Synthesis and characterization of TPO–PLA copolymer and its behavior as compatibilizer for PLA/TPO blends

Thermo-Mechanical and Creep Behaviour of Polylactic Acid/Thermoplastic Polyurethane Blends

There is a great need to develop biodegradable thermoplastics for a variety of applications in a wide range of temperatures. In this work, we prepare polymer blends from polylactic acid (PLA) and thermoplastic polyurethane (TPU) via a melting blend method at 200 °C and study the creep deformation of the PLA/TPU blends in a temperature range of 10 to 40 °C with the focus on transient and steady-state creep. The stress exponent for the power law description of the steady state creep of PLA/TPU blends decreases linearly with the increase of the mass fraction of TPU from 1.73 for the PLA to 1.17 for the TPU. The activation energies of the rate processes for the steady-state creep and transient creep decrease linearly with the increase of the mass fraction of TPU from 97.7 ± 3.9 kJ/mol and 59.4 ± 2.9 kJ/mol for the PLA to 26.3 ± 1.3 kJ/mol and 25.4 ± 1.7 kJ/mol for the TPU, respectively. These linearly decreasing trends can be attributed to the weak interaction between the PLA and the TPU. The creep deformation of the PLA/TPU blends consists of the contributions of individual PLA and TPU.

Structure-controlled lignin complex for PLA composites with outstanding antibacterial, fluorescent and photothermal conversion properties

Polylactic acid (PLA) is increasingly being considered as an ideal biodegradable candidate to replace petroleum-based polymers. However, its practical applications are often hampered by the poor mechanical robustness and solo functionality. Herein, based on the mechanical property improvement of PLA we proposed a simple process of assembling lignin-hybridized modifier and PLA matrix, as opposed to the traditional trade-off between mechanical strength and functionality, while anchoring a biofluorescent moiety onto lignin surfaces. Specifically, the fluorophore group could act as interfacial compatibilizer of complex and facilitate the shape-tailored hybrids for promoting functionality flexibility. With the bimetallic hetero-particles, the preferable lignin-assembled complex could be controllably configured as an antibacterial, fluorophore and photothermal agent. Thus, mechanical enhancement, fluorescence introduction and favorable photothermal ability of the resulting PLA composites were successfully achieved for integrated unification of structural robustness, geometric integrity and functional multiplicity, which was never seen in the other reports. The results showed that PLA composites containing 5 wt% modified lignin, 10 wt% zinc oxide, and 5 wt% silver presented excellent mechanical, fluorescent, photothermal conversion properties. By controlling the ZnO content and morphology, strong inhibition of Escherichia coli (Gram-negative) than that of Staphylococcus Aureus (Gram-positive) was also observed. The flake-shaped ZnO /Ag hybrids contributed to better overall performance of PLA composites than the rod-shaped ZnO/Ag. In this work we developed a facile strategy to assemble a bioderived fluorophore with lignin particles for constructing a structure-controlled complex as a multitasking modifier, featuring mechanical unity and functional adaptability. Specifically, the lignin reinforcement and bimetallic hybrids with different morphologies were explored as an effective fluorophore, antibacterial and photothermal agent. Through multiple dehydration reactions, a conjugating fluorophore was successfully grafted on lignin surfaces to serve as an interface modifier without physical changing its structural robustness. And morphology-tailored hybrid was advantageously immobilized on predefined hetero-particle carrier of fluorescent lignin and endowed composites with desirable antimicrobial properties. The developed strategy would expand the functional applications of PLA materials in food packaging, biopharmaceuticals and simple fluorescent anti-counterfeiting.

Core-shell nanoparticles based on zirconia covered with silver as an advantageous perspective for obtaining antimicrobial nanocomposites with good mechanical properties and less cytotoxicity

Antimicrobial nanoparticles perform a vast and promising strand of applications, among which, the silver ones stand out due to their broad antimicrobial spectrum. However, their toxicological potential in addition with their not always satisfying mechanical properties limit their wider application. In this sense, the use of core-shell systems can generate materials with improved properties. Thus, the goal of the present work was to obtain zirconia-silver core-shell nanoparticles and, after that, evaluate their properties in systems based on poly(lactide) PLA. Systems containing silver nanoparticles (AgNP), zirconium oxide (ZrNP), a physical mixture of both particles and core-shell nanoparticles (Core-shell NP) were evaluated. The Core-shell NP were characterized by dynamic light scattering (DLS), Energy Dispersive X-Ray (EDX), transmission electronic microscopy (TEM), and antimicrobial activity. The nanocomposite films were evaluated by Fourier transform infrared analysis (FTIR), thermogravimetric analysis (TGA), nano-hardness, tensile strength test, cytotoxicity, and antimicrobial activity. The results obtained from the DLS and EDX analyses confirmed the obtaining of systems covered with silver. Through the TEM analysis, the formation of the core-shell structure with a diameter of about 100 nm was observed. The films containing core-shell NP presented antimicrobial activity with a profile correspondent to the one observed for AgNP. As for cytotoxicity, these particles proved to be less cytotoxic and achieved higher values of hardness (10%), modulus (40%), and toughness (28%) than those observed for AgNP, and these properties were lower than those observed for ZrNP. The core-shell NP also exhibited even greater antimicrobial activities, less cytotoxicity, and largest elastic modulus (17%) than the physical mixture of the particles.

Effects of Organic Montmorillonite (OMMT) and Pre-Orientation on Property of Poly(l-lactic acid) (PLLA)/Ethylene Propylene Diene Monomer (EPDM) Blends

Poly(l-lactic acid)/ethylene propylene diene monomer/organic montmorillonite (PLLA/EPDM/OMMT) samples were melt-compounded and then processed into sheets via two routes, namely, compression-molding and calendering. Tensile performance, morphology, and thermal property of the samples were investigated. Tensile test showed that the incorporation of OMMT resulted in significant enhancement in the tensile ductility of the PLLA/EPDM samples. SEM observation revealed that EPDM domain size decreased largely with increasing OMMT loading, indicating the compatibility of OMMT with PLLA/EPDM blends. Moreover, the elongation at break, tensile yield strength, and modulus of the calendered samples were found to be much higher than those of the compression-molded samples. It can be attributed to the pre-oriented rigid amorphous fraction of PLLA matrix and pre-stretched EPDM phases in the calendered samples produced by the stretching/shearing effect of calendering. Compared to the spherical/ellipsoidal EPDM particles in the compression-molded samples, these stretched EPDM phases with higher aspect ratio in the calendered samples can be more effective to initiate craze, and terminate the craze growing to a crack along transversal direction. Therefore, the calendered samples show a better tensile ductility than the compression-molded ones. Moreover, annealing was carried out to increase the crystallinity of the samples. Tensile performance, morphology, and thermal property of the annealed samples were also systematically investigated.

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.

Fabrication, Crystalline Behavior, Mechanical Property and In-Vivo Degradation of Poly(l-lactide) (PLLA)-Magnesium Oxide Whiskers (MgO) Nano Composites Prepared by In-Situ Polymerization

The present work focuses on the preparation of poly(l-lactide)-magnesium oxide whiskers (PLLA-MgO) composites by the in-situ polymerization method for bone repair and implant. PLLA-MgO composites were evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and solid-state 13C and 1H nuclear magnetic resonance spectroscopy (NMR). It was found that the whiskers were uniformly dispersed in the PLLA matrix through the interfacial interaction bonding between PLLA and MgO; thereby, the MgO whisker was found to be well-distributed in the PLLA matrix, and biocomposites with excellent interface bonding were produced. Notably, the MgO whisker has an effect on the crystallization behavior and mechanical properties; moreover, the in vivo degradation of PLLA-MgO composites could also be adjusted by MgO. These results show that the whisker content of 0.5 wt % and 1.0 wt % exhibited a prominent nucleation effect for the PLLA matrix, and specifically 1.0 wt % MgO was found to benefit the enhanced mechanical properties greatly. In addition, the improvement of the degrading process of the composite illustrated that the MgO whisker can effectively regulate the degradation of the PLLA matrix as well as raise its bioactivity. Hence, these results demonstrated the promising application of PLLA-MgO composite to serve as a biomedical material for bone-related repair.

Kinetic Analysis on Thermal Decomposition of Poly(lactic acid) Toughened by Calcium Sulfate Whiskers

The biocomposites of poly (lactic acid) (PLA) involving 15 % mass fraction of calcium sulfate whiskers (CSW) were prepared via melt-blending technology, in an effort of toughening PLA and enhancing the thermal stability. The morphological structure, impact toughness, thermal stability as well as kinetic analysis on thermal decomposition for PLA/CSW composites were performed thoroughly. The results showed that CSW was organized successfully via silanization, helping to form well-bonded interfaces, and accordingly, the impact toughness increased remarkably. The thermal stability was enhanced by adding whiskers, leading to increased decomposition temperature and decreased mass conversion rate. Kinetic analysis revealed the great dispersions on the reaction order and activation energy. Though, in comparison to pure PLA, the reaction order of PLA/CSW composites increased based on calculation methods except for Carrasco's, the activation energy of the composites declined independently of the applied mathematical models, meaning that thermal decomposition of PLA phase was accelerated by the introduced CSW.

Crystallization, rheology and mechanical properties of the blends of poly(l-lactide) with supramolecular polymers based on poly(d-lactide)–poly(ε-caprolactone-co-δ-valerolactone)–poly(d-lactide) triblock copolymers

In this study, we investigated the blending of poly(l-lactide) (PLLA) with supramolecular polymers based on poly(d-lactide)–poly(ε-caprolactone-co-δ-valerolactone)–poly(d-lactide) (PDLA–PCVL–PDLA) triblock copolymers as an efficient way to modify PLLA. The supramolecular polymers (SMP) were synthesized by the terminal functionalization of the PDLA–PCVL–PDLA copolymers with 2-ureido-4[1H]-pyrimidinone (UPy). The structure, thermal properties and rheological behavior of the synthesized supramolecular polymers were studied; we found that the formation of the UPy dimers expanded the molecular chain of the polymer and the incorporation of the UPy groups suppressed the crystallization of polymers. In addition, the synthesized supramolecular polymers had a low glass transition temperature of about −50 °C, showing the characteristics of elastomers. On this basis, superior properties such as a fast crystallization rate, high melt strength, and toughness of fully bio-based, i.e., PLA-based materials were achieved simultaneously by blending PLLA with the synthesized supramolecular polymers. In the PLLA/SMP blends, PLLA could form a stereocomplex with its enantiomeric PDLA blocks of supramolecular polymers, and the stereocomplex crystals with the cross-linking networks reinforced the melt strength of the PLLA/SMP blends. The influences of the SMP composition and the SMP content in the PLLA matrix on crystallization and mechanical properties were analyzed. The supramolecular polymers SMP0.49 and SMP1.04 showed a reverse effect on the crystallization of PLLA. Tensile tests revealed that the lower content of the synthesized supramolecular polymers could achieve toughening of the PLLA matrix. Therefore, the introduction of supramolecular polymers based on PDLA–PCVL–PDLA is an effective way to control the crystallization, rheology and mechanical properties of PLLA.

Supramolecular polymer based on PDLA–PCVL–PDLA triblock copolymer was used for the modification of PLLA, and the results showed that it is an effective way to control the crystallization, rheology and mechanical properties of PLLA.

Poly (lactic acid) blends: Processing, properties and applications

Poly (lactic acid) or polylactide (PLA) is a commercial biobased, biodegradable, biocompatible, compostable and non-toxic polymer that has competitive material and processing costs and desirable mechanical properties. Thereby, it can be considered favorably for biomedical applications and as the most promising substitute for petroleum-based polymers in a wide range of commodity and engineering applications. However, PLA has some significant shortcomings such as low melt strength, slow crystallization rate, poor processability, high brittleness, low toughness, and low service temperature, which limit its applications. To overcome these limitations, blending PLA with other polymers is an inexpensive approach that could also tailor the final properties of PLA-based products. During the last two decades, researchers investigated the synthesis, processing, properties, and development of various PLA-based blend systems including miscible blends of poly l-lactide (PLLA) and poly d-lactide (PDLA), which generate stereocomplex crystals, binary immiscible/miscible blends of PLA with other thermoplastics, multifunctional ternary blends using a third polymer or fillers such as nanoparticles, as well as PLA-based blend foam systems. This article reviews all these investigations and compares the syntheses/processing-morphology-properties interrelationships in PLA-based blends developed so far for various applications.

Fully biodegradable Poly(lactic acid)/Starch blends: A review of toughening strategies

Polylactic acid (PLA) and Starch are both bio-based biodegradable polymers that have properties that are complementary to each other. PLA/starch blend exploits the good mechanical property of PLA and the low cost of Starch. However, PLA/Starch blend is intrinsically brittle. This paper reviews the current state of arts in toughening of PLA/Starch blend, which are categorized as: Additive Plasticization, Mixture Softening, Elastomer Toughening and Interphase Compatibilization. These strategies are not mutually exclusive and can be applied jointly in a single blend, opening up a wide range of toughening techniques that can be employed in PLA/Starch blend. Even though significant progress has been made in this area, there is still much room for research, in order to achieve easy to process, fully bio-based and completely biodegradable PLA/Starch blends that have mechanical properties suitable for a wide range of applications.

Thermally induced shape memory behavior, enzymatic degradation and biocompatibility of PLA/TPU blends: "Effects of compatibilization"

Poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) blends were melt-mixed and compatibilized to investigate their biocompatibility, biodegradability and thermally induced shape memory properties. The blend compositions were PLA/TPU: 80/20 (20TPU) and PLA/TPU: 50/50 (50TPU). 1,4-phenylene diisocyanate (PDI) was used in order to compatibilize the components reactively. The PDI composition was 0.5, 1, 3% by weight. Biodegradability was assessed by enzymatic degradation tests. Biocompatibility was investigated through in-vitro cell-culture experiments. Shape memory tests exhibited that 20TPU blends have higher recovery ratio than that of 50TPU blends. It was observed that the shape recovery ratio was enhanced by the addition of PDI. The highest shape recovery ratio was obtained at 3%PDI in 20TPU blends. Enzymatic biodegradability tests showed that the increasing TPU content decreased the biodegradability of the blends. It was found that compatibilization slowed down the enzymatic degradation of PLA/TPU blends. In-vitro cell-culture experiments indicated that all blends were biocompatible, and no evidence of cytotoxicity was observed.

Poly(lactic acid)-Mass production, processing, industrial applications, and end of life

Global awareness of material sustainability has increased the demand for bio-based polymers like poly(lactic acid) (PLA), which are seen as a desirable alternative to fossil-based polymers because they have less environmental impact. PLA is an aliphatic polyester, primarily produced by industrial polycondensation of lactic acid and/or ring-opening polymerization of lactide. Melt processing is the main technique used for mass production of PLA products for the medical, textile, plasticulture, and packaging industries. To fulfill additional desirable product properties and extend product use, PLA has been blended with other resins or compounded with different fillers such as fibers, and micro- and nanoparticles. This paper presents a review of the current status of PLA mass production, processing techniques and current applications, and also covers the methods to tailor PLA properties, the main PLA degradation reactions, PLA products' end-of-life scenarios and the environmental footprint of this unique polymer.