Microwave-assisted synthesis of polyacrylamide grafted lignocellulose nanofibers and their use as bio-flocculant

Polyacrylamide-based precipitating flocculants are commonly used to clarify juice and remove impurities in raw sugar production. However possible residual polyacrylamide in sugar can pose carcinogenic, neurotoxic, and environmental risks. To address this, lignocellulose nanofiber (LCNF)-based flocculants derived from sugarcane bagasse (a by-product of sugarcane processing) were introduced as a sustainable alternative. Polyacrylamide (PAM) was grafted onto LCNFs through microwave irradiation and a chemical-free radical initiator ((NH₄)₂S₂O₈), under optimized polymerization conditions. The flocculant was characterized through various analytical techniques confirming the successful grafting reaction. The flocculant achieved excellent turbidity removal rates of 99.3 %, 98.7 %, and 96.9 % for halloysite, kaolin, and sugarcane juice, respectively, at low dose (5 mg/L). It also demonstrated broad flocculation range and pH adaptability. A settling test conducted on sugarcane juice at 96 °C revealed that the 20 % commercial PAM and PAM@LCNF blend achieved a significantly enhanced initial settling rate of 111 mL/min, outperforming both the PAM@LCNF and commercial PAM. The PAM@LCNF flocculant represents a sustainable, highly effective alternative to conventional flocculants, for sugarcane juice clarification while utilizing sugarcane industry residual. Moreover, its flocculation performance is comparable to other reported biopolymer and other flocculants.