Properties and thermal analysis study of modified polyvinyl acetate (PVA) adhesive

Abstract

Polyvinyl acetate (PVA) adhesive is one of the most common types of adhesives has been used in the wood industry for decades. However, many drawbacks are still associated with this adhesive including low water resistance, poor bond strength, and low viscosity. In this reported study, two additives, sulfanilamide and N,N-dimethylethylenediamine, were used to modify a PVA adhesive to improve its comprehensive practical performance. The prepared adhesive samples were characterized by Fourier transform infrared spectroscopy (FT-IR). Furthermore, the thermal decomposition characteristics of the PVA adhesives were studied using Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry analysis (DSC) combined with the Kissinger method. The experimental results showed that when compared to the pure PVA adhesive, the solid content, viscosity, dry bond strength, and wet bond strength of the modified PVA adhesive (PVA + N,N-dimethylethylenediamine + sulfanilamide) were improved by 34.8, 41.4, 47.0 and 35.2%, respectively. FT-IR analysis indicate that these two additives altered the chemical bond ratio that resulted from the generation of new chemical bonds, which explained the improved performance of the modified PVA adhesive. The pure PVA adhesive possessed two thermal decomposition steps, while the modified PVA adhesive (PVA + N,N-dimethylethylenediamine + sulfanilamide) exhibited only one thermal decomposition step. The thermal decomposition process of the pure PVA adhesive is characterized by a quick thermal decomposition stage and a slow thermal decomposition stage. Since the ΔH > 0, ΔS < 0 and ΔG > 0 in the thermal decomposition process it can be concluded that the decomposition reactions of the PVA adhesive were non-spontaneously endothermic and the entropy decreased during the reaction.