Experimentally Determined Hansen Solubility Parameters of Biobased and Biodegradable Polyesters

Hansen solubility parameters (HSP) of 15 commercially relevant biobased and biodegradable polyesters were experimentally determined by applying a novel approach to the classic solubility study method. In this approach, the extent of swelling in polymer films was determined using a simple equation based on the mass difference between swollen and nonswollen film samples to obtain normalized solvent uptake (N). Using N and HSPiP software, highly accurate HSP values were obtained for all 15 polyesters. Qualitative evaluation of the HSP values was conducted by predicting the miscibility of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-co-HHx, 7 mol % HHx) and poly(lactic acid) (PLA) with a novel lignin-based plasticizer (ethyl 3-(4-ethoxy-3-methoxyphenyl)propanoate, EP) with a relative energy difference (RED) less than 0.4. Additionally, an HSP-predicted plasticizer (di(2-ethylhexyl) adipate, DA) with a larger RED (>0.7) was used to demonstrate the effects of less-miscible additives. Plasticized samples were analyzed by differential scanning calorimetry and polarized optical microscopy (POM) to determine the Tg depression, with EP showing linear Tg depression up to 50% plasticizer loading, whereas DA shows minimal Tg depression past 10% loading. Further analysis by POM reveals that the DA phase separates from both polymers at loadings as low as 2.5% (PHB-co-HHx, 7 mol % HHx) and 5% (PLA), while the EP phase separates at a much higher loading of 50% (PHB-co-HHx, 7 mol% HHx) and 30% (PLA).


Biodegradation Standards and Methods
Table S1 Biodegradability of polyesters studied Table S2 Heat of fusion (ΔH0) values of polyesters studied Table S3 HSP scoring criteria for each polymer Table S4 HSP scores assigned for each polymer Table S5 HSP distances and RED of both plasticizers with all polyesters Table S6 Data from DSC Scans of plasticized polyesters Table S7 Isothermal crystallization times of plasticized and unplasticized polyester samples Table S8 DSC thermograms of all polyesters Figure S1 Chemical structures of plasticizers Figure S2 DSC thermograms of plasticized polyesters Figure S3 POM Image of control PHB-co-HHx (7% HHx) Figure S4 POM Images of PHB-co-HHx (7% HHx) with DA Figures S5-S9

Definitions and Standards for Biodegradation of Polymers
Degradability of plastic products is a property desirable for many single-use articles which accumulate and contaminate the environment.However, the mechanisms for plastic degradation depend on numerous factors including oxidation, UV degradation, and microbial degradation.Many review articles have been published providing detailed information on several types and mechanisms of polymer degradation.For background information on the topic of polymer biodegradation, we have included definitions that the New Materials Institute has adopted, including the trademarked term Bioseniatic™ first introduced in the lexicon in 2019.
Degradable plastic: A material that will undergo a substantial change in chemical structure under certain specific environmental conditions, resulting in a change in the material properties such as fragmentation, thermomechanical properties, and/or discoloration.Degradable plastics are not necessarily biodegradable or compostable.The process is better described as micronization.
Biodegradable: a degradable plastic in which the degradation results from the action of naturally occurring microorganisms such as bacteria, fungi, and algae.The process of biodegradation depends on the surrounding environment (moisture, temperature, inoculum, microbial load) and on the material itself.
Compostable: a plastic that undergoes degradation by biological processes during composting to yield CO2, water, inorganic compounds, and biomass at a rate consistent with other known compostable materials and leaves no visible, distinguishable, or toxic residue.
Bioseniatic™: a naturally-sourced or synthetically-derived polymer with no additives or chemical modifications to their structure that prevent them from being biologically converted into a nonpolymeric form of naturally occurring, non-toxic compounds at a rate congruous with natural analogues.
In addition to these definitions, several national and international organizations have developed testing methods and standards for defining composability and biodegradation of polymers.Among these organizations, TÜV AUSTRIA has defined criteria which are used as basis by ASTM, ISO, DIN, EN, AS, and others as described. 1,2 etailed information on specimen type, environmental conditions, and test period for ASTM and ISO standards are listed in Table S
Synthesis of poly(ethylene furanoate) (PEF): 14.5 g of 2,5-dimethylfurandicarboxylate (1.0 eq.) and 14.67 g of ethylene glycol (3.0 eq.) were added to a 100 mL three-necked flask equipped with a distillation apparatus and mechanical stirrer.The flask was evacuated under full vacuum and backfilled five times with dry nitrogen before being heated to 160°C.
Once the contents of the flask were homogenous, 67.0 mg of titanium tert-butoxide (0.5 mol % relative to diester) was dissolved in 2.0 mL toluene and added via syringe while stirring at 150 RPM.The reaction was heated to 200°C at a rate of 10°C/hr under nitrogen.Vacuum was then slowly applied over 30 minutes until pressure was sustained below 200 mTorr.The temperature ramp was increased to 20°C/hr until 240°C, at which point the viscosity limit was reached for the apparatus.The flask and contents were cooled under vacuum to room temperature, then 75 mL of hexafluoro-2-propanol were added.The resulting solution was precipitated into 1 L cold methanol.The precipitate was dried under reduced pressure for 24 hours yielding 12.7 g of an off-white polymer (89%).

Synthesis of ethyl 3-(4-hydroxy-3-methoxyphenyl)propanoate
Hydroferulic acid was synthesized as previously reported. 31.94 g of hydroferulic acid (10 mmol), 150 mL of dry ethanol, and 0.1 mL of concentrated sulfuric acid were added to a 500 mL 2-neck flask under nitrogen and refluxed for 5 hours.The solvent was removed under reduced pressure and the residue was dissolved in ethyl acetate.The organic layer was washed three times with water and saturated sodium bicarbonate, then once with brine.The organic layer was dried over magnesium sulfate, filtered, and residual solvent was removed under reduced pressure to afford 1.90 g of ethyl 3-(4-hydroxy-3methoxyphenyl)propanoate as a clear oil (85%). 1

Synthesis of ethyl 3-(4-ethoxy-3-methoxyphenyl)propanoate (EP)
1.12 g of ethyl 3-(4-hydroxy-3-methoxyphenyl)propanoate (1.0 eq.), 2.76 g of anhydrous potassium carbonate (4.0 eq.), 20 mL of dry DMF, and 1.08g of bromoethane (2 .0eq.) were added to a pressure vessel and sealed.The contents of the flask were heated while stirring at 60°C for 12 hours before being combined with 200 mL of distilled water.The aqueous mixture was extracted with ethyl acetate then washed with brine and dried over magnesium sulfate.The mixture was filtered and the solvent was evaporated under reduced pressure to yield 1.23 g of ethyl 3-(4-ethoxy-3-methoxyphenyl)propanoate as a light tan oil (96%).Table S5.HSP scores assigned to solvents for each polyester according to criteria defined in Table S2.Table S7.Data from non-isothermal DSC Scans of PHB-co-HHx (7% HHx) and PLA -Ingeo™ 4032D with samples plasticized using EP and DA.Tm and % crystallinity (% Xc) were obtained from 1 st heating curve.Glass transition temperature (Tg) and (Tcc) were obtained from the 2 nd heating curve.

Full Size Polarized Optical Microscopy Images
The POM images displayed in Figure 2 are fitted to accommodate the author guidelines of the publication.Due to the smaller size of the images, viewing the phase separation observed in DA loaded sample is difficult.The phase separated domains of DA are dispersed throughout the spherulite surface with increasing concentrations.Phase separated domains of EP at higher plasticizer loadings are much smaller than DA domains with only small amounts of separation.Thus, full size images of the control, EP loaded, and DA loaded polymers spherulites are included in the following Figures S4-S27.

Figure S1 .
Figure S1.DSC thermograms of the first heating curve of the polymer film samples used in this study.Solubility Study Data Table S4.HSP scoring criteria for each polymer studied.All values listed are in normalized solvent uptake .(ImDis -Dissolution of film within 1 hour; DisD -Dissolution of film within 24 hours; DisT -Dissolution of film within the duration of testing; SwlUnrec -Film swells to such an extent that it is no longer recoverable) Figure S2.Plasticizers for compatibility studies.a) Ethyl 3-(4-ethoxy-3-methoxyphenyl)propanoate (EP) and b) Di-(2-ethylhexyl)adipate (DA).

Table S2 .
.1.Additionally, the polymers studied are also classified by their status measured by the standards in Table S.2.Classification of polymers studied by biodegradability in various conditions described by standards.

Table S3 .
Heat of fusion (ΔH0) values used to determine % crystallinity of polyesters.

Table S6 .
HSP distances (Ra) and RED values of EP and DA with all polyesters studied.
DSC Thermograms of Unplasticized and Plasticized Polarized Optical Microscopy Samples