Abstract
The ethylene glycol diglycidyl ether (EGDE) as a viscosity reducer, plasticizing agent, and crosslinking agent was introduced into the adhesive system to improve the properties of the soy-based adhesive. The adhesive properties including viscosity, solid content, and shear adhesion of soy protein adhesive were measured. The morphology, infrared spectra, and crystallinity of the cured adhesives were evaluated with scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The results showed that the viscosity of soybean flour (SF) adhesive was reduced by 48% and the solid content increased from 25.9% to 31.7% with the addition of 10 wt% EGDE. The wet shear strength of the plywood bonded by EGDE-modified SF adhesive was significantly improved owing to the formation of crosslinking structure in the adhesive system. The SEM, FTIR, and XRD results demonstrated that the crosslinking reaction among epoxy group of EGDE, the amino group of SF, and the hydroxyl groups of polyvinyl alcohol occurred successfully during the curing process.
Highlights
Soy-based adhesives were developed in 1923 and widely used in commercial production of plywood between 1930s and 1960s, but later they were placed by petroleum-based adhesives owing to the poor adhesion property and water resistance [1, 2]
The viscosity of ethylene glycol diglycidyl ether (EGDE)-modified soybean flour (SF) adhesive decreased with the increasing dosage of EGDE (Table 1)
The viscosity was reduced slightly along with the dosage increasing from 0 to 2 wt% EGDE, but after 4 wt% EGDE, the viscosity was reduced by 26% from 102000 to 75000 cP
Summary
Soy-based adhesives were developed in 1923 and widely used in commercial production of plywood between 1930s and 1960s, but later they were placed by petroleum-based adhesives owing to the poor adhesion property and water resistance [1, 2]. The introduction of a crosslinking agent allows the soy proteins to form a threedimensional network structure, improving the adhesion properties of soy-based adhesives. Many chemicals can be used as a crosslinking agent for soy-based adhesives such as the chemicals with epoxy group [11, 12]. Epoxy resin (EPR) can react with the amine group in soy protein and improve the water resistance of soy-based adhesives [10, 15]. Polyethylene glycol (PEG) can reduce the viscosity of soy-based adhesive, which is against the shear strength owing to the lack of reactive functional groups. EGDE as a viscosity reducer and crosslinker was introduced into the soy flour (SF) adhesive system. The viscosity, solid content, shear adhesion, morphology, infrared spectra, and crystallinity were evaluated to investigate the effects of EGDE on the adhesion property and water resistance of SF adhesives
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