Influence of monomer purity on molecular weight of racemic polylactic acid

Abstract

Aiming at the low molecular weight of polylactic acid due to the presence of water molecules in the ring-opening polymerization of racemic lactide, this paper selected racemic lactide as the main raw material, stannous caprylate as the catalyst, and cetyl alcohol as the initiator, and studied the effects of recrystallization process conditions such as the number of recrystallization and drying time on the purity of monomer. The influence of initiator dosage on the properties of racemic polylactic acid was also studied. The purity, water content and free acid content of racemic lactide were determined by infrared spectrometer, differential scanning calorimeter, Gel Permeation Chromatography and tensile testing machine. The molecular weight and mechanical properties of racemic polylactic acid were characterized. The results show that the purity of racemic lactide after recrystallization can reach 99.3%, the water content is as low as 0.008% and the free acid content is less than 0.1%. When the amount of initiator is 0.13%, the molecular weight of the prepared racemic polylactic acid is 14.06 KDa and the tensile strength is 37 MPa.