Soybeans resurface in wood glue
Soy flour could replace the phenol formaldehyde adhesives in wood composite products, reducing formaldehyde emissions.
Soy-based glues for wood products were popular until the 1950s, when they were replaced by petroleum products that had longer shelf lives and were more water-resistant. But wood products that use soy glues, which have lower toxic emissions and cheaper production costs than petroleum-based products, could be on the shelves again in a few months.
Today’s petroleum-based resins use a combination of phenol or urea with formaldehyde, resulting in emissions of volatile organic compounds (VOCs) during the manufacture and use of wood products. The U.S. EPA and the Occupational Safety and Health Administration (OSHA) classify formaldehyde as a possible carcinogen. OSHA limits workers’ exposure to 0.75 parts per million (ppm) over 8 hours, with a short-term limit of 2 ppm over 15 minutes. Currently, no U.S. regulations cover VOCs in nonindustrial indoor air, but indoor formaldehyde levels often reach more than 0.3 ppm, according to EPA. Those levels are high enough to affect human health. The American National Standards Institute requires composite wood materials to emit less than 0.2 ppm.
Some manufacturers voluntarily use proprietary methods to meet these guidelines, says Deland Myers, an Iowa State University food science professor who researches soy-protein products, including soy adhesives. “Using soy protein is another avenue to doing that,” he says. Soy-based glues could be “lower-cost, and they are bio-based... . I would assume that an adhesive that’s more bio-based would probably be something that can be recycled a lot easier.”
Because it is a byproduct of soybean oil production, soybean meal is a renewable and low-cost commodity, says Frank Trocino, CEO of Heartland Resource Technologies, an adhesives company that has consulted with Myers in the past. Depending on the cost of phenol and the amount of it replaced by soy flour, manufacturers of composite wood products could save 10–40% of their costs by making the switch.
Heartland’s soy adhesive combines phenol formaldehyde resins and soy flour in a 1:1 ratio. The company is working with researchers at the U.S. Department of Agriculture’s Forest Products Laboratory to make resins that are more than 65% soy flour. Since the product still contains phenol formaldehyde, it retains its water resistance.
“The biggest problem with soy in the past was water resistance,” says Trocino. He says that the new glue is water-resistant enough to be used outdoors. Trocino has now licensed the technology to an adhesives manufacturer and a wood-products company.
According to Philip Bibeau, executive director of the Wood Products Manufacturers Assoc., some pressure exists in California to reduce VOC emissions from wood products, but it is not enough to create a large demand for soy-based glues. Such resins are “starting to become more of a need for people looking for green types of products, [but] that demand is a very small percentage of the marketplace,” he says. “It’s not like people are contacting us and saying, ‘Please help me find a soy-based supplier for adhesives.’”
But Trocino believes otherwise, saying that tighter national emissions guidelines may pique the interest of wood-products companies. The World Health Organization (WHO) has tougher rules on formaldehyde exposure than EPA and OSHA do; it recommends an exposure limit of 0.05 ppm. In 2004, WHO went one step further and classified the gas as a known carcinogen. The move “created a lot of stir in the industry, and now everyone’s looking at [reducing] formaldehyde,” Trocino says. He suggests that if the U.S. lowers its emissions standards, wood-products manufacturers could consider using soy-based adhesives to meet them.
