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

Abstract

Poly(lactic acid) (PLA) could be a promising replacement for nondegradable polymers, only if it is toughened. However, the current technique of toughening PLA generally requires additional components or post-treatment, and the conflicts among toughness, strength, and transparency are still to be overcome. Herein, by employing a novel compressing−releasing (CCR) process, we fabricated supertough, ultrastrong, and transparent PLA directly via hot pressing. Through characterizations we obtained PLA with superior tensile strength and strain at break of 84.1 MPa and 272.4%, respectively, which are 28% and 40 times higher than conventional technique-processed PLA, as well as enhanced heat resistance. The mechanism of CCR-induced gt-to-gg conformational transition was then investigated. Moreover, the correlation between tensile properties and gg conformer was also established. To sum up, we demonstrate that this work not only promotes the sustainable development of PLA with outstanding mechanical properties but also paves a new avenue toward a controlled conformational transition of polymers under mild processing conditions.

Regulating Mesophase via Melt Volume Pulsation on an Industrial Scale for Self-Toughening and Self-Reinforcing of Polyethylene Terephthalate

“…Furthermore, the conformational transition has been induced by the vibration force field. Because the vibration force field can reduce the free volume of polymer materials and promotes the conformer transition at compressing stage, 44 the gauche conformers in the MAF and IMAF can adjust themselves to transform into trans conformers in the MAF, IMAF, and OF under the VPIM technique.…”

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

“…The difference in the aliphatic spacer length in PLLA OXA-n not only increases molecular flexibility but may also modify the topological relationship of the PLLA chains and their conformation order. As it has been investigated both experimentally and theoretically in the previous study, 43,44 there are four kinds of conformations in the amorphous PLLA, called tt, tg, gg, and gt conformers. FTIR was used to observe the conformation of the amorphous phase with melt-quenched samples, and the results are shown in Fig.…”

Toward Heat-Resistant and Transparent Poly(l-lactide) by Tailoring Crystallization with an Aliphatic Amide as a Nucleating Agent

“…Much endeavor has been devoted to tailor the crystallization of PLLA, with a particular focus on the possibility of combining rapid melt-crystallization ability and high transparency. 16,17 One possible route to combine the two conflicting properties is the incorporation of specific plasticizers with a relatively high refractive index into PLLA. 15 Theoretically, if the plasticizers can not only markedly increase the crystal growth rate but also effectively decrease the refractive index mismatch between the crystalline and amorphous regions, PLLA will maintain its original high transparency after crystallization.…”

“…Much endeavor has been devoted to tailor the crystallization of PLLA, with a particular focus on the possibility of combining rapid melt-crystallization ability and high transparency. , One possible route to combine the two conflicting properties is the incorporation of specific plasticizers with a relatively high refractive index into PLLA . Theoretically, if the plasticizers can not only markedly increase the crystal growth rate but also effectively decrease the refractive index mismatch between the crystalline and amorphous regions, PLLA will maintain its original high transparency after crystallization. , Nevertheless, according to our knowledge, no such plasticizer has been reported for the preparation of transparent PLLA products, probably owing to the great difficulty in simultaneously enhancing the molecular mobility of the PLLA matrix significantly with the refractive index of the amorphous phase.…”