Ultrasound-assisted synthesis of carboxy-methyl lignin from sawdust based lignin as a sustainable source

Abstract

Sustainable biomass offers potential for obtaining products with added value with most literature focusing on use of cellulose and hemicellulose. The current study focuses on development of lignin-based surfactant utilizing the lignin recovered from pre-treatment of sawdust. Parameters such as sodium chloroacetate to lignin ratio (1:1–4:1 w/w), temperature (60–100° C), reaction time (0.5–3 h), and NaOH concentration (1.5 M) were varied to understand the effect on synthesis using conventional method. Additionally, ultrasonic power (40–120 W) and duty cycle (30–70 %) were varied in the ultrasound assisted approach to establish the best synthesis conditions. The lowest value of critical micellar concentration (CMC) with conventional method was 0.194 at 3:1 sodium chloroacetate to lignin ratio, 90° C and 2 h, while the lowest values of CMC with ultrasound was 0.057 at the optimised parameters of 2:1 sodium chloroacetate to lignin ratio, temperature of 80° C in just 1 h period. FTIR and NMR analysis was also performed on the extracted lignin and the carboxymethylation product with or without ultrasonic treatment. It was clearly demonstrated that improved product with almost 70 % lower CMC value could be obtained using ultrasound with significant reduction in the synthesis time and requirement of sodium chloroacetate as well.