Adhesion Properties of Plywood Glue Containing Soybean Meal as Extender

Authors: Hojilla-Evangelista, Milagros - Mila

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2010
Publication Date: 4/27/2010
Citation: Hojillaevangelist, M.P. 2010. Adhesion Properties of Plywood Glue Containing Soybean Meal as Extender. Journal of the American Oil Chemists' Society. DOI: 10.1007/s11746-010-1586-x. v. 87(9):1047-1052.

Interpretive Summary: We tested soybean meal as extender in plywood glues applied by sprayline coaters. The low cost of the meal and biorenewability of soybeans make our formulation an attractive alternative glue for plywood manufacturers. The production of this soybean meal-based adhesive will also consume about 3.4 million kg (7.5 million pounds) of soybean meal per year, which will be provided by 157,000 bushels of soybeans, thus generating value-added income to soybean growers in the United States. Soybean protein products, like flour and meal, have had a successful history as adhesives in the wood products industry. However, they fell out of use with the introduction of the petrochemical-based synthetic resin adhesives. There has been renewed interest on soybean-based wood glues in recent years, largely to address environmental concerns related to formaldehyde resins, which are the main binders in many wood glues. In an earlier work, we successfully developed a soybean flour-based foamed plywood adhesive. In the present study, we evaluated soybean meal, which contains 51% crude protein, as extender in plywood glues intended for sprayline coaters. We first substituted the soybean meal for the standard extender in the industry glue (wheat flour) on a protein content basis and determined its mixing and bonding properties. We found the soybean meal glue to have acceptable mixing properties and viscosity (thickness), but it formed a weaker bond than the standard glue. To improve bond strength, we then further modified our formulation by increasing the amount of soybean meal such that it provided double the amount of protein than what was present in the original glue mix. This modified soybean meal adhesive had bond strengths that equaled that of the industry standard glue while retaining satisfactory mixing properties. Our results demonstrated that soybean meal is a viable extender in plywood glue for sprayline coater.

Technical Abstract: This study was conducted to evaluate the performance of soybean meal as protein extender in plywood adhesive intended for sprayline coaters. Ground soybean meal, with 51.5% (dry basis, db) crude protein and 1.5% (db) residual oil, replaced the current industry extender, wheat flour, in the standard glue mix. Substitution was done on protein content basis. Mixing and adhesion properties of the glue containing soybean meal were compared with those of the industry standard glue. The soybean meal-based glue showed excellent mixing characteristics and its viscosity (1240 cp) met the recommended value for this type of adhesive. Its tensile strength, however, was less than that of the standard glue and below the threshold value of 200 psi considered as indicator of strong bonding. The soybean meal glue formulation was then modified further by increasing the amount of meal such that the amount of protein present was double that contributed by wheat flour in the original mix. This adjustment resulted in higher tensile strength (208 psi), which not only met the threshold value for strong glue bonds but also equaled that of the standard glue. These results demonstrated that soybean meal is a viable extender in plywood glue for sprayline coater.