PHBV Blends Research Articles

Extruded foams from microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and its blends with cellulose acetate butyrate

AbstractExtrusion foaming of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and two blends of PHBV with cellulose acetate butyrate (CAB) were studied using an azodicarbonamide (AZ) blowing agent and a single‐screw extruder. The concentration of the blowing agent was systematically varied from 0 to 4.0 phr to achieve maximum density reduction reaching 41%, as well as to obtain information on the dependence of cell growth on blowing agent concentration. Extruded foams were characterized in terms of their bulk densities and cellular morphologies. Stereological and statistical methods permitted full characterization of the three‐dimensional cell size distributions, assessing the average cell diameters (ranging from 58 to 290 μm) and cell densities (ranging from 650 to 180,000 cm−3). The variation in cellular morphology among foams consisting of different polymer matrix or blowing agent concentration was compared. The results were analyzed by considering the influence of viscoelastic properties of the polymer matrix on the bubble growth during foaming. Significantly higher melt viscosity and elasticity and reduced gas solubility of the PHBV/CAB blends are believed to retard cell coalescence and collapse during foam expansion, resulting in more uniform cell size distribution and better homogeneity of cellular morphology. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

The Effects of Process Engineering on the Performance of PLA and PHBV Blends

AbstractThe effects of process engineering in the fabrication of PHBV, PLA and their blends prepared by melt blending are studied. The elongation of an optimized blend can be improved by 148 and 250% over the virgin PHBV and PLA polymers, respectively. DSC shows that the two polymers are immiscible in blends of any composition. The crystallinity of PHBV is hindered by the presence of PLA. UV‐Vis demonstrates the opacity of the blend with incorporation of PHBV to the PLA phase. The observed tensile modulus of the optimized sample is compared with theoretical values from the rule of mixtures. Gordon‐Taylor's equation is applied on the glass transition temperatures for theoretical modeling to explain the miscibility of the polymers. magnified image

Action of soil microorganisms on PCL and PHBV blend and films

Poly(hydroxybutyrate-co-valerate) (PHBV) and poly(e-caprolactone) (PCL) PCL/PHBV (4:1) blend films were prepared by melt-pressing. The biodegradation of the films in response to burial in soil for 30 days was investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry (TG). The PHBV film was the most susceptible to microbial attack, since it was rapidly biodegraded via surface erosion in 15 days and completely degraded in 30 days. The PCL film also degraded but more slowly than PHBV. The degradation of the PCL/PHBV blend occurred in the PHBV phase, inducing changes in the PCL phases (interphase) and resulting in an increase of its crystalline fraction.

PHBV/PLLA-based composite scaffolds containing nano-sized hydroxyapatite particles for bone tissue engineering

Composite scaffolds made of PHBV/PLLA blends and nano-sized hydroxyapatite (HA) particles can be useful for bone tissue engineering as different blends of PHBV with PLLA should have higher degradation rates than PHBV itself and scaffolds containing bioactive HA particles will provide desired osteoconductivity. In this investigation, composite scaffolds were produced via an emulsion freezing/freeze-drying process and subsequently characterised using several techniques. Highly porous and interconnected scaffolds with porosity greater than 70% could be made. It was found that the crystallinity of PHBV in the scaffolds was decreased due to blending with the PLLA polymer, which is beneficial for the faster degradation of the scaffolds in vitro and in vivo. It was shown that the incorporation of HA nanoparticles enhanced compressive mechanical properties of scaffolds.

Electrospun Biodegradable Nanofibrous Mats for Tissue Engineering

In this study, a microbial polyester, poly(3-hydroxybutyrate-co- 3-hydroxyvalerate) (PHBV), and its blends were electrospun into PHBV (10% w/v), PHBV (15% w/v), PHBV-PLLA (5% w/v), PHBV-PLGA (50:50) (15% w/v) and PHBV-P(L,DL)LA (5% w/v) fibrous scaffolds for tissue engineering. Various processing parameters affected the morphology and the dimensions of beads formed on the fibers. Concentration was highly influential on fiber properties; as it increased from 5 to 15% (w/v), fiber diameter increased from 284 +/- 133 nm to 2200 +/- 716 nm. Increase in potential (from 20 to 50 kV) did not lead to the expected decrease in fiber diameter. The blends of PHBV with lactide-based polymers led to fibers with less beads and more uniform diameter. The surface porosities for PHBV10, PHBV15, PHBV-PLLA, PHBV-PLGA (50:50) and PHBV-P(L,DL)LA were 38.0 +/- 3.8, 40.1 +/- 8.5, 53.8 +/- 4.2, 50.0 +/- 4.2 and 30.8 +/- 2.7%, respectively. In vitro studies using human osteosarcoma cells (Saos-2) revealed that the electrospun scaffolds promoted cell growth and penetration. Surface modification with oxygen plasma treatment slightly improved the improved the results in terms of cell number increase and significantly improved spreading of the cells. All scaffolds prepared by electrospinning have implied significant potential for use in further studies leading to bone tissue engineering applications. The PHBV-PLLA blend appeared to yield the best results regarding cell number increase, their attachment and spreading inside and on the scaffold.

Fully biodegradable poly(3-hydroxybutyrate-co-hydroxyvalerate)/poly(ethylene succinate) blends: Phase behavior, crystallization and mechanical properties

Poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) and poly(ethylene succinate) (PES) are both biodegradable semicrystalline polyesters. Phase behavior, crystal structure, crystallization kinetics, and mechanical properties of fully biodegradable PHBV/PES blends were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), wide angle X-ray diffraction (WAXD), and tensile tests in detail. PHBV is immiscible with PES as evidenced by the two composition independent glass transition temperatures corresponding to those of neat components. Moreover, the biphasic melt further confirms the immiscibility between PHBV and PES. Nonisothermal and isothermal crystallization of PHBV/PES blends were studied by DSC. In the case of isothermal crystallization the crystallization rates of PHBV and PES decrease with increasing the content of the other component for both PHBV-rich and PES-rich blends; however, the crystallization mechanisms do not change. The mechanical properties of PHBV/PES blends were examined by tensile testing. It is found that the tensile strength, elongation at break, Young’s modulus, and toughness of PHBV blends can be adjusted by changing blend composition. For PHBV-rich blends, blending some amount of PES can improve the elongation at break significantly while still keeping considerably high tensile strength and Young’s modulus.

Miscibility in blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(ɛ-caprolactone) induced by melt blending in the presence of supercritical CO2

Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ɛ-caprolactone) (PCL) have been produced by melt blending in the presence of supercritical CO2. Infrared spectroscopy has shown that supercritical CO2 can induce melting in PHBV at temperatures below the melting point. The miscibility of the PCL–PHBV blend system produced by both mechanical and supercritical means has been characterised by a combination of differential scanning calorimetry and dynamic mechanical thermal analysis. It has been shown that PHBV–PCL blends produced using mechanical means were immiscible, whereas the same blends produced using supercritical methods were found to be miscible as evidenced by a decrease in the glass transition temperature of the PHBV component. The development of miscibility is discussed in terms of enhanced interdiffusion resulting from the action of supercritical CO2. In addition, the infrared spectrum of the blends produced using supercritical CO2 showed negligible levels of the degradation product crotonic acid. Whereas in the samples produced using mechanical blending without supercritical CO2, there was a significant increase in the level of crotonic acid, which was interpreted as evidence of degradation.

Studies on poly (hydroxy alkanoates)/(ethylcellulose) blends

Biodegradable polymers represent one of the most significant area of research today. Among these polymers, poly (β-hydroxy butyrate co β′-hydroxy valerate) i.e. PHBV have received special attention because of their unique combination of properties. They are perfectly biocompatible, biodegradable polymers and can be processed by any conventional technique. In the present study an attempt has been made to develop the biodegradable blends of PHBV by blending them with ethyl cellulose (EC). Ethyl cellulose has been selected to monitor the biodegradation rate of PHBV and also for making the blends cost effective. The blends are thoroughly characterized for their compatibility, by the measurement of viscosity of blends and through FT-IR. Various applications of PHBV/EC blend in agriculture and pharmaceutical industries are being explored.

Thermal properties of blends of poly(hydroxybutyrate-co-hydroxyvalerate) and poly(styrene-co-acrylonitrile)

Thermal properties of blends of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and poly(styrene-co-acrylonitrile) (SAN) prepared by solution casting were investigated by differential scanning calorimetry. In the study of PHBV-SAN blends by differential scanning calorimetry, glass transition temperature and melting point of PHBV in the PHBV-SAN blends were almost unchanged compared with those of the pure PHBV. This result indicates that the blends of PHBV and SAN are immiscible. However, crystallization temperature of the PHBV in the blends decreased approximately 9–15°. From the results of the Avrami analysis of PHBV in the PHBV-SAN blends, crystallization rate constant of PHBV in the PHBV-SAN blends decreased compared with that of the pure PHBV. From the above results, it is suggested that the nucleation of PHBV in the blends is suppressed by the addition of SAN. From the measured crystallization half time and degree of supercooling, interfacial free energy for the formation of heterogeneous nuclei of PHBV in the PHBV-SAN blends was calculated and found to be 2360 (mN/m)3 for the pure PHBV and 2920–3120 (mN/m)3 for the blends. The values of interfacial free energy indicate that heterogeneity of PHBV in the PHBV-SAN blends is deactivated by the SAN. This result is consistent with the results of crystallization temperature and crystallization rate constant of PHBV in the PHBV-SAN blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 673–679, 2000

Biodegradation of starch-poly(β-hydroxybutyrate-co-valerate) composites in municipal activated sludge

Injection-molded composites were prepared by blending PHBV5 with native cornstarch (30% and 50%) and with cornstarch precoated with PEO as a binding agent. These composites were evaluated for their biodegradability in municipal activated sludge by measuring changes in their physical and chemical properties over a period of 35 days. All composites lost weight, ranging from 45 to 78% within 35 days. Interestingly, the extent and rate of weight loss were quite similar in PHBV composites with no starch, with 30% starch, and with 50% starch. Weight loss was slowest in PHBV blends prepared with PEO-coated starch. For all samples, the weight loss was accompanied by a rapid deterioration in tensile strength and percentage elongation. The deterioration of these mechanical properties exhibited a relative rate of PHBV>starch-PHBV>PEO-coated starch-PHBV. Changes in starch/PHBV composition after biodegradation were quantified by FTIR spectroscopy. Increasing the starch content resulted in more extensive starch degradation, while the PHBV content in the blends became less susceptible to hydrolytic enzymes.

Biodegradable blends and composites of polycaprolactone and starch derivatives

High-molecular-weight (40 000 and 80 000 g mol −1) polycaprolactone (PCL) has been blended with high-amylose corn starch (HA-CS, 70% amylose) and waxy corn starch granules, as well as with the non-granular starch acetate derivatives. The properties of films of these blends were evaluated using differential scanning calorimetry, dynamic mechanical thermal analysis and Instron tensile testing, and compared with similar blend films made with poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV, 11.6% HV content). All of the PCL blends and the PHBV blends with granular starch were found to be mechanically compatible but phase-separated. The PHBV/starch acetate blends were also phase-separated, but were too brittle for mechanical testing. The PCL/HA-CS blends were the strongest, with ≈15% lower tensile strength and a 50% higher modulus than PCL, up to 25 wt% HA-CS. Optical microscopy showed that the small size of the HA-CS granules (10 μm) and good dispersion of the granules in the PCL matrix were the reasons for the good mechanical properties compared with the other blends. Crosslinking was found to improve the thermal properties of the blends.