Sticky but friendly

A wood adhesive that contains up to 75% soy has been developed at the Forest Products Laboratory (FPL) in Madison, Wisconsin.

Researchers from FPL, a unit of the USDA Forest Service, collaborated with researchers from Heartland Resource Technologies of Oelwein, Iowa to create a low cost, durable product that is more environmentally friendly than today's petroleum-based adhesives.

Soy-based glues were popular in the early 20th century and worked well in plywood panels, as long as they were kept dry. But the poor water resistance of the soy-based adhesives limited their use to internal applications. This factor led to their almost complete replacement by petroleum-based adhesives, which were superior in durability and offered a lower cost. Since the transition, petroleum-based glues have dominated the markets.

The recent increase in the price of petroleum has made soy-based glues an attractive alternative if previous limitations can be overcome. Charles Frihart, Supervisory Research Chemist at FPL, and James Wescott, Chief Operations and Technical Officer of Heartland Resource Technologies, decided to study soy as an adhesive and see if they could improve upon old formulations.

'The purpose of this project was to see if we could build on the advantageous properties of soy and overcome its main deficiency of failing when wet,' said Wescott.

'Although soy research isn't new, our approach is different,' said Frihart. 'We took a very scientific, systematic approach to understanding the chemistry of soy adhesives. Others have looked at how much soy can be added to an adhesive. We're looking at making soy an integral part of the network that actually gives strength to the material.'

Researchers developed several formulations of soy and phenol hybrid adhesives and used them in the face section of strandboard. The samples were tested using standard methods, including immersing the boards in water for 24 hours and boiling them for two hours. The samples were then evaluated to determine how well they held up.

'We were able to create an adhesive that was up to 75% soy, with the remainder being phenol and formaldehyde, that proved to be very durable," said Wescott. Not only does this adhesive use much less petroleum-based phenol than a standard adhesive, but it also uses less natural gas-based formaldehyde.

In addition to studying the fundamental chemistry of the adhesive, researchers also kept in mind that what they developed had to be commercially viable.

With those two aspects of the project in mind, they created an adhesive that performs equally as well as those available today, and can be manufactured using a process very similar to those currently used in industry.