Assessment and application of phosphorus/calcium-cottonseed protein adhesive for plywood production

Authors: LI, JUN - Kansas State University; PARDYAWONG, SAROCHA - Arkansas State University; He, Zhongqi; SUN, XIUZHI, S - Kansas State University; WANG, DONGHAI - Kansas State University; Cheng, Huai; ZHONG, JUNYAN - Intertek Analytical Services

Submitted to: Journal of Cleaner Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2019
Publication Date: 8/20/2019
Citation: Li, J., Pardyawong, S., He, Z., Sun, X. S., Wang, D., Cheng, H. N., Zhong, J. 2019. Assessment and application of phosphorus/calcium-cottonseed protein adhesive for plywood production. Journal of Cleaner Production. 229:454-462. https://doi.org/10.1016/j.jclepro.2019.05.038.
DOI: https://doi.org/10.1016/j.jclepro.2019.05.038

Interpretive Summary: Adhesives are widely applied in pressed wood products, such as plywood, particle board, and medium density fiberboard, used for furniture, kitchen countertops and cabinets, flooring materials, and wall constructions. cCottonseed protein isolate (CPI) has been reported having an adhesion performance comparable to or better than soybean protein isolate (SPI), but there is still room for improvement. Thus, in this work, the effects of H3PO4, K2HPO4, CaO, and CaHPO4 at four concentrations (i.e., 20, 40, 60, and 80 mM) on the dry, wet, and soaked strengths of CPI were evaluated. The solid state 13C NMR spectroscopic features of the CPI adhesives were altered by the P compounds showing the amino groups interacted with these P compounds in the blending adhesives. With the optimal bonding conditions, the 3-plywood boards bonded by cottonseed meal-based adhesives meet the requirements of Type II plywood and could classified as Type II plywood per the US standard ANSI/HPVA HP-1-2016, indicating that the adhesive under optimal conditions can meet the water resistance requirement and can be used as a green and environmentally-friendly adhesive resource in wood industry.

Technical Abstract: Cottonseed protein isolate (CPI) is a great potential alternative to formaldehyde-based adhesives as a renewable resource without negative environmental impact in use. Like other protein-based adhesives, unmodified cottonseed protein needs improved water resistance. Thus, in this work, the effects of H3PO4, K2HPO4, CaO, and CaHPO4 at four concentrations (i.e., 20, 40, 60, and 80 mM) on the dry, wet, and soaked strengths of CPI were evaluated. Compared to the CPI without modifiers (control), H3PO4 (20 and 40 mM), K2HPO4 (40 and 60 mM), CaO (20 and 40 mM), and CaHPO4 (40, 60, and 80 mM) increased the three adhesion strengths (dry, wet, and soaked) of CPI by 20-30%, 72-88%, and 24-30%; 8-22%, 2-10, and 1-8%; 8-16%, 11%, and 6%; and 12-26%, 6-13%, and 7-14%, respectively. CPI with 40 mM H3PO4 had the best adhesive performance especially water resistance (88% increase in the wet tensile strength as compared to control), due to the increased crosslinking caused by phosphorus and CPI being at its isoelectric point caused by acidity of H3PO4 (pH, 4.13). Solid state 13C NMR spectroscopic analysis showed that the amino groups interacted with these P compounds in the blending adhesives. Finally, an optimized CPI adhesive preparation was applied to bond 3-ply pine plywood. The water resistance of these 3-ply strips passed the industrial soak test as Type II plywood used for hardwood and decorative plywood, indicating that the adhesive under optimal conditions can be used as a green and environmentally-friendly adhesive resource in wood industry.