PLA Blends Research Articles

Modification of epoxidized natural rubber as a PLA toughening agent

ABSTRACTIn the present study, the modification of epoxidized natural rubber (ENR) was investigated to improve toughness of PLA. ENR‐PLA copolymers were synthesized by 2 steps reactions. Acid hydrolysis of ENR to prepare macroinitiator (ENR‐OH) and copolymerization with lactide to obtain ENR‐PLA copolymers. The reaction time of acid hydrolysis and the lactide monomer loading was investigated. The optimum conditions were 8 h acid hydrolysis with 5wt% lactide loading to obtain ENR8‐PLA5 copolymers. A series of samples of PLA blended with ENR‐PLA copolymers was prepared using melt‐blending. The blend of PLA with ENR8‐PLA5 copolymers at 1 phr substantially improved the tensile properties. The elongation at break was increased 67%, and toughness was increased 64% compared to neat PLA. These results indicate that ENR8‐PLA5 has potential as toughening agent for PLA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48267.

Fully biobased polylactide/epoxidized soybean oil resin blends with balanced stiffness and toughness by dynamic vulcanization

Abstract In this study, we report fully biobased PLA blends with balanced stiffness and toughness through dynamic vulcanization with sebacic acid cured epoxidized soybean oil (VESO) precursors with various contents. The effect of VESO content, from 5% to 20%, on the morphology, thermal transitions, mechanical properties and toughening mechanisms were investigated in detail. The results indicated that PLA/VESO blends were partially miscible and showed phase-separated morphology with VESO dispersed in PLA matrix uniformly regardless of the VESO content. The particle size of dispersed VESO increased with its content. PLA/VESO blends with 10 wt% showed the optimal balanced mechanical strength and toughness with tensile toughness and impact strength improved by ~4200% and ~560% and the tensile strength and Young's modulus reduced by only 26.7% and 22.2%, respectively, compared to neat PLA.

Thermo-Mechanical Properties of Injection Molded Components Manufactured by Engineered Biodegradable Blends

Engineering of ductile, tough and thermal resistant PLA-based materials requires blending of PLA with other constituents by reactive twin-screw co-rotating extrusion to achieve compounds with adequate thermo-mechanical properties. Then, the compound of the polymeric blends must be melt processed to the final shape with an additional technology, namely the injection molding. The two-stage process the polymeric blends must undergo and the different rheological properties the blends must feature to be suitable to the different processing steps make extremely difficult to engineer the material. Extrusion compounding requires high viscous materials low melt flow index (MFI), while injection molding requires materials with low viscosity (high MFI). To overcome these shortcomings, this manuscript deals with the design of novel biodegradable PLA-based blends that rely on mixing PLA grades with different MFI (i.e. very low for extrusion and high for injection molding), each chosen to feature the rheological characteristics needed for each step of the two-stage transformation process. The ratio of the two PLA-grades inside the blends was the matter of the present investigation. The blends were subsequently tested for the manufacturing of single-use biodegradable and thermal resistant injection molded small cups, specifically designed for brewing of hot beverages. Lastly, the thermo-mechanical performance of the as-is and annealed cups were studied. Experimental evidences show blending of two-different grades of PLA is a promising route to formulate low impact polymeric materials suitable for demanding packaging solutions.

Effect of poly(2‐ethyl‐2‐oxazoline) and UV irradiation on the melt rheology and mechanical properties of poly(lactic acid)

ABSTRACTTo improve the suitability of poly(lactic acid) (PLA) for implantable devices, it ideally needs greater ductility without losses in strength. Here biodegradable poly(2‐ethyl‐2‐oxazoline) (PEtOx) was selected as an additive to improve hydrophilicity of PLA as well as mechanical properties, while UV irradiation was considered as a bulk modification method to increase the long‐term stability. The PLA blend showed improved tensile strength and elongation‐at‐break with small amounts of PEtOx added (1.5 wt %). Crosslinking by UV irradiation showed significant improvements with a dibutyltin dilaurate catalyst even though it produced a high degree of chain scission during melt processing. After UV irradiation for 150 h, the crosslinked material recovered mechanical properties and melt rheological properties comparable to the initial PLA‐1.5%PEtOx blend (without catalyst added). Crosslinking was only possible with the added PEtOx present. A mechanism for the crosslinking reactions examined has been proposed since it has not been previously reported in the literature. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48023.

Influence of Epoxidized Canola Oil (eCO) and Cellulose Nanocrystals (CNCs) on the Mechanical and Thermal Properties of Polyhydroxybutyrate (PHB)-Poly(lactic acid) (PLA) Blends.

Two major obstacles to utilizing polyhydroxybutyrate (PHB)—a biodegradable and biocompatible polymer—in commercial applications are its low tensile yield strength (<10 MPa) and elongation at break (~5%). In this work, we investigated the modification of the mechanical properties of PHB through the use of a variety of bio-derived additives. Poly(lactic acid) (PLA) and sugarcane-sourced cellulose nanocrystals (CNCs) were proposed as mechanical reinforcing elements, and epoxidized canola oil (eCO) was utilized as a green plasticizer. Zinc acetate was added to PHB and PLA blends in order to improve blending. Composites were mixed in a micro-extruder, and the resulting filaments were molded into 2-mm sheets utilizing a hot-press prior to characterization. The inclusion of the various additives was found to influence the crystallization process of PHB without affecting thermal stability. In general, the addition of PLA and, to a lesser degree, CNCs, resulted in an increase in the Young’s modulus of the material, while the addition of eCO improved the strain at break. Overall, samples containing eCO and PLA (at concentrations of 10 wt %, and 25 wt %, respectively) demonstrated the best mechanical properties in terms of Young’s modulus, tensile strength and strain at break.

Characterization of the compatibility of PVC/PLA blends by Aid of Rheological Responses

Among many characterization methods for the compatibility of blends, the rheological ones have attracted more and more attention due to its sensitive response to the changes of structure of blends. In this work, PVC and PLA blends were prepared by melt mixing in torque rheometer. Static and dynamic rheological responses were used to analyze the compatibility of PLA/PVC blends, and a variety of analytical methods were also used, such as SEM and DSC, to assist revealing the phase morphology of the blends. The results showed that PVC/PLA = 50/50 formed a co-continuous phase structure, the other ratio blends formed a “sea-island" structure. The blend with co-continuous structure exhibited the lowest viscosity, the highest non-Newtonian index and the lowest entrance pressure drop, and the phase separation was more difficult than those with “sea-island" structures. It was concluded that the blend with co-continuous phase structure showed the strongest rheological responses. PVC/PLA = 50/50 also showed the highest impact strength among the blends.

Super-Toughened Poly(lactic Acid) with Poly(ε-caprolactone) and Ethylene-Methyl Acrylate-Glycidyl Methacrylate by Reactive Melt Blending.

In recent years, poly(lactic acid) (PLA) has attracted more and more attention as one of the most promising biobased and biodegradable polymers. However, the inherent brittleness significantly limits its wide application. Here, ternary blends of PLA, poly(ε-caprolactone) (PCL) with various amounts of ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) terpolymer were fabricated through reactive melt blending in order to improve the toughness of PLA. The effect of different addition amounts of EMA-GMA on the mechanical properties, interfacial compatibility and phase morphology of PLA/PCL blends were studied. The reactions between the epoxy groups of EMA-GMA and carboxyl and hydroxyl end groups of PLA and PCL were investigated thorough a Fourier transform infrared (FT-IR). The miscibility and thermal behavior of the blends were studied through a dynamic mechanical analysis (DMA), differential scanning calorimetric (DSC) and X-ray diffraction (XRD). The phase morphology and impact fracture surface of the blends were also investigated through a scanning electron microscope (SEM). With the addition of 8 phr EMA-GMA, a PLA/PCL (90 wt %:10 wt %)/EMA-GMA ternary blend presenting a suitable multiple stacked phase structure with an optimum interfacial adhesion exhibited an elongation at break of 500.94% and a notched impact strength of 64.31 kJ/m2 with a partial break impact behavior. Finally, the toughening mechanism of the supertough PLA based polymers have been established based on the above analysis.

Preparation of PLA blends by polycondensation of D,L-lactic acid using supported 12-tungstophosphoric acid as a heterogeneous catalyst

Poly(lactic acid) (PLA) is a significant polymer that is based on renewable biomass resources. The production of PLA by polycondensation using heterogeneous catalysis is a focus for sustainable and economical processes. A series of samples comprising 12-tungstophosphoric acid (H3PW) supported on activated carbon, silica, and alumina induced the catalytic polymerization of D,L-lactic acid to form blends of PLA. The catalysts were characterized by multiple techniques to confirm the integrity of the Keggin anion as well as the acidity, which is the key property for relating structure to activity. The best reaction conditions were established for H3PW/C and tested for the other supported catalysts. The obtained polymer was a blend that was characterized as an enantiomeric excess (ee) of as much as 95% L-PLA (PLLA) with a mass average molar mass (Mw) of approximately 14,900 daltons. The role of H3PW in these polymerizations was demonstrated, i.e., without the Keggin acid, only oligomeric units (Mw < 10,000 daltons) could be obtained. Additionally, inverse relationships between the Mw of PLA and the enthalpy (–ΔH) of the strongest sites of the catalysts were distinguished, i.e., PLAMw-H3PW/C > PLAMw-H3PW/Al2O3 > PLAMw-H3PW/SiO2, whereas the acidity (–ΔH) order was as follows: H3PW/SiO2 > H3PW/Al2O3 > H3PW/C. These findings could be attributed to the correct tuning of strength and the accessibility of the sites to produce longer polymeric chains.

Graphene modifies the biodegradation of poly(lactic acid)-thermoplastic cassava starch reactive blend films

Biobased blend films produced from poly(lactic acid) (PLA), thermoplastic cassava starch (TPCS), and reinforced with graphene nanoplatelets (GRH) were evaluated in compost and inoculated vermiculite under composting conditions for 120 days. A reduction of the molecular number of the PLA fraction in the blends indicated early hydrolytic degradation. A priming effect was observed in compost for the physical blend of PLA with TPCS. A high biodegradation rate was observed for the TPCS fraction in each tested sample. In inoculated vermiculite, the addition of GRH resulted in a decreased hydrolytic degradation rate for PLA-GRH, attributed to the natural barrier offered by GRH to diffusion of water into the PLA matrix. In compost, incorporation of GRH at 0.1% wt. also resulted in a decreased abiotic degradation rate for PLA. Films containing GRH were associated with a longer lag-phase.

Effect of reactive group types on the properties of poly(ethylene octane) toughened poly(lactic acid)

In this work, maleic anhydride (MA) and glycidyl methacrylate (GMA) grafted poly(ethylene octane) (MPOE and GPOE) were used to toughen poly(lactic acid) (PLA). Results exhibited that the MA and GMA strongly influenced the morphology and mechanical properties of PLA. The stronger interfacial reactions between the carboxyl and/or hydroxyl of PLA and epoxy groups of GPOE induced smaller dispersed phase sizes and higher impact strength than that of PLA/MPOE blends. SEM results showed that the shear yielding properties of the PLA matrix and cavitation of rubber particles were major toughening mechanisms. Rheological investigation indicated that the PLA/GPOE blends had higher storage modulus and complex viscosity at low angular frequencies range due to the high interfacial adhesion between PLA and GPOE. The results of DMA showed that all the PLA blends had lower storage modulus due to the low stiffness of the elastomers. Compared MPOE, the addition of GPOE significantly decreased the cold crystallization and melting temperature which indicated that GPOE could enhance the crystalline ability of PLA.

Morphology and Mechanical Properties of Poly(Lactic Acid) with Propylene-Ethylene Copolymer and α-Cellulose

This work studied the improvement of poly (lactic acid) (PLA) properties by adding propylene-ethylene copolymer (PEC) and α-cellulose (AC). The PLA blends and composites were melt mixed by an internal mixer and molded by compression method. The morphological analysis observed the phase separation of PLA/PEC blends due to minor PEC phase dispersed as spherical shape in PLA phase, indicating a poor interfacial adhesion between PLA and PEC phases. The incorporation of AC did not improve the compatibility of polymer blends. Young’s modulus and tensile strength of PLA blends reduced with increasing amount of PEC because the elastics of ethylene molecules in PEC structure. Young’s modulus of PLA/PEC/AC composites increased with increasing AC contents. The stress at break of the PLA/PEC blends was improved with the presence of AC. The strain at break of PLA/PEC blends increased with increasing PEC contents, and the presence of AC showed the decrease of strain at break of PLA/PEC blends.

Uniaxial stretching and properties of fully biodegradable poly(lactic acid)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) blends.

In this work, fully biodegradable poly (lactic acid) (PLA)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) blends of various compositions were uniaxially stretched at different stretch ratios above the glass transition temperature (Tg) of PLA. These stretched blends exhibited a closed microvoid structure, as evaluated by scanning electron microscopy. Differential scanning calorimetry and wide-angle X-ray diffraction analyses verified that stretching-induced crystallization in the α-form could be achieved in the PLA matrix. This hierarchical structure could improve the multifunctional performance of PLA blends. The density of drawn blends with a P(3HB-co-4HB) content of 30 wt% and stretch ratio of 6 was reduced by 20% as compared to neat PLA. The excellent combination of strength, modulus, and ductility of drawn blends with a P(3HB-co-4HB) content of 10 wt% and stretch ratio of 6 was demonstrated; compared to neat PLA, these parameters increased by 300%, 320%, and 317%, respectively in breaking strength, modulus, and elongation at break (172.2 MPa, 4200 MPa, and 18.4%), respectively. Meanwhile, control over the degradation rate and thermomechanical-property improvement was achieved by adjusting the stretch ratio and/or blend composition. In practical terms, this processing technique provides a new way to manufacture lightweight and high-performance microvoid-containing biopolymers.

Synthesis of Nanocomposite Materials for Biodegradable Food Packaging

This paper concerns on synthesis of nancomposite materials, based on poly(D,Llactic acid)/poly(L-lactic acid). The Poly(L,D-lactic acid) (PDLLA) was produced from L,Dlactic acid through direct polycondensation method and poly(L-lactic acid) (PLLA) derived from L-lactide through ring-opening polymerization method. The PDLLA/PLLA films were produced through solvent casting method. The ratio of PDLLA in the PDLLA/PLLA matrix was determined by adjusting PDLLA fraction. The nanoclay used in this experiment were natural clay (Bentonite) and modified organoclay with quaternary ammonium salt (Cloisite 30B). The PLA blend nanocomposites was produced through solution intercalation with sonication. To determine the effect of amounts of nanoclay and sonication period, these two variable were varied. To analyze chemical structure of PLA, the PLA blend film were tested using Fourier Transform Infrared (FTIR). The dispersion of nanoclay on the PLA blend matrix was analyzed using X-Ray Diffraction (XRD) test. The properties of PLA blend nanocomposites film were then characterized using Universal Testing Machine (UTM), Water Vapor Permeability (WVP) test and the enzymatic biodegradability test. The fraction of PDLLA on the PLA blend was fixed 70 % wt. XRD test showed exfoliation of Cloisite 30B in the PLA matrix while the Bentonite was exfoliated as well as intercalated. The addition of nanoclay improved the tensile strength of PLA blend nanocomposites polymer to the number of 56.26 MPa and 37.65 MPa, respectively. Sonication period of PDLLA/PLLA nanocomposite affected the mechanical properties, barrier properties and polymer biodegradability. Moreover, from the WVP test, the barrier properties of the blend polymers was improved and increased twice compared to that of the pure PDLLA/PLLA.

Preparation of Organo-Montmorillonite Modified Poly(lactic acid) and Properties of Its Blends with Wood Flour.

In this study, poly(lactic acid) (PLA)/wood flour (WF) composites were prepared by first blending PLA with organo-montmorillonite (OMMT) at different contents (0.5, 1, 1.5, and 2 wt %). The physical and mechanical properties of the virgin and OMMT modified PLA and its WF composites were tested. The results showed that: (1) at low OMMT content (<1 wt %), OMMT can uniformly disperse into the PLA matrix with highly exfoliated structures. When the content increased to 1.5 wt %, some aggregations occurred; (2) after a second extruding process, the aggregated OMMT redistributed into PLA and part of OMMT even penetrated into the WF cell wall. However, at the highest OMMT content (2 wt %), aggregates still existed; (3) the highly exfoliated OMMT was beneficial to the physical and mechanical properties of PLA and the WF composites. The optimal group of OMMT-modified PLA was found at an OMMT content of 0.5 wt %, while for the PLA/WF system, the best properties were achieved at an OMMT content of 1.5 wt %.

Biofunctionalized curcumin-loaded nanoid polymeric scaffold for skin care treatment

Abstract The continuously evolving need to improve methods of addressing skin repair problems has triggered the development of modern, fibrous scaffolds for simulating the extracellular matrix of cells and, consequently, the quicker and most effective regeneration without the risk of toxicity. At the same time, scaffolds loaded with drug, ideal for skin care, release the drug during fiber degradation. In the present study, a suitable blend of PLA and Chitosan polymeric biomaterials was selected to construct the scaffold and curcumin drug as medicinal substance. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) demonstrated the excellent fibrous morphology of the scaffold resulting from electrospinning process. A study of drug release from the fibers was carried out in parallel with a degradation study of the fibers over time, in order to obtain information on the release rate of the drug and the mass loss of the polymer. Cytotoxicity studies were performed to prove the cellular compatibility of the construct. MTT assay, Methylene Blue staining and observation by SEM during cell proliferation indicated the enhancement of cell proliferation from the scaffold. Finally, a protein immobilization procedure was carried out to prove the possibility of bio-functionalization of the fibers in the future with a protein factor that would give it further properties and possibilities of use. This nanoplatform offers great opportunities as a drug carrier and simultaneously as a simulation of an ideal nanoenvironment for cellular growth and communication and therefore for tissue regeneration.

Monte Carlo simulations of stereocomplex formation in multiblock copolymers.

Currently, controlling the formation of stereocomplex crystallites (SCs) in enantiomeric PLA blends is a research hotspot. In the present work, we performed dynamic Monte Carlo simulations to study the formation mechanism of SCs in multiblock copolymers. The effects of block number and crystallization temperature on SC formation were revealed. The relative size of block length and crystal thickness is an important factor. In the multiblock copolymers with block length longer than crystal thickness, both the increases of crystallization temperature and block number lead to the increase of SC content attributed to the relatively high degree of supercooling for SC formation and the improved local miscibility between different blocks, respectively. In the multiblock copolymers with block length equal to crystal thickness, each block can just form one crystalline stem, and then different blocks can be more easily alternately parallel-packed during SC formation. The system thus reaches the upper limit of the ability to form SCs. Therefore, both the further increases in crystallization temperature and block number can no longer cause the enhancement in SC formation.

Incorporation of Carbon Nanofillers Tunes Mechanical and Electrical Percolation in PHBV:PLA Blends.

Biobased fillers, such as bio-derived cellulose, lignin byproducts, and biochar, can be used to modify the thermal, mechanical, and electrical properties of polymer composites. Biochar (BioC), in particular, is of interest for enhancing thermal and electrical conductivities in composites, and can potentially serve as a bio-derived graphitic carbon alternative for certain composite applications. In this work, we investigate a blended biopolymer system: poly(lactic acid) (PLA)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and addition of carbon black (CB), a commonly used functional filler as a comparison for Kraft lignin-derived BioC. We present calculations and experimental results for phase-separation and nanofiller phase affinity in this system, indicating that the CB localizes in the PHBV phase of the immiscible PHBV:PLA blends. The addition of BioC led to a deleterious reaction with the biopolymers, as indicated by blend morphology, differential scanning calorimetry showing significant melting peak reduction for the PLA phase, and a reduction in melt viscosity. For the CB nanofilled composites, electrical conductivity and dynamic mechanical analysis supported the ability to use phase separation in these blends to tune the percolation of mechanical and electrical properties, with a minimum percolation threshold found for the 80:20 blends of 1.6 wt.% CB. At 2% BioC (approximately the percolation threshold for CB), the 80:20 BioC nanocomposites had a resistance of 3.43 × 10 as compared to 2.99 × 10 for the CB, indicating that BioC could potentially perform comparably to CB as a conductive nanofiller if the processing challenges can be overcome for higher BioC loadings.

Methoxy‐Substituted Difluoroboron Benzoylacetonate Complexes with Color‐Tunable Phosphorescence

AbstractDifluoroboron β‐diketonates (BF2bdks) exhibit fluorescence (F) and room‐temperature phosphorescence (RTP) in a poly(lactic acid) (PLA) matrix. Fluorescence color tuning has been achieved by dye loading or bdk ligand modification, namely substituent effects or extended conjugation. In this study, color‐tunable RTP (450–570 nm) is achieved with 1‐benzoylacetonate derivatives by varying the number and position of methoxy groups on the benzene ring. The methoxy groups can be used to alter the energy levels of the dye or induce geometry changes (e. g. twisting) to disrupt π‐conjugation. The dyes were evaluated theoretically with density functional theory (DFT) and spectroscopy (absorbance and fluorescence) in CH2Cl2 solution and dilute PLA blends. These findings inform future boron‐based lighting devices and oxygen‐sensing bioprobe designs.

Fire safety enhancement of a highly efficient flame retardant poly(phenylphosphoryl phenylenediamine) in biodegradable poly(lactic acid).

Flame-retarded poly(lactic acid) (PLA) biodegradable materials are viewed as promising as sustainable alternatives to petroleum-based commodity polymers. A new highly efficient flame retardant, poly(phenylphosphoryl phenylenediamine) (PPDA), was synthesized by the condensation of phenylphosphoryl dichloride with p-phenylenediamine and its structure was confirmed by 1H nulear magnetic resonance and Fourier-transform infrared spectroscopy. When 3 wt% PPDA was incorporated into PLA, the limited oxygen index increased from 20.0% of neat PLA to 25.5% and its UL-94 vertical burning testing achieved V-0 rating. Moreover, the total heat release and peak heat release rate values of PLA/3 wt% PPDA material were decreased from 109.1 MJ/m2 and 643.7 kW/m2 of PLA to 98.3 MJ/m2 and 570.0 kW/m2, respectively, and the fire performance index increased from 0.081 of PLA to 0.132 m2 s/kW. The high fire safety of PPDA in PLA is mainly attributed to the combined effects of the phosphorous-containing radical inhibition and inert gases and the barrier action of the formed char layer. The addition of less than 3 wt% PPDA has little influence on the tensile and impact properties of PLA. The flame retardant PLA blends have great application potential in electrical casing, automobile interiors and three-dimensional printing materials.

The effect of dynamic vulcanization on the morphological and mechanical properties of the toughened poly (lactic acid)/epoxidized natural rubber

Poly (lactic acid)/epoxidized natural rubber (PLA/ENR) was prepared by using counter-rotating twin-screw extruder. For dynamic vulcanization process, ENR was compounded with 3 phr of N, N’-m-phenylenebismaleimide (HVA-2) as a crosslinking agent. The aim of this study is to determine the effect of unvulcanized and dynamically vulcanized of ENR on the properties of PLA/ENR blend. The blending of PLA with ENR was prepared with the various composition of ENR (0 wt% to 30 wt%). The morphology and mechanical properties of the blends were investigated by using scanning electron microscope (SEM), tensile test, and impact test. The unvulcanized blend produced a co-continuous morphology of PLA and ENR and the dynamically vulcanized blend shows the dispersed ENR rubber particles in PLA continuous matrix. For both systems, the tensile strength value was dropped with the increasing amount of ENR content. The impact strength of both systems shows the maximum value at 20 wt% of ENR content. However, dynamically vulcanized PLA/ENR blend shows a better tensile strength and impact strength value as compared with unvulcanized blend.