Recent Advances in Processing of Stereocomplex‐Type Polylactide

Abstract

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.

Flow‐induced crystallization of polylactide stereocomplex under pressure

“…Apart from that, it was reported that shear flow was more beneficial to SC formation compared to HC. Bai et al . also indicated that high shear rate caused high SC content.…”

“…Similar to other semicrystalline polymers, the crystallization process of PLA (SC and HC) is always influenced by processing parameters, such as shear flow and pressure, in practical processing. According to reports, shear flow can affect SC nucleation and crystal growth process . The effect of shear rate on SC crystallization behavior was investigated by Song et al .…”

Controlling the thermomechanical properties of biobased ABA triblock copolymers comprising polylactide (A) and poly(1,2‐propylene succinate) (B) with high molecular weight

“…PLA have two enantiomers of poly( l ‐lactide) (PLLA) and poly( d ‐lactide) (PDLA) in addition to racemic poly( dl ‐lactide). A 1: 1 stereo mixture of PLLA and PDLA forms stereocomplex (sc) crystals whose melting temperature ( T m ) is 230°С, which is 50°С higher than that of PLLA or PDLA . This stereocomplexed PLA (sc‐PLA) is more brittle in nature than PLLA, limiting its wider application despite its excellent thermal resistivity.…”

Promoted stereocomplex formation and two‐step crystallization kinetics of poly( l ‐lactic acid)/poly( d ‐lactic acid) blends induced by nucleator

“…Polymers with opposite configuration or complementary chiralities can cocrystallize in stereocomplex (SC) crystals in their blends and stereoblock copolymers . SCs are generally characteristic of denser chain packing and stronger interchain interactions than the common homocrystallites (HCs); this unique structure endows the stereocomplexed materials superior physical properties . Poly(lactic acid) (PLA) is a representative biobased and biodegradable polymer; its two stereoisomers, poly( l ‐lactic acid) (PLLA) and poly( d ‐lactic acid) (PDLA) can form SCs .…”