Structural changes of cationic grafted lignin at different drying temperatures

The reaction of glycidyl-trimethylammonium chloride (GTMAC) with lignin is promising since it generates a cationic lignin derivative with potential applications in various fields, such as wastewater treatment, ion exchange resin, dye, and textile manufacturing. Drying is an important step of polymer fabrication. This work investigates the effect of drying temperatures (-55, 80, 105, and 130ºC) on the properties of kraft lignin (KL) and cationic kraft lignin (CKL). For KL, condensation products were detected after oven-drying. Specifically, after drying at 80 and 105ºC, benzo dioxane structures and diphenylmethane-type structures were observed. Additionally, an increase in molecular weight and glass transition temperature was observed for the samples dried at 105ºC. For CKL, nitrogen-containing groups were degraded in addition to condensation. Additionally, the molecular weight of the CKL samples increased with increasing drying temperature, reaching its peak molecular weight at 105ºC, but it dropped significantly after drying at 130ºC. The CKL samples exhibited lower glass transition temperatures than KL after drying. This work demonstrates that the drying temperature of cationically grafted lignin is an important consideration in conserving the desired properties of the material.