A formaldehyde-free adhesive for particleboards based on soy flour, magnesium oxide, and a plant-derived enzymatic hydrolysate

Abstract

An adhesive for particleboards based on natural materials was prepared. Soy flour (38.9 wt%), magnesium oxide (MgO) (2.8 wt%), and a hydrolysate from an agricultural crop (13.9 wt%) were mixed with water and ground in a ball mill at 44% solids. The solubility and interaction of the soy flour proteins and the proteins contained in the plant hydrolysate were triggered by the strong basic environment created by MgO in the presence of water. The natural adhesive appeared to be thermally stable at temperatures from 130 °C to 240 °C, with unchanged mass and no major signals in the thermal analysis curves. These results, together with a viscosity of 510 Pa·s at 25 °C, suggested a good operability of the adhesive. Three-layered particleboards were manufactured with weight combinations of natural adhesive and polyamidoamine-epichlorohydrin (PAE) of 0%:100%, 33%:67%, 50%:50%, 67%:33%, and 100%:0%. The natural adhesive showed inferior internal bond strength and poor water resistance compared with urea-formaldehyde-bonded boards. Addition of the PAE significantly improved the internal bond and swelling, and for all the combinations these properties were comparable or, in most cases, better than in the urea-formaldehyde controls. All boards were formaldehyde-free, while the natural adhesive itself released no dangerous volatile substances.

Fully Biobased Soy Protein Adhesives with Integrated High-Strength, Waterproof, Mildew-Resistant, and Flame-Retardant Properties

“…Much effort has been devoted to improving the comprehensive performance of SPWAs, , including soy protein modification, chemical cross-linking, − nanoreinforcement, − and multinetwork construction. , Among them, the chemical cross-linking strategy is one of the most effective methods to enhance the bonding strength and water resistance of SPWAs . Epoxy, aldehydes, polyurethane, polyamidoamine epichlorohydrin, magnesium oxide, and phenol formaldehyde resin have been developed as the chemical cross-linker to react with the hydrophilic active groups of the soy protein backbone, which could form a continuous network and reduce the hydrophilicity of resulting adhesives. However, these chemical cross-linkers are mainly derived from nonrenewable petroleum resources, which cannot meet the green and sustainable development requirements of wood adhesives.…”