Cottonseed protein bioadhesive with high adhesion performance achieved by a synergistic dual-crosslinking strategy

Plant adhesives have great potential as substitutes for formaldehyde-based adhesives due to their environmental friendliness, low cost, and nontoxicity. However, the application of this type of adhesive is challenged by its water resistance. Herein, an environmentally friendly bioadhesive was prepared from biomaterials, including waste cottonseed protein and sawdust. Isophorone diisocyanate (IPDI) and oxidized cellulose (OC) were used as double crosslinking modifiers. A protein-based bioadhesive with excellent adhesive properties and stable hydrothermal resistance was produced. The impact of IPDI and OC on the crosslinking network was evaluated by detailed Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry analysis. It was found that IPDI and OC, as crosslinking agents, synergistically improved the dry and wet bonding strength of the adhesive. At the optimal loadings of 10% OC and 20% IPDI, the wet bonding strength of the adhesive reached 1.55 MPa on average, which is more than twice that of the Chinese Type II plywood adhesive standard (0.7 MPa). The dry bonding strength also increased to 2.67 MPa with this addition. The improvements in bonding strength as well as the water-resistance of the bioadhesive were ascribed to the formation of a dual-crosslinking network between the IPDI, OC, and cottonseed protein. Both protein-oxidized cellulose and protein-isophorone diisocyanate crosslinking networks were formed in the adhesive system, tightly combining the adhesive components. Thus, the biodegradable adhesive developed in this work provides an effective and convenient approach for the development of all-biomass-derived adhesives, and the constructed high-performance adhesive presents potential application for sustainable wood products.