ARS | Publication request: Evaluation of sorghum flour as extender in plywood adhesives for sprayline coaters or foam extrusion

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 2011
Publication Date: July 1, 2011
Citation: Hojillaevangelist, M.P., Bean, S. 2011. Evaluation of sorghum flour as extender in plywood adhesives for sprayline coaters or foam extrusion. Industrial Crops and Products. 34(1): 1168-1172.

Interpretive Summary: In this research, we tested sorghum flour as a protein extender in plywood glues for sprayline coater or foam extrusion. The biorenewability of sorghum and competitive price of its byproducts make the adhesive attractive to plywood manufacturers as alternative glue. We first analyzed the solubility and foaming properties of sorghum flour protein to predict its behavior under the highly caustic conditions of plywood adhesive. We then substituted the sorghum flour for the extender in the industry sprayline glue mix (wheat flour) on a protein content basis and determined its mixing and bonding properties. The adhesive containing sorghum flour had mixing properties and appearance that were superior to those of the standard wheat flour-based plywood glue, but its viscosity and bond strength were markedly less. To resolve these problems, we doubled the amount of sorghum flour in the glue mix to increase its protein contribution. Both viscosity and adhesion strength of the modified sorghum-based plywood glue were significantly improved to acceptable levels. The modified sorghum flour-based plywood glue also produced substantial foam that remained stable up to 3 h. These results demonstrated that sorghum flour is a viable extender in plywood glues for sprayline coater or foam extrusion. The manufacture of this sorghum flour-based adhesive will expand the 2.4 million metric tons of sorghum that is allocated for combined food, seed, and industrial use (of which such industrial products account for a minimal amount), and thus will generate more income to U.S. sorghum growers.

Technical Abstract: This study was conducted to evaluate sorghum flour as protein extender in plywood adhesive for sprayline coaters or foam extrusion. Defatted sorghum flour, containing 0.2% (dry basis, db) residual oil and 12.0% (db) crude protein, was analyzed for solubility and foaming properties. Sorghum flour proteins were least soluble (less than or equal to 12%) under acidic pH, most soluble (72%) at pH 10, and produced substantial and highly stable foam at pH 10. Sorghum flour was substituted (on protein content basis) for wheat flour in the standard glue mix. Mixing properties and bond strength of the sorghum-based glue were compared with those of the industry standard glue. The adhesive containing sorghum flour as protein extender had mixing properties and appearance that were superior to those of the standard wheat flour-based plywood glue, but its viscosity and bond strength were markedly less. Doubling the amount of protein contributed by sorghum flour in the glue mix markedly improved both viscosity (1104 cp) and adhesion strength (199 psi) of the sorghum-based plywood glue to acceptable levels. The modified sorghum flour-based plywood glue also produced substantial foam that remained stable up to 3 h. These results demonstrated that sorghum flour is a viable extender in plywood glues for sprayline coater or foam extrusion.