Study on incorporating wattle tannin in polyvinyl acetate emulsion and its effect on properties for wood bonding application

Abstract

Polyvinyl acetate emulsion (PVAc) is an essential class of adhesives for woodworking applications. However, it suffers from low water resistance. In the present research, wattle tannin was incorporated in synthesised PVAc emulsion at ratios ranging from 0 to 6 wt.% in PVAc emulsion. The study was carried out in two parts. The first part focuses on understanding the effect of the presence of tannin in PVAc emulsion on its adhesive performance. The second part deals with the study of the variation in adhesive properties of tannin PVAc emulsion adhesive by introducing isocyanate crosslinker in the system. DMA was employed to understand the glass transition and rheology behaviour. FTIR was used to assess the reaction of tannin with isocyanate crosslinker. Contact angle measurement was measured using goniometry to understand the surface wettability achieved by incorporating tannin in the PVAc emulsion system. Detail study on adhesive strength was carried out by bonding wood substrates followed by measuring bonding strength in wet conditions as per BS EN 204 and heat resistance as per DIN EN 14257 (WATT 91). The presence of tannin in the system enhances water and heat resistance property which gets further improved in the presence of isocyanate crosslinkers. The observed effect is due to better wetting of substrate by adhesive, hydrogen bonding between tannin and components in adhesive, and dense crosslinking formed by the reaction of isocyanate crosslinker.