Low-temperature sintering of stereocomplex-type polylactide nascent powder: The role of optical purity in directing the chain interdiffusion and cocrystallization across the particle interfaces

Bai, Dongyu; Diao, Xingyuan; Ju, Yilong; Liu, Huili; Bai, Hongwei; Zhang, Qin; Fu, Qiang

doi:10.1016/j.polymer.2018.07.028

Cited by 19 publications

(4 citation statements)

References 56 publications

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“…During PLA crystallization, a higher temperature may favor to produce SCs and suppress the formation of HCs, and therefore the difference in melting temperature between SC and HC, enabling a unique processing window (190–230°C) for predominant SC formation in PLA blend. Thermal annealing of PLLA/PDLA blend at this temperature range can also induce HC to SC transition for obtaining complete SCs ( Figure 2A ) because HC in the PLA matrix is melted at the specific temperature while SC can still be retained, which renders partial PLA melt with improved chain mobilty to form new SCs via molecular rearrangements (Bai et al, 2018 ; Gao et al, 2019 ). During this process, the content of SC gradually increases with extending annealing time until a complete SC formation achieved in the matrix.…”

Section: Melt Processing At Specific Temperature Windowmentioning

confidence: 99%

Recent Progress in Enhancing Poly(Lactic Acid) Stereocomplex Formation for Material Property Improvement

et al. 2020

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The production and utilization of polymers have been widely implemented into diverse applications that benefit modern human society, but one of the most valuable properties of polymers, durability, has posed a long-standing environmental challenge from its inception since plastic waste can lead to significant contamination and remains in landfills and oceans for at least hundreds of years. Poly(lactic acid) (PLA) derived from renewable resources provides a sustainable alternative to traditional polymers due to its advantages of comparable mechanical properties with common plastics and biodegradability. However, the poor thermal and hydrolytic stability of PLA-based materials limit their potential for durable applications. Stereocomplex crystallization of enantiomeric poly (l-lactide) (PLLA) and poly (d-lactide) (PDLA) provides a robust approach to significantly enhance material properties such as stability and biocompatibility through strong intermolecular interactions between L-lactyl and D-lactyl units, which has been the key strategy to further PLA applications. This review focuses on discussing recent progress in the development of processing strategies for enhancing the formation of stereocomplexes within PLA materials, including thermal processing, additive manufacturing, and solution casting. The mechanism for enhancing SC formation and resulting material property improvement enabled by each method are also discussed. Finally, we also provide the perspectives on current challenges and opportunities for improving the understanding of processing-structure-property relationship in PLA materials that could be beneficial to their wide practical applications for a sustainable society.

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Section: Melt Processing At Specific Temperature Windowmentioning

confidence: 99%

Recent Progress in Enhancing Poly(Lactic Acid) Stereocomplex Formation for Material Property Improvement

et al. 2020

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“…Polylactic acid (PLA) is one of the most promising biodegradable polymers for making plastic bottles and medical devices, − with expected market value of 6.5 billion USD by 2025 . The ring-opening polymerization of lactide (LD), a cyclic dimer of lactic acid (LA), is the most important commercial method for the production of PLA. , Given that the quality of LD is a crucial parameter for the polymerization process, LD with high chemical and optical purity is highly desired. − Nowadays, LD is manufactured from LA by a complicated two-step method, and its severe reaction conditions lead to the loss of optical purity, unwanted side products, and high operating costs. , Recently, Sels et al pioneered a simple one-step LD synthesis method via esterification of LA under mild conditions, in which 68% yield of LD with high optical purity (99%) was obtained over a shape-selective H-β zeolite at 140 °C for 3 h. The present studies mainly focus on catalyst development for this reaction. − However, few studies investigate the effect of water in the solvent on one-step LD synthesis, which indeed plays a significant role in esterification reactions. − …”

Section: Introductionmentioning

confidence: 99%

Salt-Promoted Water Removal from Reflux Toluene for Efficient One-Step Lactide Synthesis

Liu

Zhao

Song

et al. 2022

Ind. Eng. Chem. Res.

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One-step lactide (LD) synthesis from lactic acid (LA) is a promising method for an economically viable polylactic acid (PLA) industry. However, this synthesis is based on a highly water-sensitive esterification reaction, and few studies focus on developing an efficient method to improve its activity by water removal from the reaction environment. Herein, we report a new strategy coupling salt-promoted toluene–water phase separation with heteroazeotropic distillation to enhance water removal to realize highly efficient LD synthesis. Different kinds of chloride salts (LiCl, NaCl, CsCl, MgCl2, and CaCl2) were selected to study their influence on the reaction. The highest yield of LD (84.7%) was obtained when CaCl2 was added, much higher than that of the salt-free reaction (72.3%). Hydrated Ca2+ cations with relatively large charge number and small radius can efficiently reduce the solubility of water in toluene due to their strong electrostatic force to attract more water molecules. Mechanism studies demonstrate that the increased yield of LD after adding CaCl2 was attributed to its significant inhibition of LD hydrolysis resulting from the deep water removal from the toluene solvent.

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“…So far, considerable endeavors have been devoted to develop supertough PLLA materials. However, there is still very limited work on the toughening of SC-PLA probably because it is extremely difficult to fabricate highly crystalline SC-PLA products with exclusive SC crystallites. ,,,, …”

Section: Introductionmentioning

confidence: 99%

“…However, there is still very limited work on the toughening of SC-PLA probably because it is extremely difficult to fabricate highly crystalline SC-PLA products with exclusive SC crystallites. 14,17,18,53,54 In this contribution, we attempt to simultaneously enhance the melt stability and interface strength of SC-PLA/elastomer blends with a view to develop supertough and heat-resistant SC-PLA materials for potential engineering applications. To do this, the reactive poly(ethylene−methyl acrylate−glycidyl methacrylate) (E-MA-GMA) random copolymer was utilized as an elastomeric toughening agent for SC-PLA, and it has been incorporated into the mixture of PLLA and PDLA (50/ 50, w/w) by one-pot reactive melt-blending.…”

Section: Introductionmentioning

confidence: 99%

Toward Supertough and Heat-Resistant Stereocomplex-Type Polylactide/Elastomer Blends with Impressive Melt Stability via in Situ Formation of Graft Copolymer during One-Pot Reactive Melt Blending

et al. 2019

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Stereocomplexation of enantiomeric poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) chains opens up a great opportunity toward sustainable PLA engineering plastic with exceptional heat resistance and durability. However, the processing and applications of stereocomplex-type PLA (SC-PLA) are significantly blocked by its inferior melt stability (i.e., the weak melt memory effect in triggering complete SC crystallization, which makes it hard to obtain exclusive formation of SC crystallites in melt-processed products) and inherent brittleness. In this contribution, we demonstrate an unprecedented strategy to address these obstacles by one-pot reactive melt blending of the equimolar PLLA/PDLA blend with reactive poly(ethylene–methyl acrylate–glycidyl methacrylate) (E-MA-GMA) in the presence of catalyst, where both the stereocomplexation and the grafting of some PLLA/PDLA chains onto E-MA-GMA backbones take place simultaneously and competitively. Intriguingly, the E-MA-graft-PLA copolymer in situ formed can substantially improve the melt stability of SC-PLA matrix as compatibilizer, and thus highly crystalline SC-PLA/E-MA-GMA blend products with exclusive SC crystallites can be readily obtained by injection molding. Moreover, some E-MA-graft-PLA can also strengthen the blend interface as interfacial enhancer, which gives rise to an increase in the toughening efficiency. As a result, the obtained SC-PLA/E-MA-GMA blends exhibits impressive heat resistance (the Vicat softening temperature and heat deflection temperature are as high as 201 and 174 °C, respectively) and impact toughness (the notched Izod impact strength is close to 65 kJ/m2). Notably, their comprehensive performance is superior to some commercial petroleum-derived engineering plastics. Overall, the one-pot syntheses of copolymer by in situ grafting could open up a new horizon for creating super-robust SC-PLA-based engineering plastic using industrial melt-processing technologies.

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Low-temperature sintering of stereocomplex-type polylactide nascent powder: The role of optical purity in directing the chain interdiffusion and cocrystallization across the particle interfaces

Cited by 19 publications

References 56 publications

Recent Progress in Enhancing Poly(Lactic Acid) Stereocomplex Formation for Material Property Improvement

Recent Progress in Enhancing Poly(Lactic Acid) Stereocomplex Formation for Material Property Improvement

Salt-Promoted Water Removal from Reflux Toluene for Efficient One-Step Lactide Synthesis

Toward Supertough and Heat-Resistant Stereocomplex-Type Polylactide/Elastomer Blends with Impressive Melt Stability via in Situ Formation of Graft Copolymer during One-Pot Reactive Melt Blending

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