Copolyester toughened poly(lactic acid) biodegradable material prepared by in situ formation of polyethylene glycol and citric acid

Polylactic acid (PLA) is a high-modulus, high-strength bio-based thermoplastic polyester with good biodegradability, which is currently a promising environmentally friendly material. However, its inherent brittleness has hindered its widespread use. In this study, we reported a simple and non-toxic strategy for toughening PLA, using biodegradable materials such as polyethylene glycol (PEG) and citric acid (CA) as precursors. Through reactive melt blending with PLA, PEG and CA form PEGCA copolyesters in situ during blending. At the same time, CA can react with PLA and PEG, forming a copolyester structure at the interface of the two phases, improving the interfacial compatibility between PEG and PEGCA with PLA. Fourier transform infrared spectroscopy confirms this. Experimental results show that when the content of PEG/CA reaches 15% (PLA/PEG/CA-15%) in the blends, the impact strength of the blend was 4.47 kJ m-2, and the maximum elongation at break was as high as 360.1%, which were about 2 and 44 times higher than those of pure PLA, respectively. Moreover, the tensile strength was still maintained at the level of 70%. This work can expand the application of PLA in food packaging and medical supplies.

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.

Tough and antibacterial poly(l-lactic acid) composites prepared via blending with the bifunctional macromolecular ionomer

In order to expand the application of PLLA in the packaging field, improving its toughness and antibacterial activity has been widely concerned. However, seldom researches can simultaneously efficiently improve the toughness and antibacterial activity of PLLA by adding one kind of additions. To address above problems, the bifunctional branched poly(butylene adipate) ionomer additive (b-PBAUi) was synthesized. For b-PBAUi, its branched structure not only increased the plasticizing effect of additive, but also acted as reaction sites to introduce more antibacterial ionic salt. Due to the special structure of b-PBAUi, PLLA/b-PBAUi blends achieved excellent toughness and antibacterial efficiency. The elongation of blend reached 125 % even by adding 5 wt% b-PBAUi, which was 10 times higher than that of PLLA. From the analysis of phase morphology, it could be found that the microvoids promoting tensile yielding was the main tensile toughening mechanism for PLLA/b-PBAUi blends. In addition, the antibacterial activity of PLLA was significantly improved by adding b-PBAUi. For PLLA/b-PBAUi10 and PLLA/b-PBAUi15, the antibacterial efficiency against E. coli and S. aureus bacteria exceeded 99.0 %. By comprehensive consideration, the optimal blend ratio was achieved by PLLA/b-PBAUi10 due to its excellent toughness and antibacterial efficiency.

Ductile Effect of PGA/PCL Blending Plastics Using a Novel Ionic Chain Extender with Non-Covalent Bonds

Polyglycolic acid (PGA) is a promising polymer in the packaging field owing to its excellent hydrolysis, heat resistance, and gas barrier properties, but it is limited in application due to its poor toughness. For this reason, a covalently bonded chain extender is introduced to increase compatibility with flexible polymers. However, covalent bonds are unfavorable for application to degradable plastics because of the energy required for reverse reactions. Therefore, we intended to effectively control the ductility of blending plastics by using a novel ionic chain extender with a relatively weaker non-covalent bond than the existing covalent bond. Polycaprolactone (PCL), which has biodegradability and flexibility, was selected as a blending polymer. For comparison, a covalently reactive chain extender (G-CE) and a non-covalently ionic chain extender (D-CE) were synthesized and compounded with blending plastics. Each chain extender improved the compatibility between PGA and PCL, and the ductility of the PGA/PCL blending plastics was more greatly enhanced with non-covalently bonded D-CE than with covalently bonded G-CE. At this time, the ductility of the PGA/PCL(90/10) blending plastic without CE was 7.2%, the ductility of blending plastic with D-CE (10D) was 26.6%, and the ductility of blending plastic with G-CE (10G) was 18.6%. Therefore, it was confirmed that the novel ionic chain extender inducing non-covalent bonds improves the compatibility between PGA and PCL and is more advantageous in enhancing ductility through a reversible reaction.

Robust, Flame-Retardant, and Anti-Corrosive Waterborne Polyurethane Enabled by a PN Synergistic Flame-Retardant Containing Benzimidazole and Phosphinate Groups

Waterborne polyurethanes (WPUs) have attracted great interest owing to their environmentally friendly properties, and are wildly applied in production and daily life. However, waterborne polyurethanes are flammable. Up to now, the challenge remains to prepare WPUs with excellent flame resistance, high emulsion stability, and outstanding mechanical properties. Herein, a novel flame-retardant additive, 2-hydroxyethan-1-aminium (2-(1H-benzo[d]imidazol-2-yl)ethyl)(phenyl)phosphinate (BIEP-ETA) has been synthesized and applied to improve the flame resistance of WPUs, which has both phosphorus nitrogen synergistic effect and the ability to form hydrogen bonds with WPUs. The WPU blends (WPU/FRs) exhibited a positive fire-retardant effect in both the vapor and condensed phases, with significantly improved self-extinguishing performance and reduced heat release value. Interestingly, thanks to the good compatibility between BIEP-ETA and WPUs, WPU/FRs not only have higher emulsion stability, but also have better mechanical properties with synchronously improved tensile strength and toughness. Moreover, WPU/FRs also exhibit excellent potential as a corrosion-resistant coating.

Toward regulating biodegradation in stages of polyurethane copolymers with bicontinuous microphase separation

For typical biodegradable polymers, their overall performance almost declines exponentially to the degradation degree, which inevitably leads to a dilemma between the requirements of service life and retention time in the environment (both in vitro and in vivo). It is a great challenge to develop a biodegradable polymeric device with relatively stable performance in service while rapidly degrading out of service. Herein, we demonstrate an effective strategy to control degradation of biodegradable polymers in stages by constructing separated bicontinuous microphases with very different microphase degradation rates. First, polyurethane copolymers (PCL-b-CrP-U) containing two blocks, i.e., semicrystalline poly(ε-caprolactone) (PCL) blocks and amorphous random copolymer blocks (CrP) based on ε-CL and p-dioxanone (PDO), were synthesized. The microscopic morphology of PCL-b-CrP-U is investigated by an alkali-accelerated degradation experiment, which also demonstrates that the chain cleavage-induced crystallization during degradation resulted in a self-reinforcement by forming degradation residues with a scaffold-like morphology. The tensile test shows that PCL-b-CrP-U has excellent mechanical properties (1500% of elongation at break, a tensile strength of about 7.5 MPa, and an elastic modulus of 40.0 MPa). The degradation experiments with artificial pancreatic juice as a working medium reveal that PCL-b-CrP-U samples containing relatively high PDO units exhibit a three-stage degradation, i.e. an induction stage, a steady degradation stage and an accelerated degradation stage. The CrP phase preferentially hydrolyzes to form some microchannels due to its amorphous nature and relatively high hydrophilicity, effectively accelerating the entry of water and enzymes into the inner parts of the sample. Meanwhile, at this stage, those originally amorphous PCL segments gradually crystalize owing to their enhanced chain mobility induced by the chain cleavage, forming a "scaffold"-like structure, which effectively reinforces the sample to resist the damage from external force and therefore guarantees a relatively stable mechanical performance of PCL-b-CrP-U during service. With the further depletion of the CrP phase, the intermediate "scaffold"-like structure is also very beneficial to accelerate the degradation of residues owing to its large specific surface area, which is expected to be beneficial for preventing long-term retention of the implantation devices.

Interfacial distribution and compatibilization of imidazolium functionalized CNTs in poly(lactic acid)/polycaprolactone composites with excellent EMI shielding and mechanical properties

Imidazolium-functionalized polyurethane (IPU) functionalized multi-walled carbon nanotubes (CNTs) was used to control interfacial distribution and compatibilization of CNTs, and enhance electromagnetic interference (EMI) shielding and mechanical properties of poly(lactic acid)/polycaprolactone (PLA/PCL) based composites. IPU facilitated the uniformly dispersion of CNTs and induced the selectively location of CNTs at the interface and PCL phase, which is beneficial to build more effective three-dimensional network structure at the co-continuous interphase. The EMI shielding properties for the PLA/PCL/8CNT/0.8IPU composites have been evidently increased to 35.6 dB. Meanwhile, the elongation at break and the notched impact strength of the PLA/PCL/8CNT/0.8IPU composite reached 307.8 % and 51.3 kJ/m², respectively, which are increased by 27 and 53 % of PLA/PCL/8CNT because of the compatibilization effect of IPU and the distribution of CNTs. This work presented a promising prospect of polymer-based composites with satisfactory EMI shielding and mechanical properties.

Enhancing impact resistance and biodegradability of PHBV by melt blending with ENR

This research aims to enhance the mechanical characteristics of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by using epoxidized natural rubber (ENR-25 and ENR-50) as a toughening agent and polybutadiene (PB) grafted with maleic anhydride (MA) (3 MA groups/chain) as a compatibilizer. The PHBV/ENR blends were mixed in 100/0, 90/10, 80/20, and 70/30 with PB-g-MA at 0, 5, and 10% (wt./wt.), using an internal mixer set to 175 °C with a rotor speed of 50 rpm. The findings indicated that at 70/30 PHBV/ENR composition, the impact strength of the blends with 25 and 50 epoxide contents were the greatest at 6.92 ± 0.35 J m^-1 and 7.33 ± 1.19 J m^-1, respectively, which are about two times greater than that of neat PHBV. Furthermore, the biodegradability of the PHBV/ENR blends was more substantial than that of neat PHBV, showing a mass reduction of approximately 40% and 45% for PHBV/ENR-25 and PHBV/ENR-50, respectively. In comparison, while the mass loss of PHBV was approximately 37% after three months of soil burial. The results indicate that ENR improves the toughness of the blends while simultaneously increasing PHBV degradation, which could pave the way for broadening PHBV for sustainability purposes.

A comprehensive review on fused deposition modelling of polylactic acid

Fused Deposition Modelling (FDM) is one of the additive manufacturing (AM) techniques that have emerged as the most feasible and prevalent approach for generating functional parts due to its ability to produce neat and intricate parts. FDM mainly utilises one of the widely used polymers, polylactic acid, also known as polylactide (PLA). It is an aliphatic polyester material and biocompatible thermoplastic, with the best design prospects due to its eco-friendly properties; when PLA degrades, it breaks down into water and carbon dioxide, neither of which are hazardous to the environment. However, PLA has its limitations of poor mechanical properties. Therefore, a filler reinforcement may enhance the characteristics of PLA and produce higher-quality FDM-printed parts. The processing parameters also play a significant role in the final result of the printed parts. This review aims to study and discover the properties of PLA and the optimum processing parameters. This review covers PLA in FDM, encompassing its mechanical properties, processing parameters, characterisation, and applications. A comprehensive description of FDM processing parameters is outlined as it plays a vital role in determining the quality of a printed product. In addition, PLA polymer is highly desirable for various field industrial applications such as in a medical, automobile, and electronic, given its excellent thermoplastic and biodegradability properties.

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.

Ultra-Tough Polylactide/Bromobutyl Rubber-Based Ionomer Blends via Reactive Blending Strategy

A series of ultra-toughened sustainable blends were prepared from poly(lactic acid) (PLA) and bromobutyl rubber-based ionomers (i-BIIRs) via reactive blending, in which dicumyl peroxide (DCP) and Joncryl®ADR-4440 (ADR) were used as reactive blending additives. The miscibility, phase morphology and mechanical property of the PLA/i-BIIRs blends were thoroughly investigated through DMA, SEM, tensile and impact tests. The influence of different ionic groups and the effects of DCP and ADR on the compatibility between the phases, phase structure and mechanical properties were analyzed. The introduction of the imidazolium-based ionic groups and the reactive agents enable the i-BIIRs play multiple roles as effective compatibilizers and toughening agents, leading to improved interfacial compatibility and high toughness of the blends. The mechanical properties test showed that the PLA/i-BIIRs blends exhibit excellent toughness: impact strength and the elongation at break of AR-OH(30)+AD reached 95 kJ/m² and 286%, respectively. The impact fracture surface showed the large-scale plastic deformation of the PLA matrix in the blends, resulting in greatly absorbing the impact energy. The results proved that simultaneously applying reactive blend and multiple intermolecular interactions methods is an effective toughening strategy for toughening modification of the PLA blends.

Modified Polylactic Acid with Improved Impact Resistance in the Presence of a Thermoplastic Elastomer and the Influence of Fused Filament Fabrication on Its Physical Properties

The standard polylactic acid (PLA), as a biodegradable thermoplastic polymer, is commonly used in various industrial sectors, food, and medical fields. Unfortunately, it is characterized by a low elongation at break and low impact energy. In this study, a thermoplastic copolyester elastomer (TPCE) was added at different weight ratios to improve the impact resistance of PLA. DSC analysis revealed that the two polymers were immiscible. A good balance of impact resistance and rigidity was reached using the formulation that was composed of 80% PLA and 20% TPCE, with an elongation at break of 155% compared to 4% for neat PLA. This new formulation was selected to be tested in a fused filament fabrication process. The influence of the nozzle and bed temperatures as printing parameters on the mechanical and thermal properties was explored. Better impact resistance was observed with the increase in the two thermal printing parameters. The crystallinity degree was not influenced by the variation in the nozzle temperature. However, it was increased at higher bed temperatures. Tomographic observations showed an anisotropic distribution of the porosity, where it was mostly present between the adjacent printed filaments and it was reduced with the increase in the nozzle and bed temperatures.

Post-chemical grafting poly(methyl methacrylate) to commercially renewable elastomer as effective modifiers for polylactide blends

A novel poly(epichlorohydrin-co-ethylene oxide)-g-poly(methyl methacrylate) copolymer (ECO-g-PMMA) was successfully synthesized from a commercially renewable elastomer via the ATRP method. The graft copolymer was investigated as a toughening agent and compatibilizer for polylactide (PLA) and PLA/ECO blends, respectively. Binary blending PLA with the copolymers (5-15 wt%) significantly improved the strain at break of PLA above 200% without a great strength loss. More importantly, the ternary PLA/ECO/ECO-g-PMMA copolymer blends exhibited a remarkably high impact strength of 96.9 kJ/m² with non-broken behaviors. An interesting phase structure transformation from a typical sea-island structure to a unique quasi-continuous network structure was observed with varying the content of ECO-g-PMMA from 0 to 15 wt% in the ternary blends. The native toughening mechanism analysis indicated the synergistic toughening effect of the good interfacial adhesion and unique quasi-continuous morphology endowed the ternary blends with excellent mechanical performance.

Preparation of Chemically Modified Lignin-Reinforced PLA Biocomposites and Their 3D Printing Performance

Using a simple esterification reaction of a hydroxyl group with an anhydride group, pristine lignin was successfully converted to a new lignin (COOH-lignin) modified with a terminal carboxyl group. This chemical modification of pristine lignin was confirmed by the appearance of new absorption bands in the FT-IR spectrum. Then, the pristine lignin and COOH-lignin were successfully incorporated into a poly(lactic acid) (PLA) matrix by a typical melt-mixing process. When applied to the COOH-lignin, interfacial adhesion performance between the lignin filler and PLA matrix was better and stronger than pristine lignin. Based on these results for the COOH-lignin/PLA biocomposites, the cost of printing PLA 3D filaments can be reduced without changing their thermal and mechanical properties. Furthermore, the potential of lignin as a component in PLA biocomposites adequate for 3D printing was demonstrated.

Morphological and mechanical properties of biodegradable poly(glycolic acid)/poly(butylene adipate-co-terephthalate) blends with in situ compatibilization

In the present work, the biodegradable blends of poly(glycolic acid) (PGA) and poly(butylene adipate-co-terephthalate) (PBAT) with in situ compatibilization using 4,4'-methylenebis(phenyl isocyanate) (MDI) were prepared. The combined results of FTIR, DSC, SEM, DSC, POM, TGA and rheology demonstrated that the MDI was successfully reacted with PGA/PBAT, the complex viscosity and storage moduli (G') of the blends were increased. Melt elasticity and viscosity of the blends were also increased on increasing the concentration of PBAT. SEM results indicated that the compatibility was improved by in situ compatibilization. Due to the apparent differences in melting temperature (T m) between PGA and PBAT, the morphology of the dispersed phase evolved from a spherical structure to in situ microfiber when the content of PBAT was up to 60% during injection molding. The interfacial adhesion between PGA and PBAT was strengthened, consequently, the impact strength of the blend was sharply increased from 9.0 kJ m-2 to 22.2 kJ m-2. On account of the chain extension effect, the crystallinity, crystallization temperature and crystallization size were decreased, which was also of benefit for the improvement of toughness. Meanwhile, the thermal stability of the PGA was improved through blending with PBAT. A novel biodegradable blending material with enhanced toughness and thermal stability was prepared.

Renewable and Tough Poly(l-lactic acid)/Polyurethane Blends Prepared by Dynamic Vulcanization

Melt blending of homopolymers is an effective way to achieve an attractive combination of polymer properties. Dynamic vulcanization of fatty-acid-based polyester polyol with glycerol and poly(l-lactic acid) (PLLA) in the presence of hexamethylene diisocyanate (HDI) was performed with the aim of toughening PLLA. The dynamic vulcanization in an internal mixer led to the formation of a PLLA/PU biobased blend. Melt torque, Fourier transform infrared (FTIR), and gel fraction analysis demonstrated the successful formation of cross-linked polyurethane (PU) inside the PLLA matrix. Scanning electron microscopy (SEM) analysis showed that the PLLA/PU blends exhibit a sea-island morphology. Gel fraction analysis revealed that a rubbery phase was formed inside the PLLA matrix, which was insoluble in chloroform. FTIR analysis of the insoluble part shows the appearance of an absorption band centered at 1758 cm-1, related to the crystalline carbonyl vibration of the PLLA component, thus suggesting the partial involvement of PLLA chains in the cross-linking reaction. The overall content of the PU phase in the blends significantly affected the mechanical properties, thermal stability, and crystallization behavior of the materials. The overall crystallization rate of PLLA was noticeably decreased by the incorporation of PU. At the same time, polarized light optical microscopy (PLOM) analysis revealed that the presence of the PU rubbery phase inside the PLLA matrix promoted PLLA nucleation. With the formation of the PU network, the impact strength showed a remarkable increase while Young's modulus correspondingly decreased. The blends showed slightly reduced thermal stability compared to the neat PLLA.

Polyethylene glycol grafted with carboxylated graphene oxide as a novel interface modifier for polylactic acid/graphene nanocomposites

Strength and toughness are both of great importance for the application of polylactic acid (PLA). Unfortunately, these two properties are often contradictory. In this work, an effective and practical strategy is proposed by using carboxylated graphene oxide (GC) grafted with polyethylene glycol (PEG), i.e. GC-g-PEG. The synthesis procedure of GC-g-PEG is firstly optimized. Then, a series of PLA nanocomposites were prepared by the melt blending method via masterbatch. In comparison to that achieved over pure PLA, these nanocomposites are of higher crystallinity, thermal stability and mechanical strength. This is mainly attributed to well-tailored interface and good dispersion. Especially, while retaining the tensile strength of the original PLA, the elongation at break increases by seven times by adding 0.3 wt% GC-g-PEG.

Enhanced compatibility, morphology, rheological and mechanical properties of carboxylated acrylonitrile butadiene rubber/chloroprene rubber/graphene nanocomposites: effect of compatibilizer and graphene content

Elastomeric nanocomposites were prepared from carboxylated acrylonitrile butadiene rubber/chloroprene rubber (XNBR/CR), graphene and a glycidyl methacrylate (GMA)-grafted XNBR (XNBR-g-GMA) compatibilizer by using a two-roll mill. The effect of graphene and XNBR-g-GMA compatibilizer on curing characteristics, rheological and mechanical properties and morphology of the nanocomposites was investigated. The curing properties and the morphology of the nanocomposites were studied by rheometry, SEM and TEM, respectively. The results of rheometry showed that by adding the XNBR-g-GMA compatibilizer and increasing the graphene content, the scorch time and optimum curing time decreased, but the torque increased, while the curing time increased with increasing CR percentage in the blend. Also, the results of DMTA tests showed that by adding the XNBR-g-GMA compatibilizer, there was compatibility between CR and XNBR and the dispersion of graphene in the XNBR/CR matrix was improved. This phenomenon was confirmed by direct observation of exfoliated graphene nanosheets by TEM. Also, the addition of XNBR-g-GMA and the increase of graphene content in the XNBR/CR matrix caused the fracture surface of the samples to be roughened and the size of dispersed phase (CR) in the XNBR matrix becomes smaller. The results of mechanical properties showed that the addition of the XNBR-g-GMA and increasing the graphene content resulted in increased hardness, fatigue strength, tensile strength, modulus and elongation-at-break.

Triply Biobased Thermoplastic Composites of Polylactide/Succinylated Lignin/Epoxidized Soybean Oil

Soybean oil is beneficial to improve the compatibility between polylactide (PLA) and succinylated lignin (SAL), which leads to the preparation of a host of biobased composites containing PLA, SAL, and epoxidized soybean oil (ESO). The introduction of SAL and ESO enables the relatively homogeneous morphology and slightly better miscibility obtained from triply PLA/SAL/ESO composites after dynamic vulcanization compared with unmodified PLA. The rigidity of the composites is found to decline gradually due to the addition of flexible molecular chains. According to the reaction between SAL and ESO, the T_g of PLA/SAL/ESO composites is susceptible to the movement of flexible molecular chains. The rheological behaviors of PLA/SAL/ESO under different conditions, i.e., temperature and frequency, exhibit a competition between viscidity and elasticity. The thermal stability of the composites displays a slight decrease due to the degradation of SAL and then the deterioration of ESO. The elongation at break and notched impact strength of the composites with augmentation of ESO increase by 12% and 0.5 kJ/m², respectively. The triply biobased PLA/SAL/ESO composite is thus deemed as a bio-renewable and environmentally friendly product that may find vast applications.

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.

Copolycarbonates Based on a Bicyclic Diol Derived from Citric Acid and Flexible 1,4-Cyclohexanedimethanol: From Synthesis to Properties

Octahydro-2,5-pentalenediol (OPD), is a compelling citric acid-based bicyclic diol with excellent rigidity and thermal stability. Herein, a series of copolycarbonates (co-PCs) were synthesized, starting from OPD, 1,4-cyclohexanedimethanol (CHDM), and diphenyl carbonate (DPC). All polycarbonates are amorphous with glass transition temperatures increased when increasing the content in OPD units. Dynamic mechanical analysis (DMA) revealed the sub T_g β-relaxations at low temperatures originating from the CHDM conformational transition, indicative of the possibility of impact-resistance. Morphological analysis of the fracture surfaces revealed the toughening mechanism under tensile was shear yielding of the matrix triggered by internal cavitation. The incorporation of OPD steadily increased the Young's modulus, from 482 to 757 MPa, with the OPD fraction increased from 0 to 30 mol %. As the OPD content further increased, a "ductile-to-brittle" transition occurred due to the low number-average molecular weight (M_n) and the low entangled strand density (high entanglement molecular weight).

Synergistic Mechanisms Underlie the Peroxide and Coagent Improvement of Natural-Rubber-Toughened Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Mechanical Performance

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a promising bio-based and biodegradable thermoplastic with restricted industrial applications due to its brittleness and poor processability. Natural rubber (NR) has been used as a toughening agent, but further physical improvements are desired. In this study, rubber toughening efficiency was significantly improved through the synergistic use of a trifunctional acrylic coagent and an organic peroxide during reactive extrusion of PHBV and NR. The rheological, crystallization, thermal, morphological, and mechanical properties of PHBV/NR blends with 15% rubber loading were characterized. The peroxide and coagent synergistically crosslinked the rubber phase and grafted PHBV onto rubber backbones, leading to enhanced rubber modulus and cohesive strength as well as improved PHBV⁻rubber compatibility and blend homogeneity. Simultaneously, the peroxide⁻coagent treatment decreased PHBV crystallinity and crystal size and depressed peroxy-radical-caused PHBV degradation. The new PHBV/NR blends had a broader processing window, 75% better toughness (based on the notched impact strength data), and 100% better ductility (based on the tensile elongation data) than pristine PHBV. This new rubber-toughened PHBV material has balanced mechanical performance comparable to that of conventional thermoplastics and is suitable for a wide range of plastic applications.

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.

Toward Super-Tough Poly(l-lactide) via Constructing Pseudo-Cross-link Network in Toughening Phase Anchored by Stereocomplex Crystallites at the Interface

We demonstrated a novel strategy to toughen poly(l-lactide) (PLLA) by constructing pseudo-cross-link networks based on chain entanglements of long-chain branched structure in the toughening phase, which were anchored by stereocomplex (SC) crystallites at the interface. The formation of pseudo-cross-link network was achieved by simple blending of the copolymer of long-chain branched polycaprolactone and poly(d-lactide) (LB-PCL- b-DLA) with PLLA without introducing any chemical cross-linking structure or nonbiodegradable component. The microscopic morphology analysis suggests that the interface-formed SC crystallites not only enhanced the interfacial interaction between LB-PCL and PLLA but also obviously increased the matrix crystallization rate. Different from those blends without SC crystallites or long-chain branched structures, nano-microgels were observed in chloroform solution of the PLLA/LB-PCL- b-DLA blend, suggesting the formation of pseudo-cross-link network. The pseudo-cross-link network in LB-PCL toughening phase endows PLLA a significantly improved impact toughness (49.5 kJ/m²), which is almost 13 times than that of neat PLLA. Moreover, matrix crystallinity and spherulite size of the PLLA matrix also play significant roles in toughening. Only sufficiently crystallized PLLA with proper spherulite size can effectively trigger the matrix shear yielding, meanwhile, facilitate the energy dissipating.

An environmentally sustainable plasticizer toughened polylactide

Cardanol (CD), derived from renewable natural cashew nutshell liquid, has been used as a new plasticizer for polylactide (PLA), to create blends which retain the environmentally friendly features of PLA. The differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM) results all reveal that PLA and CD show good miscibility at low CD content. CD significantly decreased the glass transition temperature and enhanced the crystallization ability of PLA, demonstrating good plasticizing efficiency with PLA. At 10 wt% CD, ultimate elongation and impact toughness increased to 472% and 9.4 kJ m-2, respectively, which represented improvements of 31-fold and 2.6-fold over the corresponding measurements for neat PLA. The plasticization effect of CD was also demonstrated by the decreased melt complex viscosity and shear storage modulus at lower CD content for the blends when compared with neat PLA. Thus, the investigated CD presents an interesting candidate for a PLA plasticizer, meeting "double green" criteria. No cytotoxicity was found for the blends and hence they may be suitable for biomedical applications.