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

Abstract

Abstract 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.