Formulation of green adhesives from mixtures of soy protein isolates and rosin ester resin

Abstract

Soy protein (SP) has shown great potential for use as a renewable and environmental friendly adhesive. The early soy protein based adhesives used soy protein as the main ingredient, however, due to issues of insufficient tackiness and water resistance, the SP had to be blended together with (non-renewable and potential toxic) epoxy or phenol formaldehyde (PF) groups in wood adhesive applications. Since the 1960s soy protein adhesives have not been extensively used in the wood industry due to epoxy and phenol PF groups that are not environmentally friendly as they release volatile organic compounds into the air in addition to the elevated cost of phenol.

Because of the environmental safety pressure and high petroleum cost, there is high demand for biodegradable adhesives. In this thesis we develop environmentally benign and less toxic liquid glue from renewable sources, soy protein isolate (SPI) that was blended with a biodegradable rosin ester resin that serves as a tackifier. This modified soy protein (MSP) adhesive was formulated at different mixture ratios of soy protein isolate (SPI) and rosin ester resin to evaluate the adhesion strength and the mechanical bonding behavior as determined by measurements of viscosity and the peel adhesion strength (ASTM D3330-2) on wood and glass surfaces. Based on these preliminary studies, we found that a mixture of SPI and rosin ester resin with a tackifier/SPI mass ratio of (1.3) yielded the maximum adhesion strength on wood and glass substrates. Compared with current commercial liquid glue, this formulation of the MSP adhesive also shows similar adhesion performance. This means that the MSP adhesive is a possible alternative to the purely synthetic adhesives.