The Effect of Chain Extender on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Thermal Degradation,Crystallization, and Rheological Behaviours

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a semi-polycrystalline biopolymer from the polyhydroxyalkanonate family has in recent years become a commercial bioplastic with mechanical properties comparable to isotactic polypropylene and enhanced O₂, CO₂ and H₂O barrier properties. However, its brittleness and sensitivity to thermal and hydrolysis degradations restrict its applications. To overcome the problems associated with degradation during processing blending of PHBV and an epoxy-functionalized chain extender (Joncryl^® ADR-4368 S) was conducted in a twin screw extruder. The effect of concentration of the chain extender on thermal, crystallization and rheological behaviours of PHBV was investigated. Thermal gravimetric analysis results indicated improvement in the resistance to thermal decomposition of PHBV by introducing the chain extender. This was accompanied with calculation of thermal degradation activation energy (E_a) using the Flyn–Walls–Ozawa method which confirmed increase of E_a with the increase in content of the chain extender. The rheological behaviour and crystallization of modified PHBV was characterized by rotational rheometry and differential scanning calorimetry techniques, respectively. The results show that addition of chain extender enhanced viscosity of PHBV and also reduce the rate of crystallization.     

Fabrication and Characterization of PLA/PHBV-Chitin Nanocomposites and Their Foams

This paper examines the effect of biobased chitin nanowhisker fillers on the thermal, rheological, physical, mechanical and morphological properties of biobased polylactic acid (PLA) and PLA/polyhydroxybutyrate-co-valerate (PHBV) blended nanocomposites as well as the physical, mechanical and morphological properties of porous PLA and PLA/PHBV nanocomposite foams. Solid nanocomposites of PLA, PLA/PHBV and chitin nanowhiskers were manufactured through melt blending while porous nanocomposites foams were fabricated through a batch foaming process with the aid of CO₂ as blowing agent. It was found that by incorporating small quantities of chitin nanowhiskers (<2 wt%) the mechanical properties of solid specimens are improved while strength and expandability of the foam can be significantly improved, yielding a homogenously distributed cell morphology with average cell size of 1.5 μm.     

Thermal Stabilization of Recycled PET Through Chain Extension and Blending with PBT

This study investigates the effect of using a multifunctional epoxide chain extender (Joncryl^® ADR 4468) on the thermal stabilization and rheological properties of recycled polyethylene terephthalate (R-PET) and its blends with polybutylene terephthalate (PBT). The R-PET samples were prepared without and with chain extender (CE) contents of 0.4 wt% and 0.8 wt%. R-PET/PBT blends with weight ratios of 75w/25w, 50w/50w and 25w/75w were also prepared without and with a given CE content of 0.2 wt%. The thermal stability of the melt blended samples was analyzed through small amplitude oscillatory shear (SAOS) rheological experiments. The structure of the samples was evaluated using a Fourier transform infrared (FTIR) spectrometer. While the dynamic rheological properties of R-PET were improved with the addition of Joncryl and by blending with PBT, during the SAOS rheological experiments, the complex viscosity of R-PET further increased due to the concurrent polycondensation of R-PET and the resumption of Joncryl reaction with R-PET molecules. These reactions during the rheological experiments were further expedited with increasing the testing temperature. On the other hand, in R-PET/PBT blends, the reactivity of Joncryl was more noticeable in blends with higher R-PET contents due to the higher available internal reactive sites of much shorter R-PET molecules. It was observed that the addition of only 0.2 wt% Joncryl to the blends of R-PET/PBT (75w/25w) dramatically improves the thermal stability and dynamic rheological properties of R-PET and most likely its processability.

     

Biodegradable Composite Foams of PLA and PHBV Using Subcritical CO<Subscript>2</Subscript>

One key strategy for increasing the application potential for biodegradable plastics lies in improving the physical and mechanical characteristics, which can be attained by inducing a cellular morphology in the pure polymer with the aid of a blowing agent, as well as by blending two or more polymers with the desirable properties. This paper examines the effect that blending two biodegradable polymers has on the thermal properties and morphology of the resultant foams blown with carbon dioxide (CO₂). Polylactic acid (PLA), polyhydroxybutyrate-co-valerate (PHBV) and blends of both were foamed and characterized in terms of thermal characteristics, relative density, cell size, and foam morphology. The results indicate that although PLA and PHBV are immiscible, the presence of small quantities of PHBV (25 wt%) could lead to low density foams with finer, more uniform cells. Furthermore, the crystallinity of PHBV was found to be unaffected by the presence of PLA in the composite, which supports the immiscibility of PLA and PHBV.     

Soil Biodegradation of PHBV/Peach Palm Particles Biocomposites

There is great interest in developing eco-friendly green biocomposites from plant-derived natural fibers and crop-derived bioplastics attributable to their renewable resource-based origin and biodegradable nature. Fully biodegradable composites, made from both biodegradable polymeric matrices and natural fibers, should be advantageous in some applications, such as one way packaging. Polyhydroxyalkanoates (PHAs) are naturally occurring biodegradable polymers produced from a wide range of microorganisms, with poly(3-hydroxybutyrate) P(3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) being important examples of PHAs. In this work, biocomposites of PHBV consisting of a PHBV matrix incorporating peach palm particles (PPp), [i.e., 100/0, 90/10, 80/20 and 75/25 (%w/w) PHBV/PPp] were processed by injection molding at 160 °C. The effect of PPp loading on the thermal and the mechanical properties, as well as on the morphological behavior of the PHBV/PPp biocomposites was investigated. Soil biodegradation tests were carried out by burying specimen beakers containing aged soil and kept under controlled temperature and humidity in accordance with ASTM G160-98. Degradation of the biocomposites was evaluated by visual analysis, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) following test exposures of up to 5 months. The addition of PPp reduced the maximum strength and the elongation at break of the biocomposites. On the other hand, the Young’s modulus improved with the PPp content. Micrographs of the fracture surfaces following tensile strength testing revealed a large distance between the PHBV matrix and PPp particles although a low interaction is expected. Where measured, these distances tended increase as the PPp content of the biocomposites increased. Soil biodegradation tests indicated that the biocomposites degraded faster than the neat polymer due to the presence of cavities that resulted from introduction of the PPp and that degradation increased with increasing PPp content. These voids allowed for enhanced water adsorption and greater internal access to the soil-borne degrader microorganisms.     

Potential utilization of burned wood in manufacture of medium density fiberboard

The potential utilization of burned wood in the manufacture of medium density fiberboard (MDF) was investigated. For this aim, the MDF panels were made of various mixtures of burned pine wood (Pinus sylvestris L.), unburned beech (Fagus orientalis L.) and oak (Ouercus robur L.) woods under commercial conditions in an MDF company. The mixture ratio of the unburned beech and oak woods to the burned pine wood were 50/50 wt%. The mixing ratios of burned wood chips with unburned wood chips were 0:100, 25:75, 50:50, 75:25 and 100:0, %, respectively. A commercial urea–formaldehyde resin was used as a binder. The physical properties measured in the investigation included density and thickness swelling, while the mechanical properties examined were bending strength, modulus elasticity, internal bond, screw holding ability perpendicular to the plane of panel, and janka hardness perpendicular to the plane of the panel. Surface roughness and color of the panels were also measured. The results indicated that all the panels met the mechanical properties of general-purpose MDF requirements of EN 622-5. The surface roughness of the MDF panels containing burned wood decreased with increasing burned wood content but remained higher than the control panels. The dimensional stability of the MDF panels decreased with the incorporation of burned wood fibers as compared with the control MDF panels.     

Soybean-Oil-Based Polyisocyanurate Rigid Foams

Polyisocyanurate foams were prepared from polymeric 4,4-diphenylmethane diisocyanate (MDI), soy polyol and polypropylene oxide polyol by varying isocyanate index from 110 to 350. The higher isocyanate index produced polyisocyanurate foams with higher thermal stability, improved flame resistance, tensile strength, higher modulus, and higher glass transition. Soy-based foams displayed better thermal stability, lower flammability, higher rigidity (modulus) and higher compression strength than those based on the propylene oxide polyols of the same molecular weight and functionality.     

Thermal Properties and Biodegradability Studies of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

For investigating the relationship between thermal properties and biodegradability of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), several films of PHBV containing different polyhydroxyvalerate (HV) fractions were subjected to degradation in different conditions for up to 49 days. Differential scanning calorimetry (DSC), thermogravimetry (TG), specimen weight loss and scanning electron microscopy (SEM) were performed to characterize the thermal properties and enzymatic biodegradability of PHBV. The experimental results suggest that the degradation rates of PHBV films increase with decreasing crystallinity; the degradability of PHBV occurring from the surface is very significant under enzymatic hydrolysis; the crystallinity of PHBV decreased with the increase of HV fraction in PHBV; and no decrease in molecular weight was observed in the partially-degraded polymer.     

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 Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/Bamboo Pulp Fiber Composites: Effects of Nucleation Agent and Compatibilizer

In this study, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/bamboo pulp fiber (BPF) composites were prepared by melt compounding and injection molding. The crystallization ability, tensile strength and modulus, flexural strength and modulus, and impact strength were found substantially increased by the addition of BPF. Tensile and flexural elongations were also moderately increased at low fiber contents (<20%). BPF demonstrated not only higher strength and modulus, but also higher failure strain than the PHBV8 matrix. Boron nitride (BN) was also investigated as a nucleation agent for PHBV8 and maleic anhydride grafted PHBV8 (MA-PHBV8) as a compatibilizer for the composite system. BN was found to increase the overall properties of the neat polymer and the composites due to refined crystalline structures. MA-PHBV8 improved polymer/fiber interactions and therefore resulted in increased strength and modulus. However, the toughness of the composites was substantially reduced due to the hindrance to fiber pullout, a major energy dissipation source during the composite deformation.     

Injection-Molded Bioblends from Lignin and Biodegradable Polymers: Processing and Performance Evaluation

This paper investigates the effects of the incorporation of lignin and small quantities of epoxidized natural rubber (ENR) as an impact modifying agent on blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ε-caprolactone) (PCL). The addition of lignin resulted in a slight improvement of flexural strength and modulus of the ternary blending system. Incorporation of ENR into the blend resulted in an increase in notched Izod impact strength from 40 to 135% depending on the concentration of ENR. The addition of lignin into the blend resulted in an improvement of thermal stability of the ternary blend system. Morphological analysis showed a good dispersion of PHBV phases and lignin within the PCL matrix. Rheological characterization revealed that the presence of lignin resulted in increased storage modulus of the bioblend.     

Effect of Lignosulfonate on the Thermal and Morphological Behavior of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The effect of lignosulfonate on poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, was studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The PHBV/lignosulfonate samples were prepared by melt mixing in an internal mixer. SEM showed that PHBV/lignosulfonate samples present a cracked surface that is more intense in mixtures with high lignosulfonate proportions. According to DSC, melting and glass transition temperatures of the PHBV matrix decrease with lignosulfonate addition. The same effect was observed for melting enthalpies (ΔH_m), which indicates a decrease of crystallinity. TGA showed that thermal stability of PHBV/lignosulfonate samples was shifted to lower temperatures, which indicates the existence of an interaction between the thermal decomposition processes of PHBV and lignosulfonate.     

Rheological and Thermal Properties of the PLA Modified by Electron Beam Irradiation in the Presence of Functional Monomer

Polylactic acid (PLA) has been modified by electron beam radiation in the presence of glycidyl methacrylate (GMA) to enhance the melt strength of PLA. The modified PLA was prepared by varying both the amount of GMA and the irradiation dose and was characterized by observing the thermal properties, the melt viscoelastic properties and the gel fraction. For comparison, virgin PLA was also irradiated. All irradiated virgin PLA had a lower complex viscosity and a storage modulus compared to virgin PLA due to irradiation-induced chain scission. However, these properties were remarkably improved due to formation of long chain branching and retarding chain scission if GMA was introduced in this system. The increase in melt viscoelastic property was much dependent on the irradiation dose. At optimum doses of radiation, it showed maximum complex viscosity and storage modulus. The PLA irradiated with 20 kGy in the presence of 3 phr GMA showed a complex viscosity of about 10 times higher and a storage modulus of 100 times higher than those of virgin PLA at 0.1 rad/s. Gel fraction measurement revealed that chain scission and branching was more dominant than crosslinking. The biodegradability of irradiated PLA was slightly decreased by the presence of GMA.     

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.     

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.     

Thermal, Mechanical and Rheological Behavior of Poly(lactic acid)/Talc Composites

In the present study, influence of talc on thermal, mechanical and rheological behavior of PLA is investigated and the structure?Cproperty correlation for the PLA/talc composites is established. Poly(lactic acid)/talc composites are prepared by melt mixing of PLA with talc in twin screw extruder followed by blown film processing. Various characterizations techniques are used to evaluate thermal, morphological, mechanical and rheological behavior of PLA/talc composites and its blown film. DSC analysis showed that degree of crystallinity of PLA/talc composites was higher than that of neat PLA because of nucleating ability of talc. Spherulite morphology of PLA/talc composites showed that talc has increased nucleation density of spherulite having smaller radius than that of neat PLA. Talc is effective in enhancing tensile modulus and storage modulus of PLA due to reinforcing ability of talc particles.     

Effect of Fiber Surface Treatments on Thermo-Mechanical Behavior of Poly(Lactic Acid)/Phormium Tenax Composites

In the present study, Phormium Tenax fiber reinforced PLA composites were processed by injection molding and twin screw compounding with a fiber content ranging from 10 to 30 wt%. Three surface treatment methods have been used to improve the Phormium Tenax fiber-matrix interfacial bonding that are as follows: (1) aqueous alkaline solution, (2) silane coupling agent, and (3) a combination of alkaline and silane treatment. The mechanical, thermal and morphological properties of the resulting composites were investigated. The results have shown that the moduli of surface treated fiber reinforced composites are lower than the ones obtained for untreated composites (as a consequence of the decrease in fiber modulus caused by the chemical treatments) and no significant increase in strength was observed for any of the composites compared to neat PLA. SEM micrographs of composite fractured surfaces confirmed an improvement in the interfacial strength, which was insufficient nonetheless to significantly enhance the mechanical behavior of the resulting composites. Results from thermogravimetric analysis and differential scanning calorimetry suggest that surface treatment of Phormium affects the ability of PLA to cold crystallize, and the thermal stability of the composites at the different fiber contents was reduced with introduction of alkali and silane treated Phormium fibers.     

Biodegradable Poly(lactic acid) Blends with Chemically Modified Polyhydroxyoctanoate Through Chain Extension

Poly(lactic acid) (PLA) was blended with chemically modified Polyhydroxyoctanoate (mPHO) using a Haake twin-screw mixer. Due to the melt viscosity disparity between the two components, PHO was reacted with Hexamethylene diisocyanate (HDI) used as a chain extender to produce high molecular weight for improving compatibility and processability with PLA. The number average and weight average molecular weight of the PHO, reacted with 0.55 wt% HDI, were increased 314 and 275%, respectively, compared with those of the unmodified PHO. The blends were characterized for rheological, thermal, and mechanical properties. Infrared spectra confirmed the formation of the urethane linkages in mPHO. The shear viscosity, as a function of shear rate or shear stress, decreased with an increase in mPHO content, indicating that the PLA/mPHO blends show shear-thinning behavior along with the power-law model. DSC thermograms showed that the two components in the blends were found with two crystalline phases and two amorphous phases confirming the coexistence of two immiscible components. Tensile results indicated that tensile strength for blends decreased with increasing mPHO content up to 80%. A decrease in elastic modulus, as well as an increase in elongation at break, was seen as a function of mPHO content. Results of aging tests showed that the mechanical properties of the blends also dropped more at a higher PLA level when compared with those of the unaged samples.     

Biodegradation of Injection Molded Starch-Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) Blends in a Natural Compost Environment

Injection molded specimens were prepared by blending poly (hydroxybutyrate-co-valerate) (PHBV) with cornstarch. Blended formulations incorporated 30% or 50% starch in the presence or absence of poly-(ethylene oxide) (PEO), which enhances the adherence of starch granules to PHBV. These formulations were evaluated for their biodegradability in natural compost by measuring changes in physical and chemical properties over a period of 125 days. The degradation of plastic material, as evidenced by weight loss and deterioration in tensile properties, correlated with the amount of starch present in the blends (neat PHBV < 30% starch < 50% starch). Incorporation of PEO into starch-PHBV blends had little or no effect on the rate of weight loss. Starch in blends degraded faster than PHBV and it accelerated PHBV degradation. Also, PHBV did not retard starch degradation. After 125 days of exposure to compost, neat PHBV lost 7% of its weight (0.056% weight loss/day), while the PHBV component of a 50% starch blend lost 41% of its weight (0.328% weight loss/day). PHB and PHV moieties within the copolymer degraded at similar rates, regardless of the presence of starch, as determined by ¹H-NMR spectroscopy. GPC analyses revealed that, while the number average molecular weight (Mn) of PHBV in all exposed samples decreased, there was no significant difference in this decrease between neat PHBV as opposed to PHBV blended with starch. SEM showed homogeneously distributed starch granules embedded in a PHBV matrix, typical of a filler material. Starch granules were rapidly depleted during exposure to compost, increasing the surface area of the PHBV matrix.     

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.