Effect of Poly(Vinyl Acetate) on Mechanical Properties and Characteristics of Poly(Lactic Acid)/Natural Rubber Blends

Natural rubber grafted with poly(vinyl acetate) copolymer (NR-g-PVAc) was synthesized by emulsion polymerization. Three graft copolymers were prepared with different PVAc contents: 1 % (G1), 5 % (G5) and 12 % (G12). Poly(lactic acid) (PLA) was melt blended with natural rubber (NR) and/or NR-g-PVAc in a twin screw extruder. The blends contained 10–20 wt% rubber. The notched Izod impact strength and tensile properties were determined from the compression molded specimens. The effect of NR mastication on the mechanical properties of the PLA/NR/NR-g-PVAc blend was evaluated. Characterization by DMTA and DSC showed an enhancement in miscibility of the PLA/NR-g-PVAc blend. The temperature of the maximum tan δ of the PLA decreased with increasing PVAc content in the graft copolymer, i.e., from 71 °C (pure PLA) to 63 °C (the blend containing 10 % G12). The increase in miscibility brought about a reduction in the rubber particle diameter. These changes were attributed to the enhancement of toughness and ductility of PLA after blending with NR-g-PVAc. Therefore, NR-g-PVAc could be used as a toughening agent of PLA and as a compatibilizer of the PLA/NR blend. NR mastication was an efficient method for increasing the toughness and ductility of the blends which depended on the blend composition and the number of mastications.     

Effect of Oxidized Starch on Morphology,Rheological and Tensile Properties of Low-Density Polyethylene/Linear Low-Density Polyethylene/Thermoplastic Oxidized Starch Blends

In this work, morphology, rheological and tensile properties of low-density polyethylene/linear low-density polyethylene/thermoplastic oxidized starch (LDPE/LLDPE/TPOS) blends are studied. The blends of LDPE/LLDPE (70/30, w/w) containing 0–20 wt% TPOS in the presence of 3 wt% of PE-grafted maleic anhydride (PE-g-MA) as a compatibilizer are prepared by a twin screw extruder and then converted to appropriate thin films using an extrusion film blowing machine. Scanning electron microscopic images show that there is a relative good dispersion of oxidized starch particles in PE matrices. However, as TPOS content in the blends increases, the starch particle size increases too. The rheological analyses indicate that TPOS can decrease the elasticity and viscosity of the blends. The LDPE/LLDPE/TPOS blends show power-law behavior and as the TPOS content increases the power-law exponent (n) and consistency index (K) decrease. The ultimate tensile strength and elongation at break of the final blend films reduce, when TPOS content increases from 5 to 20 wt%. However, the required mechanical properties for packaging applications are achieved when 10 wt% oxidized starch is added, according to ASTM D4635.     

Grafting of Glycidyl Methacrylate onto Poly(lactide) and Properties of PLA/Starch Blends Compatibilized by the Grafted Copolymer

Poly(lactide)-graft-glycidyl methacrylate (PLA-g-GMA) copolymer was prepared by grafting GMA onto PLA in a batch mixer using benzoyl peroxide as an initiator. The graft content was determined with the ¹H-NMR spectroscopy by calculating the relative area of the characteristic peaks of PLA and GMA. The result shows that the graft content increases from 1.8 to 11.0 wt% as the GMA concentration in the feed varies from 5 to 20 wt%. The PLA/starch blends were prepared by the PLA-g-GMA copolymer as a compatibilizer, and the structure and properties of PLA/starch blends with or without the PLA-g-GMA copolymer were characterized by SEM, DSC, tensile test and medium resistance test. The result shows that the PLA/starch blends without the PLA-g-GMA copolymer show a poor interfacial adhesion and the starch granules are clearly observed, nevertheless the starch granules are better dispersed and covered by PLA when the PLA-g-GMA copolymer as a compatibilizer. The mechanical properties of the PLA/starch blends with the PLA-g-GMA copolymer are obviously improved, such as tensile strength at break increasing from 18.6 ± 3.8 MPa to 29.3 ± 5.8 MPa, tensile modulus from 510 ± 62 MPa to 901 ± 62 MPa and elongation at break from 1.8 ± 0.4 % to 3.4 ± 0.6 %, respectively, for without the PLA-g-GMA copolymer. In addition, the medium resistance of PLA/starch blends with the PLA-g-GMA copolymer was much better than PLA/starch blends.     

Study on the Effect of Dicumyl Peroxide on Structure and Properties of Poly(Lactic Acid)/Natural Rubber Blend

In attempt to enhance the compatibility of NR in PLA matrix, and furthermore to enhance mechanical properties of PLA, PLA/NR blends with strong interaction were prepared in Haake internal mixer, using dicumyl peroxide (DCP) as cross-linker. The effects of dicumyl peroxide on morphology, thermal properties, mechanical properties and rheological properties of PLA and PLA/NR blends were studied. The results indicated that dicumyl peroxide could increase the compatibility of poly(lactic acid) and natural rubber. With small amount of dicumyl peroxide, the effect on NR toughening PLA was enhanced and the tensile toughness of PLA/NR blends was improved. When the DCP content was up to 0.2 wt%, the PLA/NR blend reached the maximum elongation at break (26.21 %) which was 2.5 times of that of neat PLA (the elongation at break of neat PLA was 10.7 %). Meanwhile, with introducing 2 wt% DCP into PLA/NR blend, the maximum Charpy impact strength (7.36 kJ/m²) could be achieved which was 1.8 times of that of neat PLA (4.18 kJ/m²). Moreover, adding adequate amount of DCP could improve the processing properties of blends: the viscosity of PLA/NR blend decreased significantly and the lowest viscosity of the blends could be achieved when the DCP content was 0.5 wt%.     

Effect of Hexadecyl Lactate as Plasticizer on the Properties of Poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) Films for Food Packaging Applications

In this study, poly(l-lactide) (PLA) films were fabricated by melt processing and the plasticizing effect of hexadecyl lactate (HL) (0, 5, 7.5, 10, and 12.5 wt% on PLA were investigated by scanning electron microscopy (SEM), differential scanning calorimetry, thermogravimetric analysis, tensile, transparency, and water vapor permeability tests. The SEM analysis revealed that PLA with 10 wt% HL appeared uniform with extra small bumps, confirmed the interaction between PLA and HL. The thermal analysis revealed a glass transition temperature of 57.4 °C for neat PLA film, but the addition of HL elicited a decrease in the temperature of the peak (43.8 °C). The incorporation of plasticizer into PLA resulted in the increase of elongation at break, as well as the decrease of tensile strength and tensile modulus. Even though a decrease in transparency was recorded, the PLA/HL blend films appeared transparent by visually observation. The water vapor permeability of PLA/HL blend films increased with the increase of HL. The PLA/HL blend films could effectively extend the shelf-life of fresh-cut pears as the commercial low density polyethylene films. The results indicated that the properties of PLA films can be modified with the addition of HL and PLA/HL blend films could serve as an alternative as food packaging materials to reduce environmental problems associated with synthetic packaging films.     

Study of Thermo-Mechanical and Morphological Behaviour of Biodegradable PLA/PBAT/Layered Silicate Blend Nanocomposites

Poly (lactic acid) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT) blend nanocomposites were prepared using melt blending technique followed by compression moulding. The blend nanocomposites were prepared with a variation of PBAT loading along with maleic anhydride and benzoyl peroxide ranging from 5 to 20 wt% along with two different commercially available nanoclays cloisite 93A and cloisite 30B (C30B) at 3 wt% loading. The maleic anhydride and benzoyl peroxide were used during the melt blending of the blend nanocomposites as a compatibilizer and as an accelerator respectively. Maleic anhydride used to enhance the compatibility of the PLA/PBAT blend and as well as the uniform adhesion of the nanoclays with them. The properties and characterizations of PLA matrix and the PLA/PBAT blend nanocomposites have been studied. The tensile strength, % elongation and impact strength increased with the preparation of PLA/PBAT blend nanocomposites as compared with PLA matrix. PLA/PBAT/C30B blend nanocomposites exhibited optimum tensile strength at 15 wt% of PBAT loading. Differential scanning calorimetry and thermogravimetric analysis also showed improved thermal properties as compared with virgin PLA. The wide angle X-ray diffraction studies indicated an increase in d-spacing in PLA/PBAT/C30B blend nanocomposite thus revealing intercalated morphology.     

Tensile Properties of Polylactide/Poly(ethylene glycol) Blends

The blends of polylactide (PLA) and poly(ethylene glycol) (PEG) with different contents (0, 5, 10, 15, and 20 wt%) and molecular weights (\( \overline{M}_{w} \) 6000, 10,000 and 20,000, called respectively as PEG 6000, PEG 10,000, and PEG 20,000) were prepared by means of melt blending method. The effects of tensile speed, content and molecular weight of the PEG on the tensile properties of the PLA/PEG blends were investigated using a universal testing machine at 24 °C. With increasing tensile speed, the tensile modulus, strength and stress at break of the PLA/PEG blends marginally increased, while the tensile modulus and stress at break declined non-linearly, and the tensile strength dropped nearly linearly with increasing PEG 10,000 content. When the PEG 10,000 content was 5–15 wt%, the tensile strain at break of the PLA/PEG 10,000 blend markedly increased, and then decreased as the PEG 10,000 content exceeded 15 wt%. With increasing the molecular weight of PEG, tensile modulus and strength increased, whereas the tensile strain at break decreased. This showed that the application of right amount of lower molecular weight PEG was more conducive to improving the tensile toughness of the PLA/PEG blends, which was attributed to its better miscibility with PLA and increased mobility of PLA molecular chains.     

Novel Tough Crystalline Blends of Polylactide with Ethylene Glycol Derivative of POSS

Blending of polylactide (PLA) with low stereoregularity and polyhedral oligomeric silsesquioxane grafted with arms of poly(ethylene glycol) methyl ether, acting as a plasticizer, allowed us previously to obtain a novel stable elastomeric-like material. The present contribution focuses on the properties of semi-crystalline PLA plasticized with this compound. Melt blends of PLA with 5–15 wt% of the plasticizer, were compression molded, quenched and annealed, which enabled cold-crystallization. The glass transition temperature of the blends and their drawability depended on their crystallinity and plasticizer content. The best ductility was reached at the plasticizer content of 15 wt%; the achieved strain at break was 6.5 (650%) and 1.3 (130%), for the quenched and annealed material, respectively. The latter value exceeded 20 times the strain at break of neat crystalline PLA. The tensile toughness of the annealed 15 wt% blend was 12 times larger than that of crystalline PLA. Moreover, annealing of 15 wt% blend improved its yield strength by 40%. Despite the two peaks of the loss modulus, indicating the two glass transitions in this blend, no heterogeneities were found by scanning electron microscopy, indicating that the plasticizer enriched phase formed instead of distinct inclusions of the plasticizer.     

Effects of Compatibilizer and Thermoplastic Starch (TPS) Concentration on Morphological,Rheological, Tensile,Thermal and Moisture Sorption Properties of Plasticized Polylactic Acid/TPS Blends

The blends of polylactic acid plasticized with acetyl tributyl citrate (P-PLA) and thermoplastic wheat starch (TPS) were prepared by a co-rotating twin screw extruder and the effect of maleic anhydride grafted PLA (PLA-g-MA) content as reactive compatibilizer on blends compatibility through morphological, rheological and tensile properties of the blends was investigated. Considerable improvement in properties of P-PLA/TPS (70/30 w/w) blend with incorporating the optimum PLA-g-MA content of 4 phr was achieved as this blend exhibited better morphological and rheological properties with an increase by 158 and 276% in tensile strength and elongation at break, respectively, compared to the uncompatibilized blend. Also the thermal stability and moisture sorption properties of the blends as effected by TPS content were studied. Decreasing in thermal stability and increasing in equilibrium moisture content of the blends were observed with progressively increasing of TPS content. For prediction the moisture sorption behaviour of blends with various TPS contents at different relative humidity, the moisture sorption isotherm data were modeled by GAB (Guggenheim–Anderson–de Boer) model.     

A Biobased Blend of Cellulose Diacetate with Starch

Two bio-based polymers, cellulose diacetate (CDA) and starch, were used to prepare blends with reasonable properties and low cost. Due to the poor processing properties, starch was modified in the presence of glycerol and epoxidized soybean oil (ESO), and CDA was plasticized by triacetin (TA) and ESO, respectively. The morphologies of the blends with different amounts of modified starch (MST) were studied by scanning electron microscope (SEM), and the physical properties of the blends, including thermal stability, mechanical property, water and moisture resistance, were investigated. The equilibrium moisture absorption rates of the blends containing 30 and 50 wt% MST at 100 % of relative humidity(RH) were 9.4 and 15.0 %, respectively. SEM and DMA results demonstrated that CDA and MST had a certain extent of compatibility. Due to the partial plasticization of starch, the tensile strength of the blends was nearly not affected by the amount of MST. Even if 50 wt% MST was added, the tensile strength of the blend was as high as 24.7 MPa. The obtained blend containing 30 wt% MST can keep good mechanical properties at 50 % RH, and its tensile strength and elongation at break are 30.2 MPa and 3.6 %, respectively. All the results show that the CDA/MST blends have a potential as an environmental friendly material.     

Stiff Biodegradable Polylactide Composites with Ultrafine Cellulose Filler

Polylactide (PLA) composites with 10–30 wt% of commercial fine grain filler of native cellulose were prepared by melt-mixing, and examined. The composite films had esthetic appearance, glossy surface, creamy color and density close to that of neat PLA. Good dispersion of the filler in PLA matrix was achieved. The composites were stiffer than neat PLA; in the glassy region the storage modulus increased by approx. 30 %. The tensile strength of the composite materials in the temperature range from 25 to 45 °C was similar to that of neat PLA. No marked decrease in molar mass of PLA in the composites occurred during processing in comparison to neat PLA. Moreover, thermogravimetry experiments demonstrated good thermal stability of the composites; 5 % weight loss occurred well above 300 °C.     

Novel Biodegradable Thermoplastic Elastomer Based on Poly(butylene succinate) and Epoxidized Natural Rubber Simple Blends

Novel biodegradable thermoplastic elastomer based on epoxidized natural rubber (ENR) and poly(butylene succinate) (PBS) blend was prepared by a simple blend technique. Influence of blend ratios of ENR and PBS on morphological, mechanical, thermal and biodegradable properties were investigated. In addition, chemical interaction between ENR and PBS molecules was evaluated by means of the rheological properties and infrared spectroscopy. Furthermore, the phase inversion behavior of ENR/PBS blend was predicted by different empirical and semi-empirical models including Utracki, Paul and Barlow, Steinmann and Gergen models. It was found that the co-continuous phase morphology was observed in the blend with ENR/PBS about 58/42 wt% which is in good agreement with the model of Steinmann. This correlates well to morphological and mechanical properties together with degree of crystallinity of PBS in the blends. In addition, the biodegradability was characterized by soil burial test after 1, 3 and 9 months and found that the biodegradable ENR/PBS blends with optimum mechanical and biodegradability were successfully prepared.     

Biodegradability of Poly (lactic acid), Preparation and Characterization of PLA/Gum Arabic Blends

In this study, the biodegradation of PLA films using microorganisms from Lake Bogoria (Kenya) were investigated. The biodegradation tests done using certain strains of thermophilic bacteria showed faster biodegradation rates and demonstrated temperature dependency. The biodegradation of the PLA films was studied using Gel Permeation Chromatography (GPC) and light microscopy. The biodegradation of PLA was demonstrated by decrease in molecular weight. The preparation and characterization of PLA/Gum Arabic blends were also investigated using DSC, TGA, TMA and NMR. In summary, the results obtained in this research show that PLA films undergo fast biodegradation using thermophiles isolated from Lake Bogoria. The PLA/GA blends studies show it is possible to prepare films of varying hydrophobic–hydrophilic properties for various applications.     

Biodegradable Blends with Potential Use in Packaging: A Comparison of PLA/Chitosan and PLA/Cellulose Acetate Films

Poly(lactic acid) (PLA) is a biodegradable polymer that exhibits high elastic modulus, high mechanical strength, and feasible processability. However, high cost and fragility hinder the application of PLA in food packaging. Therefore, this study aimed to develop flexible PLA/acetate and PLA/chitosan films with improved thermal and mechanical properties without the addition of a plasticizer and additive to yield extruder compositions with melt temperatures above those of acetate and chitosan. PLA blends with 10, 20, and 30 wt% of chitosan or cellulose acetate were processed in a twin-screw extruder, and grain pellets were then pressed to form films. PLA/acetate films showed an increase of 30 °C in initial degradation temperature and an increase of 3.9 % in elongation at break. On the other hand, PLA/chitosan films showed improvements in mechanical properties as an increase of 4.7 % in elongation at break. PLA/chitosan film which presented the greatest increase in elongation at break proved to be the best candidate for application in packaging.     

The Effect of Gamma and Electron Beam Irradiation on the Biodegradability of PLA Films

Biodegradation of poly(lactic) acid (PLA) has been studied extensively, but there is only limited knowledge about the effect of irradiation sterilization on its biodegradability. The aim of this work was to examine the aerobic biodegradation of gamma and electron beam irradiated PLA films along with the effects of aging (3, 6, and 9 months of storage) using a direct measurement respirometric system. Commercial PLA film was exposed to a simulated aerobic compost environment, and its mineralization was 96 % at day 85. Gamma and electron beam irradiation affected the biodegradation of the post-irradiated PLA film. Aging irradiated PLA had some potential to increase the biodegradation rate, as the average value of mineralization after 9 months of storage was higher than for the non-irradiated PLA. Comparison of the effect of storage time on the biodegradability of PLA showed a significant increase in biodegradation of the gamma irradiated PLA after 3 months (70 %) and 9 months of storage (130 %). Similarly, there was a significant difference in the biodegradation of electron beam irradiated PLA between 3 months (68 %) and 9 months of storage (120 %). Due to the priming effect, the percent mineralization of gamma irradiated and E-beam irradiated PLA after 9 months of storage was greater than 100 %. Both non-irradiated and irradiated PLA films can be considered biodegradable plastics since they showed mineralization percentage larger than 90 % of that of the positive control at the end of the test period.     

Processing Stability and Biodegradation of Polylactic Acid (PLA) Composites Reinforced with Cotton Linters or Maple Hardwood Fibres

Polylactic acid (PLA) composites comprising up to 25 wt% cotton linter (CL) or up to 50 % maple wood fibre (WF) were prepared by compounding and injection moulding. A reduction of crystallinity in the PLA matrix was observed as a result of the thermal processing method. These PLACL and PLAWF composites provided excellent improvements in both stiffness (with increases in tensile and flexural modulus) and toughness (increases in notched impact strength) properties over the neat PLA resin, while the tensile and flexural strengths of the composites were generally unchanged, while the strain at break values were reduced in comparison to the neat PLA. DMA results indicated incorporating these fibres caused the mechanical loss factor (tan δ) to decrease, suggesting better damping capabilities were achieved with the composites. SEM analysis of the impact fractured surfaces of the PLACL composites showed debonding-cavitation at the matrix-fibre interface while the PLAWF composites showed good wetting along its matrix-fibre interface. The composting of these composites up to 90 days showed that the degradation onset time was increased when increasing the fibre loadings, but the maximum degree of degradation and the maximum daily rates of degradation were decreased compared to neat PLA. On a weight basis of fibre loading, the PLACL composites had a quicker onset of biodegradation, a higher maximum daily rate of biodegradation and, overall, a higher degree of biodegradation at 90 days than the PLAWF composites, possibly due to the quicker thermal hydrolysis observed in the PLA matrix of the PLACL composites during processing and composting.     

Hydrolytic Degradation of PPDO/PDLLA Blends Containing the Compatibilizer PLADO

The poly(para-dioxanone) (PPDO)/poly poly (dl-lactide) (PDLLA) blends containing various contents of compatibilizer (0, 1, 3, 5, 10 %) were prepared by solution co-precipitation, which were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) to form 10 % wt/vol solutions. Then in vitro hydrolytic degradation of PPDO/PDLLA blends containing poly (dl-lactide-co-para-dioxanone) (PLADO) as the compatibilizer was studied by the changes of weight loss, water absorption, thermal properties, surface morphology and mechanical properties of samples in phosphate buffered saline (pH 7.44) at 37 °C for 8 weeks. During the degradation, the weight loss and water absorption increased significantly for all blends, whereas hydrolysis rate of blends varied with the blend composition. The samples’ glass transition temperature decreased notably, while the degrees of crystallinity increased. Compared with uncompatibilized PPDO/PDLLA blends, PPDO/PDLLA blends with compatibilizer exhibited higher hydrolysis rate. The results suggested that the compatibilizer (PLADO) accelerated the hydrolysis rate of PPDO/PDLLA blends during the degradation.     

Mechanical Properties and Isothermal Crystallization Behaviour of Poly(lactide)/Poly(methyl methacrylate)/α-Cellulose Composites

Polylactide (PLA)/polymethylmethacrylate (PMMA)/α-cellulose composites were fabricated using a twin-screw extruder. During fabrication, α-cellulose short fibres were incorporated for improving the toughness of the brittle PLA and a chain extender was used for reducing PLA hydrolysis. Highly transparent PLA and PMMA were blended to obtain miscible and transparent blends. For evaluating the performance of the PLA/PMMA/α-cellulose composites, a series of measurements, including tensile and Izod impact tests, light transmission and haze measurements, thermomechanical analysis, and determination of isothermal crystallisation behaviour, was conducted. Adding the chain extender considerably reduced the occurrence of hydrolytic degradation. Both the chain extender and α-cellulose short fibres increased the elongation at break and Izod impact strength of the composites. Compared with the neat PLA, including 1.0 wt% α-cellulose short fibres increased the elongation at break and Izod impact strength of the composite PLA by approximately 211 and 219 %, respectively. According to the observed mechanical performance, the optimal blending ratios for PLA and PMMA were between 90:10 and 80:20. The total light transmittance of the composites was as high as 91 %, indicating that the PLA/PMMA blend was highly miscible. The haze value of the PLA/PMMA/α-cellulose composites was lower than 32 %. Incorporating cellulose short fibres increased the number of crystallisation sites and crystallinity of the PLA/PMMA/α-cellulose composites while reducing the spherulite dimensions.     

Melt Flow Behavior and Processability of Polylactic Acid/Polystyrene (PLA/PS) Polymer Blends

The present investigation dealt with the flow behavior and processability of polylactic acid/polystyrene (PLA/PS) polymer blends using a capillary rheometer. For this purpose, PLA/PS blends with different ratios of the concentrations were prepared using a single screw extruder. The shear viscosity, shear stress, shear rate, power-law index, viscous activation energy at a constant shear stress, and elongational stress were determined. PLA/PS blends exhibited a typical shear-thinning behavior over the entire range of shear rates tested, and the viscosity values of the blends would tend to decrease with increasing amount of PLA. In addition, the polymer blend of 70 % PLA and 30 % PS was found to be relatively less sensitive to the processing temperature, implying that the extrusion process was more desirable for fabrication of PLA/PS polymer blend than the injection process.     

Chemically Functionalized Plant Fibers and Carbon Nanotubes for High Compatibility and Reinforcement in Polylactic Acid (PLA) Composite

In this study, surface modification is used to improve the compatibility of Kenaf fibers (KFs) and multi-walled carbon nanotubes (MWCNTs) in a polylactic acid (PLA) matrix, as well as to enhance the mechanical properties. Through the use of a silane coupling agent, the KF is grafted with functional groups to generate a chemical bond with the PLA; the modified KF shows high compatibility in the PLA matrix. Compared to the bare PLA, the optimal KF/MWCNT/PLA composite (PC1F30-OX) shows increases of 58% in tensile strength, and 113% in impact strength. A small addition of MWCNTs (1 wt%) dramatically improves the antistatic ability by lowering the surface resistance to 3.47 GΩ. With the addition of hydrophilic KF into the PLA, the composite becomes much more environmentally friendly, and the biodegradation rate can be controlled by the amount of KF added. The addition of hydrophilic KF allowed the composite to accommodate more enzyme to hasten the biodegradation; almost complete decomposition occurred after 11 weeks.