Effects of L‐ and D‐ form oligo(lactic acid)s grafted cellulose reinforcement on the thermal properties of poly(L‐lactic acid) composites

Abstract L‐ and D‐ form oligo(lactic acid)s (OLLA and ODLA) grafted α‐cellulose (OLLA‐g‐cellulose and ODLA‐g‐cellulose) were prepared by the graft polycondensation reaction in C6H5CH3 medium at 130°C and 380 mm of mercury pressure. Para‐toluene sulphonic acid (5 wt% of oligo(lactic acid)) was used as a catalyst whereas potassium persulfate (0.01 wt% of oligo(lactic acid)) was used as a co‐catalyst in the graft polycondensation reaction. OLLA and ODLA with a degree of polymerization (DP) 6–7 used in polycondensation reaction were also prepared by ring‐opening polymerization of L‐ and D‐lactides at 140°C for 10 h with stannous octoate (C16H30O4Sn) as a motivator, L, and D monomer of lactic acids as co‐motivators. FTIR analysis proved the bonding of OLLA and ODLA onto the α‐cellulose surface. The thermal properties of poly(L‐lactic) acid (PLLA) composites were explored by thermal analysis (TG, DTA, and DTG). Degradation, melting, and maximum weight loss temperature of the composites were increased with the increase of grafted cellulose up to 10% and then decreased. TG and DTA results showed that the incorporation of grafted α‐cellulose (grafted cellulose) can improve the thermal properties of PLLA composites. Highlights Synthesis of oligo(lactic acid)s from L‐ and D‐lactides by ring‐opening polymerization reactions. α‐cellulose extraction and graft modification with oligo(lactic acid)s. Preparation of grafted α‐cellulose composite with PLLA matrix. Evaluation of thermal properties of the grafted α‐cellulose‐reinforced composites.