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The nucleation efficiency (NE) of stereocomplex crystallites (SCs) formed in asymmetric poly(L‐lactide)/poly(D‐lactide) (PLLA/PDLA) blends is generally unsatisfactory because the competition between stereocomplexation and chain mixing involved in the melt‐mixing process can cause low formation efficiency and even severe aggregation of SCs. Herein, it is attempted to achieve high‐efficient formation of finely dispersed SCs particles by designing a unique melt‐mixing procedure, where the mixing of PLLA with 0.75 wt% PDLA is first performed at elevated temperatures (far above the melting temperature of SCs) to allow the homogeneous mixing of PLLA/PDLA chains and then at a low temperature (slightly above that of homocrystallites) to permit the full stereocomplexation of the premixed chains. It is found that the SCs formed in the blends exhibit unexpectedly low NEs (e.g., 54.5%), much inferior to that (73.6%) in the counterpart without undergoing premixing. This is because the introduction of premixing leads to a remarkable deterioration in the amount of SCs particles formed, despite decreased particle size, highlighting that the direct mixing at low temperatures of 170–180 °C (about 20–30 °C lower than that used in common melt‐processing of PLA) is more effective for the construction of SCs with superior NE. The mechanisms for these striking findings are discussed. [ABSTRACT FROM AUTHOR]

Stereocomplex (SC) crystallization can prominently improve the physico-chemical properties of poly(l -lactide)/poly(d -lactide) (PLLA/PDLA) blends, yielding a novel polylactide (PLA) material. However, the predominant formation of SC crystals in the melt-processing of high-molar-mass (high-MW, >100 kg/mol) enantiomeric PLA blends remains a huge challenge due to the competition between SC crystallization and homocrystallization. Herein, double-grafted copolymer having both PLLA and PDLA side chain has been designed and synthesized as an efficient crystallization promoter for the harvest of SC crystals in the high-MW PLLA/PDLA blends. The results show that, with the addition of such a copolymer, the blends can preferentially crystallize into SC crystals in both isothermal and non-isothermal conditions. Promisingly, the SC crystals can be exclusively formed by adding only small amounts (e.g., 0.5 wt%) of the copolymer, without the formation of any homocrystals. This interesting observation can be interpreted by the crucial role of the unique copolymer in suppressing the phase separation of the opposite PLA enantiomers upon melting as an efficient compatibilizer and then encouraging the generation of alternatingly arranged PLLA/PDLA chain clusters favored for SC nucleation and crystal growth. These findings provide new inspiration for the development of high-performance PLA with desirable SC crystallizability. [Display omitted] [ABSTRACT FROM AUTHOR]

Stereocomplex-type polylactide (SC-PLA) has recently emerged as an up-and-coming engineering Bio-plastic because the SC crystallization between enantiomeric poly(l -lactide) (PLLA) and poly(d -lactide) (PDLA) can substantially enhance the heat resistance and hydrolytic stability. Unfortunately, it is exceedingly challenging for high-molecular-weight PLLA/PDLA blends to preferentially crystallize into SC crystals (SCs) during melt processing and the concomitant formation of homocrystals (HCs) causes a significant deterioration in physio-chemical properties of final products. Herein, a dibenzoylhydrazide compound has been utilized as an efficient nucleating agent (NA) for the SC crystallization of PLLA/PDLA blends. The results indicate that, in both non-isothermal and isothermal crystallizations, the SC crystallization is markedly promoted with the incorporation of 0.2–1.5 wt% NA. Specially, the enantiomeric blends with relatively high amounts (≥0.5 wt%) of NA are found to exclusively crystallize into SCs without any HCs formation. Meanwhile, the NA can accelerate the SC crystallization and reduce the crystal size. The preferential SC crystallization should be associated with the hydrogen-bonding interactions between PLAs and NA molecules, which could lower barriers for the nucleation and crystal growth of SCs. Our work provides a facile yet powerful strategy for the preparation of high-performance SC-PLA materials with exceptional SC crystallization ability. [Display omitted] • TMC can act as an efficient NA to promote the SC crystallization of PLLA/PDLA blends. • Exclusive formation of SCs is achieved after adding 0.5 wt% TMC into the blends. • The crystallization is greatly accelerated due to the increase in nucleation density. • The hydrogen bonding between TMC and PLA is responsible for the enhanced SC formation. • A facile strategy has been proved to develop SC-PLA with exceptional crystallizability. [ABSTRACT FROM AUTHOR]

In this work, we report that super-toughened and high-strength polylactide/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends can be successfully prepared by interfacial compatibilization and dynamic vulcanization during reactive melt-blending with small amounts (0.5–3 wt %) of epoxy-functional styrene-acrylic oligomers (ESA). The results show that the compatibilization is realized with the grafting of some PLA and PBAT chains onto ESA backbones to in-situ generate PLA- graft -PBAT copolymers at the blend interface. Meanwhile, the ESA-mediated vulcanization gives rise to the highly cross-linked PBAT particles with a unique network-like distribution in the PLA matrix. Both the strengthened interfaces and networked PBAT particles are favorable to the triggering of massive matrix plastic deformation required for effective energy dissipation and thus the toughening effect is substantially enhanced. Impressively, the notched Izod impact toughness and elongation at break of the PLA/PBAT (70/30) blends can reach as high as 62.4 kJ/m2 and 232%, while the tensile strength increases from 44.2 MPa to 51.5 MPa, indicating a balanced toughness and strength. Most notably, it is demonstrated that tuning the molecular structure of ESA (i.e., epoxy group density and backbone length) is essential to improving the interfacial adhesion and phase morphology, enabling high toughening efficiency. Our facile yet robust strategy presents an unprecedented opportunity for the development of high-performance fully biodegradable PLA blends. [Display omitted] • Full biodegradable PLA/PBAT blends with balanced toughness and strength are prepared. • Dynamic vulcanization leads to the highly cross-linked PBAT domains in PLA matrix. • Copolymers are in-situ generated at the interface for effective compatibilization. • The formation of PBAT particle network is responsible for the desired properties. • The key role of ESA structure in tailoring the morphology and properties is verified. [ABSTRACT FROM AUTHOR]