Supertough, Ultrastrong, and Transparent Poly(lactic acid) via Directly Hot Pressing under Cyclic Compressing–Releasing

Enhancing mechanical and heat-resistant properties of melt-spun ploy (lactic acid) fiber via crystal structure regulation: The synergistic effects of long-chain branching and drawing process

The fabrication of ploy (lactic acid) (PLA) fiber with adjustable crystal structure and property still remains a great challenge. In this work, a series of melt-spun PLA fibers with increased strength and heat-resistance are prepared via crystal structure, which is caused by the synergistic effects of dicumyl peroxide (DCP) long-chain branching (LCB) modification and drawing process. The chemical structure of LCB-PLA resin is confirmed by the NMR and FTIR spectrum, which indicates that PLA is successfully modified by DCP free radical reaction through reactive extrusion. Moreover, the crystallization behavior and rheological property of PLA resin are significantly influenced by LCB degree. Especially, the PLA-LCB with 0.05 % DCP demonstrates the most ideal crystallinity and thermal stability owing to the micro crosslinking effect of DCP. Finally, the synergistic effects of LCB modification and drawing process on the crystal structure and property of PLA fiber are investigated by WAXD, SAXS, DMA and tensile testing. The tensile strength and glass transition temperature of LCB-PLA-0.05D fiber with 2.4 drawing ratio are increased to 3.25cN/dtex and 76.5 °C, respectively. Therefore, our work presents a feasible approach to fabricate enhanced strength and heat-resistance PLA fiber via crystal structure regulation, which has a bright future of industrialization.

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.

Strengthening-toughening pure poly(lactic acid) with ultra-transparency through increasing mesophase promoted by elongational flow field

Poly(lactic acid) (PLA), as a biodegradable material, finds wide applications in packaging, automotive, and biological industries. However, achieving high strength, toughness, ultra-transparency, and heat resistance simultaneously in pure PLA through continuous one-step manufacturing remains a significant challenge. In this study, we addressed this challenge by utilizing the eccentric rotor extruder (ERE) in combination with cooling rolls to manufacture PLA sheets with outstanding mechanical performance. The ERE's elongational flow field combined with the cooling roller's weak stretching action induced orientation in the PLA molecular chains and promoted the formation of more mesophase, significantly improving mechanical properties. When the extrusion-stretch ratio (λ) value was 3.5, the tensile yield strength, Young's modulus, and elongation at break of ERE-fabricated samples ER-3.5 reached 86.2 MPa, 1777 MPa, and 57.9 %, respectively. Compared to the SE-3.5 samples manufactured with traditional methods, the increases were 38.8 %, 25.8 %, and 9.4 times, respectively. Additionally, the ERE manufactured samples maintained ultra-transparency and high heat resistance, making them suitable for food packaging, biomedicine, and other related fields. This methodology provides an efficient industrial-scale approach for manufacturing neat, biodegradable PLA with outstanding mechanical performance and ultra-transparency.

Tailoring the crystallization of poly(l-lactide) via structural optimization of hydrogen-bonding segments with different aliphatic spacer lengths

A series of hydroxy-terminated oxalamide segments (OXA-n, HO-(CH2)n-NHCOCONH-(CH2)n-OH, n = 2, 4 and 6) were designed as initiators for ring-opening polymerization and then poly(l-lactide) with OXA-n in the middle (PLLAOXA-n) were synthesized.