The Esterification of Sodium Lignosulfonate with Maleic Anhydride in Water Solution

The esterification of sodium lignosulfonate (LS) with maleic anhydride (MA), which is a by-product of the papermaking industry, was successfully carried out in water solution under mild conditions. The esterification percentage was influenced by many factors including the concentration of LS and the weight ratio of LS/MA, temperature, pH, and reaction time. Optimum conditions of the factors studied obtained after a series of single-factor experiments for lignosulfonate reacted with maleic anhydride were weight ratio of 1.2 to 1.0 under vigorous stirring at 55°C in alkaline solution for 4 h. The products were characterized by FT-IR, thermogravimetric (TG) analysis, and differential scanning calorimetry (DSC). The emergence of a 1717 cm−1 peak of the FT-IR curves indicated that the esterification reaction was successfully carried out. Moreover, the TG results showed an increase in thermal stability of esterified lignosulfonate compared to unmodified lignosulfonate.