Crystallinity effect on electron-induced molecular structure transformations in additive-free PLA

Additive-free biodegradable polylactides (PLAs) with different crystallinities from 0 to 13.3% (according to x-ray diffraction, XRD) were used as starting materials modified by the electron beam (EB) with several irradiation doses at 25 degrees C (below glass transition temperature, T-g) in nitrogen. The crystallinity effects on radical decay and molecular structure transformation were investigated. After irradiation, the main stable radical remained in PLA is -O-C*(CH3)-CO-. During irradiation, radical reactions were inhibited by high crystallinity. Large amounts of EB-induced crosslinking and long-chain branching (LCB) were introduced by performing irradiation at 80 degrees C. An increasing crystallinity has been found that restrained crosslinking and LCB due to the poor chain mobility in the crystalline areas. An increase of crystallinity from 0 to 13.3% obviously decreased the saturated crosslink content from 65% to 43% and restrained LCB formation. This study also verified that strict moisture control combined with applying an irradiation temperature above T-g can be a universal method to introduce large amounts of crosslinking and LCB in different grades of additive-free PLA.

Automated summary

In this study, high crystallinity polylactides (PLAs) were irradiated with electron beam to investigate the effects on radical decay and molecular structure transformation. It was found that high crystallinity can inhibit radical reactions and restrict the formation of crosslinking and long-chain branching.