The effect of two commercial melt strength enhancer additives on the thermal, rheological and morphological properties of polylactide

Abstract

Abstract The effect of two commercial melt strength enhancer additives, Paraloid BPMS-250 (BPMS) and Biostrength 700 (BIOS), on the thermal, rheological and morphological properties of polylactide (PLA) was studied. Thermal analyses showed that both the BPMS and BIOS additives decreased the ability of PLA to crystallize. The rheological tests indicated that zero-shear viscosity and storage modulus of the PLA/BPMS and PLA/BIOS blends were significantly increased with the additive content. These could be attributed to the entanglements between the PLA chains with those of the high molecular weight additive, creating a physical network which reduces the segmental mobility of PLA and improves the melt elasticity of the blend. The entanglement molecular weights (Me) of PLA/BPMS and PLA/BIOS blends were lower than those of unprocessed and processed PLA (Me≈4×104 g/mol), which suggests greater chain entanglements and a higher entanglement density (ve). The elongational viscosity (ηE) and melt strength values were estimated using a screw-extrusion capillary rheometer, where the PLA/BIOS blends presented the highest values. Finally, scanning electron microscopy on the samples was carried out to assess the blend morphology.