Modification of polylactide by poly(ionic liquid)-b-polylactide copolymer and bio-based ionomers: Excellent toughness, transparency and antibacterial property

Sulfonated cellulose nanocrystal modified with ammonium salt as reinforcement in poly(lactic acid) composite films

Poly(lactic acid) (PLA) composites reinforced with cellulose nanocrystals (CNCs) are promising biodegradable materials. However, the poor compatibility and dispersion of CNCs in the PLA matrix remain a significant obstacle to improving the properties of composites. In this study, the modified CNC (CNC-D) was prepared through sulfonation treatment, followed by modification with didecyl dimethyl ammonium chloride (DDAC). Then, CNC-D was mixed with PLA to prepare composite films (PLA-CNC-D). The results revealed that the PLA-CNC-D had higher tensile strength and elongation at break than PLA-CNC at 3 wt% nanofiller content, increasing by 41.53 and 22.18 %, respectively. SEM and DSC analysis indicated that surface modification improved the compatibility and dispersion of CNC-D in the PLA matrix. The sulfonation process increased the anion content on the surface of CNC-D, enabling the CNC-D surface to adsorb more cationic DDAC, consequently sharply reducing the hydrophilicity of CNC-D. Moreover, the PLA-CNC-D exhibited excellent antibacterial activity against S. aureus and E. coli. In summary, this study provides a novel CNC modification approach to enhance the physical properties and antibacterial activity of PLA composite films, enlarging the application of degradable PLA composites.

Melt stretching and quenching produce low-crystalline biodegradable poly(lactic acid) filled with β-form shish for highly improved mechanical toughness

High-toughness biodegradable poly(lactic acid) (PLA) has always been intensively pursued on the way of replacing traditional petroleum-based plastics. Regulating microstructures to achieve self-toughening holds great promise due to avoidance of incorporating other heterogeneous components. Herein, we propose a straightforward and effective way to tailor microstructures and properties of PLA through melt-stretching and quenching of slightly crosslinked samples. The melt stretching drives chains orientation and crystallization at high temperature, while the quenching followed can freeze the crystallization process to any stage. For the first time, we prepare a type of transparent and low-crystalline PLA filled with rod-like β-form shish, which displays an outstanding tensile toughness, almost 17 times that of the conventional technique-processed one. This mechanical superiority is enabled by an integration of high ductility due to oriented chain network, and high tensile stress endowed by nanofibrous filler's role of β-form shish. Furthermore, the mechanically toughened PLA is demonstrated to generate the richest micro-cracks and shear bands under loading, which can effectively dissipate the deformational energy and underlie the high toughness. This work opens a new prospect for the bottom-up design of high-performance bio-based PLA materials that are tough, ductile and transparent by precise microstructural regulation through scalable melt processing route.

Fabricating super tough polylactic acid based composites by interfacial compatibilization of imidazolium polyurethane modified carbon nanotubes

The interfacial compatibilization and dispersion of carbon nanotubes (CNTs) in incompatible poly(lactic acid)/poly(butylene terephthalate adipate) (PLA/PBAT) composites are key points for evaluating the performance of the composites. To address this, a novel compatibilizer, sulfonate imidazolium polyurethane (IPU) containing PLA and poly(1,4-butylene adipate) segments modified CNTs, employed in conjunction with multi-component epoxy chain extender (ADR) to toughen synergistically PLA/PBAT composites. The thermal stability, rheological behavior, morphology, and mechanical properties of PLA/PBAT composites were performed by TGA, DSC, dynamic rheometer, SEM, tensile, and notched Izod impact measure. Moreover, the elongation at break and notched Izod impact strength of PLA5/PBAT5/4C/0.4I composites achieved 341 % and 61.8 kJ/m² respectively, whose tensile strength was 33.7 MPa. The interfacial compatibilization and adhesion were enhanced because of the interface reaction catalyzed by IPU and the refined co-continuous phase structure. The CNTs non-covalently modified by IPU that bridged at the PBAT phase and interface transferred the stress into the matrix, prevented the development of microcracks, and absorbed impact fracture energy in the form of pull-out of the matrix, inducing shear yielding and plastic deformation. This new type of compatibilizer with modified CNTs is of great significance for realizing the high performance of PLA/PBAT composites.