Polylactide Blends Research Articles

Enhanced Interfacial Adhesion of Polylactide/Poly(ε-caprolactone)/Walnut Shell Flour Composites by Reactive Extrusion with Maleinized Linseed Oil.

Novel green composites were prepared by melt compounding a binary blend of polylactide (PLA) and poly(ε-caprolactone) (PCL) at 4/1 (wt/wt) with particles of walnut shell flour (WSF) in the 10–40 wt % range, which were obtained as a waste from the agro-food industry. Maleinized linseed oil (MLO) was added at 5 parts per hundred resin (phr) of composite to counteract the intrinsically low compatibility between the biopolymer blend matrix and the lignocellulosic fillers. Although the incorporation of WSF tended to reduce the mechanical strength and thermal stability of PLA/PCL, the MLO-containing composites filled with up to 20 wt % WSF showed superior ductility and a more balanced thermomechanical response. The morphological analysis revealed that the performance improvement attained was related to a plasticization phenomenon of the biopolymer blend and, more interestingly, to an enhancement of the interfacial adhesion of the green composites achieved by extrusion with the multi-functionalized vegetable oil.

Direct Compounding Injection Molding and Resulting Properties of Ternary Blends of Polylactide, Polybutylene Succinate and Hydrogenated Styrene Farnesene Block Copolymers

Direct compounding injection molding of ternary blends of polylactide (PLA), polybutylene succinate (PBS) and a hydrogenated styrene farnesene block copolymer (HSFC) was investigated for different blend compositions. Morphological analysis by atomic force microscopy and scanning electron microscopy showed a heterogeneous morphology of the ternary blends, with coexisting droplets of HSFC and PLA respectively PBS. Particle sizes analysis of the minor phases in the ternary blends showed mean values in the range of ∼1 μm, which is discussed in correlation to the rheological properties of the blend components as obtained by high pressure capillary rheometry. In result, with increasing HSFC content, the ternary blends showed a significant increase in notched Charpy impact strength (acN). In concrete, for the ternary blends with 15 wt% of HSFC a maximum acNof 15.8 kJ/m2was found. At the same time, incorporation of the HSFC resulted only in a moderate reduction in elastic modulus and tensile strength.

Dual-Curing Polylactide for Resorbable Bone Cement

Polymeric cement based on poly (methyl methacrylate) (PMMA) has been known as a common material for fixation of prostheses with the advantages of mechanical properties. However, one of drawbacks of PMMA cement is heat produced during polymerization. The elevating temperature during polymerization resulting from exothermic polymerization of MMA can cause bone cellular necrosis. Additionally, the residual MMA monomer after polymerization is an issue regarding the biocompatibility of cement. In this study, a resorbable cement based on polylactide (PLA) has been developed. Its physical, mechanical and biological properties were investigated as an alternative biocompatible bone cement. The dual-cured polylactide cements prepared by combining spherical powder of star-shaped and linear PLA blends with triethylene glycol dimethacrylate liquid were radically polymerized by UV-VIS light and self-curing methods. Flexural strength, maximum temperature during polymerization and biocompatibility via the percentages of cell viability using MTT assay of the dual-cured polylactide were determined to meet requirements for bone cement. The best flexural strength of 108 MPa was achieved from the cement composed of 80%-wt of star-shaped PLA with molecular weight (Mw) of 10770. The preparation of cement using paste/liquid mixing, in which the powder was allowed to wet in the liquid before mixing, significantly encouraged mechanical properties compared to powder/liquid mixing due to satisfactory solubility of PLA prior to polymerization. The amount of initiator/activator was studied to fine-tune the maximum temperature during polymerization. The maximum temperature during polymerization of the PLA cement was in the range of 80-90 degree Celsius and the percentage of osteogenic cell viability immediately after cement setting was 83 indicating a non-toxic material. Therefore, this PLA cement polymerized with a dual curing mode is promising for a resorbable bone cement.

Super Toughened Poly(lactic acid)-Based Ternary Blends via Enhancing Interfacial Compatibility.

Novel super toughened bioplastics are developed through controlled reactive extrusion processing, using a very low content of modifier, truly a new discovery in the biodegradable plastics area. The super toughened polylactide (PLA) blend showing a notched impact strength of ∼1000 J/m with hinge break behavior is achieved at a designed blending ratio of PLA, poly(butylene succinate) (PBS), and poly(butylene adipate-co-terephthalate) (PBAT), using less than 0.5 phr peroxide modifier. The impact strength of the resulting blend is approximately 10 times that of the blend with the same composition without a modifier and ∼3000% more than that of pure PLA. Interfacial compatibilization among the three biodegradable plastics took place during the melt extrusion process in the presence of a controlled amount of initiator, which is confirmed by scanning electron microscopy and rheology analysis. The synergistic effect of strong interfacial adhesion among the three blending components, the decreased particle size of the most toughened component, PBAT, to ∼200 nm, and its uniform distribution in the blend morphology result in the super tough biobased material. One of the key fundamental findings through the in situ rheology study depicts that the radical reaction initiated by peroxide occurs mainly between PBS and PBAT and not with PLA. Thus, the cross-linking degree can be controlled by adjusting renewable sourced PLA contents in the ternary blend during reactive extrusion processing. The newly engineered super toughened PLA with high stiffness and high melt elasticity modulus could reasonably serve as a promising alternative to traditional petroleum plastics, where high biobased content and biodegradability are required in diverse sustainable packaging uses.

Biodegradability of blends based on aliphatic polyester and thermoplastic starch

In this work, biodegradable aliphatic polyester blends of polycaprolactone and polylactide were melted and blended with a natural and biodegradable thermoplastic starch (TPS). The TPS employed in this study was obtained by plasticization of isolated wheat starch using glycerol as plasticizer. Morphology as well as thermal properties of the blends was investigated, and water vapor permeability as a barrier property was also monitored. The biodegradability of the biodegradable blends was performed by a composting process on laboratory scale. The composting process was conducted in an adiabatic closed reactor for 21 days and during the composting process, the temperature, pH value, % moisture and volatile matter and evolved CO2 were monitored. Biodegradation of the blends was determined by weight loss, as well as monitoring of morphological surface change. The thermophilic phase prevailed in the composting process, indicating intensive biodegradation of substrate as well as biodegradation of investigated ternary blends. Since microorganisms use starch as a carbon source, addition of TPS causes considerable acceleration of biodegradation of ternary blends due to higher water vapor permeability as a result of the hydrophilic nature of starch. The thermoplastic starch was first degraded within the blend, which was facilitated access to the microorganisms of other ingredients in the blend, encouraging the biodegradation of other components.

Monte Carlo Simulation of Strain-Enhanced Stereocomplex Polymer Crystallization.

We performed dynamic Monte Carlo simulations to investigate strain-induced polymer crystallization under separate enhancements of the driving forces for homocomponent and stereocomplex crystallization in the half-half symmetric racemic polymer blends. The results showed that the polymer strain significantly enhances the stereocomplex crystallization, in comparison to the parallel cases of template-induced crystal growth without any strain in the previous simulations. We attributed the results to the strain-induced polymer crystallization favoring intermolecular crystal nucleation at high temperatures, which benefits the stereocomplex crystallization. Our observations provided a molecular-level interpretation to the strain- or shear-enhanced stereocomplex crystallization in the racemic polylactide blends.

Localization control of carbon nanotubes in immiscible polylactide/vulcanized epoxidized soybean oil blends

Abstract In this study, we report a strategy to control the localization of carbon nanotubes (CNTs) in immiscible polymer blends of polylactide (PLA) and vulcanized epoxidized soybean oil (VESO) through the gel fraction of sebacic acid (SA) cured epoxidized soybean oil (ESO) precursors (SEP). CNTs disperse in the VESO phase for the SEP with no gel or low gel fraction. With medium gel fraction, CNTs disperse in both PLA and VESO phases. For high gel fraction, CNTs tend to locate in PLA phase and at the interface. With different locations, the composites behave different electrical conductivities . This strategy can be extended to some other particles filled immiscible polymer blends to tailor filler localizations and the final properties of the corresponding composites.

Preparation and Characterization of Poly(butylene succinate)/Polylactide Blends for Fused Deposition Modeling 3D Printing.

To obtain a new type of biodegradable material with high toughness and strength used for fused deposition modeling (FDM) printing, a series of poly(butylene succinate) (PBS)-based polymer materials was prepared via blending with polylactide (PLA). The rheological, thermal, and mechanical properties as well as FDM printing performances of the blends, such as distortion, cross section, and the interlayer bond strength, were characterized. The results show that with increasing PLA content, the blends possess higher melt viscosity, larger tensile strength, and modulus, which are more suitable for FDM printing. Especially, when the content of PLA is more than 40%, distortion due to residual stress caused by volume shrinkage disappears during the printing process and thus products with good dimensional accuracy and pearl-like gloss are obtained. The results demonstrate that the blend compositions with moderate viscosity, low degree of crystallinity, and high modulus are more suitable for FDM printing. Compared with the low elongation upon breaking of commercially FDM-printed material, the PBS/PLA blend materials exhibit a typical ductile behavior with elongation of 90–300%. Therefore, besides biodegradability, the PBS/PLA blends present excellent mechanical properties and suitability as materials for FDM printing. In addition, our study is expected to provide methods for valuating the suitability of whether a thermoplastic polymer material is suitable for FDM printing or not.

Mechanical properties and biodegradability of flax fiber-reinforced composite of polylactide and polycaprolactone

The aim of this work was to produce a composite based on the blend of polylactide and polycaprolactone and reinforced with flax fiber, intended for processing by injection molding, with improved mechanical and biodegradation properties as compared to neat polylactide (PLA) and polycaprolactone (PCL). The material was prepared by mixing PLA, PCL and flax fibers (about 5 mm long), extrusion and granulation with subsequent injection molding to obtain test samples. The composites differed in the content of PCL (0, 5, 10, 15 and 30 wt %) whereas the content of flax fibers was kept constant (20 wt %). The samples were characterized by means of scanning electron microscopy (SEM), tensile and impact strength measurements, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Biodegradation studies were carried out using proteinase K at laboratory conditions. It was found that a reduction of fiber lengths took place during the extrusion process and that addition of flax fibers to PLA/PCL blend resulted in an increase in elastic modulus and biodegradation rate. The composite impact strength was significantly improved at 30 wt % PCL fraction.

Preparation and Characteristics of Poly(butylene adipate-co-terephthalate)/Polylactide Blend Films via Synergistic Efficiency of Plasticization and Compatibilization

Polylactide (PLA) films blended with poly(butylene adipate-co-terephthalate) (PBAT) were hot melted using a twin screw extruder with the addition of triethyl citrate (TEC) as a plasticizer and toluene diisocyanate (TDI) as a compatibilizer. The synergistic effects of the two additives on the mechanical, thermal, and morphological properties of the PLA/PBAT blend films were investigated. The influence of TEC content on the plasticized PLA films and the effect of TDI’s presence on the PLA/PBAT blend films were also studied by comparing them with neat PLA. The results showed a pronounced increase in elongation at break of the plasticized PLA films with increasing TEC levels, but a slight reduction in thermal stability. Also, the addition of TEC and TDI to the blend system not only synergistically enhanced the tensile properties and tensile-impact strength of the PLA/PBAT blends, but also affected their crystallinity and cold crystallization rate, a result of the improvement of interfacial interaction between PLA and PBAT, including the enhancement of their chain mobility. The synergy of the plasticization and compatibilization processes led to the improvement of tensile properties, tensile-impact strength, and compatibility of the blends, accelerating cold crystallization without affecting crystallization.

Highly toughened polylactide (PLA) by reactive blending with novel polycaprolactone-based polyurethane (PCLU) blends

Polylactide (PLA)/polycaprolactone-based polyurethane (PCLU) blends were prepared by reactive blending of PLA with poly (caprolactone) triol (PCL-polyols) and isophorone diisocyanate (IPDI). The interfacial compatibility was markedly improved by the reaction of the terminal hydroxyl groups of PLA and the N=C=O groups of IPDI, as confirmed by Fourier transform infrared spectroscopy. Results of tensile testing and a notched impact test suggest that the elongation at break and impact strength of PLA/PCLU blends increased to more than 20 and 5 times those of neat PLA, respectively. Moreover, the tensile strength of PLA/PCLU blends slightly decreased. Excellent interfacial adhesion enabled the dispersed polyurethane elastomeric particles to act as effective stress concentration areas. The shearing yielding of PLA matrix triggered by internal cavitation was the main mechanical toughening mechanism.

Mechanical and flame‐retardant properties of biodegradable polylactide composites with hyperbranched silicon‐containing polymer

A hyperbranched polymer (HBP‐B2) containing siloxane chains was synthesized via bulk polymerization of diepoxide with a primary amine in the presence of monoepoxide. The weight‐average molecular weight of the prepared polymers was approximately 9200. Composites of polylactide (PLA) with aluminum trihydroxide (ATH) and the HBP‐B2 were prepared via direct melt compounding using a brabender. The test results showed that the LOI could be raised to 34% for the PLA composite with 25 wt% ATH and 5% HBP‐B2. The surface thermal profile of the composite during UL94 V test was further captured by an infrared camera, which was helpful to understand the flame‐retardant properties of the different samples. A V‐0 rating could be achieved by adding ATH and HBP‐B2 to the PLA matrix. Incorporation of HBP‐B2 as a plasticizer could increase the impact strength of a PLA blend or composite. For example, an addition of 10 wt% of HBP and 20 wt% ATH increased the elongation at break from 5% for neat PLA to 155% for the PLA composite.

Highly-Toughened Polylactide- (PLA-) Based Ternary Blends with Significantly Enhanced Glass Transition and Melt Strength: Tailoring the Interfacial Interactions, Phase Morphology, and Performance

The inherent shortcomings of polylactide (PLA) including brittleness, low glass transition temperature, and melt strength during processing were addressed through a facile melt blending of PLA with polybutadiene-g-poly(styrene-co-acrylonitrile) (PB-g-SAN) core–shell impact modifier and poly(methyl methacrylate) (PMMA). Highly tough PLA-based ternary blends with drastically enhanced glass transition temperature (≈ 21 °C) and melt strength were successfully prepared. The effect of PMMA content (ranging from 0 to 30 wt %) on the phase miscibility, morphology, mechanical properties, thermal behavior, rheological properties, and toughening mechanisms of PLA/PB-g-SAN/PMMA blends with 30% PB-g-SAN was systematically investigated. It was found that PMMA can effectively tune the interfacial interactions, phase morphology and performance of incompatible PLA/PB-g-SAN blend owing to its partial miscibility with PLA matrix and miscibility with SAN shell of PB-g-SAN, as evidenced by DMTA analysis. Increase in PMMA cont...

Effect of polyethylene glycol plasticizer on long‐term antibacterial activity and the release profile of bacteriocin nisin from polylactide blends

This work describes the synergetic effect of polyethylene glycol (PEG) in polylactide (PLA) blends, wherein the polyether acts as both the plasticizer and functional additive, ensuring the long‐term antimicrobial activity of bacteriocin nisin. Two types of PEG with the molecular weights of 1000 and 6000 g.mol−1(20 wt.%) were used to plasticize the PLA blends. The aforementioned bacteriocin nisin, at concentrations ranging between 0.02 and 0.15 wt.% (8000‐60 000 IU.g−1), was incorporated into the samples by the solvent cast technique. The effect of various PEG on the structural, mechanical, and thermal properties of the PLA‐based blends were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, stress‐strain analysis, differential scanning calorimetry, and dynamic mechanical analysis, respectively. The antibacterial activity of the samples was detected by the agar diffusion technique againstMicrococcus luteus. Furthermore, the antibacterial properties of the samples were tested according the ISO 22196 standard against Gram‐negative (Escherichia coli) and Gram‐positive (Staphylococcus aureus,Listeria monocytogenes) bacterial strains. The nisin was detected by high performance liquid chromatography, the device having been equipped with a UV/vis detector. The results show that the PEG, besides its plasticizing effect, significantly enhances the release profile and sustains long‐term antibacterial activity of nisin in a PLA matrix.

(Bio)degradable polymeric materials for a sustainable future – part 1. Organic recycling of PLA/PBAT blends in the form of prototype packages with long shelf-life

Prediction studies of advanced (bio)degradable polymeric materials are crucial when their potential applications as compostable products with long shelf-life is considered for today’s market. The aim of this study was to determine the effect of the polylactide (PLA) content in the blends of PLA and poly(butylene adipate-co-terephthalate) (PBAT); specifically how the material’s thickness corresponded to changes that occurred in products during the degradation process. Additionally, the influence of talc on the degradation profile of all samples in all environments was investigated. It was found that, differences in the degradation rate of materials tested with a similar content of the PLA component could be caused by differences in their thickness, the presence of commercial additives used during processing or a combination of both. The obtained results indicated that the presence of talc may interfere with materials behavior towards water and consequently alter their degradation profile.

Combined effects of Sepiolite and Cloisite 30B on morphology and properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/polylactide blends

The aim of the work was to investigate the combined effect of Sepiolite and Cloisite 30B on the morphology and properties of PHBV/PLA 50/50 w/w blend. Scanning electron microscopic analysis showed that the morphology of PHBV/PLA blend was relatively regular and homogeneous in the presence of Cloisite 30B and Sepiolite compared to the virgin blend, indicating a better compatibility between the two base polymers. The thermal stability of PHBV/PLA blend was enhanced by the clay fillers. Modulus and hardness were also increased in comparison with the virgin blend. The rheological measurements showed a significant increase in both the complex viscosity and storage modulus of the filled blend due to interactions between the clays fillers and the PHBV/PLA blend.

Composite Materials Based on Polylactide and Poly-3-hydroxybutyrate “Green” Polymers

Blends of polylactide with low-density polyethylene and of poly-3-hydroxybutyrate with synthetic ethylene–propylene rubber with the component weight ratios of 30 : 70, 50 : 50, and 70 : 30 were prepared and studied in comparison with the pure components. The thermal characteristics of these blends were determined by differential scanning calorimetry. The melting point of polyhydroxybutyrate and polylactide in the blends changes insignificantly, by 1–2°C. The dependence of the morphology on the composition for both polymer systems was examined by scanning electron microscopy. The physicomechanical properties of the samples are determined by the major phase. The blends undergo biodegradation in soil at 20 ± 3°С. The process occurs faster for blends of polyhydroxybutyrate with ethylene–propylene rubber of all the compositions studied.

Relating Chemical Structure to Toughness via Morphology Control in Fully Sustainable Sebacic Acid Cured Epoxidized Soybean Oil Toughened Polylactide Blends

The use of soybean oil or its derivatives to toughen polylactide (PLA) usually leads to limited toughening efficiency, due to the incompatibility between toughening agents and parent PLA. Herein, we report a dynamic vulcanization method to toughen PLA using sebacic acid cured epoxidized soybean oil (VESO), a fully sustainable and biodegradable component. A series of sebacic acid cured epoxidized soybean oil precursors (SEPs) were prepared with different carboxyl/epoxy equivalent ratio (R), which consequently dictates the chemical structure and the morphology of PLA/VESO blends after the dynamic vulcanization. We demonstrated that the chemical structure of VESO plays a critical role in the compatibility, morphology, and toughness of the PLA/VESO blends. By optimizing the R-value, supertoughened PLA blends can be obtained, as evidenced by the significant improvement in the tensile toughness (up to 150.6 MJ/m3) and the impact strength (up to 542.3 J/m). The results of the toughening mechanism from the morpho...

Synergistic Efficiency of Tricresyl Phosphate and Montmorillonite on the Mechanical Characteristics and Flame Retardant Properties of Polylactide and Poly(butylene succinate) Blends

The main aim of this research was to investigate the synergistic influence of additives and poly(butylene succinate) (PBS) in improving both the mechanical and flame retardant properties of polylactide (PLA) blends. Tricresyl phosphate (TCP) and montmorillonite (MMT) were the additives used to improve the mechanical characteristics and fire resistance of PLA. Differential scanning calorimetry (DSC) thermograms revealed that the addition of TCP and MMT significantly affected their thermal behaviors. The results of the mechanical and morphological characterizations were in agreement with the changes in thermal behavior. The impact strength and limiting oxygen index (LOI) value of PLA significantly increased with the presence of PBS. The failure mode of the blends as evidenced by scanning electron microscopy (SEM) changed from brittle to ductile. The addition of TCP and MMT produced excellent anti-dripping and self-extinguishing behaviors of the blends, achieving V-0 rating. For the PLA/PBS blends, the synergistic combination of PBS and additives led to an acceleration of cold crystallization, a significant increment of flexibility and impact toughness, and an improvement of flame retardancy.

Biodegradable PBAT/PLA Blend with Bioactive MCPA-PHBV Conjugate Suppresses Weed Growth.

The herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) conjugated with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was prepared via a melt transesterification route. The resultant bioactive oligomer was then mixed with a blend of polylactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) with different loadings to manufacture films to be used as a bioactive, biodegradable mulch to deliver the herbicide to target broadleaf weed species. The biological targeting of the MCPA-PHBV conjugate in the mulch film was investigated under glasshouse conditions using faba bean (Vicia faba) as a selective (nontarget) model crop species having broadleaf morphology. The presence of the MCPA-PHBV conjugate in the biodegradable PBTA/PLA blend was shown to completely suppress the growth of broadleaf weed species while displaying only a mild effect on the growth of the model crop. The degradation of the mulch film under glasshouse conditions was quite slow. The release of the MCPA-PHBV during this process was detected using NMR, GPC, EDS, and DSC analyses, indicating that the majority of the MCPA diffused out after MCPA-PHBV conjugate bond scission. These data provide a strong "proof of concept" and show that this biodegradable, bioactive film is a good candidate for future field applications and may be of wide agricultural applicability.