Facile Approach for Glutaraldehyde Cross-Linking of PVA/Aluminophosphate Adhesives for Wood-Based Panels

The application of aluminophosphate adhesives in wood-based panel industries is limited by the adhesives’ inherent disadvantage of poor water resistance caused by their mesoporous nature. In this study, poly(vinyl alcohol) was used as the modifier while glutaraldehye was employed as the cross-linker to reduce the water-uptake of the aluminophosphate bond interface in Pinus massoniana plywood. The influence of the cross-linking on the reaction mechanism, morphology, thermal stability of the adhesives, and tensile strength of the plywood was examined using FTIR, XRD, XPS, TGA, and SEM analyses. The SEM images showed the absence of pores on the adhesive surface at 1, 3, and 5% glutaraldehyde. Crystalline peaks were observed in aluminophosphate adhesives at a lower reaction temperature (110 °C). The C–O bonds were reduced, leading to the increase in C–C/C–H that could account for the bond stability in water after revealing hydrogen bonding between the plywood interfaces. Consequently, the wet tensile strength of PVA/aluminophosphate-based plywood was enhanced significantly (P < 0.05) above the type II Chinese standard, achieving a strength as high as 1.02 MPa. Also, the dry tensile strength improved slightly to 2.34 MPa compared to unmodified aluminophosphate adhesive. Therefore, modification with PVA and the addition of glutaraldehyde as a cross-linker could enhance the water stability of aluminophosphate-based plywood. This research has demonstrated the potential improvement of the plywood bondline and the industrial utilization of formaldehyde-free aluminophosphate adhesive for the wood-based panels.