Properties of a new renewable sesame protein adhesive modified by urea in the absence and presence of zinc oxide

Abstract

Sesame protein (SP) is a new renewable resource for wood adhesives because of its brilliant performance, which is non-toxic and harmless to human health during the process of using plywood. This study was focused on the application of sesame protein to produce wood adhesive via urea and zinc oxide (ZnO) modification. The pH value, solid content, apparent viscosity, bonding strength, infrared spectra, thermal stability, and fracture surface of urea-modified sesame protein adhesives in the absence of ZnO (USP) and in the presence of ZnO (ZUSP) were investigated in detail. The results suggested that the pH value and solid content of the ZUSP adhesives increased, whereas the apparent viscosity of the ZUSP adhesives showed an increasing trend when ZnO was introduced. The wet shear strength of the ZUSP adhesives improved remarkably, which achieved the required value for interior use (≥0.70 MPa), which was in accordance with the China National Standard. The infrared spectra (FTIR) indicated that the chelation reaction occurred between the USP adhesive and ZnO that improved the water resistance. The thermal stability of the ZUSP adhesives was better than that of the USP adhesive, as confirmed by the thermogravimetric analysis (TGA). After ZnO was introduced, the fracture surface of the ZUSP adhesives became more compact as compared to that of the USP adhesive, as confirmed by scanning electron microscopy. The ZUSP adhesive is a favorable potential candidate as a green-adhesive for the plywood industry, which will promote the utilization of sesame protein.