A low-cost, formaldehyde-free, and high-performance starch-based wood adhesive

An environmentally friendly starch-based wood adhesive was developed using cassava starch (CS) and polyvinyl alcohol (PVOH). A set amount of polymethylene polyphenylene isocyanate (PAPI, modified in the laboratory) was used as the cross-linking agent to improve the water resistance. To evaluate the mechanical properties of the adhesive, the shear strength was measured by a mechanical testing machine. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were used to characterize the properties of the adhesive and the curing products. The results indicated that the adhesive using PVOH with a low alcoholysis degree was better than high alcoholysis degree and adding 7 wt% PVOH1 (RS-1717) could obtain good mechanical properties; the dry shear strength was 7.77 MPa, reaching 1.36 MPa in the wet state. The favorable results were attributed to reactive hydrogens in the wood and CS, which can form a cross-linking network with the -NCO groups of PAPI to obtain excellent shear strength and water resistance.