Submitted to: Starch
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/1999
Publication Date: N/A
Citation: Interpretive Summary: New markets are needed for farm commodities, including corn. Developing wood adhesive from corn starch is one useful approach. Not only will it utilize a renewable resource produced in abundance in the United States, but it will help alleviate environmental and health concerns. Currently available wood adhesives are derived from synthetic resins (containing formaldehyde and phenolic compounds) which are considered priority pollutants by the EPA. Health risks posed by their emission in the environment and workers' exposure at manufacturing facilities are issues. This report describes a starch- based adhesive which exhibited excellent mechanical and moisture resistance properties compared to commercially available synthetic adhesives. This approach not only reduces the amount of petroleum based materials conventionally used in manufacturing construction grade plywood but also adds value to an important agricultural crop. The research is of interest to other scientists, farmers, corn processors, and wood manufacturers.
Technical Abstract: An environmentally friendly wood adhesive was developed by crosslinking cornstarch and polyvinyl alcohol (PVOH) with hexamethoxymethylmelamine (Cymel 323). Citric acid was used as a catalyst, and latex (UCar 443) was added to improve moisture resistance. The adhesive was evaluated for its utility in plywood manufacture. It exhibited excellent mechanical properties comparable to many of the commercially available urea-formaldehyde plywood adhesives used for interior applications. The viscosity of the adhesive at 27% (wt/vol) was 7000 cps, allowing easy application to wood surfaces by brush. The minimum concentration of crosslinking agent needed to achieve good mechanical properties in plywood was 15% (wt/wt proportion of total solids). Optimum curing temperature and curing time were 175 deg C and 15 minutes, respectively. Addition of latex to the adhesive formulation improved both moisture resistance properties and physical properties of plywood test samples. Samples prepared with an optimal adhesive formulation, when completely immersed in water for 2 hours or exposed at 93% or 50% relative humidity (RH) for 30 days, exhibited >90% failure in the veneer as opposed to <10% failure in the adhesive joints.