Peel adhesion properties of modified soy protein adhesive on a glass panel

Soybean proteins have shown great potential for use as renewable, environmentally friendly adhesives. In this research, peel adhesion properties of NaHSO3-modified soy protein (MSP) adhesives between a paper label and glass substrate were studied. Soy protein isolates (SPIs), soy flour (SF) suspension, and commercial polyvinyl acetate (PVAc) based adhesive were used as comparison. With a 30 g/m2 coating cured at 24 °C, peel strength of MSP on a glass substrate increased rapidly with curing time and resulted in paper cohesive failure at about 150 s of curing time. Paper cohesive failure occurred at about 180 s for SPI and SF suspension and at 10 min for PVAc. At a higher curing temperature, less curing time for MSP was needed to reach the same peel strength. MSP had better water resistance than SPI, SF suspension, and PVAc in terms of “sweating” peel strength. When blended with MSP, PVAc showed shorter curing time, higher water resistance, and lower viscosity. Thermal and morphological studies showed that no chemical reaction occurred between soy protein and PVAc.