PLA Blends Research Articles

Characterization of rhodamine loaded PEG-g-PLA nanoparticles (NPs): Effect of poly(ethylene glycol) grafting density

In our previous study, PEG-g-PLA nanoparticles were developed and characterized. The aim of the present work is to investigate the effect of PEG grafting density (% PEG inserted onto poly( d, l)-lactide, PLA backbone) on both physicochemical and biological properties (mainly plasma protein binding and in vitro macrophage uptake) of PEG-g-PLA NPs. Rhodamine B (RHO) loaded NPs were prepared from a 1:1 (wt/wt) blend of PLA and PEG-g-PLA copolymer of varying PEG grafting density (1, 7, or 20% mol/mol of lactic acid monomer) by an o/w emulsion solvent evaporation method. These NPs were characterized with regard to their morphology, size, surface charge, loading efficiency, and rhodamine release. The extent of protein adsorption to the surface of different NPs was qualitatively investigated by dynamic light scattering technique. Additionally, the in vitro macrophage uptake following incubation of RAW 264.7 cells with rhodamine loaded PEG-g-PLA and PLA particles was investigated by confocal laser scanning microscopy (CLSM). The amount of NPs phagocytosed following incubation of RAW 264.7 cells with different concentrations of rhodamine loaded PLA or pegylated NPs for 24 h at 37 °C was also determined by fluorescence spectroscopy. ALL lyophilized NPs showed larger diameter in the range of 300–400 nm compared to freshly prepared NPs suspension indicating particle aggregation upon lyophilization. % EE of rhodamine was found to be between 10% and 68% wt/wt depending on PEG grafting density. The higher the grafting density of PEG over PLA backbone, the more the entrapment efficiency. All pegylated NPs showed low zeta potential (close to zero) values. In vitro release analysis revealed that rhodamine leaked from all nanoparticles at a very slow rate at physiological pH, thus making it suitable for both imaging and uptake studies with RAW 264.7 cells. All PEG-g-PLA NPs of different PEG grafting density were well tolerated and exhibited no toxicity to RAW 264.7 cells as seen by cell proliferation assays. Cellular uptake of NPs was mainly dependent on polymer type as well as PEG grafting density. Grafted copolymer NPs resulted in lower degree of macrophage uptake compared to PLA NPs in macrophages cell lines. The higher the PEG grafting density, the lower the uptake of NPs by macrophage cells. Minimum NPs uptake for all the investigated concentrations was achieved when the PEG grafting density was 7% mol/mol of lactic acid. When increasing the PEG grafting density in the nanoparticles above 7%, no significant reduction in NPs phagocytosis was achieved. Thus, this study shows that the optimal PEG density required for designing stealth PEG-g-PLA NPs suitable for drug delivery applications might vary from 4 to 7%.

The Effects of Process Engineering on the Performance of PLA and PHBV Blends

AbstractThe effects of process engineering in the fabrication of PHBV, PLA and their blends prepared by melt blending are studied. The elongation of an optimized blend can be improved by 148 and 250% over the virgin PHBV and PLA polymers, respectively. DSC shows that the two polymers are immiscible in blends of any composition. The crystallinity of PHBV is hindered by the presence of PLA. UV‐Vis demonstrates the opacity of the blend with incorporation of PHBV to the PLA phase. The observed tensile modulus of the optimized sample is compared with theoretical values from the rule of mixtures. Gordon‐Taylor's equation is applied on the glass transition temperatures for theoretical modeling to explain the miscibility of the polymers. magnified image

Incorporation of wheat starch and coupling agents into poly(lactic acid) to develop biodegradable composite

Composites of poly (lactic acid) (PLA)/wheat starch and PLA/wheat starch/methyldiphenyldiisocyanate, were prepared and characterised in this study. The effects of incorporating different coupling agents on the physical properties and morphology of the composites were studied. Extrusion technology and injection moulding techniques were used to prepare standard tensile and impact test pieces. Tensometry was used to investigate the tensile properties of the composites and impact testing using falling weight technique was used to investigate impact strength. To investigate the thermal behaviour of the composites, differential scanning calorimetry was employed. Water absorption properties of the composites were also investigated. Scanning electron microscopy was used to investigate the morphology of the composites. Starch can be incorporated in a PLA matrix at 10% level without difficulty in processing by extrusion followed by injection moulding to make shaped mouldings in the presence of MDI. With 10% wheat starch and 2% MDI, blends of wheat starch/PLA can reach the tensile strength, elongation, impact strength properties of raw PLA. In the presence of 2% MDI and 10% glycerol, blends of PLA and starch make an entirely flexible material.

Biodegradability assessment of aliphatic polyesters‐based blends using standard methods

AbstractImportant information concerning polymer's final fate in the environment can be achieved in biodegradation studies. In this context, the focus of this study was to evaluate the biodegradability of blends containing aliphatic polyesters using standard methods. Blends of high‐density polyethylene, biodegradable polymer, and polyethylene modified with maleic anhydride (used as compatibilizer) were prepared in a corotating twin‐screw extruder. Biodegradable polymers used were poly(lactic acid) (PLA), poly(ε‐caprolactone) (PCL), and Mater‐Bi (thermoplastic starch with PLA or PCL). Biodegradation tests were carried out using two standard methods: (i) ISO 14851 (1999), biochemical oxygen demand in a closed respirometer and (ii) ASTM G 22‐76, microbial growth of test microorganisms. Both biodegradability tests suggested that the blend containing PCL is more biodegradable than the one containing PLA. Addition of starch increased the biodegradability of the PLA blend. The biodegradability of the blends evaluated in this study by the biochemical oxygen demand method ranged from 22% (PLA 60) to 52% for corn starch/PCL 30/70 (% wt) (SPCL 70). Therefore, the blends may not be considered “readily biodegradable” according to the OECD standard. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Impact Modification of Polylactide with a Biodegradable Ethylene/Acrylate Copolymer

AbstractThe effectiveness and efficiency of an ethylene/acrylate copolymer in toughening semicrystalline and amorphous PLA through melt blending is studied. The mechanical properties, phase morphologies, miscibilities, and toughening mechanisms of the blends are assessed. The ethylene/acrylate impact modifier effectively improved the impact strength of the blends, regardless of the PLA type. The semicrystalline blends showed decreased tensile strength and modulus with increased impact modifier content. In contrast, the ductility, elongation at break, and energy to break increased significantly. The relatively low BDT temperature obtained for the PLA blends renders the ethylene/acrylate copolymer impact modifier a desirable additive to toughen PLA for use in cold temperatures.magnified image

Preparation and characterization of microspheres based on blend of poly(lactic acid) and poly(ɛ-caprolactone) with poly(vinyl alcohol) as emulsifier

In this paper, microspheres were prepared by oil-in-water (o/w) emulsion solvent evaporation method. Biodegradable polymer such as blend of poly (lactic acid) (PLA) and poly(ɛ-caprolactone) (PCL) with certain compositions and characteristics was used to prepare the microspheres with poly(vinyl alcohol) (PVA) as an emulsifier. This study observed the microspheres particle’s size distribution at various concentrations of PVA (1%, 1.5%, 2%, and 2.5% PVA). The PVA volume variations effects during the process (50, 100, 150, 200, and 250mL) were also observed. The blend of PLA and PCL is formed only by physical interaction between them. This can be seen from the FTIR spectrum which shows both PLA and PCL component. The microspheres physical size and appearance were observed by optical microscope (MO). The overall results of this study showed that the formula which used 50–150mL of 2.5% polyvinyl alcohol produced the microspheres with the most uniform size distribution.

Mechanical and thermal properties, morphology and relaxation characteristics of poly(lactic acid) and soy flour/wood flour blends

AbstractPoly(lactic acid) (PLA) is a biodegradable polymer derived from sugar‐based materials, and its applications are varied. PLA blends are commonly employed to overcome certain disadvantages such as poor impact strength, low heat distortion temperature, poor processability and relatively high cost. In this study, blending PLA with soy flour (SF), wood flour (WF) and sodium bisulfite‐modified SF was used to improve the adhesion to PLA. In all cases, 0.5 wt% methylenediphenyl diisocyanate (MDI) was used as a coupling agent. Mechanical and thermal properties, morphology and relaxation characteristics of the blends were investigated. The results showed that MDI was an effective coupling agent for the WF/PLA system in improving tensile strength and elongation. Differential scanning calorimetry results indicated that SF and modified SF act as nucleation agents and facilitate the crystallization behavior of PLA by increasing the percentage crystallinity. From mechanical relaxation of the temperature‐variant system, we determined how the mechanical relaxation time evolves during the course of heating and obtained the Kohlrausch–Williams–Watts parameter and activation energy (ΔE). PLA and its blends exhibited highly homogeneous relaxational dynamics in their transition from glass to liquid, and ΔE of PLA and its blends is mainly affected by their densities and compositions. Copyright © 2010 Society of Chemical Industry

Effect of amphiphilic molecules on characteristics and tensile properties of thermoplastic starch and its blends with poly(lactic acid)

Three different types of amphiphilic molecules — Tween 60, linoleic acid, and zein were used as additives for the production of thermoplastic starch (TPS). The addition of those amphiphiles resulted in: (i) improved plasticization and processability, (ii) enhanced extensibility, (iii) increased crystallinity, and (iv) decreased stiffness, strength and rigidity of the TPS materials. Zein facilitated more effective plasticization, melting and processability of TPS material than did linoleic acid and Tween 60, respectively. However, Tween 60 allowed greater reduction of T g and produced softer TPS material than did linoleic acid and zein, respectively. Binary blends of those TPS materials and poly(lactic acid) (PLA) were also fabricated by varying PLA content, i.e. 30, 50 and 70% (w/w). The melt flow index, tensile strength and elastic modulus of the TPF-PLA blends increased significantly with increasing PLA content. In addition, amphiphiles facilitated processability, flowability and extensibility of the blends. Linoleic acid was a more effective additive to enhance flowability of the TPS–PLA blends than were Tween 60 and zein, respectively.

Structural, Electrical, Mechanical, and Thermal Properties of Electrospun Poly(lactic acid)/Polyaniline Blend Fibers

AbstractConducting electrospun fiber mats based on PLA and PAni blends were obtained with average diameter values between 87 and 1 006 nm with PAni quantities from 0 to 5.6 wt.‐%. Structural characteristics of fiber mats were compared to cast films with the same amount of PAni and studied by SEM, SAXS, and AFM. Thermal properties of fiber mats and cast films were compared by DSC analyses. Mechanical properties of fiber mats were also evaluated. It was found that electrospinning process governs the crystal structure of the fibers and strongly affects fiber properties. New properties of PLA/PAni blends are reported due to the size fiber reduction.magnified image

Plasticizer effect of novel PBS ionomer in PLA/PBS ionomer blends

Poly(lactic acid)(PLA) was blended with poly(butylene succinate)(PBS) and PBS ionomer (PBSi) at various compositions, and their compatibility and crystallization behavior were examined by dynamic mechanical analysis (DMA), tensile testing, scanning electron microscopy, differential scanning calorimetry, and polarized optical microscopy. The DMA data showed lower storage moduli with increasing PBS and PBSi content, and the tan δ peaks of the blends showed lower values than those of PLA. The tensile test results and fractured surface morphology indicated that PLA/PBSi blends have more flexible and compatible characteristics than the PLA/PBS blends. The interaction parameters calculated from the Flory-Huggins equation predicted that the PLA/PBSi blends have more compatible characteristics than the PLA/PBS blends. The Avrami exponent (n) and crystallization kinetics constant (K) were derived from isothermal crystallization experiments to predict the crystallization phenomenon of the blends. The use of PBS or PBS ionomer resulted in faster crystallization rates of the blends. From an observation of the overall crystallization rate and spherulite radial growth rate, it was concluded that the abundant ion groups increased the compatibility between the PLA and PBSi chains, and the PBSi molecules acted as a plasticizer in the PLA blends.

Poly(lactic acid) Toughening with a Better Balance of Properties

AbstractPoly(lactic acid) (PLA) toughening is often associated with significant modulus and/or strength losses making it unsuitable for many consumer and biomedical applications. The major objective of this research was to toughen PLA without significant loss in modulus and strength and to introduce reactive acid groups using reactive blending of PLA with a combination of polymers. PLA was reactive blended with poly(acrylic acid) (PAA) followed by physical blending with poly(ethylene glycol) (PEG) in solution. The modified PLA was extruded into films using a co‐rotating twin‐screw extruder and characterized using tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical analyses (DMA). This technology resulted in films with a ten‐fold increase in toughness compared to neat PLA with little or no decrease in strength and modulus.magnified image

Biomass Carbon Ratio of Biomass Chemicals Measured by Accelerator Mass Spectrometry

Abstract The biomass carbon ratios of various chemical products were studied. The biomass carbon ratios of chemicals such as polymers, their monomers, starches, cellulose, calcium carbonate, charcoal, ethanol, and polymer blends were estimated by the ratios of 14C to 12C measured by accelerator mass spectrometry (AMS) based on ASTM D 6866. Preparations of the gaseous and liquid samples for the AMS measurements are described, and the pretreatment for carbonate is also explained. Repeatability and accuracy of the biomass carbon ratio evaluation by AMS are discussed. It was found that a new correction factor is necessary for cellulose other than 0.93, which is regulated as the correction factor for present modern carbon newer than 1950 in ASTM D 6866. The developed sample preparations of gaseous materials and carbonate were confirmed to be applicable for the AMS measurement of the biomass carbon ratio. The repeatability and accuracy of the biomass carbon ratio evaluation by AMS were confirmed for ethanol derived from biomass (bioethanol), a polymer blend of biomass-based poly(lactic acid) (PLA), and petroleum-based poly(butylene succinate) (PBS). Standard deviations of the bioethanol and the blend of PLA and PBS are 0.36 and 0.84%, respectively. The biomass carbon ratio evaluation by AMS has been proposed for the International Standard (ISO).

The effect of free radical reactions on structure and properties of poly(lactic acid) (PLA) based blends

The blending of PLA with poly(butylene-adipate-co-terephthalate) (PBAT) is a promising strategy to achieve a toughened multiphase material. The blends ductility could be further improved through reactive compatibilization, i.e. inducing the formation of comb PLA-PBAT copolymers during the melt blending. In the present work a non-selective strategy was adopted which consisted in the use of a peroxide, 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane. The phase morphology development and the final properties (torque, fluidity in the melt, tensile behaviour, thermal and dynamical–mechanical features) of the blends were studied as a function of the peroxide concentration. The elongation at break was improved up to a maximum value thanks to this approach and a corresponding minimum was observed in the value of the dispersed phase diameter. A structural characterization of the macromolecules formed during the reactive process was attempted by using size exclusion chromatography of the blends and comparison with the pure polymers obtained by processing in the presence of the peroxide.

Poly(Lactic Acid) (PLA)-reinforced Kenaf Bast Fiber Composites: The Effect of Triacetin

In this article, the mechanical, morphological, and dynamic-mechanical properties of the blends of PLA and kenaf bast short fiber were investigated. The composites, with different fiber loading and triacetin content, were prepared by melt blending techniques using a Brabender internal mixer at 60 rpm and 170°C for 10 min and their properties were examined. Pure PLA was used as a reference for the biocomposite samples. Triacetin was used as a plasticizer for PLA and PLA/kenaf composites in order to study the improvement in tensile properties. The tensile strength and stiffness of unplasticized biocomposite materials decreased with the addition of kenaf bast fibers but improved with the addition of triacetin. The optimum fiber loading was 30 wt% kenaf fibers in the PLA matrix with the addition of 5% triacetin. The dynamic mechanical analyses showed that triacetin improved the thermal stability of the biocomposites. The triacetin increased the storage modulus and gave a lower softening temperature for plasticized biocomposites. The micrographs of the tensile specimens and their fractured surfaces, which were examined by scanning electron microscopy, demonstrated that better adhesion between the fibers and the matrix was achieved with the addition of the plasticizer.

Phase Structure of Compatibilized Poly(Lactic Acid)/Linear Low-Density Polyethylene Blends

Blends of PLA and linear low-density polyethylene (LLDPE) were compatibilized with glycidyl methacrylate (GMA)–grafted poly(ethylene-octene) copolymer (mPOE). Effects of compatilizer on phase structure of compatibilized PLA/LLDPE were studied by spreading coefficient calculation prediction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD) analysis. The spreading coefficient calculations, based on experimental and calculated surface tension data, show that mPOE spreads on LLDPE extensively to encapsulate LLDPE completely, which is in good agreement with the results of DSC, SEM, and WAXD analysis. The chemical reaction between the end carboxyl groups or end hydroxyl groups of PLA and epoxy groups of mPOE, which is suggested as the driving force leading to an ideal interfacial adhesion between PLA and the dispersed phase, was confirmed by Fourier transform infrared ray (FT-IR) spectroscopy analysis.

Crystallization behavior of fully biodegradable poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) blends

AbstractBoth poly(lactic acid) (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) are fully biodegradable polyesters. The disadvantages of poor mechanical properties of PLA limit its wide application. Fully biodegradable polymer blends were prepared by blending PLA with PBAT. Crystallization behavior of neat and blended PLA was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X‐ray diffraction (WAXD). Experiment results indicated that in comparison with neat PLA, the degree of crystallinity of PLA in various blends all markedly was increased, and the crystallization mechanism almost did not change. The equilibrium melting point of PLA initially decreased with the increase of PBAT content and then increased when PBAT content in the blends was 60 wt % compared to neat PLA. In the case of the isothermal crystallization of neat PLA and its blends at the temperature range of 123–142°C, neat PLA and its blends exhibited bell shape curves for the growth rates, and the maximum crystallization rate of neat PLA and its blends all depended on crystallization temperature and their component. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Study on Polylactide/Poly(ether block amide) Composite Biomaterials and Shape-Memory Effect

Melt blending of PLA and biodegradable PE-b-A has been performed in an effort to toughen the PLA. With the PE-b-A contents increasing, the elongation at break of composites increased and the brittle break became ductile break. When the PE-b-A content is 10%, the tensile strength of composite is similar with neat PLA, and the elongation increased significantly. The composites showed wonderful shape-memory effect. The composites occurred to deformation upon tensile load, and recovered to original shape quickly with temperature increasing. PE-b-A acts as stress concentrator in system with the stress release locally and energy-dissipation process. These will prevent PLA matrix from breaking under high deformation and make the PLA molecular orientation. Consequently, releasing the stress by heating up the material will reform the shape back to the original shape.

Hybrid composites based on fibres of marine origin

A series of polymeric formulations has been prepared based on oxobiodegradable (PVA) and hydrobiodegradable (starch, PLA, Bionolle) macromolecular materials used as continuous matrices and fillers derived from a marine sea-weed (Zostera). The formulations have been submitted to processing trials under different experimental conditions selected in order to prevent the thermal decomposition of the fillers utilised in the form of powder. Composite specimen produced by either casting from water suspension and compression moulding, were submitted to mechanical characterisation with the aim of selecting formulations enabling promising practical exploitation. Composites based on blends of PLA and Bionolle, used as plasticiser turned out to be processable in tomato clip, as a typical example of agriculture environmentally compatible items, susceptible to be disposed their service life to controlled composting infrastructures together with the agricultural waste.

Super-tough poly(lactic acid) materials: Reactive blending with ethylene copolymer

Poly(lactic acid) (PLA) is well known as a biocompatible, bioresorbable, and biodegradable polymer superior to petrochemical polymers from the standpoint of total energy consumption and life-cycle CO2 emission, since it can be obtained from natural sources. However, the brittleness of PLA is a big drawback for its wide application. Although many studies have been carried out modifying PLA, there is very limited work on reactive blending of PLA. This study demonstrates a dramatic improvement in the mechanical characteristics of PLA by its reactive blending with poly(ethylene-glycidyl methacrylate) (EGMA). It is shown that the interfacial reaction between the component polymers contributes to the formation of super-tough PLA materials, superior to benchmark acrylonitrile–butadiene–styrene (ABS) resins. The novel material highlights the importance of interface control in the preparation of multi-component materials.

Characterization and gas transport properties of poly(lactic acid) blend membranes

The characterization and gas transport properties (i.e., permeability, diffusivity, and solubility) of poly(lactic acid) (PLA) blend membranes were systematically investigated. PLA blends had a glass transition temperature of 60°C, a crystallization temperature of 116°C, and a melting temperature of 149°C. The membrane density increased with increasing crystallinity. In contrast, the fractional free volume determined using a group contribution method of van Krevelen decreased with increasing crystallinity. The ranking of the gas permeability at 35°C in all PLA blend membranes used in this study was hydrogen > carbon dioxide > oxygen > nitrogen. In general, as the crystallinity in a polymer membrane increases, gas permeability decreases. Interestingly, the permeability coefficient of some gases in the PLA blend membrane with higher crystallinity was larger than that with lower crystallinity. This result suggests that the size and distribution of free volume in the crystalline PLA blend membrane are different from those in other crystalline polymer membrane.