Poly(lactic acid) or poly(lactide) (PLA) is a renewable, bio-based, and biodegradable aliphatic thermoplastic polyester that is considered a promising alternative to petrochemical-derived polymers in a wide range of commodity and engineering applications. However, PLA is inherently brittle, with less than 10% elongation at break and a relatively poor impact strength, which limit its use in some specific areas. Therefore, enhancing the toughness of PLA has been widely explored in academic and industrial fields over the last two decades. This work aims to summarize and organize the current development in super tough PLA fabricated via polymer blending. The miscibility and compatibility of PLA-based blends, and the methods and approaches for compatibilized PLA blends are briefly discussed. Recent advances in PLA modified with various polymers for improving the toughness of PLA are also summarized and elucidated systematically in this review. Various polymers used in toughening PLA are discussed and organized: elastomers, such as petroleum-based traditional polyurethanes (PUs), bio-based elastomers, and biodegradable polyester elastomers; glycidyl ester compatibilizers and their copolymers/elastomers, such as poly(ethylene-co-glycidyl methacrylate) (EGMA), poly(ethylene-n-butylene-acrylate-co-glycidyl methacrylate) (EBA-GMA); rubber; petroleum-based traditional plastics, such as PE and PP; and various biodegradable polymers, such as poly(butylene adipate-co-terephthalate) (PBAT), polycaprolactone (PCL), poly(butylene succinate) (PBS), and natural macromolecules, especially starch. The high tensile toughness and high impact strength of PLA-based blends are briefly outlined, while the super tough PLA-based blends with impact strength exceeding 50 kJ m−2 are elucidated in detail. The toughening strategies and approaches of PLA based super tough blends are summarized and analyzed. The relationship of the properties of PLA-based blends and their morphological parameters, including particle size, interparticle distance, and phase morphologies, are presented.

https://pubs.rsc.org/en/content/articlepdf/2020/RA/D0RA01801E

Super tough poly(lactic acid) blends: a comprehensive review

Different ratios of poly(lactic acid)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends were prepared by melt blending in the presence of a multifunctional epoxy oligomers as reactive compatibilizer. During reactive blending, the compatibilizer could react with PLA and PBAT chains to increase melt elasticity, viscosity, and compatibility, as indicated by rheological curve and Han plot analyses. Adding the compatibilizer improved the tensile and impact toughness for all ratios of PLA/PBAT blends. The elongation at break and the notched impact strength of the blend reached 579.9% and 29.6 kJ/m2, respectively, which were 75.3 and 12.3 times that of neat PLA. The shear yield deformation of impact fractured surface and the fuzzy phase interface of cryo-fractured surface showed that the high toughness can be attributed to the reaction of the epoxy group of reactive compatibilizer with the terminal carboxyl and hydroxyl groups of PLA and PBAT to form a large number of branched copolymers. Thus, the improvement of the interfacial adhesion and compatibility of the two polymers induced that brittle-ductile transition occurred in the failure of the blend.

Mechanical properties, rheological behaviors, and phase morphologies of high-toughness PLA/PBAT blends by in-situ reactive compatibilization

4D printing of shape memory polylactic acid (PLA)

Poly(butylene adipate-co-terephthalate) (PBAT) and poly(lactic acid) (PLA) are well-known biodegadable polyesters due to their outstanding performance. The biodegradation behavior of PLA/PBAT blends in freshwater with sediment is investigated in this study by analyzing the appearance, chemical structure and aggregation structure of their degraded residues via SEM, TG, DSC, gel permeation chromatography (GPC) and XPS. The effect of aggregation structure, hydrophilia and biodegradation mechanisms of PBAT and PLA on the biodegradability of PLA/PBAT blends is illuminated in this work. After biodegradation, the butylene terephthalate unit in the molecular structure of the components and the molecular weight of PLA/PBAT blends decreased, while the content of C-O bond in the composites increased, indicating that the samples indeed degraded. After 24 months of degradation, the increase in the relative peak area proportion of C-O to C=O in PLA/PBAT-25, PLA/PBAT-50 and PLA/PBAT-75 was 62%, 46% and 68%, respectively. The biodegradation rates of PBAT and PLA in the PLA/PBAT blend were lower than those for the respective single polymers.

Biodegradation Behavior of Poly(Butylene Adipate-Co-Terephthalate) (PBAT), Poly(Lactic Acid) (PLA), and Their Blend in Freshwater with Sediment.

Constructing stable co-continuous morphology of commercial immiscible polymer blends remains an ongoing challenge in terms of complex presynthetic routes, multiple parameter dependency, and intrinsic instability of phase morphology. Herein, we demonstrate a full biodegradable polymer blend, poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate), where hitherto inaccessible co-continuous with asymmetric compositions (70/30) can be obtained with the assistance of interfacial stereocomplex crystallites (i-SCs) through reactive blending. By taking full advantages of this unprecedented compatibilizer, nanostructured co-continuous blends with synergistically enhanced comprehensive performance are achieved. First, due to the “rigid” i-SC, co-continuous morphology is induced through a simple melt blending procedure; second, considerable augmentation of the crystallization rate of the PLA matrix is accomplished on account of the in situ formed nucleation agent (i.e., i-SC); third, a super toughened material with simultaneously enhanced tensile strength, ductility, and impact strength can be acquired, resulting from the i-SC-induced co-continuous morphology; and fourth, i-SC can function as a “rigid” supporting layer between phases even above 200 °C, resulting in significantly enhanced morphology stability in melt. The versatile, facile, and practical strategy offers an industrially relevant technique to fabricate super-robust and fully biobased polymer materials.

Stable Co-Continuous PLA/PBAT Blends Compatibilized by Interfacial Stereocomplex Crystallites: Toward Full Biodegradable Polymer Blends with Simultaneously Enhanced Mechanical Properties and Crystallization Rates

Strategies and techniques for improving heat resistance and mechanical performances of poly(lactic acid) (PLA) biodegradable materials.

Recent progress of preparation of branched poly(lactic acid) and its application in the modification of polylactic acid materials.

Abstract Ground tire rubber (GTR) with crosslinked structure shows hardly any plasticity and processability, giving rise to its relatively poor properties. The thermal-mechanical shearing devulcanization can effectively break the three-dimension crosslinked network structure and restore a certain extent of plasticity and processability. In this work, reclaimed rubber (RR) was obtained by thermal-mechanical shearing devulcanization as a potential filler for natural rubber. The vulcanization process, mechanical properties, microstructure of RR/natural rubber (NR) compounds composites were investigated. It was found that the NR vulcanizates containing 30 phr of RR as filler showed the higher tensile strength and elongation at break. Microstructural characterization analysis on a sample containing 30 phr of RR revealed the existence of strong interactions between the natural rubber matrix and RR, suggesting that RR and NR appeared to be well-matched, undergoing simultaneous curing and forming a continuous phase.

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Shaoxian Peng

Papers

Super tough poly(lactic acid) blends: a comprehensive review

Mechanical properties, rheological behaviors, and phase morphologies of high-toughness PLA/PBAT blends by in-situ reactive compatibilization

Strategies and techniques for improving heat resistance and mechanical performances of poly(lactic acid) (PLA) biodegradable materials.

Recent progress of preparation of branched poly(lactic acid) and its application in the modification of polylactic acid materials.

Curing behaviors, mechanical properties, dynamic mechanical analysis and morphologies of natural rubber vulcanizates containing reclaimed rubber