Preparation and its Properties of the Urea Modified Soy Protein Isolate Adhesives

Abstract

Soy proteins have shown great potential for use as renewable and environmentally friendly adhesives. The orthogonal experiments are designed for the urea-modified soy protein isolate(SPI) adhesives and the optimum formula is obtained. The mass concentrations of SPI and urea are 14% and 8%(relative to the total mass of SPI and water), the reaction temperature and time are 35°C and 60 min, respectively. Some basic and adhesion properties and its structure of the modified SPI adhesive for the optimum formula are measured. The viscosity is 43Pa.s, and the dry- and wet-state adhesion strengths of the urea-modified SPI optimum formula are 0.96MPa and 0.78MPa(>0.72MPa), respectively according to GB/T10724-2006, which satisfied with the requirement of the II-type plywood. Its surface hydrophobicity is improved and the thermal properties is slightly improved after 200°C. Recently, some concerns about environmental pollution, resource scarcity, and related health issues have pushed scientists to replace the petrochemicals-based synthetic polymers, which are used extensively in construction, packaging, glue and plywood industries, with the bio-based adhesives. SPI adhesives have shown great potential for use as environmentally friendly adhesives in plywood since 1930s when it’s first be developed. And it has been modified by chemical alkali[1], sodium dodecyl sulfate(SDS)[2,3], and urea[2], guanidine hydrochloride[4], etc. However, most of these modifications can not very well improve the water resistance and the bonding strength separately. Poor water resistance is a fatal weakness which seriously restricts the application in the industry. Many studies[5~8] have shown that the adhesives with some enhanced performances, for example, adhesion strength and water-resistant, can be obtained by unloading SPI molecular chain with the hydrophobic group using urea, SDS, other surfactant and guanidine hydrochloride, etc. And the unloading mechanism of the SPI molecular chain with the hydrophobic group is proclaimed. The optimum concentration of urea is 1mol/L for the water-resistant. The aim of this research was to improve the tacky strength and the water resistance[9] by using urea to modify SPI and evaluate the resulting adhesive’s potential for use in the plywood.