Effect of chemical modification on the thermal and rheological properties of polylactide

Abstract

Today PLA is one of the most important bioplastics on the market. A disadvantage of commercial polylactide is that it is not readily foamable, due to its low molecular weight, its low melt stability, and the lack of strain hardening effects. Therefore, commercially available polylactide has to be modified. In this study, the effects on properties by adding different modifiers were investigated. Adding of the modifiers and their chemical reaction were performed by means of reactive extrusion on a twin screw extruder. The molecular weight was increased by modifiers, which can be attributed to a changed chain topology. The highest molecular weight was achieved with organic peroxide. The rheological studies show that a changed chain topology can be assumed for the modified PLA. The most pronounced effect on the melt properties—the melt viscosity and also the melt strength—again was observed with the organic peroxide. The melt strength was increased for PLA modified with the organic peroxide. Furthermore, the organic peroxide was the only modifier that enhanced the crystallization rate, which is also favorable for extrusion foaming. POLYM. ENG. SCI., 57:1242–1251, 2017. © 2017 Society of Plastics Engineers