Complete stereo-complexation of enantiomeric polylactides for scalable continuous production

- A continuous and eco-friendly method for complete stereo-complexation (sc) was proposed.
- Quantitative relationship between ratio of sc-crystallites and hydrolysis resistance was investigated.
- Quantitative relationship between ratio of sc-crystallites and softening point was investigated.
- Sc-PLA fibers had softening point and MW retention rose by up to 61 °C and up to 170%, respectively.
- Improvements of softening point and hydrolysis resistance contributed to industrial application.

A facile and clean technology for stereo-complexation of polylactides (PLAs) shows potential to be readily incorporated into continuous industrial processes for manufacture of films, fibers and other plastic products. Using this approach, complete stereo-complexation of high-molecular-weight PLAs could be achieved via simple thermal treatment, rendering the production of durable PLA commodities inexpensive and industrially scalable. Currently, due to their high susceptibility to water and heat, PLA products have restricted industrial applications, and cannot compete with their petroleum-derived counterparts. Stereo-complexation of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) could effectively decrease water and heat sensitivity of common PLLA products. However, many stereo-complexation processes required harmful solvents or nucleating agents, and thus, were costly, complicated, and had low potential for short-term industrialization. Moreover, complete stereo-complexation was mostly achieved for PLAs with weight-average molecular weight lower than 1 × 105. In this research, PLLA and PDLA both with viscosity-average molecular weight of 3 × 105 were completely stereo-complexed (sc) via simple thermal treatment. Comparing to PLLA fibers, sc-PLA fibers had softening points 60 °C higher, and their thermal and hydrolytic stability significantly enhanced. Relationship among temperature of thermal treatment, degree of stereo-complexation and performance properties of sc-PLA fibers were also established. This clean technology makes possible industrial-scale production of commercializable biobased plastics.

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