Abstract
Stereocomplexation between enantiomeric poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) provides an avenue to greatly enhance performance of eco-friendly polylactide (PLA). Unfortunately, although the manufacturing of semicrystalline polymers generally involves melt processing, it is still hugely challenging to create high-performance stereocomplexed polylactide (sc-PLA) products from melt-processed high-molecular-weight PLLA/PDLA blends due to the weak crystallization memory effect of stereocomplex (sc) crystallites after complete melting as well as the substantial degradation of PLA chains at elevated melt-processing temperatures of ca. 240–260 °C. Inspired by the concept of powder metallurgy, here we report a new facile route to address these obstacles by sintering of sc-PLA powder at temperatures as low as 180–210 °C, which is distinctly different from traditional sintering of polymer powders performed at temperatures far exceeding their melting temperatures. The enantiomeric PLA chain segments from adjacent powder particles can interdiffuse across particle interfaces and co-crystallize into new sc crystallites capable of tightly welding the interfaces during the low-temperature sintering process, and thus highly transparent sc-PLA products with outstanding heat resistance, mechanical strength, and hydrolytic stability have been successfully fabricated for the first time.
Highlights
Stereocomplexation between enantiomeric poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) provides an avenue to greatly enhance performance of eco-friendly polylactide (PLA)
Most physical properties are equivalent to those of generally used engineering plastics such as polystyrene (PS) and poly(butylene terephthalate) (PBT), the current incorporation of PLA into large-scale commercial applications has been greatly restricted by several obstacles, especially its inferior heat resistance limited by the relatively low melting temperature (T m) of 150–180 °C and poor long-lasting durability related to the hydrolytic degradation during its service life[6,7,8]
The HMW stereocomplexed polylactide (sc-PLA) powder was prepared by solution blending of equimolar PLLA and PDLA, and the low-temperature sintering of the as-prepared sc-PLA powder was carried out in a standard hydraulic press equipped with a self-made piston-cylinder high-pressure apparatus
Summary
The HMW sc-PLA powder was prepared by solution blending of equimolar PLLA and PDLA, and the low-temperature sintering of the as-prepared sc-PLA powder was carried out in a standard hydraulic press equipped with a self-made piston-cylinder high-pressure apparatus. 80 MPa) at 204.9 °C is even comparable to that for compression-molded product at 164.7 °C, distinctly indicating that high-performance sc-PLA products can only be achieved when the interfaces of the sintered powder are tightly welded by the crystalline network of sc crystallites formed at appropriate sintering temperatures. At temperatures as low as 180–210 °C, just below the melting temperature (215–220 °C) of sc crystallites, the enantiomeric PLA chain segments from adjacent powder particles can interdiffuse across particle interfaces and co-crystallize into new sc crystallites in the interfacial regions to strongly bind the initially isolated particles together. The interfacial-localized crystalline network can impart the sintered sc-PLA sheet products with outstanding heat resistance, impressive transparency, good mechanical strength, and favorable hydrolytic stability. We believe this work could open a promising way towards industrial-scale fabrication of sc-PLA-based products using conventional polymer sintering equipments
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