An Eco-Friendly Wood Adhesive from Alfalfa Leaf Protein

According to the preparation method commonly used for soy proteinbased adhesives, alfalfa leaf protein was used as the raw material to prepare alfalfa leaf protein-based wood adhesive. Differential scanning calorimetry analyzer (DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize properties of the alfalfa leaf protein-based adhesive in this paper. The results revealed the following: (1) Chemical compositions and chemical structures of the alfalfa leaf protein were basically identical with those of the soy protein, both belonging to spherical proteins with the basis and potential for protein adhesives preparation, and spatial cross-linked network structures would be easily formed. (2) Alfalfa leaf protein and soy protein adhesives had the similar curing behaviors, curing temperature of alfalfa leaf protein-based adhesive was relatively lower, and the heating rate had minor influence on curing temperature of alfalfa leaf protein-based adhesive. At different heating rates, change tendencies of curing reaction degrees of both the two adhesives were not totally the same. (3) Activation energy and reaction frequency factor of the alfalfa leaf protein-based adhesive were higher than those of soy protein-based adhesive, indicating that the curing reaction of the alfalfa leaf protein adhesive was more difficult than soy protein-based adhesive, thus the dry shear strength and water resistance of alfalfa protein-based adhesive were lower than those of soy protein-based adhesive. Dynamics models of curing reactions of alfalfa leaf protein-based adhesive and soy protein-based adhesive are dα/dt = 1.06 × 1013e-97370/RT (1 — α)0.938 and dα/dt = 1.09 × 1011e-84260/RT (1 — α)0.928 respectively. The results of this study will expand the selection of raw materials for protein-based wood adhesives.