Study of thermal durability properties of tannin–lignosulfonate adhesives

Abstract

This paper aims to study certain aspects of the preparation of tannin–lignin adhesives. Mimosa tannins and lignosulfonates were used in wood adhesives formulation to substitute resins based on formaldehyde. Two ammonium lignosulfonates and two sodium lignosulfonates were glyoxalated to be more reactive. The thermal stability of the lignosulfonates before and after glyoxalation was analysed by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The proportion of mimosa tannins and sodium lignosulfonates varied from 20 % tannins to 60 % tannins. 40 % of mimosa tannins were mixed with either glyoxalated sodium lignosulfonates or glyoxalated ammonium lignosulfonates. The thermal properties of the resins were studied by TG, DSC and thermomechanical analysis (TMA). The results showed that after glyoxalation, the degradation of lignosulfonates started at 125 °C instead of 171 °C for the non-glyoxalated lignosulfonates. The results obtained showed that the 40 mass% tannins resin was the most efficient. The TMA results showed that the curing of the resins started at 100–110 °C. The TG and DSC results of the cured resins showed a thermal stability of the adhesives up to approximately 200 °C.