Use of maleic anhydride compatibilization to improve toughness and other properties of polylactide blended with thermoplastic elastomers

Polylactide (PLA) being a very brittle biopolymer could be toughened by blending with thermoplastic elastomers such as thermoplastic polyurethane elastomer (TPU) and thermoplastic polyester elastomer (TPE); unfortunately, these blends are immiscible forming round domains in the PLA matrix. Therefore, the purpose of this study was to investigate the effects of using maleic anhydride (MA) compatibilization on the toughness and other properties of PLA blended with TPU and TPE. MA grafting on the PLA backbone (PLA‐g‐MA) was prepared separately by reactive extrusion and added during melt blending of PLA/thermoplastic elastomers. IR spectroscopy revealed that MA graft might interact with the functional groups present in the hard segments of TPU and TPE domains via primary chemical reactions, so that higher level of compatibilization could be obtained. SEM studies indicated that PLA‐g‐MA compatibilization also decreased the size of elastomeric domains leading to higher level of surface area for more interfacial interactions. Toughness tests revealed that Charpy impact toughness and fracture toughness (K_IC and G_IC) of inherently brittle PLA increased enormously when the blends were compatibilized with PLA‐g‐MA. For instance, G_IC fracture toughness of PLA increased as much as 166%. It was also observed that PLA‐g‐MA compatibilization resulted in no detrimental effects on the other mechanical and thermal properties of PLA blends. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhancing toughness of poly (lactic acid)/Thermoplastic polyurethane blends via increasing interface compatibility by polyurethane elastomer prepolymer and its toughening mechanism

Due to the environmental pollution caused by the petroleum-based polymer, poly (lactic acid) (PLA), a biodegradable and biocompatible polymer that obtained from natural and renewable sources, has attracted widespread attention. However, the brittleness of PLA greatly limits its application. In this study, the super toughened PLA-based blends were obtained by compatibilizing the PLA/thermoplastic polyurethane (TPU) blends with the polyurethane elastomer prepolymer (PUEP) as an active compatibilizer. The mechanical properties, thermal properties and corresponding toughening mechanism of PLA/TPU/PUEP system were studied by tensile test, instrumented impact test, dynamic mechanical analysis (DMA), scanning electronic microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). All the results demonstrate that the isocyanate (−NCO) group in PUEP is successfully reacted with the –OH groups at both sides of the PLA and the obtained polyurethane (PU)~PLA copolymer (PU ~ cõ PLA) significantly improves the interfacial compatibility of PLA/TPU blends. The gradually refined dispersed phase size and fuzzy phase interface as displayed in SEM images suggest a good interfacial compatibilization in the PLA/TPU/PUEP blends, probably due to the isocyanate reaction between PLA and PUEP. And the interfacial reaction and compatibilization among the components led to the formation of super toughened PLA/TPU/PUEP blends. And the instrumented impact results indicate that most of the impact toughness is provided by the crack propagation rather than the crack initiation during the entire fracture process.     

Structure and blood compatibility of highly oriented poly(lactic acid)/thermoplastic polyurethane blends produced by solid hot stretching

Highly oriented poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) blends were fabricated through solid hot stretching technology in an effort to improve the mechanical properties and blood biocompatibility of PLA as blood‐contacting medical devices. It was found that the tensile strength and modulus of the blends can be improved dramatically by stretching. With the increase of draw ratio, the cold crystallization peak became smaller, and the glass transition and the melting peak moved to high temperature, while the crystallinity increased, and the grain size of PLA decreased, indicating of the stress‐induced crystallization during drawing. The oriented blends exhibited structures with longitudinal striations which indicate the presence of micro‐fibers. TPU phase was finely and homogeneously dispersed in the PLA, and after drawing, TPU domains were elongated to ellipsoid. The introduction of TPU and orientation could enhance the blood compatibility of PLA by prolonging kinetic clotting time, and decreasing hemolysis ratio and platelet activation. Copyright © 2013 John Wiley & Sons, Ltd.     

Improvement in Toughness of Polylactide by Melt Blending with Bio-based Poly（ester）urethane

Polylactide （PLA） was successfully toughened by blending with bio-based poly（ester）urethane （TPU） elastomers which contained bio-based polyester soft segments synthesized from biomass diols and diacids. The miscibility, mechanical properties, phase morphology and toughening mechanism of the blend were investigated. Both DSC and DMTA results manifested that the addition of TPU elastomer not only accelerated the crystallization rate, but also increased the final degree of crystallinity, which proved that TPU has limited miscibility with PLA and has functioned as a plasticizer. All the blend samples showed distinct phase separation phenomenon with sea-island structure under SEM observation and the rubber particle size in the PLA matrix increased with the increased contents of TPU. The mechanical property variation of PLA/TPU blends could be quantitatively explained by Wu＇s model. With the variation of TPU, a brittle-ductile transition has been observed for the TPU/PLA blends. When these blends were under tensile stress conditions, the TPU particles could be debonded from the PLA matrix and the blends showed a high ability to induce large area plastic deformation before break, which was important for the dissipation of the breaking energy. Such mechanism was demonstrated by tensile tests and scanning electron microcopy （SEM） observations.     

TG-FTIR study of the thermal degradation of polyoxymethylene (POM)/thermoplastic polyurethane (TPU) blends

A series of blends of polyoxymethylene (POM)/thermoplastic polyesterurethane (TPU) has been obtained by mechanical processing using a double screw extruder. The thermal stability and the thermal degradation profiles of POM/TPU blends were investigated by thermogravimetric analysis (TG) coupled on-line with Fourier transform infrared spectroscopy (FTIR). It was found that incorporation of TPU into POM matrix resulted in increase of thermal stability of blends in comparison with pristine materials. The thermal degradation of TPU in inert gas atmosphere proceeds in two steps while the thermal degradation of POM is basically a one step process with a substage in a higher temperature range. The most abundant volatile products of the thermal degradation were identified; the possibly routes of their formation have been presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of ethylene-co-vinyl acetate-glycidylmethacrylate and cellulose microfibers on the thermal,rheological and biodegradation properties of poly(lactic acid) based systems

The properties and biodegradation behavior of blends of poly(lactic acid) (PLA) and ethylene-vinyl acetate-glycidylmethacrylate copolymer (EVA-GMA), and their composites with cellulose microfibers (CF) were investigated. The blends and composites were obtained by melt mixing and the morphology, phase behavior, thermal and rheological properties of PLA/EVA-GMA blends and PLA/EVA-GMA/CF composite films were investigated as a function of the composition. The disintegrability in composting conditions was examined by means of morphological, thermal and chemical analyses to gain insights into the post-use degradation processes. The results indicated a good compatibility of the two polymers in the blends with copolymer content up to 30 wt.%, while at higher EVA-GMA content a phase separation was observed. In the composites, the presence of EVA-GMA contributes to improve the interfacial adhesion between cellulose fibers and PLA, due to interactions of the epoxy groups of GMA with hydroxyls of CF. The addition of cellulose microfibers in PLA/EVA-GMA system modifies the rheological behavior, since complex viscosity increased in presence of fibers and decreased with an increase in frequency. Disintegration tests showed that the addition of EVA-GMA influence the PLA disintegration process, and after 21 days in composting conditions, blends and composites showed faster degradation rate in comparison with neat PLA due to the different morphologies induced by the presence of EVA-GMA and CF phases able to allow a faster water diffusion and an efficient PLA degradation process.     

Thermal and Morphological Studies on Poly(Methyl Methacrylate)/Thermoplastic Polyurethane Blends

Poly(methyl methacrylate) (PMMA) and thermoplastic polyurethane (TPU) blends in different compositions viz., 95/05, 90/10, 85/15 and 80/20 (by wt/wt% of PMMA/TPU) have been prepared by melt mixing using a twin screw extruder. The thermal stability of these blends has been characterized by thermogravimetric (TG) analysis. All the blends are stable up to 381°C and complete degradation occurs at 488°C. A slight improvement in thermal stability was noticed with an increase in TPU content in the blends. Surface morphology of the blends has been studied by an optical microscope. Optical microphotographs revealed two‐phase morphology for all the blends.     

Preparation of Polylactide/Poly(ether)urethane Blends with Excellent Electro-actuated Shape Memory <Emphasis Type="Italic">via</Emphasis> Incorporating Carbon Black and Carbon Nanotubes Hybrids Fillers

In this work, hybrid conductive fillers of carbon black (CB) and carbon nanotubes (CNTs) were introduced into polylactide (PLA)/thermoplastic poly(ether)urethane (TPU) blend (70/30 by weight) to tune the phase morphology and realize rapid electrically actuated shape memory effect (SME). Particularly, the dispersion of conductive fillers, the phase morphology, the electrical conductivities and the shape memory properties of the composites containing CB or CB/CNTs were comparatively investigated. The results suggested that both CB and CNTs were selectively localized in TPU phase, and induced the morphological change from the sea-island structure to the co-continuous structure. The presence of CNTs resulted in a denser CB/CNTs network, which enhanced the continuity of TPU phase. Because the formed continuous TPU phase provided stronger recovery driving force, the PLA/TPU/CB/CNTs composites showed better shape recovery properties compared with the PLA/TPU/CB composites at the same CB content. Moreover, the CB and CNTs exerted a synergistic effect on enhancing the electrical conductivities of the composites. As a result, the prepared composites exhibited excellent electrically actuated SME and the shape recovery speed was also greatly enhanced. This work demonstrated a promising strategy to achieve rapid electrically actuated SME via the addition of hybrid nanoparticles with self-networking ability in binary PLA/TPU blends over a much larger composition range.     

Preparation of Polylactide/Poly(ether)urethane Blends with Excellent Electro-actuated Shape Memory via Incorporating Carbon Black and Carbon Nanotubes Hybrids Fillers

In this work, hybrid conductive fillers of carbon black(CB) and carbon nanotubes(CNTs) were introduced into polylactide(PLA)/thermoplastic poly(ether)urethane(TPU) blend(70/30 by weight) to tune the phase morphology and realize rapid electrically actuated shape memory effect(SME). Particularly, the dispersion of conductive fillers, the phase morphology, the electrical conductivities and the shape memory properties of the composites containing CB or CB/CNTs were comparatively investigated. The results suggested that both CB and CNTs were selectively localized in TPU phase, and induced the morphological change from the sea-island structure to the co-continuous structure. The presence of CNTs resulted in a denser CB/CNTs network, which enhanced the continuity of TPU phase.Because the formed continuous TPU phase provided stronger recovery driving force, the PLA/TPU/CB/CNTs composites showed better shape recovery properties compared with the PLA/TPU/CB composites at the same CB content. Moreover, the CB and CNTs exerted a synergistic effect on enhancing the electrical conductivities of the composites. As a result, the prepared composites exhibited excellent electrically actuated SME and the shape recovery speed was also greatly enhanced. This work demonstrated a promising strategy to achieve rapid electrically actuated SME via the addition of hybrid nanoparticles with self-networking ability in binary PLA/TPU blends over a much larger composition range.     

Largely improved toughness of poly(lactic acid) by unique electrospun fiber network structure of thermoplastic polyurethane

Oriented thermoplastic polyurethane (TPU) fiber and fiber network were first prepared by electrospinning. The as-prepared TPU fiber or fiber network was then pre-fixed in poly(lactic acid) (PLA)/TPU composite to improve the toughness of PLA. For comparison purpose, TPU/PLA composites with sea-island morphology were also prepared by traditional solution blending and mechanical blending. The results show that the toughness of PLA is greatly increased by the special pre-fixed oriented TPU fibers even at a low content, and the toughness is further increased by the TPU fiber network. Our results indicate for the first time that the toughening effect of special TPU fibers or fiber network is much better than that of traditional TPU with sea-island morphology. This study provides guidance to largely improve the toughness of PLA by designing the special phase morphology of TPU.     

Simultaneously toughening and reinforcing poly(lactic acid)/thermoplastic polyurethane blend via enhancing interfacial adhesion by hydrophobic silica nanoparticles

This work focuses on satisfactorily toughening and reinforcing poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) blend with low TPU content (10 wt%) using appropriate amounts of hydrophobic silica nanoparticles (SiO₂) via simple melt mixing. Both thermodynamic prediction and transmission electron microscopy micrographs demonstrate that most SiO₂ nanoparticles distribute at interfaces between the PLA and TPU phases. This improves interfacial adhesion between the phases, which is attributed to good bonding strength between the PLA and SiO₂ via hydrophobic interaction and formation of hydrogen bonds between the TPU and SiO₂. The PLA/TPU (90/10) ternary blend nanocomposite with 2 wt% SiO₂ exhibits obviously high impact strength (about 5.0 and 12.6 times that of the corresponding blend and PLA, respectively) and higher tensile strength than the blend and even the PLA. Crazing is the main reason for improved impact toughnesses of the blend nanocomposites. This work provides a simple and effective strategy to endow PLA/elastomer blends with optimum strength–toughness balance by adding appropriate amounts of nanoparticles.     

聚酯／聚酸酐共混体系的降解和药物释放行为

聚酯／聚酸酐共混体系的降解和药物释放行为唐爱军，贺晓晖，李福绵（北京大学化学系北京１００８７１）关键词聚癸二酸，聚乳酸，聚己内酯，降解行为，药物释放行为聚酸酐，特别是脂肪类聚酸酥由于其化学价键的水解活泼性，是一类快速生物降解材料．由于聚酸团的水解机制...     

Structure evolution of bio-based PLA/ENR thermoplastic vulcanizates during dynamic vulcanization processing

The thermoplastic vulcanizates (TPVs) of Polylactide (PLA)/Epoxidized natural rubber (ENR) were prepared by dynamic vulcanization technology. The processing torque, crosslink density, morphology of PLA/ENR blends, and PLA's molecular weight during the processing were investigated by HAAKE rheometer, swelling measurement, scanning electron microscopy (SEM), and gel permeation chromatography (GPC). It was found that the vulcanization of ENR completed at the turning point after torque peak. After the turning point, the torque and crosslink density decreased with the processing time increasing. Moreover, the morphology of PLA/ENR blends showed bi-continuous structure during the dynamic vulcanization processing, and the phase size of PLA/ENR was increased with processing time and temperature. GPC results showed PLA degradation mainly happened after torque turning point. Thermal gravimetric analysis (TGA) results indicated that some parts of PLA would graft on ENR during processing, and the higher the processing temperature, the more the PLA was grafted.     

Advances in properties and biodegradability of co-continuous,immicisible, biodegradable,polymer blends

A series of blends consisting of polylactic acid (PLA) and aliphatic succinate polyester (Bionolle#3000) have been prepared. The results of the mechanical property investigation have shown that using more than 20 wt % Bionolle#3000 can significantly increase the toughness of the PLA, increase the elongation at break (more than 200%) and increase the impact strength (more than 70 J/m). These properties were not significantly affected by the aging behavior of PLA for more than two months. DMA results show that Bio#3000 reduces the elastic modulus of the blends between −15°C and 60°C. Soil degradation rates of the PLA/Bio#3000 blends also increase with increasing Bio#3000 content. However, for the blends with less than 30 wt % of Bio#3000, the degradation rates do not significantly increase. Enzymatic degradation rates of the blends are higher than for those of the two polymers, and these rates increase with increasing PLA content. Composting biodegradation rates increase with increasing Bio#3000 content.     

Compatibilized blends of thermoplastic polyurethane (TPU) and polypropylene

Compatibilized blends of thermoplastic polyurethane (TPU) and polypropylene (PP) were developed using amine (primary or secondary) functionalized PP's (PP-g-NH₂ or PP-g-NHR). The strategy of reactive compatibilization is based on fast reactions between amine functional groups and urethane linkages or traces of free isocyanates released by thermal degradation of TPU. Excellent compatibilization between TPU and PP was confirmed by rheological, morphological, and mechanical properties. Much finer domain size, higher interfacial adhesion, and more stable morphologies were clearly observed by scanning electron microscopy. Significant improvements in the overall mechanical properties (tensile, tear, abrasion) imply significantly more reaction between TPU and PP phases in the two TPU/PP blends containing PP-g-NH₂ or PP-g-NHR than a TPU/PP blend using PP-g-MA as a compatibilizing agent.     

Polyaniline/thermoplastic polyurethane blends: Preparation and evaluation of electrical conductivity

Conducting polymer blends whose undiluted components have different properties are promising materials for specific applications and have attracted interest in recent years. The aim of this study was to obtain and evaluate the electrical conductivity of polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA)/polyurethane thermoplastic (TPU) blends. The PAni.DBSA was synthesized from DBSA-aniline (DBSAn) salt through an emulsion polymerization in tetrahydrofurane (THF) or in the presence of polyurethane thermoplastic solution, resulting in pure PAni.DBSA or PAni.DBSA/TPU blends. Blends of PAni.DBSA/TPU were also prepared through casting, at room temperature, after dissolving both components in THF as a common solvent. The insulator-conductor transition was very sharp and the percolation threshold was lower than 2.7 wt% of PAni.DBSA. The electrical conductivity of PAni.DBSA/TPU blends, prepared by both methods, reached maximum values at a PAni.DBSA concentration of 40 wt%, close to the value observed for the undiluted conducting polymer. However, for a PAni.DBSA content lower than 30 wt%, the electrical conductivity was dependent on the blend preparation method. Blends were characterized by infrared spectroscopy, thermogravimetric analysis (TG) and optical microscopy. The electrical conducting characteristics of the PAni.DBSA/TPU blends prepared using different procedures indicate a high potential for their successful application in electrical processes.     

Mechanical,aging, optical and rheological properties of toughening polylactide by melt blending with poly(ethylene glycol) based copolymers

Two novel biodegradable copolymers, including poly(ethylene glycol)-succinate copolymer (PES) and poly(ethylene glycol)-succinate-l-lactide copolymer (PESL), have been successfully synthesized via melt polycondensation using SnCl₂ as a catalyst. The copolymers were used to toughen PLA by melt blending. The DSC and SEM results indicated that the two copolymers were compatible well with PLA, and the compatibility of PESL was superior to that of PES. The results of tensile testing showed that the extensibility of PLA was largely improved by blending with PES or PESL. At same blending ratios, the elongation at break of PLA/PESL blends was far higher than that of PLA/PES ones. The elongation maintained stable through aging for 3 months. The moisture absorption of the blends enhanced due to the strong moisture absorption of PEG segments in PES or PESL molecules, which did not directly lead to enhance the hydrolytic degradation rate of the PLA. The PLA blends containing 20–30 wt% PES or PESL were high transparent materials with high light scattering. The toughening PLA materials could potentially be used as a soft biodegradable packaging material or a special optical material.     

Properties of immiscible and ethylene-butyl acrylate-glycidyl methacrylate terpolymer compatibilized poly (lactic acid) and polypropylene blends

Poly(lactic acid) (PLA) and polypropylene (PP) blends of various proportions were prepared by melt-compounding. The miscibility, phase morphology, thermal behavior, and mechanical and rheological properties of the blends were investigated. The blends were immiscible systems with two typical morphologies, spherical droplet and co-continuous, and could be obtained at various compositions. Complex viscosity, storage modulus and loss modulus depend on the PP content. Thermal degradation of all blends led to two weight losses, for PLA and PP. The incorporation of PP improved the thermal stability of the blend. The effect of compatibilizer (ethylene-butyl acrylate-glycidyl methacrylate terpolymer, EBA-GMA) on the morphology and mechanical properties of 70/30 w/w PLA/PP blends was investigated. The tensile strength of these blends reached a maximum for 2.5 wt% EBA-GMA, and impact strength increased with increasing EBA-GMA content, suggesting that EBA-GMA is an effective compatibilizer for PLA/PP blends.     

Crystallization Kinetics and Melting Behavior of PA1010/Ether-based TPU Blends

Polyamide 1010(PA1010)/thermoplastic poly(ether urethane) elastomer(ether-based TPU) blends were prepared via melt extrusion. The crystallization kinetics and melting behavior of PA1010/ether-based TPU blends were systematically investigated using differential scanning calorimetry. The crystallization kinetics results show that the addition of ether-based TPU hinders the crystallization of PA1010, and the hindrance effect increases with the increase of the concentration of ether-based TPU. Both pure PA1010 and PA1010/ether-based TPU blends exhibit double melting peaks in the process of nonisothermal crystallization. The double melting peaks change differently with the variation of cooling rate and blend composition. The cooling rate only influences the lower melting peak; however, the blend composition influences not only the lower melting peak but also the higher melting peak. The reason for the phenomenon must be the interaction between the two compositions.     

Hydrolytic And Enzymatic Degradation Characteristics Of Biodegradable Aliphatic Polysters

Aliphatic polyesters, especially those derived from lactide (PLA), glycolide (PGA) and ε-caprolactone (PCL), are being investigated worldwide for applications in the field of surgery (suture material, devices for internal bone fracture fixation), pharmacology (sustained drug delivery systems), and tissue engineering (scaffold for tissue regeneration) [1,2]. This is mainly due to their good biocompatibility and variable degradability. These polymers present also a growing interest for environmental applications in agriculture (mulch films) and in our everyday life (packaging material)as the development of biodegradable materials is now considered as one of the potential solutions to the problem of plastic waste management.For both biomedical and environmental applications, it is of major importance to understand the degradation characteristics of the polymers. The hydrolytic degradation of aliphatic polyesters has been investigated by many research groups. Our group has shown that degradation of PLAGA large size devices is faster inside than at the surface. This heterogeneous degradation is due to the autocatalytic effect of carboxylic endgroups formed by ester bond cleavage. Moreover,degradation-induced morphological and compositional changes were also elucidated. In the case of PCL, the hydrolytic degradation is very slow due to its hydrophobicity and crystallinity.The enzymatic degradation of these polymers has been investigated by a number of authors. A specific enzyme, proteinase K, has been shown to have significant effects on PLA degradation. This enzyme preferentially degrade L-lactate units as opposed to D-lactate ones, amorphous zones as opposed to crystalline ones [3]. The enzymatic degradation of PCL polymers has also been investigated. A number of lipase-type enzymes were found to significantly accelerate the degradation of PCL despite its high crystallinity. In the case of PLA/PCL blends, the two components exhibited well separated crystalline domains. The selective degradation of PCL or PLA components by enzymes revealed the inner morphology of the blends with formation of microsphere-like or island-like structures [5].