Over the past two decades, biomass‐derived and biodegradable polylactide (PLA) has sparked tremendous attention as a sustainable alternative to traditional petroleum‐derived polymers for diverse applications. Unfortunately, the current applications of PLA have been mainly limited to biomedical and commodity fields, mostly because the poor heat resistance (resulting from low melting temperature) and hydrolysis stability make it hard to use as an engineering plastic. Stereocomplexation between enantiomeric poly(l‐lactide) (PLLA) and poly(d‐lactide) (PDLA) opens a new avenue toward PLA‐based engineering plastics with improved properties. The formation, crystal structure, properties, and potential applications of stereocomplex‐type PLA (SC‐PLA) are summarized by some research groups. However, since it is challenging to achieve full stereocomplexation from high‐molecular‐weight PLLA/PDLA blends and to avoid serious thermal degradation of the PLAs after complete melting, the advances and progress in the processing of SC‐PLA into useful products are quite rare in open publication. In this review, some important strategies for enhancing stereocomplex crystallization in practical processing operations are presented and recently developed processing technologies for SC‐PLA are highlighted, such as low‐temperature sintering. Furthermore, major challenges and future developments are briefly discussed. This review is expected to potentially open up new research activities in the processing of SC‐PLA.

Selective cross-linking of PLLA and PDLA chain couples in the amorphous phase allows for the formation of stereocomplex (sc) crystallites in the continuous melting and recrystallization process to be perfectly reversible.

Preparing super-tough and heat-resistant PLLA/elastomer blends by constructing stereocomplex crystallites at the interface to simultaneously tailor interface and matrix properties.

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.

Stereocomplex (SC) crystallization between highmolecular-weight poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) provides a promising route to substantially improve the properties of polylactide (PLA), but conventional melt processing of the SC-type PLA (SC-PLA) is nearly impossible primarily due to the poor crystallization memory effect as well as serious thermal degradation after complete melting of SC crystallites with high melting temperatures of above 220 °C. Recently, we reported an innovative low-temperature (180−210 °C) sintering technology for fabricating SC-PLA products from its nascent powder. Unfortunately, its practical application has been significantly hindered by an extremely high pressure of 1 GPa, which must be utilized to ensure good surface wetting of the densified powder particles. With this challenge in mind, herein, the role of powder crystallinity in the low-temperature sintering has been investigated. Interestingly, we first demonstrate that depressing powder crystallinity is favorable for the particle wetting under a much lower pressure during the densification stage of the nascent powders because the deformation of the powders becomes easier with the decrease in the fraction of rigid crystal network. Moreover, during the subsequent interface welding stage, more PLLA/PDLA chains could be involved in the interdiffusion and SC crystallization across particle interfaces, thus forming large amounts of new SC crystallites capable of tightly welding the interfaces. As a consequence, SC-PLA sheets with excellent heat resistance and mechanical properties have been successfully fabricated by sintering under a pressure of as low as 300 MPa. Overall, these fascinating findings not only provide new fundamental understandings on the role of initial crystallinity in the low-temperature sintering of SC-PLA powder but also indicate an avenue toward industrial-scale fabrication of SC-PLA products from low-crystallinity nascent powder using conventional polymer sintering equipment.

A low-temperature sintering technology is devised to fabricate electrospun sc-PLA membranes with superior mechanical strength and unprecedented separation performance via forming sc crystallites between adjacent fibers.

We propose a facile strategy to develop high-performance PLLA/MWCNT nanocomposites by constructing stereocomplex structures at the interface.

No abstract