Polyhydroxybutyrate-co-valerate Research Articles

Dry fractionation of olive pomace for the development of food packaging biocomposites

Three lignocellulosic fractions with contrasted properties were produced by dry fractionation of olive pomace (OP): a stone-rich fraction (SF) rich in cellulose and having high polarity, a pulp-rich fraction (PF) richer in lignin and less polar, and a crude pomace fraction (CF) with intermediate properties. These fractions were used as fillers in two thermoplastic matrices, i.e. polyprolylene (PP) and polyhydroxybutyrate-co-valerate (PHBV). Tensile tests showed a decrease of both the stress and the elongation at break for all biocomposites, while the Young’s modulus was not significantly affected. At low filler contents, no effect of filler composition was observed whereas at high filler content (30 wt%), the decrease in the stress at break was less pronounced for PHBV-PF, with respective reduction values of 36%, 65% and up to 78% for PHBV-PF (30%), PHBV-CF (30%)and PHBV-SF (30%) composites, as compared to the neat PHBV. The elongation at break also greatly decreased according to the filler content. The highest reduction was recorded in the case of SF fillers, with a reduction of 74% for PHBV-SF composites. Mechanical properties were better preserved in the case of the PF filler due to better interfacial adhesion towards the matrices, as revealed by work of adhesion calculations, SEM observations and mechanical modelling. Water vapour permeability (WVP) of both matrices was increased in presence of both SF and CF fillers, while oxygen permeability was not significantly affected by the fillers. As an example, WVP increased from 0.9 ± 0.1 × 10−12 mol m−1 s−1 Pa−1 for the neat PHBV up to 15.1 ± 2.6 × 10−12 mol m−1 s−1 Pa−1 for PHBV-CF (30%). This supports a promising use of SF/CF fractions in sustainable biocomposites packaging for respiring food products, the PF-based formulations being more appropriate for non-respiring and water sensitive products. Our results demonstrated that the conditioning of lignocellulosic biomass by dry fractionation is important for the control of bio-based fillers properties and the resulting functionalities of biocomposites. Besides, the PP-based composites developed in this study allow reducing costs and dependence to fossil resources, while PHBV-based biocomposites also have the advantage of being fully bio-based and biodegradable.

Biomineralization potential and cellular response of PHB and PHBV blends with natural anionic polysaccharides

In this paper, the biomineralization potential and cellular response of novel blend films of the anionic sulfated polysaccharides kappa-carrageenan (KCG) and fucoidan (FUC) derived from seaweeds with semi-crystalline polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV), respectively, were analyzed. The incorporation of KCG and FUC into PHB and PHBV, which has been studied here for the first time, led to an overall decrease in crystallinity, enhanced surface hydrophilicity, reduced brittleness and faster degradation of the polymer blend films. All PHB/KCG, PHBV/KCG and PHBV/FUC films exhibited a two-stage mass loss profiles with pH stabilization. PHBV/KCG film showed the highest biomineralization activity due the presence of sulfate groups on the surface of the films. NIH3T3 cells attached and proliferated well on all blend films on account of enhanced surface hydrophilicity and improved flexibility. PHBV/KCG led to a promoted cellular activity compared to PHBV/FUC, presumably due to phase separation and higher amount of biopolymer on the film surface that was a consequence of the immiscibility of the polymers in the blend films.

Third generation poly(hydroxyacid) composite scaffolds for tissue engineering

Bone tissue engineering based on scaffolds is quite a complex process as a whole gamut of criteria needs to be satisfied to promote cellular attachment, proliferation and differentiation: biocompatibility, right surface properties, adequate mechanical performance, controlled bioresorbability, osteoconductivity, angiogenic cues, and vascularization. Third generation scaffolds are more of composite types to maximize biological-mechanical-chemical properties. In the present review, our focus is on the performance of micro-organism-derived polyhydroxyalkanoates (PHAs)-polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV)-composite scaffolds with ceramics and natural polymers for tissue engineering applications with emphasis on bone tissue. We particularly emphasize on how material properties of the composites affect scaffold performance. PHA-based composites have demonstrated their biocompatibility with a range of tissues and their capacity to induce osteogenesis due to their piezoelectric properties. Electrospun PHB/PHBV fiber mesh in combination with human adipose tissue-derived stem cells (hASCs) were shown to improve vascularization in engineered bone tissues. For nerve and skin tissue engineering applications, natural polymers such as collagen and chitosan remain the gold standard but there is scope for development of scaffolds combining PHAs with other natural polymers which can address some of the limitations such as brittleness, lack of bioactivity and slow degradation rate presented by the latter. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1667-1684, 2017.

Biopolymer blends based on polylactic acid and polyhydroxy butyrate-co-valerate: Effect of clay on mechanical and thermal properties

Biodegradable polymer blends consisting of polylactic acid (PLA) and polyhydroxy butyrate-co-valerate (PHBV) have been prepared by melt mixing in a twin screw extruder and followed by injection molding technique. Cereplast PLA containing starch as an additive was used to make the blends. The effects of three different types of clay (montmorillonite, bentonite, and chemically modified bentonite) on the mechanical and thermal properties of the blends were studied. The ratio of PLA and PHBV (w/w) was maintained at 70:30 while the weight of clay was fixed at 1%. The addition of clay was found to result in a slight increase in tensile strength and modulus. Viscoelastic studies revealed that the damping property of the blends decreased with the addition of clay. This was attributed to the decreased segmental motion in the molecular chains. The morphology of the blends has been investigated by environmental scanning electron microscopy and a homogenous surface was observed for the blend containing montmorillonite. POLYM. COMPOS., 36:2042–2050, 2015. © 2014 Society of Plastics Engineer

Selection of Polyhydroxybutyrate-Co-Valerate (PHBV) as An Improved Polymer Choice in FTY720 Loaded Nanofibers for Islet Transplant

Introduction: These studies aim to determine a biodegradeable polymer that can be used within a tissue engineering device that does not reduce the viability of islets to the same degree as poly(lactic-co-glycolic acid) (PLAGA), but can still be successfully electrospun and loaded with FTY720. Drug release profile and in vivo immune response support the new polymer choice. Methods: Nanofibers are electrospun resulting in scaffolds consisting of several types of polymers, including equal blends by weight with polycaprolactone (PCL), with and without FTY720. Images are obtained from dorsal skinfold window chambers where a FTY720 loaded implant and an unloaded implant are placed in the same animal immediately following window surgery. Microvessel metrics are quantified with a MATLAB program. Islets are stained for viability (Propidium Iodide and Fluorescein Diacetate). Release samples are analyzed with Liquid Chromatography-Mass Spectrometry (LC-MS) following lipid extraction. Hematoxylin and Eosin stained slides are obtained from paraffin embedded tissue samples. Results: Human islets tested with PLAGA/PCL nanofibers displayed a decrease in viability compared to the media only controls (68% PLAGA/PCL verses 78% media only). Other polymer types polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV) performed better in this assay (75% and 79% respectively). LC-MS assisted in vitro release data indicate that a burst release (>10% loaded drug within 48 hours) is followed by a steady release resulting in 25% of the loaded FTY720 released by 2 weeks. Water droplet absorption time into nanofiber scaffolds indicate differences when FTY720 is added (< 5 sec FTY720 Loaded verses >3 min Unloaded scaffold, until complete wetting) likely related to the amphiphilic character of FTY720. Image analysis of window chambers with dual implants, indicate that after an initial 3 day time period a preferential blood flow in the area surrounding the FTY720 loaded implant exists as measured by both volume of blood in the tissue and length of visible blood vessels. Preliminary histology from subcutaneous implant studies indicate that the PLAGA/PCL fiber scaffolds contain more inflammatory cells and are characterized by tertiary lymphoid tissue development. In contrast, the PHBV/PCL fibers elicit an immune response, but do not result in formation of lymphoid tissue. Conclusion: The monomers of PLAGA are acidic. A decrease in culture media pH may contribute to a loss in islet viability with PLAGA fibers, which is less of an issue with the slower degrading PHBV. FTY720 releases from the fibers at a rate which can drive microvessel remodeling following injury perhaps by the recruitment of microvessel support cells. A depot of FTY720 is maintained however that will release for an extended period of time. Water droplet absorption combined with the burst release suggest that some of the FTY720 is locating near the surface of the fibers. PHBV scaffolds improved viability of islets in culture over PLAGA/PCL scaffolds. Preliminary in vivo studies demonstrate that PHBV/PCL fibers instigate less of an immune response than PLAGA/PCL fibers. In conclusion, PHBV has shown promise as a replacement polymer for PLAGA in FTY720 loaded nanofiber scaffolds for islet transplant.

Electrospinning of PHBV/ZnO membranes: Structure and properties

Polyhydroxy butyrate-co-valerate (PHBV) — Zinc oxide (ZnO) nano composite fibers were prepared using electrospinning. The structural and optical properties were studied using Fourier transform infrared spectroscopy (FT-IR), Xray diffraction (XRD) and photoluminescence study (PL). The morphology observed with scanning electron microscope (SEM) revealed no significant changes in the nano composite fibers as compared to bare polymer. The low concentration of ZnO nanoparticles resulted in an increase in overall crystallinity of the polymer matrix which was confirmed from FT-IR and XRD results. The photoluminescence (PL) study indicated the quenching of visible emission in the composite fibers. The ratio of UV to visible emission (Iuv/Ivis) intensity was found to be 12.8 times enhanced in the composite fibers compared to bare ZnO nanoparticles. The nanofibrous mats are self supported and hence offer potential applications in optoelectronic devices and the biomedical imaging.

Studies on recyclability of polyhydroxybutyrate‐co‐valerate bioplastic: Multiple melt processing and performance evaluations

AbstractRecyclability of the bioplastic polyhydroxybutyrate‐co‐valerate (PHBV) was studied with multiple melt processing (five cycles), with their performances evaluated. A batch of PHBV was processed with a twin screw extrusion followed by injection molding. This operation was repeated five times and samples were collected from each cycle for characterization. For each cycle, the mechanical properties were characterized with tensile, flexural, and impact testing, along with dynamic mechanical analysis. The results showed that the mechanical properties are maintained for four cycles; but in the fifth cycle, there was slight decrease in the properties. Gel permeation chromatography studies revealed that the molecular weight of the polymer does not decrease drastically; however, a drop was observed after third, fourth, and fifth cycle (8.7% decrease after third cycle, 13.5% decrease after fourth cycle, and 16.6% decrease after fifth cycle). The differential scanning calorimeter showed that the glass transition and melting temperatures did not change upon reprocessing, but the degree of crystallinity was reduced as a consequence of melt processing. The thermal gravimetric analysis showed that the onset value of thermal decomposition decreased very slightly. It was observed by Fourier transform infrared spectroscopy that the chemical structure of PHBV was maintained without any side chain reaction during processing. Scanning electron microscopy studies from the fractured surfaces of Cycles 1 and 5 confirmed that the uniformity of PHBV surfaces was maintained after five cycles, coinciding with the mechanical tests. The density measurements revealed that there was no change in the density of PHBV. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Novel clay‐based nanobiocomposites of biopolyesters with synergistic barrier to UV light, gas, and vapour

AbstractThis article presents novel solvent cast biocomposites of poly(lactic acid) (PLA), polyhydroxybutyrate‐co‐valerate (PHBV), and polycaprolactone (PCL) with enhanced barrier properties to UV light, oxygen, water, and limonene by means of incorporating an organomodified mica‐based clay grade. The TEM results suggested a good clay dispersion but with no exfoliation in the three biopolyesters. In agreement with the crystallinity data, which was found to generally increase with increasing filler content, oxygen but specially water and d‐limonene permeability coefficients were seen to decrease to a significant extent in the biocomposites and an optimum property balance was found for 5 wt % of clay loading in the three biopolymers. With increasing clay content, the light transmission of these biodegradable biocomposites decreased by up to 90% in the UV wavelength region due to the specific UV blocking nature of the clay used. As a result, these new biocomposites can have significant potential to develop packaging films, coatings and membranes with enhanced gas and vapor barrier properties and UV blocking performance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Improvement of UV stability and mechanical properties of biopolyesters through the addition of β-carotene

β-carotene, the most abundant carotenoid in nature and a natural antioxidant, has been added at a concentration of 2 × 10 −4 g per mL of polymer film forming solution to three biopolyester matrices, poly(lactic acid) (PLA), polycaprolactone (PCL) and polyhydroxybutyrate-co-valerate (PHBV). The dispersion and stability of the antioxidant within the films was studied using confocal Raman imaging spectroscopy, colorimetry and UV/visible spectrophotometry. The films were characterized in terms of thermal and mechanical properties in comparison with control films without β-carotene. Addition of β-carotene to the three biopolyesters studied resulted in significant increases in the deformation at break and lower Young modulus. This antioxidant is thought to act as a plasticizer in the biopolyesters, thus increasing their free volume and causing a change in their thermal properties. Moreover, when exposed to UV light the mechanical properties of the films with β-carotene were less affected displaying, in general, higher modulus and similar ultimate tensile strength while keeping the films more ductile than the pure films. Therefore, β-carotene can be potentially used as a natural additive to increase the UV stability of the biopolyesters.

Effect of addition of carbon nanofibers and carbon nanotubes on properties of thermoplastic biopolymers

This paper presents the properties of nano-bio-composites of solvent cast polyhydroxybutyrate-co-valerate (PHBV) and polycaprolactone (PCL) containing carbon nanofiber or carbon nanotubes as a function of filler content. It is found that carbon nanotubes and nanofibers can be used to enhance the conductivity, thermal, mechanical and to enhance gas barrier properties of thermoplastic biopolyesters.

Hybrid bio-composite from talc, wood fiber and bioplastic: Fabrication and characterization

This investigation deals with the development of hybrid composites from wood fiber, talc and a bioplastic i.e., polyhydroxybutyrate-co-valerate (PHBV) using the extrusion–injection molding. Synergistic improvement in the mechanical properties of PHBV–wood fiber composites were obtained with the additional reinforcement of micro sized talc in it. The compositional design of hybrid green composites primarily focuses to create a balance among the cost effectiveness, the environment friendliness and the characteristics of the hybrid composites. The hybrid green composites showed a pronounced leap of 200% in the Young’s and flexural modulus with the dual reinforcement of 20 wt.% talc and 20 wt.% wood fiber in PHBV matrix. The dynamic-mechanical and thermo-mechanical properties of the composite were experimentally determined and show similar trend. The theoretical reasoning based on the surface energy parameters of the interacting components in the composite is elaborated to explain the reinforcing effect of talc and wood fiber. The Morphological analysis of the hybrid composite was carried out using the scanning electron microscopy (SEM), to study the interfacial interactions among the different components in the hybrid composite. The quantitative decrease of 36% in coefficient of linear thermal expansion, and the improvement in heat deflection temperature of the hybrid composite was also observed. This investigation was based on the structure–property-processing, co-relationships of the three components in order to obtain hybrid composites.

Construction of PHB and PHBV multiple-gene vectors driven by an oil palm leaf-specific promoter

One of the targets in oil palm genetic engineering programme is the production of polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV) in the oil palm leaf tissues. Production of PHB requires the use of phbA (β-ketothiolase type A), phbB (acetoacetyl-CoA reductase) and phbC (PHB synthase) genes of Ralstonia eutropha, whereas bktB (β-ketothiolase type B), phbB, phbC genes of R. eutropha and tdcB (threonine dehydratase) gene of Escherichia coli were used for PHBV production. Each of these genes was fused with a transit peptide ( Tp) of oil palm acyl-carrier-protein ( ACP) gene, driven by an oil palm leaf-specific promoter ( LSP1) to genetically engineer the PHB/PHBV pathway to the plastids of the leaf tissues. In total, four transformation vectors, designated pLSP15 (PHB) and pLSP20 (PHBV), and pLSP13 (PHB) and pLSP23 (PHBV), were constructed for transformation in Arabidopsis thaliana and oil palm, respectively. The phosphinothricin acetyltransferase gene ( bar) driven by CaMV35S promoter in pLSP15 and pLSP20, and ubiquitin promoter in pLSP13 and pLSP23 were used as the plant selectable markers. Matrix attachment region of tobacco (RB7MAR) was also included in the vectors to stabilize the transgene expression and to minimize silencing due to positional effect. Restriction digestion, PCR amplification and/or sequencing were carried out to ensure sequence integrity and orientation.

Biodegradable Composite Foams of PLA and PHBV Using Subcritical CO2

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.

Renewable resource based biocomposites from natural fiber and polyhydroxybutyrate-co-valerate (PHBV) bioplastic

Abstract Renewable resource based green biocomposites were prepared using a bacterial polyester i.e., poly(hydroxybutyrate-co-valerate) (PHBV) and natural bamboo fiber. Fabrication of the biocomposites was carried out by injection molding following extrusion compounding of PHBV and bamboo fiber with 30 or 40 wt.% fiber. The mechanical, thermo-mechanical and morphological properties of the biocomposites were evaluated. Little variation in the thermo-mechanical and impact properties was observed when the fiber content was varied. The tensile modulus of biocomposites at 40 wt.% fiber improved by 175% as compared to that of neat PHBV. The theoretical tensile modulus of the biocomposites was calculated using Christensen’s equations and compared with the experimental results. It was found to be in near approximation to the experimental data. The storage modulus was affected slightly by the variation of fiber content from 30 to 40 wt.% in biocomposites. The heat deflection temperature of PHBV increased by 9 °C at 40 wt.% of fiber reinforcement. Morphological aspects and thermal stability were studied using scanning electron microscopy and thermo-gravimetric analysis, respectively. In addition, a comparative analysis of bamboo fiber–PHBV with wood fiber–PHBV biocomposites was performed. Statistical analysis of both biocomposites was carried out by performing a two-way ANOVA on their tensile and flexural moduli in order to evaluate the effect of fiber type and content in the PHBV matrix.

Morphology and barrier properties of solvent cast composites of thermoplastic biopolymers and purified cellulose fibers

This paper shows and discusses the morphology, thermal and transport properties of solvent cast biocomposites of poly(lactic acid) (PLA), polyhydroxybutyrate-co-valerate (PHBV) and polycaprolactones (PCL) containing purified alfa micro-cellulose fibers as a function of filler content. The SEM, optical microscopy and Raman imaging results indicate that a good dispersion of the fibers in the matrix was achieved for the three biopolymers. However, detrimental fiber agglomeration was clearly observed to take place for samples with fiber contents in excess of 5 wt%. The heat of fusion (related to crystallinity) of the semicrystalline PCL and PHBV biopolymers was seen to decrease, particularly in low fiber content biocomposites, but it seemed to increase slightly in the highly amorphous PLA biocomposites. In accordance with the morphology data, water and d-limonene direct permeability were seen to decrease to a significant extent in the biocomposites with low fiber contents. The permeability reduction was mostly related to a decrease in diffusivity but solubility was also found to be favorable. The main conclusion from this work is that purified cellulose fibers can also be used to enhance the barrier properties of thermoplastic biopolyesters of interest in, for instance, packaging and membrane applications.

Fabrication and Characterisation of Polymer and Composite Scaffolds Based on Polyhydroxybutyrate and Polyhydroxybutyrate-Co-Hydroxyvalerate

This paper reports the fabrication and characterization of three-dimensional, highly porous polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-valerate (PHBV) and composite scaffolds made by the emulsion freezing / freezing-drying technique. Freeze-drying of the polymer/solvent/ water phase emulsions produced hard and tough scaffolds with interconnected pores. The effects of the fabrication parameters such as polymer concentration in emulsions and emulsion stabilizer were examined and optimized. The density of polymer scaffolds was found to increase with an increasing polymer concentration. Structural analyses of selected samples using scanning electron microscopy indicated that the scaffolds had pore sizes ranging from several microns to a few hundred microns. The porosity of scaffolds of up to 85% was achieved and it increased with a decreasing polymer concentration. It was found that mechanical properties of composite scaffolds increased with the increasing amount of hydroxyapatite (HA) incorporated in the scaffolds.

Wood fiber reinforced bacterial bioplastic composites: Fabrication and performance evaluation

Renewable resource based green composites were prepared from wood fiber and a bacterial polyester i.e., polyhydroxybutyrate-co-valerate (PHBV) via extrusion–injection molding process. The fabricated PHBV based biocomposites contained 10–40 wt% of the maple wood fiber. The effects of increasing wood fiber weight contents on mechanical, thermomechanical and morphological properties of the PHBV based biocomposites were evaluated. The tensile and flexural modulus of PHBV based biocomposites reinforced with 40 wt% of wood fiber was improved by ∼167% when compared with neat PHBV. The theoretical tensile modulus values of PHBV based biocomposites obtained from Halpin-Tsai and Tsai-Pagano equations were consistent with the experimental tensile modulus values. The storage modulus values of the PHBV based biocomposites also exhibited the increasing trend with the enrichment of wood fiber in PHBV matrix. The effectiveness of fibers on the storage modulus of the composite was evaluated by a coefficient factor, C. The heat deflection temperature was increased by 21%, while coefficient of linear thermal expansion was reduced by 18% of PHBV based biocomposites having 40 wt% of wood fiber content. Morphological aspects and thermal stability of the biocomposites were studied using scanning electron microscopy and thermogravimetric analysis, respectively.

Optimal carbon source switching strategy for the production of PHA copolymers

AbstractDuring polymerization in a nongrowing cell population of Ralstonia eutropha, alternating between two different carbon sources (fructose and fructose/valeric acid) could lead to the production of block copolymers consisting of blocks of homo‐poly‐3‐hydroxybutyrate (PHB) and polyhydroxybutyrate‐co‐valerate (PHBV) copolymer. The problem of finding the optimal number of carbon source switches and corresponding switching times that maximize the final concentration of diblock copolymers (PHB‐PHBV and PHBV‐PHB) was addressed. It was mathematically formulated in the mixed‐integer nonlinear programming (MINLP) framework, which allows the decomposition of the original problem into the primal and master problems. The primal problem corresponds to the original problem for a fixed number of carbon source switches, whereas the master problem consists of finding the number of carbon source switches that maximizes the optimum solutions of all possible primal problems. The global optimum was obtained for 39 carbon source switches. It corresponds to a mass fraction of 50.6% of final diblock copolymer concentration over the final total polymer concentration.

The effect of melt-processing on the degradation of selected polyhydroxyacids: polylactides, polyhydroxybutyrate, and polyhydroxybutyrate- co-valerates

A series of resorbable polyhydroxyacids were studied by size exclusion chromatography (SEC), viscosity measurements, and differential scanning calorimetry (DSC) for the effect of the injection moulding process on the molecular weight and thermal properties of the polymers. The polymers studied were polylactides (PLA), polyhydroxybutyrate (PHB) and polyhydroxybutyrate- co-valerate (PHB/VA) (5–22% VA content). All polylactides underwent extensive degradation, in the range of 50–88%, and an increase in molecular weight distribution (MWD) following injection moulding at temperatures ranging from 130 to 215°C. In contrast to the polylactides, the decrease in molecular weight of the PHB and PHB/VA polymers after injection moulding at temperatures from 135 to 160°C was less dramatic, in the range of 4–53%. This was accompanied by a decrease of the MWD. No evidence for low molecular weight non-volatile degradation products was observed. Injection moulding led to a decrease in the melting temperature ( T m) and the heat of melting ( ΔH m) of PLA. Conversely, the moulding process did not significantly affect the melting temperature and heat of melting of polyhydroxybutyrate/valerates.