capture the whole range of pore sizes in a sample volume. However, we found that the porosity values obtained from MicroCT imaging are useful for explaining observations on morphological differences between the flame-retardant aerogel samples.
The effect of SBC addition on the apparent porosity is illustrated in Figure 3a. Apparent porosity increased from 74% of pure CNF aerogel to 84% when the SBC concentration was 10 wt %. Further increase in the SBC concentration showed only a minor influence on the apparent porosity, and the maximum value of 87% was obtained at 30 wt % SBC. The apparent porosity of pure CNF aerogel is lower than the reported density-based porosities (28,18) of CNF aerogels prepared using the freeze-drying procedure. However, density-based porosities for all of our aerogels shown in the Supporting Information Table S2 were >99.5%, in agreement with published data. (18) The deviation between apparent and density-based porosities is therefore anticipated to result from macroscale changes due to the heating step during the aerogel preparation, which would promote the aggregation of nanofibrils, thus causing layer formation and reduction in the apparent porosity.
Figure 3
Figure 3. Effect of sodium bicarbonate on the morphology of CNF aerogels. (a) Apparent porosity and (b) mean pore diameter and mean fibril layer length. Values of apparent porosity, pore diameter, and mean fibril length were obtained from image analysis of MicroCT data.
The pure CNF aerogel had the lowest average pore diameter of 181 μm, whereas among the flame-retardant CNF aerogels, C-SB20 exhibited the highest average pore diameter of 419 μm (Figure 3b.) Furthermore, SBC had a disruptive effect on the fibril layers, decreasing the fibril layer length from 615 μm in the pure CNF to 494 μm in C-SB20 and further to 319 μm in C-SB30 (Figure 3b). These observations were supported by the FESEM image analysis and volumetric rendering of MicroCT data (Figure 4).
Figure 4
Figure 4. Morphological appearance of pure CNF aerogel and SBC-containing aerogels. (a–c) Pure CNF aerogel, (d–f) C-SB10, and (g–i) C-SB30. (b, e, h) 3D volumetric rendering from MicroCT data. (a, d, g) and (c, f, i) FESEM images in radial and axial directions, respectively. (j) Aerogel sample sketch detailing cross-section and radial and axial directions.
Pure CNF aerogel contained an organized fibril layer structure, which converges toward the center of the aerogel (Figure 4a). Fibrils are highly interconnected, hence causing a dense aerogel structure. The outer surface of pure CNF aerogel exhibited a smooth 2D sheetlike structure (Figure 4c) with a few pores present on the surface. Important differences compared to the pure CNF aerogel were observed already at the lowest sodium bicarbonate dosing. The smooth outer surface of the pure CNF aerogel became disrupted in C-SB10 aerogel due to the emergence of large pores of diameter 356 μm (Figure 4f). The radial micrograph (Figure 4d) also depicted dissimilarities in terms of surface and pore morphology with respect to pure CNF aerogel (Figure 4a). C-SB30 exhibited a honeycomb-like structure in the radial direction (Figure 4g), forming a cellular structure with a wall thickness of approximately 3–5 μm. The outer surface of C-SB30 (Figure 4i) displayed a disrupted fibril layer structure with a smaller pore diameter compared to C-SB10. At the highest concentration of SBC (C-SB40), the aerogel structure collapsed, forming a microstructure composed of smaller pores with a pore diameter of 330 μm (Supporting Information Figure S1). Importantly, regardless of such high loading of SBC, the connectivity of the fibril layer structure was still preserved, maintaining physical integrity of the aerogel.
During the freeze-drying process, cellulose nanofibrils align laterally and form layer structures of varying lengths due to the diffusion forces or interfibrillar hydrogen bonding. (29) The SBC content played a decisive role in the resulting morphology of aerogels. Partial decomposition of sodium bicarbonate resulting in the formation of carbon dioxide and the presence of sodium carbonate or bicarbonate crystals near cellulose nanofibrils may have hindered the interfibrillar attraction, hence causing disruption of the fibril layer structure. This likely explains the aforementioned differences observed in the apparent porosity and surface morphology of the CNF aerogels (Figure 3).
FTIR spectroscopy was used to determine the presence of sodium bicarbonate and sodium carbonate residues and their possible interaction with cellulose within the aerogels. Typical absorptions of the cellulose backbone (30) (υO–H 3340 cm–1, υC–H 2904 cm–1, 1429 cm–1, υH–O–H 1641 cm–1, υC–C 1160 cm–1, υC–O–C 1054 cm–1, υβ-linkage 896 cm–1) were observed (Figure 5).
Figure 5
Figure 5. FTIR spectra of pure and flame-retardant CNF aerogels.
In the wavelength region of 2000–4000 cm–1, the normalized spectra of pure CNF and modified aerogels exhibited similar characteristic bands; however, at lower wavenumbers, a new absorption band at 833 cm–1 emerged in the spectra of the SBC-containing aerogels. This band is associated with the CO2 bending vibrations present in NaHCO3. (31) The height of this band increased with increasing concentration of SBC (Supporting Information Figure S2). Furthermore, three consecutive bands at 1619, 1660, and 1695 cm–1 in the IR spectra of C-SB40 were assigned to the CO2 out-of-phase stretching in sodium bicarbonate. (31) The emergence of new absorption bands confirmed the expected presence of SBC in the flame-retardant aerogels. The products of thermal decomposition of SBC are sodium carbonate, water, and carbon dioxide; however, no characteristic signal was observed for sodium carbonate. Furthermore, the comparison of theoretical and calculated SBC content in the flame retardant aerogels indicated only limited decomposition in the heating stage prior to aerogel formation (Supporting Information Figure S5).
3.3. Thermal Properties of Flame-Retardant CNF Aerogels
Considering the heat insulation application, thermal stability of flame-retardant aerogels is of great importance. (26) Thermal analysis can also assist in understanding the mechanisms of fire resistance. Thermal analyses were performed in nitrogen atmosphere over the temperature range of 25–600 °C. Addition of SBC in flame-retardant aerogels caused multiple changes in their thermal characteristics compared to those of pure CNF aerogel (Figure 6). The major decomposition peak of flame-retardant aerogels shifted toward lower temperatures and the decomposition peak became less pronounced, which support the argument that sodium bicarbonate is an effective flame retardant.
Figure 6
Figure 6. Thermogravimetric analysis (TGA) (a) and derivative thermogravimetry (DTG) (b) curves of sodium bicarbonate, pure CNF aerogel, and flame-retardant CNF aerogels.
The TGA image of pure CNF aerogel consisted of a single cellulose decomposition (32) phase in the temperature range of 306–359 °C, whereas the major decomposition peak for C-SB10 shifted toward lower temperatures with an onset temperature of 277 °C. At the highest concentration of SBC, the C-SB40 aerogel exhibited an onset temperature of 223 °C and maximum decomposition at 262 °C. These changes likely result from the decomposition of sodium bicarbonate, as also indicated by the emergence of a new peak at 115–121 °C in the DTG images of C-SB20, C-SB30, and C-SB40 (Figure 6b). The amount of residue generated by C-SB40 is 36%, which is 19% more than that of the pure CNF aerogel. Sodium bicarbonate exhibited a single decomposition peak with an onset temperature of 144 °C. To assess possible decomposition of sodium bicarbonate during the heating stage of aerogel preparation, the remaining SBC content was determined from the TGA data at 200 °C and compared to the theoretical input values (Supporting Information Table S4 and Figure S5). The data showed that the theoretical and quantified SBC contents were essentially similar, indicating insignificant losses of SBC. The amount of residue generated during pure sodium bicarbonate decomposition is 63%, which explains the higher residue in flame-retardant aerogels. Flame-retardant aerogels displayed multiple peaks in DTG curves. It is considered that the multiple peaks displayed by the flame-retardant aerogels represent the exothermic changes during the decomposition and gas liberation process. (33) Values of the onset decomposition temperature (Ton), the temperature at the maximum degradation rate (Td), weight loss at each stage, and residue for pure and flame-retardant aerogel samples are tabulated in Supporting Information Table S1. The presence of sodium bicarbonate works as a green flame retardant in two separate ways. First, it absorbs heat to decompose, and once decomposed, it liberates carbon dioxide and water. The CO2 deprives the supply of oxygen required during the burning process, while water requires energy to vaporize, hence consuming more energy. (33)
The insulation performance of pure CNF and flame-retardant aerogels is shown in Figure 7a. Importantly, the thermal conductivity remained practically unchanged upon addition of sodium bicarbonate, with the maximum difference being only 0.8 mW m–1 K–1 between the pure CNF aerogel (27.7 mW m–1 K–1) and C-SB40 (28.5 mW m–1 K–1). This shows that despite the extensive improvement in the flame-retardant properties upon addition of SBC, the thermal insulating properties were not hampered, which is rather unique for modified CNF aerogels. In fact, the thermal conductivity values presented in this study are superior to those presented in the literature. For CNF-based flame-retardant aerogels, typical previously reported values of thermal conductivity vary between 30 and 80 mW m–1 K–1. (16,12,34,35) (16,12,34,35) The lowest reported (18) thermal conductivity value for CNF-based flame-retardant nanocomposites is 15 mW m–1 K–1. This was measured in the radial direction, while the thermal conductivity for these composites in the axial direction was 170 ± 3 mW m–1 K–1. Here, it is important to mention that the thermal conductivity values in the present study were evaluated in the axial direction, which are significantly lower compared to the reported value of CNF-based flame-retardant nanocomposites. (18)
Figure 7
Figure 7. Thermal conductivities of aerogels. (a) Thermal conductivity (λ) values of pure and flame-retardant CNF aerogels. (b) Ashby plot of thermal conductivity versus density for commonly used insulation materials including this study and values obtained from ref (36).
The Ashby plot presented in Figure 7b displays thermal conductivity of various thermal insulation materials as a function of density. It is evident that the heat insulating properties of the flame-retardant aerogels reported in the present work are significantly better than those of conventional thermal insulating materials, such as glass wool, expanded polystyrene (EPS), polyurethane foams, and rock wool. Among these thermal insulating materials, EPS is largely employed in construction, but due to its high flammability, organohalogen flame retardants, such as hexabromocyclododecane, bisallylether of tetrabromobisphenol A, and tribromophenyl allyl ester, are used. However, these halogenated flame-retarding agents produce harmful substances during combustion, causing concerns to human health and environment. (37)
Silica aerogels have the lowest thermal conductivity values ranging between 17 and 21 mW m–1 K–1; however, the manufacturing process of silica aerogels involves the use of hazardous solvents, a supercritical drying process, and high pressure and temperature. (38) Moreover, silica aerogels also suffer from fragility and brittleness, which limit their applications in many fields. (39,40) In contrast, the thermal conductivities of CNF-based flame-retardant aerogels prepared in this work are superior to the expanded polystyrene (EPS) and comparable to polyurethane insulation foam, both of which occupy considerable market shares today.
3.4. Polymer and Moisture Absorption
To assess the feasibility of flame-retarding aerogels for polymer-based nanocomposites manufacturing, the polymer (PVA) absorption capacity of pure CNF and flame-retardant aerogels was calculated by soaking aerogels in aqueous 15 wt % PVA solution. The polymer absorption capacity was directly related to the CNF content (Supporting Information Figure S3). The pure CNF aerogel showed the highest polymer absorption capacity, while the lower mass fraction of nanocellulose in the flame-retardant aerogels reduced the polymer absorption. This can be a result of lower number of exposed hydroxyl groups on the surface of aerogels. Hydroxyl groups could form hydrogen bonds with PVA molecules; hence, the availability of hydroxyl groups would influence PVA absorption.
From the moisture absorption data, it was found that increased concentration of sodium bicarbonate led to an increment in the moisture uptake (%) of the flame-retardant aerogels. Pure CNF aerogel exhibits a moisture uptake of 6.2%, whereas C-SB40 aerogel demonstrates a moisture uptake value of 16.7% (Supporting Information Figure S4).
4. Conclusions
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Flame-retardant and heat insulating CNF aerogels were successfully fabricated by incorporating sodium bicarbonate as a flame-retarding agent. This facile and environmentally friendly approach produced physically stable aerogels with high porosity, low thermal conductivity, and considerable flame retardancy. Different concentrations of sodium bicarbonate altered the microstructure of flame-retardant aerogels, providing control over the aerogel morphology. This low-cost method reinforces the use of readily available renewable materials without the need for harmful additives. Furthermore, the flame-retardant properties of the CNF aerogels in this study make them well-suited candidates for thermal insulation, not only due to their bio-based origin and competitive thermal conductivity values, but also due to the harmless gases produced during the flameless pyrolysis. The developed method can pave the way for the production of green insulating aerogels for replacing oil-based insulation materials in various sectors.
Supporting Information
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b04376.
Additional FESEM images of pure CNF and flame-retardant aerogels (Figure S1); FTIR peak ratio (833:896) as a function of SBC concentration (Figure S2); polymer absorption capacity of pure CNF and flame-retardant CNF aerogels submerged in 15 wt % PVA solution during 2 min (Figure S3); moisture absorption of pure CNF and flame-retardant aerogels at 80% RH (Figure S4); comparison of theoretical and calculated SBC content of flame-retardant CNF aerogels (Figure S5); comparison of theoretical and experimental densities of pure and flame-retardant CNF aerogels (Figure S6); values of the onset decomposition temperature (Ton), temperature at the maximum degradation rate (Td), and weight loss at each stage and residue for sodium bicarbonate, pure CNF, and flame-retardant aerogel samples (Table S1); porosity values of pure and flame-retardant CNF aerogels (Table S2); TGA mass balance comparison of theoretical and calculated SBC content at 200 °C of flame-retardant CNF aerogels (Table S4); experimental and theoretical densities of pure and flame-retardant CNF aerogels (Table S5) (PDF)
Videos of combustion of pure CNF and flame-retardant aerogels (Video S1); combustion of pure CNF aerogel (AVI)
Combustion of C-SB10 aerogel (Video S2) (AVI)
Combustion of C-SB30 aerogel (Video S3) (AVI)
Videos of the 3D porous structure of pure CNF and flame-retardant aerogels (Video S4); visualization of 3D porous structure of pure CNF aerogel (AVI)
Visualization of 3D porous structure of C-SB10 aerogel (Video S5) (AVI)
Visualization of 3D porous structure of C-SB30 aerogel (Video S6) (AVI)
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Author Information
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- Monika Österberg - School of Chemical Engineering, Department of Bioproducts and Biosystems and , Aalto University, P.O. Box 16300, FI-00076, Aalto, Finland;
http://orcid.org/0000-0002-3558-9172;
- Mika H. Sipponen - School of Chemical Engineering, Department of Bioproducts and Biosystems and , Aalto University, P.O. Box 16300, FI-00076, Aalto, Finland;http://orcid.org/0000-0001-7747-9310
M.F. conducted the experiments and analyzed the data in collaboration with M.H.S. and M.Ö. A.S. helped with performing thermal conductivity measurements. M.F. wrote the manuscript with inputs from all of the authors. All of the authors discussed the results and read and approved the manuscript.
Acknowledgments
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The authors acknowledge the provision of facilities and technical support by Aalto University at OtaNano—Nanomicroscopy Center (Aalto-NMC) and Bioeconomy facilities and University of Helsinki for X-ray microtomography (MicroCT) imaging system. M.H.S. and M.Ö. acknowledge financial support from the Academy of Finland (postdoctoral and project grants 296547 and 278279, respectively). M.F. acknowledges Aalto CHEM for the financial support.
References
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- 1Zhu, H.; Luo, W.; Ciesielski, P. N.; Fang, Z.; Zhu, J. Y.; Henriksson, G.; Himmel, M. E.; Hu, L. Wood-Derived Materials for Green Electronics, Biological Devices, and Energy Applications. Chem. Rev. 2016, 116, 9305– 9374, DOI: 10.1021/acs.chemrev.6b00225Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1amsr7N&md5=5dc0871010690ce2c953402b37b91d7cWood-Derived Materials for Green Electronics, Biological Devices, and Energy ApplicationsZhu, Hongli; Luo, Wei; Ciesielski, Peter N.; Fang, Zhiqiang; Zhu, J. Y.; Henriksson, Gunnar; Himmel, Michael E.; Hu, LiangbingChemical Reviews (Washington, DC, United States) (2016), 116 (16), 9305-9374CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)With the arising of global climate change and resource shortage, in recent years, increased attention has been paid to environmentally friendly materials. Trees are sustainable and renewable materials, which give us shelter and oxygen and remove carbon dioxide from the atm. Trees are a primary resource that human society depends upon every day, for example, homes, heating, furniture, and aircraft. Wood from trees gives us paper, cardboard, and medical supplies, thus impacting our homes, school, work, and play. All of the above-mentioned applications have been well developed over the past thousands of years. However, trees and wood have much more to offer us as advanced materials, impacting emerging high-tech fields, such as bioengineering, flexible electronics, and clean energy. Wood naturally has a hierarchical structure, composed of well-oriented microfibers and tracheids for water, ion, and oxygen transportation during metab. At higher magnification, the walls of fiber cells have an interesting morphol.-a distinctly mesoporous structure. Moreover, the walls of fiber cells are composed of thousands of fibers (or macrofibrils) oriented in a similar angle. Nanofibrils and nanocrystals can be further liberated from macrofibrils by mech., chem., and enzymic methods. The obtained nanocellulose has unique optical, mech., and barrier properties and is an excellent candidate for chem. modification and reconfiguration. Wood is naturally a composite material, comprised of cellulose, hemicellulose, and lignin. Wood is sustainable, earth abundant, strong, biodegradable, biocompatible, and chem. accessible for modification; more importantly, multiscale natural fibers from wood have unique optical properties applicable to different kinds of optoelectronics and photonic devices. Today, the materials derived from wood are ready to be explored for applications in new technol. areas, such as electronics, biomedical devices, and energy. The goal of this study is to review the fundamental structures and chemistries of wood and wood-derived materials, which are essential for a wide range of existing and new enabling technologies. The scope of the review covers multiscale materials and assemblies of cellulose, hemicellulose, and lignin as well as other biomaterials derived from wood, in regard to their major emerging applications. Structure-properties-application relationships will be investigated in detail. Understanding the fundamental properties of these structures is crucial for designing and manufg. products for emerging applications. Today, a more holistic understanding of the interplay between the structure, chem., and performance of wood and wood-derived materials is advancing historical applications of these materials. This new level of understanding also enables a myriad of new and exciting applications, which motivate this review. There are excellent reviews already on the classical topic of woody materials, and some recent reviews also cover new understanding of these materials as well as potential applications. This review will focus on the uniqueness of woody materials for three crit. applications: green electronics, biol. devices, and energy storage and bioenergy.
- 2Faruk, O.; Bledzki, A. K.; Fink, H.-P.; Sain, M. Progress Report on Natural Fiber Reinforced Composites. Macromol. Mater. Eng. 2014, 299, 9– 26, DOI: 10.1002/mame.201300008Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpvVCjsb4%253D&md5=94faf0c4356365ff5ddc2559ee0f69d5Progress Report on Natural Fiber Reinforced CompositesFaruk, Omar; Bledzki, Andrzej K.; Fink, Hans-Peter; Sain, MohiniMacromolecular Materials and Engineering (2014), 299 (1), 9-26CODEN: MMENFA; ISSN:1438-7492. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. This century has witnessed remarkable achievements in green technol. in material science through the development of natural fiber reinforced composites. The development of high-performance engineering products made from natural resources is increasing worldwide day by day. There is increasing interest in materials demonstrating efficient use of renewable resources. Nowadays, more than ever, companies are faced with opportunities and choices in material innovations. Due to the challenges of petroleum-based products and the need to find renewable solns., more and more companies are looking at natural fiber composite materials. The primary driving forces for new bio-composite materials are the cost of natural fibers (currently priced at one-third of the cost of glass fiber or less), wt. redn. (these fibers are half the wt. of glass fiber), recycling (natural fiber composites are easier to recycle) and the desire for green products. This Review provides an overview of natural fiber reinforced composites focusing on natural fiber types and sources, processing methods, modification of fibers, matrixes (petrochem. and renewable), and their mech. performance. It also focuses on future research, recent developments and applications and concludes with key issues that need to be resolved. This article critically summarizes the essential findings of the mostly readily utilized reinforced natural fibers in polymeric composite materials and their performance from 2000 to 2013.
- 3Dale, B. E. ’Greening’ the Chemical Industry: Research and Development Priorities for Biobased Industrial Products. J. Chem. Technol. Biotechnol. 2003, 78, 1093– 1103, DOI: 10.1002/jctb.850Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXnslKhsrk%253D&md5=f6d8fd25cb10d3c3a61e3d9224e741c0"Greening" the chemical industry: Research and development priorities for biobased industrial productsDale, Bruce E.Journal of Chemical Technology and Biotechnology (2003), 78 (10), 1093-1103CODEN: JCTBED; ISSN:0268-2575. (John Wiley & Sons Ltd.)The chem. industry developed over the past century using petroleum as its primary feedstock. A variety of economic, political and social forces are now leading the chem. industry to use or consider renewable plant-based feedstocks in addn. to or instead of petroleum. The next century may see a gradual transition away from petroleum as the primary feedstock for chems., materials and liq. fuels. If this transition is to occur, and if the chem. industry is to become more sustainable, a considerable amt. of research must be done. This paper summarizes the research and development priorities for a more sustainable, or green, chem. industry based on renewable plant resources and relies heavily on a recent report of the National Research Council (NRC) of the US.
- 4Carole, T. M.; Pellegrino, J.; Paster, M. D. Opportunities in the Industrial Biobased Products Industry. Appl. Biochem. Biotechnol. 2004, 115, 871– 885, DOI: 10.1385/ABAB:115:1-3:0871Google ScholarThere is no corresponding record for this reference.
- 5Lavoine, N.; Bergstrom, L. Nanocellulose-Based Foams and Aerogels: Processing, Properties, and Applications. J. Mater. Chem. A 2017, 5, 16105– 16117, DOI: 10.1039/C7TA02807EGoogle Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvVKjsrs%253D&md5=d0338a5ada8e8c630c490b4087ed3f52Nanocellulose-based foams and aerogels: processing, properties, and applicationsLavoine, Nathalie; Bergstroem, LennartJournal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (31), 16105-16117CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)A review. Nanocellulose is a renewable and biocompatible nanomaterial with a high strength low d. and tunable surface chem. This review summarizes the main processing routes and significant properties of nanocellulose-based foams and aerogels. Challenges, such as how to produce long-term stable wet foams or how to avoid structural collapse of the material during solvent removal using e.g. supercrit. drying, are discussed. Recent advances in the use of ice templating to generate iso- or anisotropic foams with tunable mech. and thermal properties are highlighted. We illustrate how the porous architecture and properties of nanocellulose-based foams and aerogels can be tailored for applications in e.g. thermal insulation and energy storage.
- 6Uetani, K.; Hatori, K. Thermal Conductivity Analysis and Applications of Nanocellulose Materials. Sci. Technol. Adv. Mater. 2017, 18, 877– 892, DOI: 10.1080/14686996.2017.1390692Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkt1Cmtbo%253D&md5=b42dca7beb041611149061b4da5780c4Thermal conductivity analysis and applications of nanocellulose materialsUetani, Kojiro; Hatori, KimihitoScience and Technology of Advanced Materials (2017), 18 (1), 877-892CODEN: STAMCV; ISSN:1878-5514. (Taylor & Francis Ltd.)A review. In this review, we summarize the recent progress in thermal cond. anal. of nanocellulose materials called cellulose nanopapers, and compare them with polymeric materials, including neat polymers, composites, and traditional paper. It is important to individually measure the in-plane and through-plane heat-conducting properties of two-dimensional planar materials, so steady-state and non-equil. methods, in particular the laser spot periodic heating radiation thermometry method, are reviewed. The structural dependency of cellulose nanopaper on thermal conduction is described in terms of the crystallite size effect, fiber orientation, and interfacial thermal resistance between fibers and small pores. The novel applications of cellulose as thermally conductive transparent materials and thermal-guiding materials are also discussed. It is expected that thermally conductive cellulose nanopapers can be used as heat exhaust base materials for flexible electronics, such as printed circuit boards and light-emitting diodes. For such applications, films with both transparency and high thermal cond. are required. They believe that heat-guiding materials can be produced by controlling the nanocellulose fiber alignment using the intrinsic thermal cond. anisotropy.
- 7Carosio, F.; Kochumalayil, J.; Cuttica, F.; Camino, G.; Berglund, L. Oriented Clay Nanopaper from Biobased Components—Mechanisms for Superior Fire Protection Properties. ACS Appl. Mater. Interfaces 2015, 7, 5847– 5856, DOI: 10.1021/am509058hGoogle ScholarThere is no corresponding record for this reference.
- 8Österberg, M.; Vartiainen, J.; Lucenius, J.; Hippi, U.; Seppälä, J.; Serimaa, R.; Laine, J. A Fast Method to Produce Strong NFC Films as a Platform for Barrier and Functional Materials. ACS Appl. Mater. Interfaces 2013, 5, 4640– 4647, DOI: 10.1021/am401046xGoogle Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXmvVynt78%253D&md5=938696c0b6995c977885355f42b6d493A Fast Method to Produce Strong NFC Films as a Platform for Barrier and Functional MaterialsOsterberg, Monika; Vartiainen, Jari; Lucenius, Jessica; Hippi, Ulla; Seppala, Jukka; Serimaa, Ritva; Laine, JanneACS Applied Materials & Interfaces (2013), 5 (11), 4640-4647CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)In this study, we present a rapid method to prep. robust, solvent-resistant, nanofibrillated cellulose (NFC) films that can be further surface-modified for functionality. The oxygen, water vapor, and grease barrier properties of the films were measured, and in addn., mech. properties in the dry and wet state and solvent resistance were evaluated. The pure unmodified NFC films were good barriers for oxygen gas and grease. At a relative humidity below 65%, oxygen permeability of the pure and unmodified NFC films was below 0.6 cm3 μm m-2 d-1 kPa-1, and no grease penetrated the film. However, the largest advantage of these films was their resistance to various solvents, such as water, methanol, toluene, and dimethylacetamide. Although they absorbed a substantial amt. of solvent, the films could still be handled after 24 h of solvent soaking. Hot-pressing was introduced as a convenient method to not only increase the drying speed of the films but also enhance the robustness of the films. The wet strength of the films increased due to the pressing. Thus, they can be chem. or phys. modified through adsorption or direct chem. reaction in both aq. and org. solvents. Through these modifications, the properties of the film can be enhanced, introducing, for example, functionality, hydrophobicity, or bioactivity. Herein, a simple method using surface coating with wax to improve hydrophobicity and oxygen barrier properties at very high humidity is described. Through this modification, the oxygen permeability decreased further and was below 17 cm3 μm m-2 d-1 kPa-1 even at 97.4% RH, and the water vapor transmission rate decreased from 600 to 40 g/m2 day. The wax treatment did not deteriorate the dry strength of the film. Possible reasons for the unique properties are discussed. The developed robust NFC films can be used as a generic, environmentally sustainable platform for functional materials.
- 9Klemm, D.; Heublein, B.; Fink, H.-P.; Bohn, A. Cellulose: Fascinating Biopolymer and Sustainable Raw Material. Angew. Chem., Int. Ed. 2005, 44, 3358– 3393, DOI: 10.1002/anie.200460587Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXlsV2jtbY%253D&md5=804d758e637b3111b640b7272bea4de1Cellulose: Fascinating biopolymer and sustainable raw materialKlemm, Dieter; Heublein, Brigitte; Fink, Hans-Peter; Bohn, AndreasAngewandte Chemie, International Edition (2005), 44 (22), 3358-3393CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. As the most important skeletal component in plants, the polysaccharide cellulose is an almost inexhaustible polymeric raw material with fascinating structure and properties. Formed by the repeated connection of D-glucose building blocks, the highly functionalized, linear stiff-chain homopolymer is characterized by its hydrophilicity, chirality, biodegradability, broad chem. modifying capacity, and its formation of versatile semicryst. fiber morphologies. In view of the considerable increase in interdisciplinary cellulose research and product development over the past decade worldwide, this paper assembles the current knowledge in the structure and chem. of cellulose, and in the development of innovative cellulose esters and ethers for coatings, films, membranes, building materials, drilling techniques, pharmaceuticals, and foodstuffs. New frontiers, including environmentally friendly cellulose fiber technologies, bacterial cellulose biomaterials, and in-vitro syntheses of cellulose are highlighted together with future aims, strategies, and perspectives of cellulose research and its applications.
- 10Dorez, G. Thermal and Fire Behavior of Natural Fibers/PBS Biocomposites. Polym. Degrad. Stab. 2013, 98, 87– 95, DOI: 10.1016/j.polymdegradstab.2012.10.026Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhslaku7fF&md5=0e6c8cef3a735eadf4e75294cee60842Thermal and fire behavior of natural fibers/PBS biocompositesDorez, G.; Taguet, A.; Ferry, L.; Lopez-Cuesta, J. M.Polymer Degradation and Stability (2013), 98 (1), 87-95CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)This paper investigates and compares the thermal degrdn. and fire reaction of different natural fibers and their corresponding biocomposites. Polybutylene succinate (PBS) was used as polymer matrix. Cellulose, hemp, flax, sugar cane and bamboo were used as natural fibers and ammonium polyphosphate (APP) was used as fire retardant agent. The influence of fiber type, fiber content and the addn. of APP were investigated using TGA, PCFC and cone calorimetry. The incorporation of fibers in PBS reduces the thermal stability, and the time to ignition (TTI) of biocomposites, but it increases the mass residue corresponding to the formation of a char barrier. These results are ascribed to the components of fibers, and the flammability of the gas released by the lignocellulosic fibers. The fiber content does not influence the TTI, but affects significantly the peak of heat released rate (pHRR). Thus, a min. content of fibers is required to form a protective barrier during fire test. The addn. of APP in the biocomposite leads to hot hydrolysis of PBS and phosphorylation of flax. Hence, the fire retarded biocomposite forms a barrier layer due to the charring of the matrix and the preservation of the fiber skeleton and therefore shows a significant decrease of the pHRR.
- 11Wang, D. Y. Novel Fire Retardant Polymers and Composite Materials; Elsevier: Amsterdam, 2016.Google ScholarThere is no corresponding record for this reference.
- 12Li, Y.; Wang, B.; Sui, X.; Xu, H.; Zhang, L.; Zhong, Y.; Mao, Z. Facile Synthesis of Microfibrillated Cellulose/Organosilicon/Polydopamine Composite Sponges with Flame Retardant Properties. Cellulose 2017, 24, 3815– 3823, DOI: 10.1007/s10570-017-1373-zGoogle Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVGgu7vL&md5=8139206b12868c262233bcf594af2d08Facile synthesis of microfibrillated cellulose/organosilicon/polydopamine composite sponges with flame retardant propertiesLi, Yingzhan; Wang, Bijia; Sui, Xiaofeng; Xu, Hong; Zhang, Linping; Zhong, Yi; Mao, ZhipingCellulose (Dordrecht, Netherlands) (2017), 24 (9), 3815-3823CODEN: CELLE8; ISSN:0969-0239. (Springer)Cellulose composite sponges with good mech., heat-insulating and flame retardant properties were constructed by a facile method. Simultaneous polymn. of dopamine and hydrolysis of organosilicon in the suspension of microfibrillated cellulose could provide the stiffness and flame ratardancy of the composite sponges. The hybrid sponges had low d. (15.1-28.5 mg/cm3) and desirable compression strength (76.6-135.8 kPa). SEM (SEM) and thermal cond. tests revealed that the sponges are composed of a three-dimensional cellulosic network and the porous structure endowed them low thermal cond. [∼0.046 W/(m K)]. With the addn. of organosilicon (45 wt.%) and polydopamine (PDA) (10 wt.%), a 456% improvement in BET surface area of the sponge could be achieved. The limiting oxygen index (LOI) of the composite sponge could be as high as 29.5 with 15 wt.% PDA and could self-extinguish at once when it was removed from torch. That was owing to the promoted materials carbonization ability of silicon and radical scavenging activity of dopamine.
- 13Costes, L.; Laoutid, F.; Brohez, S.; Dubois, P. Bio-Based Flame Retardants: When Nature Meets Fire Protection. Mater. Sci. Eng., R 2017, 117, 1– 25, DOI: 10.1016/j.mser.2017.04.001Google ScholarThere is no corresponding record for this reference.
- 14Anon Flame retardants: European Union Risk Assessments Update. Plast. Addit. Compd. 2004, 6, 26– 29, DOI: 10.1016/S1464-391X(04)00135-7Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXks1Khsbw%253D&md5=4021ca431db3bfae4f9353f660b59f79Mineral modifiers take on new rolesAnon.Plastics Additives & Compounding (2004), 6 (3), 26-31CODEN: PACOFK; ISSN:1464-391X. (Elsevier Science Ltd.)Minerals used as fillers in plastic compds. have traditionally been used to reduce material costs by replacing a portion of the polymer with a less expensive material. However, nowadays many functional fillers or mineral modifiers are required to modify processing characteristics or finished part properties. Many are now also being used to reduce the level of more expensive additives such as pigments, flame retardants, and impact modifiers. Examples are given for CaCO3, talc, kaolin, BaSO4, alumina trihydrate, and nanomaterials.
- 15Hale, R. C.; La Guardia, M. J.; Harvey, E.; Gaylor, M. O.; Mainor, T. M. Brominated Flame Retardant Concentrations and Trends in Abiotic Media. Chemosphere 2006, 64, 181– 186, DOI: 10.1016/j.chemosphere.2005.12.006Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XlsFKrtLc%253D&md5=ea8335ca31f1520f839e3c7072444efaBrominated flame retardant concentrations and trends in abiotic mediaHale, Robert C.; La Guardia, Mark J.; Harvey, Ellen; Gaylor, Michael O.; Mainor, T. MattChemosphere (2006), 64 (2), 181-186CODEN: CMSHAF; ISSN:0045-6535. (Elsevier B.V.)A review concerning brominated flame retardant (BFR) concns. and trends in abiotic media, emphasizing potential sources, is given. Topics discussed include: BFR sources; outdoor and indoor air; soil, indoor dust, and wastewater treatment sludge; water; and sediment.
- 16Han, Y.; Zhang, X.; Wu, X.; Lu, C. Flame Retardant, Heat Insulating Cellulose Aerogels from Waste Cotton Fabrics by in Situ Formation of Magnesium Hydroxide Nanoparticles in Cellulose Gel Nanostructures. ACS Sustainable Chem. Eng. 2015, 3, 1853– 1859, DOI: 10.1021/acssuschemeng.5b00438Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFSrtLbO&md5=b2bcef4cfb31168e8dd41222f1417b10Flame Retardant, Heat Insulating Cellulose Aerogels from Waste Cotton Fabrics by in Situ Formation of Magnesium Hydroxide Nanoparticles in Cellulose Gel NanostructuresHan, Yangyang; Zhang, Xinxing; Wu, Xiaodong; Lu, CanhuiACS Sustainable Chemistry & Engineering (2015), 3 (8), 1853-1859CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Cellulose aerogels with low d., high mech. strength, and low thermal cond. are promising candidates for environmentally friendly heat insulating materials. The application of cellulose aerogels as heat insulators in building and domestic appliances, however, is hampered by their highly flammable characteristics. In this work, flame retardant cellulose aerogels were fabricated from waste cotton fabrics by in situ synthesis of magnesium hydroxide nanoparticles (MH NPs) in cellulose gel nanostructures, followed by freeze-drying. Our results demonstrated that the three-dimensionally nanoporous cellulose gel prepd. from the NaOH/urea soln. could serve as scaffold/template for the nonagglomerated growth of MH NPs. The prepd. hybridized cellulose aerogels showed excellent flame retardancy, which could extinguish within 40 s. Meanwhile, the thermal cond. of the composite aerogel increased moderately from 0.056 to 0.081 W m-1 k-1 as the sp. surface area decreased slightly from 38.8 to 37.6 cm2 g-1, which indicated that the excellent heat insulating performance of cellulose aerogel was maintained. Because the concepts of the process are simple and biomass wastes are sustainable and readily available at low cost, the present approach is suitable for industrial scale prodn. and has great potential in the future of green building materials.
- 17He, C.; Huang, J.; Li, S.; Meng, K.; Zhang, L.; Chen, Z.; Lai, Y. Mechanically Resistant and Sustainable Cellulose-Based Composite Aerogels with Excellent Flame Retardant, Sound-Absorption, and Superantiwetting Ability for Advanced Engineering Materials. ACS Sustainable Chem. Eng. 2018, 6, 927– 936, DOI: 10.1021/acssuschemeng.7b03281Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVyhu7jJ&md5=0e11386f61f20904381285995ba506acMechanically Resistant and Sustainable Cellulose-Based Composite Aerogels with Excellent Flame Retardant, Sound-Absorption, and Superantiwetting Ability for Advanced Engineering MaterialsHe, Chenglin; Huang, Jianying; Li, Shuhui; Meng, Kai; Zhang, Liyuan; Chen, Zhong; Lai, YuekunACS Sustainable Chemistry & Engineering (2018), 6 (1), 927-936CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)The prodn. of cellulose-based aerogels from the conversion of cheap and rich precursors using environmentally friendly techniques is a very attractive subject in materials chem. In this work, we reports a facile strategy to construct flame retardant, sound-adsorption and mech. enhancement cellulose-based composite aerogels by the incorporation of aluminum hydroxide nanoparticles (AH NPs) into cellulose gels via an in-situ sol-gel process, followed by freeze-drying to coat AH NPs on cellulose composite aerogels (AH NPs@cellulose composite aerogels). The results demonstrated that the AH NPs homogeneous dispersion within cellulose aerogel, and the presence of AH NPs did not have a remarkable influence on the homogeneous porous structure of cellulose aerogels when compared with cellulose aerogel prepd. from the NaOH/urea/thiourea soln. The prepd. composite cellulose aerogels showed excellent flame retardancy, the peak of heat release rate (PHRR) of the composite aerogels decreased significantly from 280 W/g of the control sample to 22 W/g, and total heat release (THR) of the composite aerogels decreased remarkably from 13.2 kJ/g to 1.6 kJ/g. Moreover, the incorporation of AH NPs composite aerogels exhibited remarkable mech. properties, the compressive strength of the composite aerogels increased significantly from 0.08 MPa to 1.5 MPa. In addn., AH NPs composite cellulose aerogels have excellent sound absorption at high frequencies with a max. sound absorption coeff. of 1. AH NPs composite cellulose aerogels have strong water and oil affinity. After immersing the samples in mixed silica nanoparticles, heptadecafluorononanoic acid, and fluoroalkyl silane solns. they became super-antiwetting, with a water contact angle (CA) larger than 150° and oil CA larger than 140°. In summary, this study provides a facile strategy to rationally construct flame retardant, mech. robust, high-efficiency sound-adsorption and superamphiphobic cellulose-based composite aerogels, which have promising applications in the future as green engineering materials.
- 18Wicklein, B.; Kocjan, A.; Salazar-Alvarez, G.; Carosio, F.; Camino, G.; Antonietti, M.; Bergström, L. Thermally Insulating and Fire-Retardant Lightweight Anisotropic Foams Based on Nanocellulose and Graphene Oxide. Nat. Nanotechnol. 2015, 10, 277, DOI: 10.1038/nnano.2014.248Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvVGitbnL&md5=47b483b4e2aa7b9246a3b45d9170f39dThermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxideWicklein, Bernd; Kocjan, Andraz; Salazar-Alvarez, German; Carosio, Federico; Camino, Giovanni; Antonietti, Markus; Bergstroem, LennartNature Nanotechnology (2015), 10 (3), 277-283CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal cond. of 15 mW m-1 K-1, which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.
- 19Lowe, S. E.; Zhong, Y. L. Challenges of Industrial-Scale Graphene Oxide Production. In Graphene Oxide: Fundamentals and Applications; Dimiev, A. M., Eigler, S., Eds.; John Wiley & Sons: West Sussex, United Kingdom, 2016; pp 410– 431.Google ScholarThere is no corresponding record for this reference.
- 20Köklükaya, O.; Carosio, F.; Wågberg, L. Superior Flame-Resistant Cellulose Nanofibril Aerogels Modified with Hybrid Layer-by-Layer Coatings. ACS Appl. Mater. Interfaces 2017, 9, 29082– 29092, DOI: 10.1021/acsami.7b08018Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cfjsV2gtQ%253D%253D&md5=7a9452b356f0df7704634e312469bcbaSuperior Flame-Resistant Cellulose Nanofibril Aerogels Modified with Hybrid Layer-by-Layer CoatingsKoklukaya Oruc; Wagberg Lars; Carosio FedericoACS applied materials & interfaces (2017), 9 (34), 29082-29092 ISSN:.Nanometer thin films consisting of cationic chitosan (Ch), anionic poly(vinylphosphonic acid) (PVPA), and anionic montmorillonite clay (MMT) are deposited on highly porous, wet-stabilized cellulose nanofibril (CNF) aerogels via the layer-by-layer (LbL) technique. Model experiments with silicon oxide surfaces are used to study the details of LbL formation and the multilayer structure. Formation of layers on the aerogels is also investigated as a function of solution concentration by use of polyelectrolyte titration. Thermogravimetric analysis indicates that the LbL coating significantly improves thermal stability of the CNF aerogel. Horizontal flame test shows that aerogels coated with five quadlayers of Ch/PVPA/Ch/MMT, using solutions/dispersion of high concentration, are able to self-extinguish immediately after removal of flame, and LbL-coated aerogels do not ignite under heat flux (35 kW/m(2)) in cone calorimetry. The LbL-coated aerogel can prevent flame penetration from a torch focused on the surface, achieving temperature drops up to 650 °C across the 10 mm thick specimen for several minutes. LbL treatment is hence a rapid and highly effective way to specifically tailor the surface properties of CNF aerogels in order to confer unprecedented flame-retardant characteristics.
- 21Yuan, B.; Zhang, J.; Mi, Q.; Yu, J.; Song, R.; Zhang, J. Transparent Cellulose–Silica Composite Aerogels with Excellent Flame Retardancy via an in Situ Sol–Gel Process. ACS Sustainable Chem. Eng. 2017, 5, 11117– 11123, DOI: 10.1021/acssuschemeng.7b03211Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1KnsLzP&md5=fd5122870d58d46e547642dc7ad3cb54Transparent Cellulose-Silica Composite Aerogels with Excellent Flame Retardancy via an in Situ Sol-Gel ProcessYuan, Bin; Zhang, Jinming; Mi, Qinyong; Yu, Jian; Song, Rui; Zhang, JunACS Sustainable Chemistry & Engineering (2017), 5 (11), 11117-11123CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Cellulose-silica composite aerogels were prepd. by in situ formation of silica nanoparticles via a two-step sol-gel process in cellulose gel, which was prepd. by dissolving cotton pulp in 1-allyl-3-methylimidazolium chloride ionic liq. (AmimCl) and then regenerating from AmimCl/water bath. Related properties were studied with UV-visible spectrometer, SEM, compression tests, thermogravimetric anal., and ignition tests and a microscale combustion calorimeter. The composite aerogels displayed increasing transparency, compressive properties, and thermal and thermal-oxidative stability with increasing of silica content. The incorporation of silica nanoparticles also improved the mesoporous characteristics of aerogels including sp. surface area and mesopore vol. and significantly delayed the decompn. of cellulose, suppressing the heat release during combustion. The composite aerogels with high silica content (33.6% or more) exhibited good transparency with light transmittance as high as 78.4% at 800 nm, even higher than the neat cellulose aerogels, and presented excellent flame retardant performance, achieving self-extinguishment after ignition. The transparent cellulose-silica composite aerogels with enhanced mech. performance and improved flame retardancy might show great potential in a wide variety of applications.
- 22Nakashima, H.; Omae, K.; Sakai, T.; Yamazaki, K.; Sakurai, H. Acute and Subchronic Inhalation Toxicity of Tetraethoxysilane (TEOS) in Mice. Arch. Toxicol. 1994, 68, 277– 283, DOI: 10.1007/s002040050069Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXkt1yrtL0%253D&md5=0611740b7ad026da1e111927efa38ee9Acute and subchronic inhalation toxicity of tetraethoxysilane (TEOS) in miceNakashima, Hiroshi; Omae, Kazuyuki; Sakai, tohru; Yamazaki, Kazuto; Sakurai, HaruhikoArchives of Toxicology (1994), 68 (5), 277-83CODEN: ARTODN; ISSN:0340-5761.To clarify the acute and subchronic inhalation toxicity of tetraethoxysilane [TEOS, Si(OC2H5)4], groups of 10 male ICR mice (SPF grade) were exposed to 1000 ppm TEOS for 1, 2, 4, or 8 h (acute inhalation study), or to 200 ppm TEOS for 6 h/day, 5 days/wk, for 2 or 4 wk (subchronic inhalation study). The nos. of mice that died during 2 wk of observation were 0, 1, 1, and 6 in the 1-, 2-, 4-, and 8-h inhalation expts. and 0 in the subchronic inhalation study. In the acute inhalation study, body wt. decreased after TEOS exposure and did not reach the level of control mice during 2 wk of observation except in the 1-h inhalation study. In the subchronic exposure study, wt. gain was suppressed during the exposure period. Body wt. in mice exposed for 2 wk reached the level of nonexposed mice during the 2-wk observation period, but did not do so in mice exposed for 4 wk. Acute tubular necrosis (ATN) and acute splenic atrophy (ASA) were obsd. in all dead mice in the acute inhalation study, and tubulointerstitial nephritis (TIN) was frequently found in the surviving mice in both the acute and subchronic studies. However, blood biochem. examns. revealed no evidence of renal dysfunction. The olfactory epithelium was necrotic in all dead mice. In the subchronic inhalation study, infiltration of polymorphonuclear neutrophils in the nasal mucosa was obsd. in all mice killed 1 day after exposure. Thus, the LCL0 for 1-h exposure to TEOS and LC50 for 4-h exposure are >1000 ppm, and the kidney and nasal mucosa are the target organs for TEOS inhalation.
- 23Nakashima, H. Time Course of Effects of Tetraethoxysilane (TEOS) on the Kidney and Blood Silicon Concentration in Mice. Arch. Toxicol. 1994, 69, 59– 64, DOI: 10.1007/s002040050138Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXjvFGqsr8%253D&md5=bdee1b5c3fa458da5d12f144951cbef6Time course of effects of tetraethoxysilane (TEOS) on the kidney and blood silicon concentration in miceNakashima, HiroshiArchives of Toxicology (1994), 69 (1), 59-64CODEN: ARTODN; ISSN:0340-5761. (Springer)To clarify the time course of toxicol. effects of tetraethoxysilane [Si(OC2H5)4, TEOS] on the kidney and the relationship between blood silicon levels (Si-B) and the effects, 250 mg/kg or 500 mg/kg TEOS was i.p. administered to ten 5-wk-old male ICR mice (SPF grade) in each group, and morphol. and functional changes of the kidney were assessed at 12 h, 24 h, 3 days and 2 wk after administration of TEOS. Injury to tubular epithelial cells was obsd. in mice killed 12 and 24 h after administration, and its severity increased with increasing dosage. The mean values of blood urea nitrogen exhibited dose-related increase in mice sacrificed 24 h after the administration. The concns. of Si-B increased in order of the administered doses of TEOS, and then decreased steadily. The results of Si-B were consistent with the concept that renal toxicity of TEOS is mediated by siliceous compds. The kidney was recovering from injury 3 days after administration, and had developed tubulointerstitial nephritis, which could be regarded as repaired lesion of acute injury, by 2 wk after administration.
- 24Swerin Deswelling of Hardwood Kraft Pulp Fibers by Cationic Polymers the Effect on Wet Pressing and Sheet Properties. Nord. Pulp Pap. Res. J. 1990, 05, 188– 196, DOI: 10.3183/NPPRJ-1990-05-04-p188-196Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXktlWgu7k%253D&md5=e436e25918f4629daa943d7845be125eDeswelling of hardwood kraft pulp fibers by cationic polymers: the effect on wet pressing and sheet propertiesSwerin, Agne; Oedberg, Lars; Lindstroem, TomNordic Pulp & Paper Research Journal (1990), 5 (4), 188-96CODEN: NPPJEG; ISSN:0283-2631.The effect of Polybrene and Agefloc WT20 on the degree of swelling of unbleached hardwood kraft pulp fibers of different degrees of beating was studied. The deswelling of the pulp fibers was caused by an ion-exchange reaction between the cationic polyelectrolyte and the cationic counterions to the ionic groups in the pulp fiber cell wall. Sheets made from pulp deswollen by cationic polyelectrolyte did not lose their strength to the extent expected from the decrease in water retention value (WRV). The fiber flexibility introduced by beating was important for sheet strength and the strength increase due to this increased flexibility is only partly lost on deswelling. Trials on an exptl. paper machine indicated that in a practical papermaking situation the increase in max. solids content reached during pressing as a result of the addn. of cationic polyelectrolyte was substantially lower than that obsd. in lab. trials.
- 25Schindelin, J.; Arganda-Carreras, I.; Frise, E.; Kaynig, V.; Longair, M.; Pietzsch, T.; Preibisch, S.; Rueden, C.; Saalfeld, S.; Schmid, B.; Tinevez, J.-Y.; White, D. J.; Hartenstein, V.; Eliceiri, K.; Tomancak, P.; Cardona, A. Fiji: An Open-Source Platform for Biological-Image Analysis. Nat. Methods 2012, 9, 676, DOI: 10.1038/nmeth.2019Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtVKnurbJ&md5=ad150521a33367d37a800bee853dd9dbFiji: an open-source platform for biological-image analysisSchindelin, Johannes; Arganda-Carreras, Ignacio; Frise, Erwin; Kaynig, Verena; Longair, Mark; Pietzsch, Tobias; Preibisch, Stephan; Rueden, Curtis; Saalfeld, Stephan; Schmid, Benjamin; Tinevez, Jean-Yves; White, Daniel James; Hartenstein, Volker; Eliceiri, Kevin; Tomancak, Pavel; Cardona, AlbertNature Methods (2012), 9 (7_part1), 676-682CODEN: NMAEA3; ISSN:1548-7091. (Nature Publishing Group)Fiji is a distribution of the popular open-source software ImageJ focused on biol.-image anal. Fiji uses modern software engineering practices to combine powerful software libraries with a broad range of scripting languages to enable rapid prototyping of image-processing algorithms. Fiji facilitates the transformation of new algorithms into ImageJ plugins that can be shared with end users through an integrated update system. We propose Fiji as a platform for productive collaboration between computer science and biol. research communities.
- 26Otsu, N. A Threshold Selection Method from Gray-Level Histograms. IEEE Trans. Syst. Man Cybern. 1979, 9, 62– 66, DOI: 10.1109/TSMC.1979.4310076Google ScholarThere is no corresponding record for this reference.
- 27Steger, C. An Unbiased Detector of Curvilinear Structures. IEEE Trans. Pattern Anal. Mach. Intell. 1998, 20, 113– 125, DOI: 10.1109/34.659930Google ScholarThere is no corresponding record for this reference.
- 28Pääkkö, M.; Vapaavuori, J.; Silvennoinen, R.; Kosonen, H.; Ankerfors, M.; Lindstrom, T.; Berglund, L. A.; Ikkala, O. Long And Entangled Native Cellulose I Nanofibers Allow Flexible Aerogels and Hierarchically Porous Templates for Functionalities. Soft Matter 2008, 4, 2492– 2499, DOI: 10.1039/b810371bGoogle Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtlGrtrnO&md5=7fb9675ed7f01b0455d631153b439ec6Long and entangled native cellulose I nanofibers allow flexible aerogels and hierarchically porous templates for functionalitiesPaakko, Marjo; Vapaavuori, Jaana; Silvennoinen, Riitta; Kosonen, Harri; Ankerfors, Mikael; Lindstrom, Tom; Berglund, Lars A.; Ikkala, OlliSoft Matter (2008), 4 (12), 2492-2499CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)Recently it was shown that enzymic and mech. processing of macroscopic cellulose fibers lead to disintegration of long and entangled native cellulose I nanofibers in order to form mech. strong aq. gels (Paakko et al., Biomacromols., 2007, 8, 1934). Here we demonstrate that (1) such aq. nanofibrillar gels are unexpectedly robust to allow formation of highly porous aerogels by direct water removal by freeze-drying, (2) they are flexible, unlike most aerogels that suffer from brittleness, and (3) they allow flexible hierarchically porous templates for functionalities, e.g. for elec. cond. No crosslinking, solvent exchange nor supercrit. drying are required to suppress the collapse during the aerogel prepn., unlike in typical aerogel prepns. The aerogels show a high porosity of ∼98% and a very low d. of ca. 0.02 g cm-3. The flexibility of the aerogels manifests as a particularly high compressive strain of ca. 70%. In addn., the structure of the aerogels can be tuned from nanofibrillar to sheet-like skeletons with hierarchical micro- and nanoscale morphol. and porosity by modifying the freeze-drying conditions. The porous flexible aerogel scaffold opens new possibilities for templating org. and inorg. matter for various functionalities. This is demonstrated here by dipping the aerogels in an elec. conducting polyaniline-surfactant soln. which after rinsing off the unbound conducting polymer and drying leads to elec. conducting flexible aerogels with relatively high cond. of around 1 × 10-2 S cm-1. More generally, we foresee a wide variety of functional applications for highly porous flexible biomatter aerogels, such as for selective delivery/sepn., tissue-engineering, nanocomposites upon impregnation by polymers, and other medical and pharmaceutical applications.
- 29Peng, Y.; Gardner, D. J.; Han, Y. Drying Cellulose Nanofibrils: In Search of a Suitable Method. Cellulose 2012, 19, 91– 102, DOI: 10.1007/s10570-011-9630-zGoogle Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XlvVWiug%253D%253D&md5=7d73488bce1576a0e2ff44a83f1c1328Drying cellulose nanofibrils: in search of a suitable methodPeng, Yucheng; Gardner, Douglas J.; Han, YousooCellulose (Dordrecht, Netherlands) (2012), 19 (1), 91-102CODEN: CELLE8; ISSN:0969-0239. (Springer)Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufg. approaches. Cellulose nanofibrils (CNFs) are typically processed as aq. suspensions because of their hydrophilic nature. One of the major manufg. challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examd. to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercrit. drying (SCD), and (4) spray-drying (SD). The particle size and morphol. of the CNFs were detd. via dynamic light scattering, transmission electron microscopy, SEM, and morphol. anal. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were obsd. in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a tech. suitable manufg. process to dry CNF suspensions.
- 30Chen, W.; Li, Q.; Wang, Y.; Yi, X.; Zeng, J.; Yu, H.; Liu, Y.; Li, J. Comparative Study of Aerogels Obtained from Differently Prepared Nanocellulose Fibers. ChemSusChem 2014, 7, 154– 161, DOI: 10.1002/cssc.201300950Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmtVSgtQ%253D%253D&md5=cb727f602a8c3dc3849df531586f53b9Comparative Study of Aerogels Obtained from Differently Prepared Nanocellulose FibersChen, Wenshuai; Li, Qing; Wang, Youcheng; Yi, Xin; Zeng, Jie; Yu, Haipeng; Liu, Yixing; Li, JianChemSusChem (2014), 7 (1), 154-161CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)This article describes the fabrication of nanocellulose fibers (NCFs) with different morphologies and surface properties from biomass resources as well as their self-aggregation into lightwt. aerogels. By carefully modulating the nanofibrillation process, four types of NCFs could be readily fabricated, including long aggregated nanofiber bundles, long individualized nanofibers with surface C6-carboxylate groups, short aggregated nanofibers, and short individualized nanofibers with surface sulfate groups. Free-standing lightwt. aerogels were obtained from the corresponding aq. NCF suspensions through freeze-drying. The structure of the aerogels could be controlled by manipulating the type of NCFs and the concn. of their suspensions. A possible mechanism for the self-aggregation of NCFs into two- or three-dimensional aerogel nanostructures was further proposed. Owing to web-like structure, high porosity, and high surface reactivity, the NCF aerogels exhibited high mech. flexibility and ductility, and excellent properties for water uptake, removal of dye pollutants, and the use as thermal insulation materials. The aerogels also displayed sound-adsorption capability at high frequencies.
- 31Larkin, P. J. Infrared and Raman Spectroscopy; Principles and Spectral Interpretation; Elsevier: Waltham, MA, 2011.Google ScholarThere is no corresponding record for this reference.
- 32Peng, Y.; Gardner, D. J.; Han, Y.; Kiziltas, A.; Cai, Z.; Tshabalala, M. A. Influence of Drying Method on the Material Properties of Nanocellulose I: Thermostability and Crystallinity. Cellulose 2013, 20, 2379– 2392, DOI: 10.1007/s10570-013-0019-zGoogle Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVOlur%252FF&md5=7846d00cb02ab57ffa12e779723619f4Influence of drying method on the material properties of nanocellulose I: thermostability and crystallinityPeng, Yucheng; Gardner, Douglas J.; Han, Yousoo; Kiziltas, Alper; Cai, Zhiyong; Tshabalala, Mandla A.Cellulose (Dordrecht, Netherlands) (2013), 20 (5), 2379-2392CODEN: CELLE8; ISSN:0969-0239. (Springer)The effect of drying method on selected material properties of nanocellulose was investigated. Samples of nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNC) were each subjected to four sep. drying methods: air-drying, freeze-drying, spray-drying, and supercrit.-drying. The thermal stability and crystallinity of the dried nanocellulose were evaluated using thermogravimetric anal. (TGA) and X-ray diffraction. Supercrit.-drying produced NFCs with the least thermal stability and the lowest crystallinity index. Air-drying or spray-drying produced NFCs which were more thermally stable compared with freeze-dried NFCs. The CNCs dried by the three methods (air-drying, freeze-drying, and spray-drying) have similar onset temp. of thermal degrdn. The different drying methods resulted in various char wt. percentages at 600° for the dried NFCs or CNCs from TGA measurements. The dried NFCs were pure cellulose I while the dried CNCs consist of cellulose I and II. The calcd. crystallinity indexes differ with each drying method. The cellulose II content in CNCs changes as a function of drying method. For the application of nanocellulose in non polar thermoplastics, spray-dried products were recommended according to their higher thermal stability and higher crystallinity index.
- 33Bakirtzis, D.; Delichatsios, M. A.; Liodakis, S.; Ahmed, W. Fire Retardancy Impact of Sodium Bicarbonate on Ligno-Cellulosic Materials. Thermochim. Acta 2009, 486, 11– 19, DOI: 10.1016/j.tca.2008.12.012Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXitFykurg%253D&md5=8930e0f18d8dfe98f7c8772a3d585680Fire retardancy impact of sodium bicarbonate on ligno-cellulosic materialsBakirtzis, D.; Delichatsios, M. A.; Liodakis, S.; Ahmed, W.Thermochimica Acta (2009), 486 (1-2), 11-19CODEN: THACAS; ISSN:0040-6031. (Elsevier B.V.)In this paper, the effect of NaHCO3 as fire retardant additive during pyrolysis and combustion has been investigated. Four different contents (5%, 10%, 15%, and 20% wt./wt.) of NaHCO3 have been tested on Pinus brutia, Laurus nobilis and Nerium oleander; forest species commonly dispersed in the Mediterranean region. Pyrolysis expts. have been conducted using a thermogravimetric analyzer (TGA) employing nitrogen (N2) flow of 50 mL/min, under a heating rate of 10°/min. Expts. for flaming combustion have been conducted in a specially designed furnace, isothermally controlled, under an air flow supply of 1.5 l/min-1; key parameters including time to self ignition and duration of flame combustion were measured. Pyrolysis data revealed that the addn. of NaHCO3 induces a shift towards lower thermal degrdn. temps. for each of the forest specie considered. Thus, sodium bicarbonate decreases the threshold of initial temp. of pyrolysis of forest species (promotion effect). On the other hand NaHCO3 increases the self ignition delay time and combustion duration of forest species (inhibition effect). In addn. the presence of NaHCO3 increases the pyrolysis mass residue of forest species, esp. when sodium carbonate applied on N. oleander.
- 34Mi, Q.-y.; Ma, S.-r.; Yu, J.; He, J.-s.; Zhang, J. Flexible and Transparent Cellulose Aerogels with Uniform Nanoporous Structure by a Controlled Regeneration Process. ACS Sustainable Chem. Eng. 2016, 4, 656– 660, DOI: 10.1021/acssuschemeng.5b01079Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XoslyqsA%253D%253D&md5=48e7905b494a5b0a0172fbf901e6981bFlexible and Transparent Cellulose Aerogels with Uniform Nanoporous Structure by a Controlled Regeneration ProcessMi, Qin-yong; Ma, Shu-rong; Yu, Jian; He, Jia-song; Zhang, JunACS Sustainable Chemistry & Engineering (2016), 4 (3), 656-660CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Monolithic cellulose aerogels were prepd. via a dissoln.-regeneration route by dissolving cellulose in 1-allyl-3-methylimidazolium chloride (AMIMCl). Using a high concn. aq. AMIMCl soln. as the regeneration bath endowed cellulose aerogels with high flexibility and transparency. Possessing homogeneous nanoscale porous morphol., the strong cellulose aerogels have excellent compressive properties, low densities, and low thermal conductivities.
- 35Shi, J.; Lu, L.; Guo, W.; Sun, Y.; Cao, Y. An Environment-Friendly Thermal Insulation Material from Cellulose and Plasma Modification. J. Appl. Polym. Sci. 2013, 130, 3652– 3658, DOI: 10.1002/app.39615Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVWgurfF&md5=7b1b1f78381f91395bc827ada7bbf622An environment-friendly thermal insulation material from cellulose and plasma modificationShi, Jianjun; Lu, Lingbin; Guo, Wantao; Sun, Yujia; Cao, YangJournal of Applied Polymer Science (2013), 130 (5), 3652-3658CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)Cellulose aerogels were prepd. by combining the NaOH/thiourea/H2O solvent system and the freeze-drying technol. Hydrophobic aerogels were obtained with the cold plasma modification technol. The results showed that cellulose aerogel had good heat insulation performance, while the main factors affecting thermal cond. were d. and porosity. Thermal cond. decreased with the decrease of d. and the increase of porosity. It could be as low as 0.029 W/(m K). Cellulose aerogel adsorbed moisture easily. The moisture adsorption had a significant influence on the heat insulation performance of aerogel. After conducting hydrophobic modification using CCl4 as plasma, cellulose aerogel was changed from hydrophilic to hydrophobic and water contact angle was as high as 102°. Hydrophobic modification did not affect the heat insulation performance of aerogel. This work provided a foundation for the possibility of applying cellulose aerogels in the insulating material field. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013.
- 36Kunič, R. Forest-Based Bioproducts Used for Construction and Its Impact on the Environmental Performance of a Building in the Whole Life Cycle. In Environmental Impacts of Traditional and Innovative Forest-Based Bioproducts; Kutnar, A., Muthu, S. S., Eds.; Springer: Singapore, 2016; pp 173– 204.Google ScholarThere is no corresponding record for this reference.
- 37Wang, G.; Chen, X.; Liu, P.; Bai, S. Flame-Retardant Mechanism of Expandable Polystyrene Foam with a Macromolecular Nitrogen–Phosphorus Intumescent Flame Retardant. J. Appl. Polym. Sci. 2017, 134 (1), 44356, DOI: 10.1002/app.44356Google ScholarThere is no corresponding record for this reference.
- 38Dou, B.; Li, J.; Wang, Y.; Wang, H.; Ma, C.; Hao, Z. Adsorption and Desorption Performance of Benzene Over Hierarchically Structured Carbon–Silica Aerogel Composites. J. Hazard. Mater. 2011, 196, 194– 200, DOI: 10.1016/j.jhazmat.2011.09.019Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsVWktrvO&md5=127eba25041a4b2a3395baf296e4ac0aAdsorption and desorption performance of benzene over hierarchically structured carbon-silica aerogel compositesDou, Baojuan; Li, Jinjun; Wang, Yufei; Wang, Hailin; Ma, Chunyan; Hao, ZhengpingJournal of Hazardous Materials (2011), 196 (), 194-200CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)Hierarchically structured carbon-silica aerogel (CSA) composites were synthesized from cheap water glass precursors and granulated activated carbon via a post-synthesis surface modification with trimethylchlorosilane and a low-cost ambient pressure drying procedure. The resultant CSA composites possess micro/mesoporous structure and hydrophobic surface. The adsorption and desorption performance of benzene on carbon-silica aerogel composite (CSA-2) under static and dynamic conditions were investigated, comparing with pure silica aerogel (CSA-0) and microporous activated carbon (AC). It was found that CSA-2 has high affinity towards arom. mols. and fast adsorption kinetics. Excellent performance of dynamic adsorption and desorption obsd. on CSA-2 is related to its higher adsorption capacity than CSA-0 and less mass transfer resistance than AC, arising from the well-developed microporosity and open foam mesostructure in the CSA composites.
- 39Li, Z.; Gong, L.; Li, C.; Pan, Y.; Huang, Y.; Cheng, X. Silica Aerogel/Aramid Pulp Composites with Improved Mechanical and Thermal Properties. J. Non-Cryst. Solids 2016, 454, 1– 7, DOI: 10.1016/j.jnoncrysol.2016.10.015Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslCrurnN&md5=fda8595c63b594db622107a9227c04a9Silica aerogel/aramid pulp composites with improved mechanical and thermal propertiesLi, Zhi; Gong, Lunlun; Li, Congcong; Pan, Yuelei; Huang, Yajun; Cheng, XudongJournal of Non-Crystalline Solids (2016), 454 (), 1-7CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier B.V.)For maintaining the integrality and improving the mech. strength of fiber/silica aerogel composites without compromising thermal insulation properties, aramid pulp reinforced silica aerogel composites were prepd. under ambient pressure drying by adding aramid pulps into silica sol directly. The microstructures indicated the ample fibrillated fibers of aramid pulps were inlaid in silica aerogel matrix which retained the integrality and nice interface adhesion, instead of sepg. the aerogel matrix into small fragments. As the aramid pulp content increased, the compressive strength was enhanced obviously up to about 1.2 MPa and the low thermal cond. of 0.0232-0.0278 W·m- 1·K- 1 approximated linear growth. TG-DTA anal. indicated that the thermal stability of the as-prepd. composites was about 260 °C which primarily depended on the thermal stability of pure silica aerogels. Thus it concluded that excellent silica aerogel composites with intact microstructures, improved mech. strength and tailored thermal properties can be prepd. by using aramid pulps as reinforcements.
- 40Zhong, L.; Chen, X.; Song, H.; Guo, K.; Hu, Z. Highly Flexible Silica Aerogels Derived from Methyltriethoxysilane and Polydimethylsiloxane. New J. Chem. 2015, 39, 7832– 7838, DOI: 10.1039/C5NJ01477HGoogle Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1amsLvJ&md5=565b0c9a9c76a666b453deaba4ff6b9dHighly flexible silica aerogels derived from methyltriethoxysilane and polydimethylsiloxaneZhong, Liang; Chen, Xiaohong; Song, Huaihe; Guo, Kang; Hu, ZijunNew Journal of Chemistry (2015), 39 (10), 7832-7838CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)Highly flexible silica aerogels were synthesized using methyltriethoxysilane (MTES) and polydimethylsiloxane (PDMS) as co-precursors via a two-step acid-base sol-gel method followed by ambient pressure drying. The effects of vol. ratio of PDMS to MTES (S) on the flexibility were investigated in detail. It was found that, with the increase of S from 5% to 8.75%, both Young's modulus and the d. of obtained aerogels decrease from 0.136 to 0.030 MPa and 0.098 to 0.064 g cm-3, resp. Aerogels produced at S of 8.75% show excellent compressional and recoverable properties with, their maximal recoverable compressive strain being 70%. The unrecovered strains calcd. immediately and 12 h after compression to 60% strain twenty times are 10.9% and 3.1%, resp. The excellent flexibility performance of silica aerogels derived from MTES-PDMS makes them a promising silica aerogel material for special applications.
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Abstract
Figure 1
Figure 1. Schematics of the flame-retardant aerogel fabrication procedure and proposed fibrillar structure at each stage.
Figure 2
Figure 2. Horizontal flame test of pure CNF aerogel and flame-retardant CNF aerogels containing 10–40 wt % sodium bicarbonate. (a) Combustion velocities determined from the videos recorded during the flame test. Still images of the aerogels (b) before combustion and (c) after 10 s combustion, except for pure CNF where the still image is taken after 2 s of combustion.
Figure 3
Figure 3. Effect of sodium bicarbonate on the morphology of CNF aerogels. (a) Apparent porosity and (b) mean pore diameter and mean fibril layer length. Values of apparent porosity, pore diameter, and mean fibril length were obtained from image analysis of MicroCT data.
Figure 4
Figure 4. Morphological appearance of pure CNF aerogel and SBC-containing aerogels. (a–c) Pure CNF aerogel, (d–f) C-SB10, and (g–i) C-SB30. (b, e, h) 3D volumetric rendering from MicroCT data. (a, d, g) and (c, f, i) FESEM images in radial and axial directions, respectively. (j) Aerogel sample sketch detailing cross-section and radial and axial directions.
Figure 5
Figure 5. FTIR spectra of pure and flame-retardant CNF aerogels.
Figure 6
Figure 6. Thermogravimetric analysis (TGA) (a) and derivative thermogravimetry (DTG) (b) curves of sodium bicarbonate, pure CNF aerogel, and flame-retardant CNF aerogels.
Figure 7
Figure 7. Thermal conductivities of aerogels. (a) Thermal conductivity (λ) values of pure and flame-retardant CNF aerogels. (b) Ashby plot of thermal conductivity versus density for commonly used insulation materials including this study and values obtained from ref (36).
References
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- 8Österberg, M.; Vartiainen, J.; Lucenius, J.; Hippi, U.; Seppälä, J.; Serimaa, R.; Laine, J. A Fast Method to Produce Strong NFC Films as a Platform for Barrier and Functional Materials. ACS Appl. Mater. Interfaces 2013, 5, 4640– 4647, DOI: 10.1021/am401046x8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXmvVynt78%253D&md5=938696c0b6995c977885355f42b6d493A Fast Method to Produce Strong NFC Films as a Platform for Barrier and Functional MaterialsOsterberg, Monika; Vartiainen, Jari; Lucenius, Jessica; Hippi, Ulla; Seppala, Jukka; Serimaa, Ritva; Laine, JanneACS Applied Materials & Interfaces (2013), 5 (11), 4640-4647CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)In this study, we present a rapid method to prep. robust, solvent-resistant, nanofibrillated cellulose (NFC) films that can be further surface-modified for functionality. The oxygen, water vapor, and grease barrier properties of the films were measured, and in addn., mech. properties in the dry and wet state and solvent resistance were evaluated. The pure unmodified NFC films were good barriers for oxygen gas and grease. At a relative humidity below 65%, oxygen permeability of the pure and unmodified NFC films was below 0.6 cm3 μm m-2 d-1 kPa-1, and no grease penetrated the film. However, the largest advantage of these films was their resistance to various solvents, such as water, methanol, toluene, and dimethylacetamide. Although they absorbed a substantial amt. of solvent, the films could still be handled after 24 h of solvent soaking. Hot-pressing was introduced as a convenient method to not only increase the drying speed of the films but also enhance the robustness of the films. The wet strength of the films increased due to the pressing. Thus, they can be chem. or phys. modified through adsorption or direct chem. reaction in both aq. and org. solvents. Through these modifications, the properties of the film can be enhanced, introducing, for example, functionality, hydrophobicity, or bioactivity. Herein, a simple method using surface coating with wax to improve hydrophobicity and oxygen barrier properties at very high humidity is described. Through this modification, the oxygen permeability decreased further and was below 17 cm3 μm m-2 d-1 kPa-1 even at 97.4% RH, and the water vapor transmission rate decreased from 600 to 40 g/m2 day. The wax treatment did not deteriorate the dry strength of the film. Possible reasons for the unique properties are discussed. The developed robust NFC films can be used as a generic, environmentally sustainable platform for functional materials.
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- 10Dorez, G. Thermal and Fire Behavior of Natural Fibers/PBS Biocomposites. Polym. Degrad. Stab. 2013, 98, 87– 95, DOI: 10.1016/j.polymdegradstab.2012.10.02610https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhslaku7fF&md5=0e6c8cef3a735eadf4e75294cee60842Thermal and fire behavior of natural fibers/PBS biocompositesDorez, G.; Taguet, A.; Ferry, L.; Lopez-Cuesta, J. M.Polymer Degradation and Stability (2013), 98 (1), 87-95CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)This paper investigates and compares the thermal degrdn. and fire reaction of different natural fibers and their corresponding biocomposites. Polybutylene succinate (PBS) was used as polymer matrix. Cellulose, hemp, flax, sugar cane and bamboo were used as natural fibers and ammonium polyphosphate (APP) was used as fire retardant agent. The influence of fiber type, fiber content and the addn. of APP were investigated using TGA, PCFC and cone calorimetry. The incorporation of fibers in PBS reduces the thermal stability, and the time to ignition (TTI) of biocomposites, but it increases the mass residue corresponding to the formation of a char barrier. These results are ascribed to the components of fibers, and the flammability of the gas released by the lignocellulosic fibers. The fiber content does not influence the TTI, but affects significantly the peak of heat released rate (pHRR). Thus, a min. content of fibers is required to form a protective barrier during fire test. The addn. of APP in the biocomposite leads to hot hydrolysis of PBS and phosphorylation of flax. Hence, the fire retarded biocomposite forms a barrier layer due to the charring of the matrix and the preservation of the fiber skeleton and therefore shows a significant decrease of the pHRR.
- 11Wang, D. Y. Novel Fire Retardant Polymers and Composite Materials; Elsevier: Amsterdam, 2016.There is no corresponding record for this reference.
- 12Li, Y.; Wang, B.; Sui, X.; Xu, H.; Zhang, L.; Zhong, Y.; Mao, Z. Facile Synthesis of Microfibrillated Cellulose/Organosilicon/Polydopamine Composite Sponges with Flame Retardant Properties. Cellulose 2017, 24, 3815– 3823, DOI: 10.1007/s10570-017-1373-z12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVGgu7vL&md5=8139206b12868c262233bcf594af2d08Facile synthesis of microfibrillated cellulose/organosilicon/polydopamine composite sponges with flame retardant propertiesLi, Yingzhan; Wang, Bijia; Sui, Xiaofeng; Xu, Hong; Zhang, Linping; Zhong, Yi; Mao, ZhipingCellulose (Dordrecht, Netherlands) (2017), 24 (9), 3815-3823CODEN: CELLE8; ISSN:0969-0239. (Springer)Cellulose composite sponges with good mech., heat-insulating and flame retardant properties were constructed by a facile method. Simultaneous polymn. of dopamine and hydrolysis of organosilicon in the suspension of microfibrillated cellulose could provide the stiffness and flame ratardancy of the composite sponges. The hybrid sponges had low d. (15.1-28.5 mg/cm3) and desirable compression strength (76.6-135.8 kPa). SEM (SEM) and thermal cond. tests revealed that the sponges are composed of a three-dimensional cellulosic network and the porous structure endowed them low thermal cond. [∼0.046 W/(m K)]. With the addn. of organosilicon (45 wt.%) and polydopamine (PDA) (10 wt.%), a 456% improvement in BET surface area of the sponge could be achieved. The limiting oxygen index (LOI) of the composite sponge could be as high as 29.5 with 15 wt.% PDA and could self-extinguish at once when it was removed from torch. That was owing to the promoted materials carbonization ability of silicon and radical scavenging activity of dopamine.
- 13Costes, L.; Laoutid, F.; Brohez, S.; Dubois, P. Bio-Based Flame Retardants: When Nature Meets Fire Protection. Mater. Sci. Eng., R 2017, 117, 1– 25, DOI: 10.1016/j.mser.2017.04.001There is no corresponding record for this reference.
- 14Anon Flame retardants: European Union Risk Assessments Update. Plast. Addit. Compd. 2004, 6, 26– 29, DOI: 10.1016/S1464-391X(04)00135-714https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXks1Khsbw%253D&md5=4021ca431db3bfae4f9353f660b59f79Mineral modifiers take on new rolesAnon.Plastics Additives & Compounding (2004), 6 (3), 26-31CODEN: PACOFK; ISSN:1464-391X. (Elsevier Science Ltd.)Minerals used as fillers in plastic compds. have traditionally been used to reduce material costs by replacing a portion of the polymer with a less expensive material. However, nowadays many functional fillers or mineral modifiers are required to modify processing characteristics or finished part properties. Many are now also being used to reduce the level of more expensive additives such as pigments, flame retardants, and impact modifiers. Examples are given for CaCO3, talc, kaolin, BaSO4, alumina trihydrate, and nanomaterials.
- 15Hale, R. C.; La Guardia, M. J.; Harvey, E.; Gaylor, M. O.; Mainor, T. M. Brominated Flame Retardant Concentrations and Trends in Abiotic Media. Chemosphere 2006, 64, 181– 186, DOI: 10.1016/j.chemosphere.2005.12.00615https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XlsFKrtLc%253D&md5=ea8335ca31f1520f839e3c7072444efaBrominated flame retardant concentrations and trends in abiotic mediaHale, Robert C.; La Guardia, Mark J.; Harvey, Ellen; Gaylor, Michael O.; Mainor, T. MattChemosphere (2006), 64 (2), 181-186CODEN: CMSHAF; ISSN:0045-6535. (Elsevier B.V.)A review concerning brominated flame retardant (BFR) concns. and trends in abiotic media, emphasizing potential sources, is given. Topics discussed include: BFR sources; outdoor and indoor air; soil, indoor dust, and wastewater treatment sludge; water; and sediment.
- 16Han, Y.; Zhang, X.; Wu, X.; Lu, C. Flame Retardant, Heat Insulating Cellulose Aerogels from Waste Cotton Fabrics by in Situ Formation of Magnesium Hydroxide Nanoparticles in Cellulose Gel Nanostructures. ACS Sustainable Chem. Eng. 2015, 3, 1853– 1859, DOI: 10.1021/acssuschemeng.5b0043816https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFSrtLbO&md5=b2bcef4cfb31168e8dd41222f1417b10Flame Retardant, Heat Insulating Cellulose Aerogels from Waste Cotton Fabrics by in Situ Formation of Magnesium Hydroxide Nanoparticles in Cellulose Gel NanostructuresHan, Yangyang; Zhang, Xinxing; Wu, Xiaodong; Lu, CanhuiACS Sustainable Chemistry & Engineering (2015), 3 (8), 1853-1859CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Cellulose aerogels with low d., high mech. strength, and low thermal cond. are promising candidates for environmentally friendly heat insulating materials. The application of cellulose aerogels as heat insulators in building and domestic appliances, however, is hampered by their highly flammable characteristics. In this work, flame retardant cellulose aerogels were fabricated from waste cotton fabrics by in situ synthesis of magnesium hydroxide nanoparticles (MH NPs) in cellulose gel nanostructures, followed by freeze-drying. Our results demonstrated that the three-dimensionally nanoporous cellulose gel prepd. from the NaOH/urea soln. could serve as scaffold/template for the nonagglomerated growth of MH NPs. The prepd. hybridized cellulose aerogels showed excellent flame retardancy, which could extinguish within 40 s. Meanwhile, the thermal cond. of the composite aerogel increased moderately from 0.056 to 0.081 W m-1 k-1 as the sp. surface area decreased slightly from 38.8 to 37.6 cm2 g-1, which indicated that the excellent heat insulating performance of cellulose aerogel was maintained. Because the concepts of the process are simple and biomass wastes are sustainable and readily available at low cost, the present approach is suitable for industrial scale prodn. and has great potential in the future of green building materials.
- 17He, C.; Huang, J.; Li, S.; Meng, K.; Zhang, L.; Chen, Z.; Lai, Y. Mechanically Resistant and Sustainable Cellulose-Based Composite Aerogels with Excellent Flame Retardant, Sound-Absorption, and Superantiwetting Ability for Advanced Engineering Materials. ACS Sustainable Chem. Eng. 2018, 6, 927– 936, DOI: 10.1021/acssuschemeng.7b0328117https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVyhu7jJ&md5=0e11386f61f20904381285995ba506acMechanically Resistant and Sustainable Cellulose-Based Composite Aerogels with Excellent Flame Retardant, Sound-Absorption, and Superantiwetting Ability for Advanced Engineering MaterialsHe, Chenglin; Huang, Jianying; Li, Shuhui; Meng, Kai; Zhang, Liyuan; Chen, Zhong; Lai, YuekunACS Sustainable Chemistry & Engineering (2018), 6 (1), 927-936CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)The prodn. of cellulose-based aerogels from the conversion of cheap and rich precursors using environmentally friendly techniques is a very attractive subject in materials chem. In this work, we reports a facile strategy to construct flame retardant, sound-adsorption and mech. enhancement cellulose-based composite aerogels by the incorporation of aluminum hydroxide nanoparticles (AH NPs) into cellulose gels via an in-situ sol-gel process, followed by freeze-drying to coat AH NPs on cellulose composite aerogels (AH NPs@cellulose composite aerogels). The results demonstrated that the AH NPs homogeneous dispersion within cellulose aerogel, and the presence of AH NPs did not have a remarkable influence on the homogeneous porous structure of cellulose aerogels when compared with cellulose aerogel prepd. from the NaOH/urea/thiourea soln. The prepd. composite cellulose aerogels showed excellent flame retardancy, the peak of heat release rate (PHRR) of the composite aerogels decreased significantly from 280 W/g of the control sample to 22 W/g, and total heat release (THR) of the composite aerogels decreased remarkably from 13.2 kJ/g to 1.6 kJ/g. Moreover, the incorporation of AH NPs composite aerogels exhibited remarkable mech. properties, the compressive strength of the composite aerogels increased significantly from 0.08 MPa to 1.5 MPa. In addn., AH NPs composite cellulose aerogels have excellent sound absorption at high frequencies with a max. sound absorption coeff. of 1. AH NPs composite cellulose aerogels have strong water and oil affinity. After immersing the samples in mixed silica nanoparticles, heptadecafluorononanoic acid, and fluoroalkyl silane solns. they became super-antiwetting, with a water contact angle (CA) larger than 150° and oil CA larger than 140°. In summary, this study provides a facile strategy to rationally construct flame retardant, mech. robust, high-efficiency sound-adsorption and superamphiphobic cellulose-based composite aerogels, which have promising applications in the future as green engineering materials.
- 18Wicklein, B.; Kocjan, A.; Salazar-Alvarez, G.; Carosio, F.; Camino, G.; Antonietti, M.; Bergström, L. Thermally Insulating and Fire-Retardant Lightweight Anisotropic Foams Based on Nanocellulose and Graphene Oxide. Nat. Nanotechnol. 2015, 10, 277, DOI: 10.1038/nnano.2014.24818https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvVGitbnL&md5=47b483b4e2aa7b9246a3b45d9170f39dThermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxideWicklein, Bernd; Kocjan, Andraz; Salazar-Alvarez, German; Carosio, Federico; Camino, Giovanni; Antonietti, Markus; Bergstroem, LennartNature Nanotechnology (2015), 10 (3), 277-283CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal cond. of 15 mW m-1 K-1, which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.
- 19Lowe, S. E.; Zhong, Y. L. Challenges of Industrial-Scale Graphene Oxide Production. In Graphene Oxide: Fundamentals and Applications; Dimiev, A. M., Eigler, S., Eds.; John Wiley & Sons: West Sussex, United Kingdom, 2016; pp 410– 431.There is no corresponding record for this reference.
- 20Köklükaya, O.; Carosio, F.; Wågberg, L. Superior Flame-Resistant Cellulose Nanofibril Aerogels Modified with Hybrid Layer-by-Layer Coatings. ACS Appl. Mater. Interfaces 2017, 9, 29082– 29092, DOI: 10.1021/acsami.7b0801820https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cfjsV2gtQ%253D%253D&md5=7a9452b356f0df7704634e312469bcbaSuperior Flame-Resistant Cellulose Nanofibril Aerogels Modified with Hybrid Layer-by-Layer CoatingsKoklukaya Oruc; Wagberg Lars; Carosio FedericoACS applied materials & interfaces (2017), 9 (34), 29082-29092 ISSN:.Nanometer thin films consisting of cationic chitosan (Ch), anionic poly(vinylphosphonic acid) (PVPA), and anionic montmorillonite clay (MMT) are deposited on highly porous, wet-stabilized cellulose nanofibril (CNF) aerogels via the layer-by-layer (LbL) technique. Model experiments with silicon oxide surfaces are used to study the details of LbL formation and the multilayer structure. Formation of layers on the aerogels is also investigated as a function of solution concentration by use of polyelectrolyte titration. Thermogravimetric analysis indicates that the LbL coating significantly improves thermal stability of the CNF aerogel. Horizontal flame test shows that aerogels coated with five quadlayers of Ch/PVPA/Ch/MMT, using solutions/dispersion of high concentration, are able to self-extinguish immediately after removal of flame, and LbL-coated aerogels do not ignite under heat flux (35 kW/m(2)) in cone calorimetry. The LbL-coated aerogel can prevent flame penetration from a torch focused on the surface, achieving temperature drops up to 650 °C across the 10 mm thick specimen for several minutes. LbL treatment is hence a rapid and highly effective way to specifically tailor the surface properties of CNF aerogels in order to confer unprecedented flame-retardant characteristics.
- 21Yuan, B.; Zhang, J.; Mi, Q.; Yu, J.; Song, R.; Zhang, J. Transparent Cellulose–Silica Composite Aerogels with Excellent Flame Retardancy via an in Situ Sol–Gel Process. ACS Sustainable Chem. Eng. 2017, 5, 11117– 11123, DOI: 10.1021/acssuschemeng.7b0321121https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1KnsLzP&md5=fd5122870d58d46e547642dc7ad3cb54Transparent Cellulose-Silica Composite Aerogels with Excellent Flame Retardancy via an in Situ Sol-Gel ProcessYuan, Bin; Zhang, Jinming; Mi, Qinyong; Yu, Jian; Song, Rui; Zhang, JunACS Sustainable Chemistry & Engineering (2017), 5 (11), 11117-11123CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Cellulose-silica composite aerogels were prepd. by in situ formation of silica nanoparticles via a two-step sol-gel process in cellulose gel, which was prepd. by dissolving cotton pulp in 1-allyl-3-methylimidazolium chloride ionic liq. (AmimCl) and then regenerating from AmimCl/water bath. Related properties were studied with UV-visible spectrometer, SEM, compression tests, thermogravimetric anal., and ignition tests and a microscale combustion calorimeter. The composite aerogels displayed increasing transparency, compressive properties, and thermal and thermal-oxidative stability with increasing of silica content. The incorporation of silica nanoparticles also improved the mesoporous characteristics of aerogels including sp. surface area and mesopore vol. and significantly delayed the decompn. of cellulose, suppressing the heat release during combustion. The composite aerogels with high silica content (33.6% or more) exhibited good transparency with light transmittance as high as 78.4% at 800 nm, even higher than the neat cellulose aerogels, and presented excellent flame retardant performance, achieving self-extinguishment after ignition. The transparent cellulose-silica composite aerogels with enhanced mech. performance and improved flame retardancy might show great potential in a wide variety of applications.
- 22Nakashima, H.; Omae, K.; Sakai, T.; Yamazaki, K.; Sakurai, H. Acute and Subchronic Inhalation Toxicity of Tetraethoxysilane (TEOS) in Mice. Arch. Toxicol. 1994, 68, 277– 283, DOI: 10.1007/s00204005006922https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXkt1yrtL0%253D&md5=0611740b7ad026da1e111927efa38ee9Acute and subchronic inhalation toxicity of tetraethoxysilane (TEOS) in miceNakashima, Hiroshi; Omae, Kazuyuki; Sakai, tohru; Yamazaki, Kazuto; Sakurai, HaruhikoArchives of Toxicology (1994), 68 (5), 277-83CODEN: ARTODN; ISSN:0340-5761.To clarify the acute and subchronic inhalation toxicity of tetraethoxysilane [TEOS, Si(OC2H5)4], groups of 10 male ICR mice (SPF grade) were exposed to 1000 ppm TEOS for 1, 2, 4, or 8 h (acute inhalation study), or to 200 ppm TEOS for 6 h/day, 5 days/wk, for 2 or 4 wk (subchronic inhalation study). The nos. of mice that died during 2 wk of observation were 0, 1, 1, and 6 in the 1-, 2-, 4-, and 8-h inhalation expts. and 0 in the subchronic inhalation study. In the acute inhalation study, body wt. decreased after TEOS exposure and did not reach the level of control mice during 2 wk of observation except in the 1-h inhalation study. In the subchronic exposure study, wt. gain was suppressed during the exposure period. Body wt. in mice exposed for 2 wk reached the level of nonexposed mice during the 2-wk observation period, but did not do so in mice exposed for 4 wk. Acute tubular necrosis (ATN) and acute splenic atrophy (ASA) were obsd. in all dead mice in the acute inhalation study, and tubulointerstitial nephritis (TIN) was frequently found in the surviving mice in both the acute and subchronic studies. However, blood biochem. examns. revealed no evidence of renal dysfunction. The olfactory epithelium was necrotic in all dead mice. In the subchronic inhalation study, infiltration of polymorphonuclear neutrophils in the nasal mucosa was obsd. in all mice killed 1 day after exposure. Thus, the LCL0 for 1-h exposure to TEOS and LC50 for 4-h exposure are >1000 ppm, and the kidney and nasal mucosa are the target organs for TEOS inhalation.
- 23Nakashima, H. Time Course of Effects of Tetraethoxysilane (TEOS) on the Kidney and Blood Silicon Concentration in Mice. Arch. Toxicol. 1994, 69, 59– 64, DOI: 10.1007/s00204005013823https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXjvFGqsr8%253D&md5=bdee1b5c3fa458da5d12f144951cbef6Time course of effects of tetraethoxysilane (TEOS) on the kidney and blood silicon concentration in miceNakashima, HiroshiArchives of Toxicology (1994), 69 (1), 59-64CODEN: ARTODN; ISSN:0340-5761. (Springer)To clarify the time course of toxicol. effects of tetraethoxysilane [Si(OC2H5)4, TEOS] on the kidney and the relationship between blood silicon levels (Si-B) and the effects, 250 mg/kg or 500 mg/kg TEOS was i.p. administered to ten 5-wk-old male ICR mice (SPF grade) in each group, and morphol. and functional changes of the kidney were assessed at 12 h, 24 h, 3 days and 2 wk after administration of TEOS. Injury to tubular epithelial cells was obsd. in mice killed 12 and 24 h after administration, and its severity increased with increasing dosage. The mean values of blood urea nitrogen exhibited dose-related increase in mice sacrificed 24 h after the administration. The concns. of Si-B increased in order of the administered doses of TEOS, and then decreased steadily. The results of Si-B were consistent with the concept that renal toxicity of TEOS is mediated by siliceous compds. The kidney was recovering from injury 3 days after administration, and had developed tubulointerstitial nephritis, which could be regarded as repaired lesion of acute injury, by 2 wk after administration.
- 24Swerin Deswelling of Hardwood Kraft Pulp Fibers by Cationic Polymers the Effect on Wet Pressing and Sheet Properties. Nord. Pulp Pap. Res. J. 1990, 05, 188– 196, DOI: 10.3183/NPPRJ-1990-05-04-p188-19624https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXktlWgu7k%253D&md5=e436e25918f4629daa943d7845be125eDeswelling of hardwood kraft pulp fibers by cationic polymers: the effect on wet pressing and sheet propertiesSwerin, Agne; Oedberg, Lars; Lindstroem, TomNordic Pulp & Paper Research Journal (1990), 5 (4), 188-96CODEN: NPPJEG; ISSN:0283-2631.The effect of Polybrene and Agefloc WT20 on the degree of swelling of unbleached hardwood kraft pulp fibers of different degrees of beating was studied. The deswelling of the pulp fibers was caused by an ion-exchange reaction between the cationic polyelectrolyte and the cationic counterions to the ionic groups in the pulp fiber cell wall. Sheets made from pulp deswollen by cationic polyelectrolyte did not lose their strength to the extent expected from the decrease in water retention value (WRV). The fiber flexibility introduced by beating was important for sheet strength and the strength increase due to this increased flexibility is only partly lost on deswelling. Trials on an exptl. paper machine indicated that in a practical papermaking situation the increase in max. solids content reached during pressing as a result of the addn. of cationic polyelectrolyte was substantially lower than that obsd. in lab. trials.
- 25Schindelin, J.; Arganda-Carreras, I.; Frise, E.; Kaynig, V.; Longair, M.; Pietzsch, T.; Preibisch, S.; Rueden, C.; Saalfeld, S.; Schmid, B.; Tinevez, J.-Y.; White, D. J.; Hartenstein, V.; Eliceiri, K.; Tomancak, P.; Cardona, A. Fiji: An Open-Source Platform for Biological-Image Analysis. Nat. Methods 2012, 9, 676, DOI: 10.1038/nmeth.201925https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtVKnurbJ&md5=ad150521a33367d37a800bee853dd9dbFiji: an open-source platform for biological-image analysisSchindelin, Johannes; Arganda-Carreras, Ignacio; Frise, Erwin; Kaynig, Verena; Longair, Mark; Pietzsch, Tobias; Preibisch, Stephan; Rueden, Curtis; Saalfeld, Stephan; Schmid, Benjamin; Tinevez, Jean-Yves; White, Daniel James; Hartenstein, Volker; Eliceiri, Kevin; Tomancak, Pavel; Cardona, AlbertNature Methods (2012), 9 (7_part1), 676-682CODEN: NMAEA3; ISSN:1548-7091. (Nature Publishing Group)Fiji is a distribution of the popular open-source software ImageJ focused on biol.-image anal. Fiji uses modern software engineering practices to combine powerful software libraries with a broad range of scripting languages to enable rapid prototyping of image-processing algorithms. Fiji facilitates the transformation of new algorithms into ImageJ plugins that can be shared with end users through an integrated update system. We propose Fiji as a platform for productive collaboration between computer science and biol. research communities.
- 26Otsu, N. A Threshold Selection Method from Gray-Level Histograms. IEEE Trans. Syst. Man Cybern. 1979, 9, 62– 66, DOI: 10.1109/TSMC.1979.4310076There is no corresponding record for this reference.
- 27Steger, C. An Unbiased Detector of Curvilinear Structures. IEEE Trans. Pattern Anal. Mach. Intell. 1998, 20, 113– 125, DOI: 10.1109/34.659930There is no corresponding record for this reference.
- 28Pääkkö, M.; Vapaavuori, J.; Silvennoinen, R.; Kosonen, H.; Ankerfors, M.; Lindstrom, T.; Berglund, L. A.; Ikkala, O. Long And Entangled Native Cellulose I Nanofibers Allow Flexible Aerogels and Hierarchically Porous Templates for Functionalities. Soft Matter 2008, 4, 2492– 2499, DOI: 10.1039/b810371b28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtlGrtrnO&md5=7fb9675ed7f01b0455d631153b439ec6Long and entangled native cellulose I nanofibers allow flexible aerogels and hierarchically porous templates for functionalitiesPaakko, Marjo; Vapaavuori, Jaana; Silvennoinen, Riitta; Kosonen, Harri; Ankerfors, Mikael; Lindstrom, Tom; Berglund, Lars A.; Ikkala, OlliSoft Matter (2008), 4 (12), 2492-2499CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)Recently it was shown that enzymic and mech. processing of macroscopic cellulose fibers lead to disintegration of long and entangled native cellulose I nanofibers in order to form mech. strong aq. gels (Paakko et al., Biomacromols., 2007, 8, 1934). Here we demonstrate that (1) such aq. nanofibrillar gels are unexpectedly robust to allow formation of highly porous aerogels by direct water removal by freeze-drying, (2) they are flexible, unlike most aerogels that suffer from brittleness, and (3) they allow flexible hierarchically porous templates for functionalities, e.g. for elec. cond. No crosslinking, solvent exchange nor supercrit. drying are required to suppress the collapse during the aerogel prepn., unlike in typical aerogel prepns. The aerogels show a high porosity of ∼98% and a very low d. of ca. 0.02 g cm-3. The flexibility of the aerogels manifests as a particularly high compressive strain of ca. 70%. In addn., the structure of the aerogels can be tuned from nanofibrillar to sheet-like skeletons with hierarchical micro- and nanoscale morphol. and porosity by modifying the freeze-drying conditions. The porous flexible aerogel scaffold opens new possibilities for templating org. and inorg. matter for various functionalities. This is demonstrated here by dipping the aerogels in an elec. conducting polyaniline-surfactant soln. which after rinsing off the unbound conducting polymer and drying leads to elec. conducting flexible aerogels with relatively high cond. of around 1 × 10-2 S cm-1. More generally, we foresee a wide variety of functional applications for highly porous flexible biomatter aerogels, such as for selective delivery/sepn., tissue-engineering, nanocomposites upon impregnation by polymers, and other medical and pharmaceutical applications.
- 29Peng, Y.; Gardner, D. J.; Han, Y. Drying Cellulose Nanofibrils: In Search of a Suitable Method. Cellulose 2012, 19, 91– 102, DOI: 10.1007/s10570-011-9630-z29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XlvVWiug%253D%253D&md5=7d73488bce1576a0e2ff44a83f1c1328Drying cellulose nanofibrils: in search of a suitable methodPeng, Yucheng; Gardner, Douglas J.; Han, YousooCellulose (Dordrecht, Netherlands) (2012), 19 (1), 91-102CODEN: CELLE8; ISSN:0969-0239. (Springer)Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufg. approaches. Cellulose nanofibrils (CNFs) are typically processed as aq. suspensions because of their hydrophilic nature. One of the major manufg. challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examd. to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercrit. drying (SCD), and (4) spray-drying (SD). The particle size and morphol. of the CNFs were detd. via dynamic light scattering, transmission electron microscopy, SEM, and morphol. anal. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were obsd. in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a tech. suitable manufg. process to dry CNF suspensions.
- 30Chen, W.; Li, Q.; Wang, Y.; Yi, X.; Zeng, J.; Yu, H.; Liu, Y.; Li, J. Comparative Study of Aerogels Obtained from Differently Prepared Nanocellulose Fibers. ChemSusChem 2014, 7, 154– 161, DOI: 10.1002/cssc.20130095030https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmtVSgtQ%253D%253D&md5=cb727f602a8c3dc3849df531586f53b9Comparative Study of Aerogels Obtained from Differently Prepared Nanocellulose FibersChen, Wenshuai; Li, Qing; Wang, Youcheng; Yi, Xin; Zeng, Jie; Yu, Haipeng; Liu, Yixing; Li, JianChemSusChem (2014), 7 (1), 154-161CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)This article describes the fabrication of nanocellulose fibers (NCFs) with different morphologies and surface properties from biomass resources as well as their self-aggregation into lightwt. aerogels. By carefully modulating the nanofibrillation process, four types of NCFs could be readily fabricated, including long aggregated nanofiber bundles, long individualized nanofibers with surface C6-carboxylate groups, short aggregated nanofibers, and short individualized nanofibers with surface sulfate groups. Free-standing lightwt. aerogels were obtained from the corresponding aq. NCF suspensions through freeze-drying. The structure of the aerogels could be controlled by manipulating the type of NCFs and the concn. of their suspensions. A possible mechanism for the self-aggregation of NCFs into two- or three-dimensional aerogel nanostructures was further proposed. Owing to web-like structure, high porosity, and high surface reactivity, the NCF aerogels exhibited high mech. flexibility and ductility, and excellent properties for water uptake, removal of dye pollutants, and the use as thermal insulation materials. The aerogels also displayed sound-adsorption capability at high frequencies.
- 31Larkin, P. J. Infrared and Raman Spectroscopy; Principles and Spectral Interpretation; Elsevier: Waltham, MA, 2011.There is no corresponding record for this reference.
- 32Peng, Y.; Gardner, D. J.; Han, Y.; Kiziltas, A.; Cai, Z.; Tshabalala, M. A. Influence of Drying Method on the Material Properties of Nanocellulose I: Thermostability and Crystallinity. Cellulose 2013, 20, 2379– 2392, DOI: 10.1007/s10570-013-0019-z32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVOlur%252FF&md5=7846d00cb02ab57ffa12e779723619f4Influence of drying method on the material properties of nanocellulose I: thermostability and crystallinityPeng, Yucheng; Gardner, Douglas J.; Han, Yousoo; Kiziltas, Alper; Cai, Zhiyong; Tshabalala, Mandla A.Cellulose (Dordrecht, Netherlands) (2013), 20 (5), 2379-2392CODEN: CELLE8; ISSN:0969-0239. (Springer)The effect of drying method on selected material properties of nanocellulose was investigated. Samples of nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNC) were each subjected to four sep. drying methods: air-drying, freeze-drying, spray-drying, and supercrit.-drying. The thermal stability and crystallinity of the dried nanocellulose were evaluated using thermogravimetric anal. (TGA) and X-ray diffraction. Supercrit.-drying produced NFCs with the least thermal stability and the lowest crystallinity index. Air-drying or spray-drying produced NFCs which were more thermally stable compared with freeze-dried NFCs. The CNCs dried by the three methods (air-drying, freeze-drying, and spray-drying) have similar onset temp. of thermal degrdn. The different drying methods resulted in various char wt. percentages at 600° for the dried NFCs or CNCs from TGA measurements. The dried NFCs were pure cellulose I while the dried CNCs consist of cellulose I and II. The calcd. crystallinity indexes differ with each drying method. The cellulose II content in CNCs changes as a function of drying method. For the application of nanocellulose in non polar thermoplastics, spray-dried products were recommended according to their higher thermal stability and higher crystallinity index.
- 33Bakirtzis, D.; Delichatsios, M. A.; Liodakis, S.; Ahmed, W. Fire Retardancy Impact of Sodium Bicarbonate on Ligno-Cellulosic Materials. Thermochim. Acta 2009, 486, 11– 19, DOI: 10.1016/j.tca.2008.12.01233https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXitFykurg%253D&md5=8930e0f18d8dfe98f7c8772a3d585680Fire retardancy impact of sodium bicarbonate on ligno-cellulosic materialsBakirtzis, D.; Delichatsios, M. A.; Liodakis, S.; Ahmed, W.Thermochimica Acta (2009), 486 (1-2), 11-19CODEN: THACAS; ISSN:0040-6031. (Elsevier B.V.)In this paper, the effect of NaHCO3 as fire retardant additive during pyrolysis and combustion has been investigated. Four different contents (5%, 10%, 15%, and 20% wt./wt.) of NaHCO3 have been tested on Pinus brutia, Laurus nobilis and Nerium oleander; forest species commonly dispersed in the Mediterranean region. Pyrolysis expts. have been conducted using a thermogravimetric analyzer (TGA) employing nitrogen (N2) flow of 50 mL/min, under a heating rate of 10°/min. Expts. for flaming combustion have been conducted in a specially designed furnace, isothermally controlled, under an air flow supply of 1.5 l/min-1; key parameters including time to self ignition and duration of flame combustion were measured. Pyrolysis data revealed that the addn. of NaHCO3 induces a shift towards lower thermal degrdn. temps. for each of the forest specie considered. Thus, sodium bicarbonate decreases the threshold of initial temp. of pyrolysis of forest species (promotion effect). On the other hand NaHCO3 increases the self ignition delay time and combustion duration of forest species (inhibition effect). In addn. the presence of NaHCO3 increases the pyrolysis mass residue of forest species, esp. when sodium carbonate applied on N. oleander.
- 34Mi, Q.-y.; Ma, S.-r.; Yu, J.; He, J.-s.; Zhang, J. Flexible and Transparent Cellulose Aerogels with Uniform Nanoporous Structure by a Controlled Regeneration Process. ACS Sustainable Chem. Eng. 2016, 4, 656– 660, DOI: 10.1021/acssuschemeng.5b0107934https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XoslyqsA%253D%253D&md5=48e7905b494a5b0a0172fbf901e6981bFlexible and Transparent Cellulose Aerogels with Uniform Nanoporous Structure by a Controlled Regeneration ProcessMi, Qin-yong; Ma, Shu-rong; Yu, Jian; He, Jia-song; Zhang, JunACS Sustainable Chemistry & Engineering (2016), 4 (3), 656-660CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Monolithic cellulose aerogels were prepd. via a dissoln.-regeneration route by dissolving cellulose in 1-allyl-3-methylimidazolium chloride (AMIMCl). Using a high concn. aq. AMIMCl soln. as the regeneration bath endowed cellulose aerogels with high flexibility and transparency. Possessing homogeneous nanoscale porous morphol., the strong cellulose aerogels have excellent compressive properties, low densities, and low thermal conductivities.
- 35Shi, J.; Lu, L.; Guo, W.; Sun, Y.; Cao, Y. An Environment-Friendly Thermal Insulation Material from Cellulose and Plasma Modification. J. Appl. Polym. Sci. 2013, 130, 3652– 3658, DOI: 10.1002/app.3961535https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVWgurfF&md5=7b1b1f78381f91395bc827ada7bbf622An environment-friendly thermal insulation material from cellulose and plasma modificationShi, Jianjun; Lu, Lingbin; Guo, Wantao; Sun, Yujia; Cao, YangJournal of Applied Polymer Science (2013), 130 (5), 3652-3658CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)Cellulose aerogels were prepd. by combining the NaOH/thiourea/H2O solvent system and the freeze-drying technol. Hydrophobic aerogels were obtained with the cold plasma modification technol. The results showed that cellulose aerogel had good heat insulation performance, while the main factors affecting thermal cond. were d. and porosity. Thermal cond. decreased with the decrease of d. and the increase of porosity. It could be as low as 0.029 W/(m K). Cellulose aerogel adsorbed moisture easily. The moisture adsorption had a significant influence on the heat insulation performance of aerogel. After conducting hydrophobic modification using CCl4 as plasma, cellulose aerogel was changed from hydrophilic to hydrophobic and water contact angle was as high as 102°. Hydrophobic modification did not affect the heat insulation performance of aerogel. This work provided a foundation for the possibility of applying cellulose aerogels in the insulating material field. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013.
- 36Kunič, R. Forest-Based Bioproducts Used for Construction and Its Impact on the Environmental Performance of a Building in the Whole Life Cycle. In Environmental Impacts of Traditional and Innovative Forest-Based Bioproducts; Kutnar, A., Muthu, S. S., Eds.; Springer: Singapore, 2016; pp 173– 204.There is no corresponding record for this reference.
- 37Wang, G.; Chen, X.; Liu, P.; Bai, S. Flame-Retardant Mechanism of Expandable Polystyrene Foam with a Macromolecular Nitrogen–Phosphorus Intumescent Flame Retardant. J. Appl. Polym. Sci. 2017, 134 (1), 44356, DOI: 10.1002/app.44356There is no corresponding record for this reference.
- 38Dou, B.; Li, J.; Wang, Y.; Wang, H.; Ma, C.; Hao, Z. Adsorption and Desorption Performance of Benzene Over Hierarchically Structured Carbon–Silica Aerogel Composites. J. Hazard. Mater. 2011, 196, 194– 200, DOI: 10.1016/j.jhazmat.2011.09.01938https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsVWktrvO&md5=127eba25041a4b2a3395baf296e4ac0aAdsorption and desorption performance of benzene over hierarchically structured carbon-silica aerogel compositesDou, Baojuan; Li, Jinjun; Wang, Yufei; Wang, Hailin; Ma, Chunyan; Hao, ZhengpingJournal of Hazardous Materials (2011), 196 (), 194-200CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)Hierarchically structured carbon-silica aerogel (CSA) composites were synthesized from cheap water glass precursors and granulated activated carbon via a post-synthesis surface modification with trimethylchlorosilane and a low-cost ambient pressure drying procedure. The resultant CSA composites possess micro/mesoporous structure and hydrophobic surface. The adsorption and desorption performance of benzene on carbon-silica aerogel composite (CSA-2) under static and dynamic conditions were investigated, comparing with pure silica aerogel (CSA-0) and microporous activated carbon (AC). It was found that CSA-2 has high affinity towards arom. mols. and fast adsorption kinetics. Excellent performance of dynamic adsorption and desorption obsd. on CSA-2 is related to its higher adsorption capacity than CSA-0 and less mass transfer resistance than AC, arising from the well-developed microporosity and open foam mesostructure in the CSA composites.
- 39Li, Z.; Gong, L.; Li, C.; Pan, Y.; Huang, Y.; Cheng, X. Silica Aerogel/Aramid Pulp Composites with Improved Mechanical and Thermal Properties. J. Non-Cryst. Solids 2016, 454, 1– 7, DOI: 10.1016/j.jnoncrysol.2016.10.01539https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslCrurnN&md5=fda8595c63b594db622107a9227c04a9Silica aerogel/aramid pulp composites with improved mechanical and thermal propertiesLi, Zhi; Gong, Lunlun; Li, Congcong; Pan, Yuelei; Huang, Yajun; Cheng, XudongJournal of Non-Crystalline Solids (2016), 454 (), 1-7CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier B.V.)For maintaining the integrality and improving the mech. strength of fiber/silica aerogel composites without compromising thermal insulation properties, aramid pulp reinforced silica aerogel composites were prepd. under ambient pressure drying by adding aramid pulps into silica sol directly. The microstructures indicated the ample fibrillated fibers of aramid pulps were inlaid in silica aerogel matrix which retained the integrality and nice interface adhesion, instead of sepg. the aerogel matrix into small fragments. As the aramid pulp content increased, the compressive strength was enhanced obviously up to about 1.2 MPa and the low thermal cond. of 0.0232-0.0278 W·m- 1·K- 1 approximated linear growth. TG-DTA anal. indicated that the thermal stability of the as-prepd. composites was about 260 °C which primarily depended on the thermal stability of pure silica aerogels. Thus it concluded that excellent silica aerogel composites with intact microstructures, improved mech. strength and tailored thermal properties can be prepd. by using aramid pulps as reinforcements.
- 40Zhong, L.; Chen, X.; Song, H.; Guo, K.; Hu, Z. Highly Flexible Silica Aerogels Derived from Methyltriethoxysilane and Polydimethylsiloxane. New J. Chem. 2015, 39, 7832– 7838, DOI: 10.1039/C5NJ01477H40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1amsLvJ&md5=565b0c9a9c76a666b453deaba4ff6b9dHighly flexible silica aerogels derived from methyltriethoxysilane and polydimethylsiloxaneZhong, Liang; Chen, Xiaohong; Song, Huaihe; Guo, Kang; Hu, ZijunNew Journal of Chemistry (2015), 39 (10), 7832-7838CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)Highly flexible silica aerogels were synthesized using methyltriethoxysilane (MTES) and polydimethylsiloxane (PDMS) as co-precursors via a two-step acid-base sol-gel method followed by ambient pressure drying. The effects of vol. ratio of PDMS to MTES (S) on the flexibility were investigated in detail. It was found that, with the increase of S from 5% to 8.75%, both Young's modulus and the d. of obtained aerogels decrease from 0.136 to 0.030 MPa and 0.098 to 0.064 g cm-3, resp. Aerogels produced at S of 8.75% show excellent compressional and recoverable properties with, their maximal recoverable compressive strain being 70%. The unrecovered strains calcd. immediately and 12 h after compression to 60% strain twenty times are 10.9% and 3.1%, resp. The excellent flexibility performance of silica aerogels derived from MTES-PDMS makes them a promising silica aerogel material for special applications.
Supporting Information
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b04376.
Additional FESEM images of pure CNF and flame-retardant aerogels (Figure S1); FTIR peak ratio (833:896) as a function of SBC concentration (Figure S2); polymer absorption capacity of pure CNF and flame-retardant CNF aerogels submerged in 15 wt % PVA solution during 2 min (Figure S3); moisture absorption of pure CNF and flame-retardant aerogels at 80% RH (Figure S4); comparison of theoretical and calculated SBC content of flame-retardant CNF aerogels (Figure S5); comparison of theoretical and experimental densities of pure and flame-retardant CNF aerogels (Figure S6); values of the onset decomposition temperature (Ton), temperature at the maximum degradation rate (Td), and weight loss at each stage and residue for sodium bicarbonate, pure CNF, and flame-retardant aerogel samples (Table S1); porosity values of pure and flame-retardant CNF aerogels (Table S2); TGA mass balance comparison of theoretical and calculated SBC content at 200 °C of flame-retardant CNF aerogels (Table S4); experimental and theoretical densities of pure and flame-retardant CNF aerogels (Table S5) (PDF)
Videos of combustion of pure CNF and flame-retardant aerogels (Video S1); combustion of pure CNF aerogel (AVI)
Combustion of C-SB10 aerogel (Video S2) (AVI)
Combustion of C-SB30 aerogel (Video S3) (AVI)
Videos of the 3D porous structure of pure CNF and flame-retardant aerogels (Video S4); visualization of 3D porous structure of pure CNF aerogel (AVI)
Visualization of 3D porous structure of C-SB10 aerogel (Video S5) (AVI)
Visualization of 3D porous structure of C-SB30 aerogel (Video S6) (AVI)
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