Spectroscopic Characterization of the Chemical Changes Occurring in Soy Wood Composite Adhesives When Exposed to Moisture

Solid-state surface attenuated total reflectance Fourier transform infrared spectroscopy (SATR-FTIR) and solid-state nuclear magnetic resonance spectroscopy (SSNMR) were used to characterize the physiochemical changes in solid soy-flour adhesives upon exposure to water. Comparisons were made between adhesives that were prepared with and without the crosslinking chemical polyamideamine-epichlorohydrin (PAE). Comparisons were also made between neat monolithic adhesive films, and adhesives that were laminated to yellow poplar ( Liriodendron tulipifera ). FTIR data revealed that the relative surface concentration of water-soluble components on neat monolithic adhesives was higher prior to water-exposure as compared with the adhesive laminated to wood. Moreover, the chemical composition of the water-soluble extract was affected by PAE. After soaking in water, the water-soluble components were observed to dissolve and disappear from the surfaces of the adhesives, as well as from the surfaces of water-soaked wood-laminate specimens. Similarly, SSNMR results corroborated with the dissolution and disappearance of the water-soluble components from the neat monolithic adhesives after water soaking. Moreover, it was discovered that the water-soluble components have a plasticization effect when PAE is used as a crosslinker. The implications of these findings as they pertain to the mechanism of adhesion will be discussed.