Rheology,Morphology, Crystallization Behaviors,Mechanical and Thermal Properties of Poly(lactic acid)/Polypropylene/Maleic Anhydride-Grafted Polypropylene Blends

The rheologies, morphologies, crystallization behaviors, mechanical and thermal properties of poly(lactic acid) (PLA)/polypropylene (PP) blends and PLA/PP/maleic anhydride-grafted PP (MAPP) blends were investigated. The results showed that the complex viscosities of PLA/PP blends were between those of neat PLA and neat PP, and MAPP had a thinning effect on those of the blends. PLA/PP blends exhibited the distinct phase separation morphologies due to the limited partial miscibility of the blend components. MAPP slightly improved the miscibility between PLA and PP. Both the cold crystallization of PLA component and melt crystallization of PP component were enhanced, probably because PLA and PP were reciprocal nucleating agents. The tensile strength and flexural modulus decreased, while the tensile strain at break and heat deflection temperature (HDT) increased with the increasing PP content. MAPP had the positive effects on the notched impact strength and HDT of PLA-rich blends and also increased the flexural modulus of the binary blends. The thermal stability of the blend was improved by PP, and the incorporation of MAPP further enhanced the thermal stability.     

Reactive Compatibilization of Biobased Polyurethane Prepolymer Toughening Polylactide Prepared by Melt Blending

Polylactide (PLA) is a major biodegradable polymer, which has received extensive interests over the past decades and holds great potential to replace several petroleum-based polymeric materials. Nevertheless, the inherent brittleness and low impact strength have restricted its invasion to niche markets. In this paper, the authors demonstrate that the entirely bio-sourced blends, namely PLA and castor oil-based polyurethane prepolymer (COPUP), were first melt-compounded in an effort to prepare novel biodegradable materials with an excellent balance of properties. NCO-terminated COPUP was successfully synthesized and subsequently mixed with variable concentration of PLA matrix using melt-compounded by twin-screw extrusion technique. The miscibility, phase morphology, mechanical properties, and thermal resistance of the blends were investigated. During FTIR analysis, it suggests that the interfacial compatibilization between COPUP and PLA phase occurred by the reaction of –NCO group of MDI with terminal hydroxyl group of PLA. DMA analysis showed that COPUP and PLA showed some limited miscibility with shifted glass transition temperature. The morphologies of fracture surface showed a brittle-to-ductile transition owing by the addition of COPUP. The crystallization behavior was studied by differential scanning calorimeter (DSC). The strain at break and notched impact strength of PLA/COPUP blends were increased more than 112–15.4 times elegant of neat PLA; the increase is superior to previous toughening effect by using petroleum-based tougheners. Furthermore, the thermal resistances and melt flow properties of the materials were also examined by analysis of the melt flow index and heat deflection temperature use in the work. With enhanced toughness, the PLA/COPUP blends could be used as replacements for some traditional petroleum-based polymeric materials.     

Preparation and Properties of Biodegradable Poly(lactic acid)/Poly(butylene adipate-co-terephthalate) Blend with Epoxy-Functional Styrene Acrylic Copolymer as Reactive Agent

Poly (lactic acid) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT) are biodegradable polyesters and can be blended by twin-screw extrusion. Epoxy-functional styrene acrylic copolymer (ESA) was used as reactive agent for PLA/PBAT blends and the mechanical properties, phase morphology, thermal properties, melt properties, and melt rheological behaviors of the blends were investigated. During thermal extrusion, ESA was mainly a chain extender for the PLA matrix but had no evident reaction with PBAT. The great improvement in the toughness of PLA based blends was achieved by the addition of PBAT of no less than 15 wt% and that of ESA of no more than 0.5 wt%. Although SEM micrographs and the reduced deviation of the terminal slope of G′ and G″ indicated better compatibility and adhesion between the two phases, the blend with ESA was still a two-phase system as indicated in DSC curves. Rheological results reveal that the addition of ESA increased the storage modulus (G′), loss modulus (G″) and complex viscosity of the blend at nearly all frequencies. The melt strength and melt elasticity of the blend are improved by addition of ESA.     

Influence of TiO<Subscript>2</Subscript> Nanoparticles on the Crystallization Behaviour and Tensile Properties of Biodegradable PLA and PCL Nanocomposites

This paper investigated the influence of TiO₂ nanoparticles on the morphologies, as well as crystallization behaviour and kinetics, of neat PLA and PCL, and of these polymers in different PLA/PCL blends. We used transmission electron microscopy to evaluate the morphologies of the systems, while the crystallization behaviour and kinetics were investigated through differential scanning calorimetry (DSC). In addition to standard and modulated (StepScan) DSC analyses, the self-nucleation temperatures of neat PCL and PCL in the different nanocomposites were determined, followed by a self-nucleation and annealing thermal fractionation analysis of PCL crystallization and an Avrami isothermal kinetic analysis of PCL crystallization and PLA cold crystallization. We found that the nanoparticles were well dispersed, but only in the PLA phase of the blends, with only a few on the interface or in the PCL phase. They did nucleate and accelerate, and influence the mechanism of, the PCL crystallization in neat PCL, but had little influence on PCL crystallization in the blends. They strongly influenced the rate of cold crystallization of PLA, but had little influence on this parameter in the blends. The tensile properties were also determined, and changes in these properties could be related to the morphologies of the systems.     

Study of Effects of Processing Aids on Properties of Poly(lactic acid)/Soy Protein Blends

In this work, two processing aids, acetyl tri-n-butyl citrate and an alkene bis fatty amide (wax), were investigated for their effects on rheological properties, morphology, thermal transition temperatures, and mechanical properties of the poly(lactic acid) (PLA)/soy protein concentrate blends. Acetyl tri-n-butyl citrate and alkene bis fatty amide played different roles in improving the processability of the blends, with the former functioning as a plasticizer for PLA and the latter as an internal/external lubricant. The amide wax was more effective in reducing blend melt viscosity through its dual functions of internal and external lubrication. Acetyl tri-n-butyl citrate displayed a stronger effect in facilitating PLA nucleation than the amide wax. Both processing aids decreased tensile strength and modulus of the blends and increased break strain and impact strength.     

Fabrication of Admicelled Natural Rubber by Polycaprolactone for Toughening Poly(lactic acid)

Natural rubber (NR) with polycaprolactone (PCL) core–shell (NR-ad-PCL), synthesized by admicellar polymerization, was acted as an impact modifier for poly(lactic acid) (PLA). PLA and NR-ad-PCL were melt-blended using a co-rotating twin screw extruder. The morphology of PLA/NR-ad-PCL blends showed good adhesion as smooth boundary around rubber particles and PLA matrix. Only 5 wt% of rubber phase, NR-ad-PCL was more effective than NR to enhance toughness and mechanical properties of PLA. The contents of the NR-ad-PCL were varied from 5, 10, 15 and 20 wt%. From thermal results, the incorporation of the NR-ad-PCL decreased the glass transition temperature and slightly increased degree of crystallinity of PLA. Mechanical properties of the PLA/NR-ad-PCL blends were investigated by dynamic mechanical analyser, pendulum impact tester and universal testing machine for tension and flexural properties. The increasing NR-ad-PCL contents led to decreasing Young’s and storage moduli but increasing loss modulus. Impact strength and elongation at break of the PLA/NR-ad-PCL blends increased with increasing NR-ad-PCL content up to 15 wt% where the maximum impact strength was about three times higher than that of pure PLA and the elongation at break increased to 79%.     

Effect of Nucleating Agents on Physical Properties of Poly(lactic acid) and Its Blend with Natural Rubber

Poly(lactic acid) (PLA) presents high strength and modulus, but very low toughness as well as slow crystallization. Natural rubber (NR) was blended to enhance the toughness and nucleating agent was added to improve the crystallization. Cyclodextrin (CD), considered as a green compound, as well as calcium carbonate (CaCO₃) and talc were used as nucleating agents. Effects of these nucleating agents on crystallization, mechanical properties and morphology of neat PLA and PLA/NR blend were investigated. It was found that the addition of talc and CD decreased cold crystallization temperature (T_cc) of the PLA. Same result was obtained in PLA/NR blend containing talc. All nucleating agents increased the degree of crystallinity (Χ_C) of PLA, whereas only talc and CaCO₃ increased Χ_C of PLA in PLA/NR blends. The enhanced toughness of PLA by the addition of nucleating agent was attributed to its increased crystallinity, as well as decreased spherulite size. For PLA/NR blends, the increase in toughness was mainly contributed by the presence of the rubber.     

Thermal and Rheological Properties of Poly(lactic acid)/Low-Density Polyethylene Blends and Their Supercritical CO<Subscript>2</Subscript> Foaming Behavior

Low-density polyethylene (LDPE) was employed to improve the thermal and rheological properties as well as the supercritical CO₂ foaming behavior of poly(lactic acid) (PLA) through melt mixing and batch foaming method, due to its long branched chain structure, moderate crystallization capacity and good foamability. The differential scanning calorimetry and polarized optical microscope results showed that the introduction of LDPE had a slight effect for promoting the crystallization of PLA. An important synergistic effect on the rheological properties of PLA/LDPE blends was found through rotational rheometer. With the content of LDPE, the size of spherical LDPE dispersion phase became bigger gradually, which was observed by scanning electron microscope (SEM). A very interesting cellular morphology evolution from flower-like cellular structure to complex cellular structure and then to mono-porous cell structure was found in the SEM images of the PLA/LDPE blending foams with the foaming temperature at 95 °C. The effect of blending ratio and foaming temperature on the cellular morphology and foaming parameters was investigated.     

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%.     

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.     

Renewable Resource-Based Composites of Acorn Powder and Polylactide Bio-Plastic: Preparation and Properties Evaluation

Renewable resource-based composites were prepared with acorn powder and Thermoplastic resin poly(lactic acid) (PLA) by twin-screw extrusion followed by injection molding processing or hot-compression molding processing. The study of the composites microstructure showed poor adhesion between acorn powder and PLA matrix. The hygroscopicity, mechanical properties and melt flow property of composites were promising even though the composites had a 70 wt% content of acorn powder. Silane coupling agent, 4,4′-Methylenebis (phenyl isocyanate) and PLA grafted with maleic anhydride did not show obvious effect on mechanical properties of composites. The impact resistance strength of reinforced composites with steel fiber webs were improved greatly in comparison with those having no steel fiber webs. Thermal properties results of DSC and DMA showed that the presence of acorn powder significantly affected the crystallinity, crystallization temperature (T_c), glass transition temperature (T_g) and melting temperature (T_m) of PLA matrix. The study results proved that composites had superior mechanical properties, enough to partially replace the conventional thermoplastic plastics.     

Polylactide (PLA)—Halloysite Nanocomposites: Production, Morphology and Key-Properties

To evaluate the potential of halloysite nanotubes (HNT) as nanofiller for polylactide (PLA), various nanocomposites have been successfully produced by melt-blending the polyester matrix with HNT (HNT(QM)). HNT were also surface treated by silanization reaction with 3-(Trimethoxysilyl) propyl methacrylate (TMSPM). The morphology, thermal, tensile and impact strength properties of the nanocomposites containing 3?C12?% HNT were evaluated and compared to those of pristine (unfilled) PLA. The nanocomposites were characterized by higher rigidity (with Young??s modulus increasing with HNT loading), higher tensile strength (about 70?MPa at 6?% HNT(QM)), whereas the elongation at break and impact strength did not decrease. As demonstrated under dynamic solicitation (DMA), melt-blending PLA with HNT led to enhancement of storage modulus (E??) and offers the possibility to use PLA in applications requiring higher temperatures of utilization. However, with few exceptions, TGA and DSC measurements did not reveal important changes of thermal parameters. The surface silanization treatment proved to improve the quality of the nanofiller dispersion even at higher loading. As a result, good thermal stability associated to high tensile strength, and noticeable increases in impact properties were recorded. Furthermore, enhanced nucleating ability and crystallization kinetics of the PLA matrix were revealed as specific characteristics.     

Poly(Ethylene Glycol) as a Compatibilizer for Poly(Lactic Acid)/Thermoplastic Starch Blends

A new route to prepare poly(lactic acid) (PLA)/thermoplastic starch (TPS) blends is described in this work using poly(ethylene glycol) (PEG), a non-toxic polymer, as a compatibilizer. The influence of PEG on the morphology and properties of PLA/TPS blends was studied. The blends were processed using a twin-screw micro-compounder and a micro-injector. The morphologies were analyzed by scanning and transmission electron microscopies and the material properties were evaluated by dynamic-mechanical, differential scanning calorimetry, thermogravimetric analysis and mechanical tests. PLA/TPS blends presented large TPS phase size distribution and low adhesion between phases which was responsible for the lower elastic modulus of this blend when compared to pure PLA. The addition of PEG resulted in the increase of PLA crystallization, due to its plasticizing effect, and improvement of the interfacial interaction between TPS and PLA matrix. Results show that incorporation of PEG increased the impact strength of the ternary blend and that the elastic modulus remained similar to the PLA/TPS blend.     

Biodegradability and Thermal Properties of Novel Natural Rubber/Linear Low Density Polyethylene/Thermoplastic Starch Ternary Blends

This work aimed to prepare biodegradable thermoplastic elastomers based on NR/LLDPE/TPS ternary simple blends to achieve some exclusive properties, i.e., good biodegradability in terms of water absorption and weight loss after burial, together with reasonable mechanical and thermal properties. A comparative study on biodegradability and other related properties of NR/LLDPE binary and NR/LLDPE/TPS ternary blends was performed. It was found that increasing the TPS proportion decreased storage modulus and complex viscosity. In addition, the size of dispersed TPS domains in the NR/LLDPE co-continuous matrix increased with TPS proportion, while the mechanical properties in terms of 100% moduli, tensile strength, elongation at break, and hardness decreased. This might be attributed to decreased interfacial adhesion with increasing size of TPS domains. Furthermore, increasing the TPS loading in the blend reduced the temperatures for 5 or 50% mass loss (T₅ or T₅₀) and the degradation temperature (T _d ). However, the biodegradability improved, in terms of increased water absorption and weight loss after burial in soil, with the loading level of TPS.     

Comparison of Polylactic Acid/Kenaf and Polylactic Acid/Rise Husk Composites: The Influence of the Natural Fibers on the Mechanical, Thermal and Biodegradability Properties

This paper investigates and compares the performances of polylactic acid (PLA)/kenaf (PLA-K) and PLA/rice husk (PLA-RH) composites in terms of biodegradability, mechanical and thermal properties. Composites with natural fiber weight content of 20% with fiber sizes of less than 100 μm were produced for testing and characterization. A twin-screw extrusion was used to compound PLA and natural fibers, and extruded composites were injection molded to test samples. Flexural and Izod impact test, TGA, soil burial test and SEM were used to investigate properties. All results were compared to a pure PLA matrix sample. The flexural modulus of the PLA increased with the addition of natural fibers, while the flexural strength decreased. The highest impact strength (34 J m⁻¹), flexural modulus (4.5 GPa) and flexural strength (90 MPa) were obtained for the composite made of PLA/kenaf (PLA-K), which means kenaf natural fibers are potential to be used as an alternative filler to enhance mechanical properties. On the other hand PLA-RH composite exhibits lower mechanical properties. The impact strength of PLA has decreased when filled with natural fibers; this decrease is more pronounced in the PLA-RH composite. In terms of thermal stability it has been found that the addition of natural fibers decreased the thermal stability of virgin PLA and the decrement was more prominent in the PLA-RH composite. Biodegradability of the composites slightly increased and reached 1.2 and 0.8% for PLA-K and PLA-RH respectively for a period of 90 days. SEM micrographs showed poor interfacial between the polymer matrix and natural fibers.     

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.     

High Toughness and Fast Crystallization Poly(Lactic Acid)/Polyamide 11/SiO<Subscript>2</Subscript> Composites

A poly(lactic acid) (PLA)/polyamide 11 (PA11)/SiO₂ composite was mixed from PLA, PA11, and nanosilica particles through twin-screw extrusion. The PLA/PA11/SiO₂ composite was evaluated with tensile and Izod impact tests, light transmission and haze measurement, and isothermal and nonisothermal crystallization behavior determinations. The PLA/PA11/SiO₂ (97.0/3.0) composite had approximately 10.8% less ultimate tensile strength than neat PLA, but it had greater ductility and approximately ninefold greater elongation at break. A dimple morphology was observed on the fractural surface of the PLA/PA11/SiO₂ composite, indicating that the incorporation of PA11 and nanosilica particles increased the ductility of the PLA matrix. PLA with less than 3 wt% of PA11 and 0.5 phr of nanosilica particles had an Izod impact strength of 8.72 kJ/m². PA11 and nanosilica particles effectively toughened this PLA polymer; they accelerated both isothermal and nonisothermal crystallization rates and increased the crystallinities of the resulting composites under isothermal and nonisothermal crystallization processes.     

Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)/Polylactide Blends: Thermal Stability,Flammability and Thermo-Mechanical Behavior

Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactide (PLA) with different PHBV/PLA weight ratios (100/0, 75/25, 50/50, 25/75, 0/100) were prepared by melt compounding. Their mutual contributions in terms of thermal stability, flammability resistance, mechanical properties and rheological behavior were investigated. The study showed that the increase in PLA content in PHBV/PLA blends leads to enhanced properties. Consequently, thermal stability and flammability resistance were improved. Further, the rheological measurements indicated an increase in storage modulus and loss modulus of PHBV matrix by addition of PLA.     

Poly(Lactic Acid) Blended with Cellulolytic Enzyme Lignin: Mechanical and Thermal Properties and Morphology Evaluation

“Green”/bio-based blends of poly(lactic acid) (PLA) and cellulolytic enzyme lignin (CEL) were prepared by twin-screw extrusion blending. The mechanical and thermal properties and the morphology of the blends were investigated. It was found that the Young’s modulus of the PLA/CEL blends is significantly higher than that of the neat PLA and the Shore hardness is also somewhat improved. However, the tensile strength, the elongation at break, and the impact strength are slightly decreased. Thermogravimetric analysis (TGA) shows that the thermal stability of the PLA is not significantly affected by the incorporation of the CEL, even with 40 wt% CEL. The results of FT-IR and SEM reveal that the CEL and the PLA are miscible and there are efficient interactions at the interfaces between them. These findings show that the CEL is a kind of feasible filler for the PLA-based blends.     

The Investigation of the Toughening Mechanism of PHBV/PBAT with a Novel Hyperbranched Ethylenediamine Triazine Polymer Based Modifier: The Formation of the Transition Layer and the Microcrosslinking Structure

A new type of designed hyperbranched ethylenediamine trazine polymer (HBETP) is successfully synthesized and characterized based upon NMR and GPC. The prepared HBETP is used to modify the poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)/poly(butylene adipate-co-terephthalate) (PBAT) blends. The effect of HBETP on the microstructure, mechanical properties and thermal properties of the blends is studied. The results indicate that upon addition of 1.0 wt% of HBETP, the impact strength of the PHBV/PBAT blends is increased by 47.1%; ?T_g of the blends decreases from 53.2 to 49.9 °C. These results, together with the morphology analysis of the fractured surface of the blends, conclude the formation of the transition layer between PHBV and PBAT. Also, the XRD result shows that the addition of HBETP can limit the growth of the PHBV crystals and causes the decrease of both the crystallinity and the grain crystalline size. The DSC result demonstrates that the addition of HBETP mainly affects the crystallization of the HB-HV binary eutectic region within PHBV. The mechanism of PHBV/PBAT toughening is due to the formation of the strong physical hydrogen bonding and the chemical micro-crosslinking between HBETP and PHBV/PBAT, which is proposed based on XPS characterization.