High temperature performance of soy-based adhesives

We studied the high temperature performance of soy meal processed to different protein concentrations (flour, concentrate, and isolate), as well as formulated soy-based adhesives, and commercial nonsoy adhesives for comparison. No thermal transitions were seen in phenol-resorcinol-formaldehyde (PRF) or soy-phenol-formaldehyde (SoyPF) or in as-received soy flour adhesive during differential scanning calorimetry scans heating at 10 degrees C/min between 35 and 235 degrees C. Heat flow rates decreased in the order soy flour (as received)>SoyPF>PRF>emulsion polymer isocyanate (EPI). In thermogravimetric analysis (TGA) scans from 110 to 300 degrees C at 2 degrees C/min, total weight loss decreased in the order soy flour (as-received)>SoyPF>PRF>casein>maple>EPI. For bio-based materials, the total weight loss (TGA) decreased in the order soy flour (as-received) > concentrate, casein>isolate. Dynamic mechanical analysis from 35 to 235 degrees C at 5 degrees C/min of two veneers bonded by cured adhesive showed 30-40% decline in storage modulus for maple compared to 45-55% for the adhesive made from soy flour in water (Soy Flour) and 70-80% for a commercial poly(vinyl acetate) modified for heat resistance. DMA on glass fiber mats showed thermal softening temperatures increasing in the order Soy Flour