Enhancing Impact Toughness of Renewable Poly(lactic acid)/Thermoplastic Polyurethane Blends via Constructing Cocontinuous-like Phase Morphology Assisted by Ethylene–Methyl Acrylate–Glycidyl Methacrylate Copolymer

In-situ self-crosslinking strategy for super-tough polylactic acid/ bio-based polyurethane blends

As a bio-based degradable plastic, polylactic acid (PLA) is highly commercialized, but its inherent brittleness limits its widespread use. In-situ polymerization techniques are effective in improving the toughness of PLA. However, the enhancement of the toughening effect in polyurethanes (PUs) through in-situ self-crosslinking still requires improvement and heavily relies on petroleum-derived feedstocks in certain approaches. In this paper, 1,3-polypropanediol (PO3G) of bio-based origin rather than conventional polyols like polyethylene glycol (PEG) and poly propylene glycol (PPG) was used. PLA/PO3G-PU blends were prepared via an in-situ self-crosslinking strategy. With a notch impact and tensile strength of 55.95 kJ/m2 and 47.77 MPa (a retention rate of 68.9 % compared with pure PLA), respectively, PLA/PO3G-PU blends achieved a better balance between stiffness and toughness. This work provides a new option for PLA to achieve a stiffness-toughness balance and get rid of dependence on petrochemical resources.

Phase Morphology and Mechanical Properties of Super-Tough PLLA/TPE/EMA-GMA Ternary Blends

The inherent brittleness of poly(lactic acid) (PLA) limits its use in a wider range of applications that require plastic deformation at higher stress levels. To overcome this, a series of poly(l-lactic acid) (PLLA)/biodegradable thermoplastic polyester elastomer (TPE) blends and their ternary blends with an ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) copolymer as a compatibilizer were prepared via melt blending to improve the poor impact strength and low ductility of PLAs. The thermal behavior, crystallinity, and miscibility of the binary and ternary blends were analyzed by differential scanning calorimetry (DSC). Tensile tests revealed a brittle-ductile transition when the binary PLLA/20TPE blend was compatibilized by 8.6 wt. % EMA-GMA, and the elongation at break increased from 10.9% to 227%. The "super tough" behavior of the PLLA/30TPE/12.9EMA-GMA ternary blend with the incomplete break and notched impact strength of 89.2 kJ∙m-2 was observed at an ambient temperature (23 °C). In addition, unnotched PLLA/40TPE samples showed a tremendous improvement in crack initiation resistance at sub-zero test conditions (-40 °C) with an impact strength of 178.1 kJ∙m-2. Morphological observation by scanning electron microscopy (SEM) indicates that EMA-GMA is preferentially located at the PLLA/TPE interphase, where it is partially incorporated into the matrix and partially encapsulates the TPE. The excellent combination of good interfacial adhesion, debonding cavitation, and subsequent matrix shear yielding worked synergistically with the phase transition from sea-island to co-continuous morphology to form an interesting super-toughening mechanism.

The effect of dynamic vulcanization on the morphology and biodegradability of super toughened poly(lactic acid)/unsaturated poly(ether-ester) blends

Preparing a super-tough polylactic acid (PLA) material while maintaining its biodegradability is a significant challenge. This study synthesized a biodegradable unsaturated poly(butylene succinate-co-fumarate)-poly(ethylene glycol) multiblock copolymer (PBSFG) and dynamically vulcanized it with PLA to obtain super-tough blends. The PBSFG self-vulcanized and formed a crosslinked "hard-soft" core-shell rubber phase in the blending process, where the PBSF segment acted as the core and PEG as the shell. As a result, the elongation at break and notched Izod impact strength of PLA increased significantly from 3 % to 66 % and from 3.2 to 58.0 kJ/m2, respectively. Furthermore, adding a small amount of dicumyl peroxide (DCP) promoted dynamic vulcanization and improved the compatibility between PLA and PBSFG. With the addition of 0.03 % DCP, the elongation at break and notched Izod impact strength of PLA/PBSFG were further increased to 218 % and 88.9 kJ/m2, respectively. Meanwhile, the crystallization rate of PLA was enhanced by the addition of PBSFG and DCP. The PLA/PBSFG blends also degraded in a proteinase K Tris-HCl buffered buffer solution. Finally, fully biodegradable and super-tough PLA blends were achieved.

Syntheses and properties of tri- and multi-block copolymers consisting of polybutadiene and polylactide segments

Biomaterials have drawn considerable attention in recent years because of environmental concerns. In this paper, several different poly(lactide)-b-poly(butadiene)-b-poly(lactide) (PLA-b-PB-b-PLA) triblock copolymers were synthesized by the bulk ring-opening polymerization of lactide initiated by flexible macro-initiator hydroxyl-terminated polybutadiene (HTPB) by adjusting the ratio of HTPB to lactide and the optical isomer of lactide. Afterwards, a chain-extension reaction with hexamethylene diisocyanate (HDI) was carried out to prepare (PLA-b-PB-b-PLA)_n multi-block copolymers with enhanced molecular weight. The structures and properties of these block copolymers were then characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), atomic force microscope (AFM) and Fourier-transform infrared (FTIR). Toughening effect of the (PLA-b-PB-b-PLA)_n multiblock copolymers on biodegradable poly(l-lactide) (PLLA) film was investigated and the blended film with higher (poly(d-lactide)-b-poly(butadiene)-b-poly(d-lactide))_n (PDLA-b-PB-b-PDLA)_n loading (15 wt%) exhibited better toughness nearly without loss of the tensile strength. The mechanical properties of the (PLA-b-PB-b-PLA)_n/PLLA blended film were proved to be influenced by the different isomers of PLA and rubbery PB chains.

Toughen effect of the multiblock copolymers (PLA-b-PB-b-PLA)_n on PLLA was investigated and the mechanical properties of the blended films were proved to be influenced by the optical isomers of PLA, stereocomplexation and the rubbery PB chains.

Polyurethanes Based on Polylactic Acid for 3D Printing and Shape-Memory Applications

Polylactic acid (PLA) has received increased attention in the development of shape-memory polymers and biomedical materials owing to its excellent physical properties and good biocompatibility and biodegradability. However, the inherent brittleness and high shape-recovery temperature of this material limit its application in the human body. Herein, we fabricated a PLA-based thermoplastic polyurethane (PLA-TPU) prepared from modified PLA-diol, dicyclohexylmethane-4,4'-diisocyanate, and 1,4-butanediol to solve the limitations of pure PLA. The glass transition temperature (T_g) of the designed TPU can be tailored from 6 to 40.5 °C by adjusting the content of hard segments or molecular weight of soft segments. The shape of the designed TPU can be fixed at room temperature and recovered at temperatures above 37 °C. Moreover, the prepared PLA-TPUs exhibited recyclability, three-dimensional printing capability, non-cytotoxicity, blood compatibility, and biodegradability. The shape of PLA-TPU/nano-Fe₃O₄ composites can be recovered by exposure to near-infrared light. These results collectively indicate that PLA-TPUs and their composites may have potential applications as intelligent flexible medical scaffolds for surgical and medical implantation equipment.

Enhancing Toughness of PLA/ZrP Nanocomposite through Reactive Melt-Mixing by Ethylene-Methyl Acrylate-Glycidyl Methacrylate Copolymer

The nanofiller zirconium phosphate (ZrP) was mixed into poly(lactic acid) (PLA) to ameliorate its thermal stability. The elastomer ethylene-methyl acrylate-glycidyl methacrylate copolymer (E-MA-GMA) was introduced into the PLA/ZrP nanocomposite through melt-mixing to improve its toughness and obtain a super-tough PLA/ZrP/E-MA-GMA nanocomposite. The impact strength of the PLA/ZrP/E-MA-GMA nanocomposite, with a composition ratio of 72/3/25, was improved to 71.5 kJ/m², about 25 times greater than the impact strength of pure PLA. The dynamic mechanical analysis (DMA) confirmed that E-MA-GMA has excellent compatibility with the matrix of PLA. A typical core–shell structure that can cause massive shear-yielding deformation was characterized by transmission electron microscopy (TEM), which gave the nanocomposite excellent toughness.

Investigating Physio-Thermo-Mechanical Properties of Polyurethane and Thermoplastics Nanocomposite in Various Applications

The effect of the soft and hard polyurethane (PU) segments caused by the hydrogen link in phase-separation kinetics was studied to investigate the morphological annealing of PU and thermoplastic polyurethane (TPU). The significance of the segmented PUs is to achieve enough stability for further applications in biomedical and environmental fields. In addition, other research focuses on widening the plastic features and adjusting the PU-polyimide ratio to create elastomer of the poly(urethane-imide). Regarding TPU- and PU-nanocomposite, numerous studies investigated the incorporation of inorganic nanofillers such as carbon or clay to incorporating TPU-nanocomposite in several applications. Additionally, the complete exfoliation was observed up to 5% and 3% of TPU-clay modified with 12 amino lauric acid and benzidine, respectively. PU-nanocomposite of 5 wt.% Cloisite®30B showed an increase in modulus and tensile strength by 110% and 160%, respectively. However, the nanocomposite PU-0.5 wt.% Carbone Nanotubes (CNTs) show an increase in the tensile modulus by 30% to 90% for blown and flat films, respectively. Coating PU influences stress-strain behavior because of the interaction between the soft segment and physical crosslinkers. The thermophysical properties of the TPU matrix have shown two glass transition temperatures (Tg's) corresponding to the soft and the hard segment. Adding a small amount of tethered clay shifts Tg for both segments by 44 °C and 13 °C, respectively, while adding clay from 1 to 5 wt.% results in increasing the thermal stability of TPU composite from 12 to 34 °C, respectively. The differential scanning calorimetry (DSC) was used to investigate the phase structure of PU dispersion, showing an increase in thermal stability, solubility, and flexibility. Regarding the electrical properties, the maximum piezoresistivity (10 S/m) of 7.4 wt.% MWCNT was enhanced by 92.92%. The chemical structure of the PU-CNT composite has shown a degree of agglomeration under disruption of the sp2 carbon structure. However, with extended graphene loading to 5.7 wt.%, piezoresistivity could hit 10-1 S/m, less than 100 times that of PU. In addition to electrical properties, the acoustic behavior of MWCNT (0.35 wt.%)/SiO2 (0.2 wt.%)/PU has shown sound absorption of 80 dB compared to the PU foam sample. Other nanofillers, such as SiO2, TiO2, ZnO, Al2O3, were studied showing an improvement in the thermal stability of the polymer and enhancing scratch and abrasion resistance.

Polyoxymethylene/thermoplastic polyamide elastomer blends: Morphology, crystallization, mechanical, and antistatic properties

Polyoxymethylene/thermoplastic polyamide elastomer (POM/TPAE) blends were prepared through melt extrusion in an attempt to improve the toughness and electrical properties of POM. The TPAE used in the study had the permanent antistatic effect, and its brand was MV2080. Acrylonitrile-butadiene-styrene copolymer grafted maleic anhydride (ABS-g-MAH) was added while preparing the POM/TPAE blends to improve the compatibility between TPAE and POM. The effects of TPAE and ABS-g-MAH on the morphologies, melting crystallization, dynamic mechanical analysis, surface resistivity and mechanical properties were examined in detail with various techniques. It was found that after adding 15 phr MV2080 as the modifier, the distribution of MV2080 in the blends was presented as many continuous long strips, which can be called “antistatic networks.” When using ABS-g-MAH as a compatibilizer, the surface resistivity of the samples 5#, 6#, and 7# which all containing 15 phr MV2080 with the best antistatic properties reached 107 Ω, and the impact strength of the above samples was all increased by more than 66%.

Empowering self-reporting polymer blends with orthogonal optical properties responsive in a broader force range

Self-reporting polymers, which can indicate damage with perceptible optical signals in a tailored force range, are useful as stress-sensitive sensors. We demonstrate a simple approach to realize this function by embedding two distinct mechanophores - rhodamine (Rh) and bis(adamantyl)-1,2-dioxetane (Ad), in polyurethane/polylactic acid blends. The deformed blends generate red coloration and red chemiluminescence. Such a unique dual-responsive behavior was evaluated by solid-state UV-vis spectroscopy, macroscopic tensile tests with in situ RGB and light intensity analyses, which supported a stress-correlated occurrence of the ring-opening of Rh, the scission of Ad and the fluorescence resonance energy transfer process between the respective mechanochemical species. Complementarity stemming from the difference in properties and manifestations of the two mechanophores is essential. That is, the more labile Rh allows shifting the appreciable optical changes to a much lower force threshold; the transient nature and high dynamic range of mechanochemiluminescence from Ad map in real time where and when many of the covalently incorporated dioxetane bonds break; besides, the disrupted yet non-scissile structure of Rh acts as a fluorescent acceptor to effectively harvest chemiluminescence from ruptured Ad. The current strategy is thus empowering multi-functional mechano-responsive polymers with greatly improved sensitivity and resolution for multimodal stress reporting.

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

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.

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.

Phase Morphology and Performance of Supertough PLA/EMA-GMA/ZrP Nanocomposites Prepared through Reactive Melt-Blending

Nanofiller zirconium phosphate (ZrP) and ethylene-methyl acrylate-glycidyl methacrylate copolymer (EMA-GMA) were introduced into poly(lactic acid) (PLA) through reactive melt-blending method to improve its toughness. The impact strength of PLA/EMA-GMA/ZrP (82/15/3) nanocomposites was improved about 22 times that of pure PLA to 65.5 kJ/m2. Fourier transform infrared spectroscopy (FTIR) analysis indicated there were compatibilization reactions between the components. The miscibility and thermal behavior of the blends were investigated by dynamic mechanical analysis (DMA), differential scanning calorimetric (DSC), and thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to observe the fractured surface and phase morphology to study the toughness mechanism. A typical core-shell morphology, ZrP wrapped by EMA-GMA phase, was observed in the nanocomposites, which can cause plastic deformations. The supertough effect of the compound was mainly confirmed by effective interfacial compatibilization and massive shear-yielding deformation achieved by the synergy of EMA-GMA with ZrP in the PLA matrix.