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Polylactide (PLA) has been receiving significant attention in biopolymer research due to its excellent biodegradability, biocompatibility and sustainability. The mass production of PLA from renewable agricultural resources has delved this green material as a top alternative to replace the petroleum-based conventional polymers. However, the inherent weaknesses of PLA in its raw state such as brittleness, low heat distortion temperature and recrystallization rate, as well as the inadequate crystallization ability and degree after fast processing have limited the competitive edge of PLA over traditional synthetic plastics in industrial use or for biomedical applications. Being different from other types of biodegradable polymers, the diverse isomeric forms of PLA have provided great opportunities for thermal and mechanical enhancement through stereocomplexation formation. In this review, we present the most recent development in thermal and mechanical enhancement of PLA via stereocomplexation of PLA in different polymeric systems, including enantiomeric PLA homopolymers, PLA-based block and graft copolymers, as well as enantiomeric PLA materials having unique architectures such as cyclic, star, dendritic and comb-shaped. Insightful discussion on the influence of crystal structure and intermolecular interactions between PLLA and PDLA in the different polymeric systems on the enhanced performance of the resultant materials are provided. The enhanced PLA with diverse functions oriented toward engineering materials and their biosignificance in different areas are also covered in this review.

Poly­(l-lactide) cellulose nanocrystals-filled nanocomposites were fabricated by blending of cellulose nanocrystals-g-rubber-g-poly­(d-lactide) (CNC-rD-PDLA) and commercial PLLA, in which CNC-g-rubber was synthesized by ring opening polymerization (ROP) of d-lactide and a ε-caprolactone mixture to obtain CNC-P­(CL-DLA), followed by further polymerization of d-lactide to obtain CNC-rD-PDLA. X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and solubility tests confirmed successful grafting of the rubber segment and the PDLA segment onto CNC. Stereocomplexation between CNC-rD-PDLA nanofillers and PLLA matrix was confirmed by FT-IR, XRD, and differential scanning calorimetry (DSC) characterization. The PLLA/CNC-rD-PDLA nanocomposites exhibited greatly improved tensile toughness. With 2.5% CNC-rD-PDLA loading, strain at break of PLLA/CNC-rD-PDLA was increased 20-fold, and the composite shows potential to replace poly­(ethylene terephthalate). SEM and small-angle X-ray scattering (SAXS) investigations revealed that fibrillation and crazing during deformation of PLLA/CNC-rD-PDLA nanocomposites were the major toughening mechanisms in this system. The highly biodegradable and tough cellulose nanocrystals-filled PLLA nanocomposites could tremendously widen the range of industrial applications of PLA.

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The sustainable biopolymer, poly(lactide) (PLA), has been intensely researched over the past decades because of its excellent biodegradability, renewability, and sustainability. The boundless potential of this sustainable biopolymer could resolve the adverse negative impact caused by the petroleum-based polymers. However, the inherent drawback of PLA such as brittleness, low heat distortion temperature, and slow recrystallization rate narrowed the broad applications in biomedical, automotive, and structural fields. In this study, we successfully synthesized a PHB-based filler (PHB-di-rub) displaying synergetic functions of (1) effective nucleation and (2) extreme toughening of the PLA matrix at only 5% (1.5 wt % PHB content). Remarkably, the storage modulus improves by 15%; tensile elongation extends by 57-fold (300% strain) and toughness by 38-fold while maintaining its original strength and stiffness. Likewise, 10% of PHB-di-rub (3 wt % PHB content) has an even higher improvement with a storage modulus improvement by 32%, elongation by 128-fold (680% strain), and toughness by 84-fold, with a marginal change in strength and stiffness. NMR results confirmed the structure of PHB-di-rub, where PHB acts as the rigid core and the poly(lactide-cocaprolactone) (DLA-co-CL) random copolymer confers the flexibility. DSC, WAXD, and POM display the excellent nucleating ability of PHB-di-rub. SEM shows the morphology of elongated fibrils structure with strong matrix−filler interaction and homogeneous filler dispersion. SAXS, WAXS, and WAXD elucidate the extreme toughening mechanism to be a combination of rubber-induced crazing effect and highly orientated PLA matrix with PHB-di-rub. The Herman's orientation function further quantifies the extreme elongation (680%) owing to the perfect alignment. This highly biodegradable biocomposite with high strength and toughness shows potential in replacing the current petroleum-based polymers, which open up to broader prospects in the biomedical, automotive, and structural application.

The future of green electronics possessing great strength and toughness proves to be a promising area of research in this technologically advanced society. This work develops the first fully bendable and malleable toughened polylactic acid (PLA) green composite by incorporating a multifunctional polyhydroxybutyrate rubber copolymer filler that acts as an effective nucleating agent to accelerate PLA crystallization and performs as a dynamic plasticizer to generate massive polymer chain movement. The resultant biocomposite exhibits a 24‐fold and 15‐fold increment in both elongation and toughness, respectively, while retaining its elastic modulus at >3 GPa. Mechanism studies show the toughening effect is due to an amalgamation of massive shear yielding, crazing, and nanocavitation in the highly dense PLA matrix. Uniquely distinguished from the typical flexible polymer that stretches and recovers, this biocomposite is the first report of PLA that can be “bend, twist, turn, and fold” at room temperature and exhibit excellent mechanical robustness even after a 180° bend, attributes to the highly interconnected polymer network of innumerable nanocavitation complemented with an extensively unified fibrillar bridge. This unique trait certainly opens up a new horizon to future sustainable green electronics development.

The runaway production and consumption of oilbased plastics are key drivers of global warming and the increased carbon footprint. Besides, most of this plastic debris ends up in the oceans and constitutes about 80% of all marine debris. This pollution problem calls for a seismic shift to eco-friendly plastics and marine biodegradable ones. Unlike other biobased polymers, polyhydroxyalkanoates (PHAs) take pride in their degradation in soil and marine environments. This intriguing marine biodegradation property of PHAs sets it apart as the best choice to curb microplastics, particularly in marine ecosystems. PHAs have also grown in popularity due to other quintessential properties such as biocompatibility, structural variety, and similarity to conventional plastics in terms of physical properties. PHAs are being widely researched for various applications, including packaging, medical, energy, and agriculture. This perspective comprehensively focuses on the state-of-art production and applications of PHA plastics as well as the practical recycling strategies for postconsumer PHAs. The innovative "next generation industrial biotechnology" (NGIB) is well covered in this perspective. Moreover, the nexus between end-of-life strategies and life cycle assessment (LCA) of PHAs waste is elucidated to understand its impact on the environment thoroughly.

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