Liquefaction Of Soy Protein, And Its Characterization And Utilization

Adhesives play a critical role in the qualities of wood-based panels. In our country, petroleum-based adhesives (urea-formaldehyde, phenol-formaldehyde and melamine-formaldehyde) are extensively used to manufacture wood-based panels. However, the raw materials of these adhesives rely on non-renewable fossil fuels, and have a problem of the emission of the toxic gases. As a result, development and using of environmentally friendly adhesive which prepared by renewable resources attract extensive attentions. Soybean protein is the best option to prepare environmentally friendly adhesive, because soy protein is a source of abundant, easy to chemically and physically modified natural polymers. However, due to the special structure of soy protein and larger molecular weight, so that the traditional soybean protein-based adhesives feature a high viscosity and a low solids content, resulting in their poor technical applicability, low bonding strength and poor water resistance, limiting their industrial applications widely.For the complicated structure of soy protein and larger molecular weight, this paper was to utilize physical modification, combined modification and denaturing treatment to prepare a liquefied soybean protein which featured higher solid content, lower viscosity and suitable molecular weight. In this study, the effects of the temperature, the addition amount of sodium sulfite, urea and SDS on the structural properties of the liquefied soybean proteins were examined respectively. Meanwhile, the liquefied soybean proteins blended with the thermal-acid pretreated soybean protein (TSP) and modified polyamide (MPA) to prepare adhesives for plywood which were evaluated by plywood evaluation and viscosity tracing. The results showed that increasing the temperature of the liquefaction system of soybean protein appropriately could improve the technological applicability and bonding strength of soybean protein adhesive; introducing a certain amount of sodium sulfite, urea and SDS to the liquefaction system of soybean protein could enhance the bonding strength and water resistance of soybean protein adhesive efficiently, and prolong the pot life of soybean protein adhesive. When the liquefaction temperature was 70-75 ℃, the addition amount of sodium sulfite, urea and SDS were 1.5wt%,5.0wt% and 1.0wt% respectively, the soybean protein liquefied product possessed lower viscosity, narrow molecular weight distribution, suitable molecular weight and more active groups. At the same time, the soybean protein adhesive for plywood had excellent bonding strength, water resistance and longer pot life.Meanwhile, the optimized soybean protein liquefied product blended with PAE to prepare adhesive for green and environment-friendly particleboard. In this paper, the effects of density and the amount of PAE on the properties of the particleboards were investigated respectively. The results indicated that the internal bond strength and modulus of rupture of particleboard gradually increased, and the thickness swelling decreased as the density of particleboard increased, but when the density of particleboard exceeded 0.70g/cm3, the internal bond strength and modulus of rupture of particleboard declined slightly. When the amount of PAE of the soy protein adhesive gradually increased, the internal bond strength and modulus of rupture of particleboard increased, and the thickness swelling of particleboard decreased significantly.