Effect of degree of acetylation on thermoplastic and melt rheological properties of acetylated konjac glucomannan

A series of acetylated konjac glucomannan (AKGM) with different degrees of substitution (DS) were prepared by the reaction of konjac glucomannan (KGM) and acetic anhydride catalyzed with methanesulfonic acid. The degree of acetylation was enhanced with increase of substitution degree (DS), which affected markedly on the thermal stability, thermoplastic and melt rheological properties of AKGM. The thermal stability of KGM and AKGM was increased in the following sequence: AKGM2 (DS 1.25), AKGM1 (DS 0.37), KGM and AKGM3 (DS 2.48) and the AKGM3 with the highest DS had the best thermal stability. Only the AKGM with DS more than 1.25 possessed thermoplastic property and could melt before thermal decomposition. The melt rheological properties of AKGM2 and AKGM3 were influenced by temperature and frequency. The melt fluidness of AKGM3 was better than AKGM2, and the processing flow of AKGM3 can be adjusted by regulating the temperature.