Effect of glassy carbon addition and photodegradation on the biodegradation in aqueous medium of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/glassy carbon green composites

The use of biodegradable polymers is an interesting way to reduce the polymeric waste accumulation in the environment. However, the addition of fillers to biodegradable polymer matrices may decrease their biodegradability. Glassy carbon (GC) is a promising carbon material that can be employed as a filler in the production of antistatic packaging utilized to protect electronic components. The use of a biodegradable polymeric matrix such as poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) can be an excellent alternative for the preparation of green composites to be used in these packages. This work aims to evaluate the effect of the GC addition and the GC particle size on the biodegradability of the PHBV matrix, as well as to study the result of the employment of a previous photodegradation treatment on the biodegradation in aqueous medium of PHBV/GC composites. Scanning electron microscopy, residual weight measurement (%) and surface roughness showed that GC does not interfere negatively with PHBV biodegradability. Differential scanning calorimetry analysis and residual weight measurement permitted to suggest that the increase in the crystallinity degree of PHBV and PHBV/GC samples occasioned by the ultraviolet radiation hindered the water and enzyme access to the bulk of the materials, decreasing the biodegradability.     

聚(3-羟基丁酸酯-co-3-羟基戊酸酯)的改性研究

细菌合成的聚（3－羟基丁酸酯－co-3-羟基戊酸酯）（PHBV）具有优良的生物降解和生物相容性。本文从热性能、机械性能和降解性等方面综述了PHBV近年来在物理改性和化学改性方面的进展。     

Environmental factors and kinetics of microbial degradation of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) in an aqueous medium

Environmental factors such as oxygen, temperature, and microbial species may have significant effects on decomposition of biodegradable polymers. A representative biodegradable, thermoplastic polymer, poly(3‐hydroxybutyrate‐co‐hydroxyvalerate) (PHBV), was decomposed in an aqueous medium under controlled laboratory conditions by soil microbes for the intrinsic degradation kinetics and the effects of the environmental factors on polymer biodegradation. The amount of proteins, including the PHBV depolymerases, that attached to the polymer surfaces was quite constant during the period of significant mass loss of the polymer specimens. The microbial polymer degradation followed a zero‐order rate model, so the residual mass fraction of PHBV films declined linearly with time. The mixed aerobic microbial organisms from fertile soil showed a higher activity of polymer degradation than an aerobic PHBV‐producing bacterium and the mixed anaerobes in the same soil. The mixed anaerobic microorganisms from barren soil decomposed the polymer at a slower rate than the anaerobes from fertile soil, and this was attributed to fewer microbial cells in the barren soil instead of the difference in the microbial species. The temperature effect on PHBV degradation can be described with an Arrhenius equation, and the activation energy is around 16 kcal/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 205–213, 2003     

Formulation of silver chloride/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (AgCl/PHBV) films for potential use in bone tissue engineering

Orthopedic implant failure due to bacterial infection has been a concern in bone tissue engineering. Here, we have formulated a composite made of biodegradable polymer, i.e., poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and silver chloride. Ag⁺ ions released from the AgCl/PHBV film can promote an aseptic environment by promoting inhibition of bacterial growth while maintaining bone cell growth, depending on AgCl loading. The objective of this study is to formulate AgCl/PHBV film(s) of varying composition so as to evaluate the dependence of AgCl loading in the film on antimicrobial activity and cytotoxicity. The release kinetics of silver ions from AgCl/PHBV film in aqueous and Dulbecco's Modified Eagle Medium showed similarity in the initial burst of ions during the first day of desorption followed by a gradual release of ions over extended time period. The antibacterial efficacy of AgCl/PHBV film against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa was evaluated by microbiological assay, while cytotoxicity of the film toward MC3T3‐E1 cells was determined by MTT assay. For all compositions studied, a clear zone of inhibition around AgCl/PHBV film was noticed on a modified Kirby‐Bauer disk diffusion assay. We established that MC3T3‐E1 cell attachment on AgCl/PHBV film is strongly related to loading of AgCl in the film. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45162.     

Effect of carbon nanotubes on the biodegradability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nanocomposites

In this work, the effect of carbon nanotubes (CNT) on the biodegradability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanocomposites with 1 and 2% (w/w) of CNT has been evaluated by biodegradation assays in aqueous medium containing microorganisms extracted from garden soil. After biodegradation process, samples of PHBV and PHBV/CNT were compared regarding magnitude of degradation by visual macroscopic analysis, by measurement of percentage of weight loss and by scanning electron microscopy (SEM). The samples were further characterized regarding roughness and hydrophilicity by contact angle measurement. The final residue resultant from biodegradation of PHBV/CNT was analyzed in a FEI Inspect F50 field emission scanning electron microscope (FESEM) in order to verify the presence of CNT. Our results indicated that CNT did not compromise the biodegradability of PHBV matrix although the biodegradation rate has decreased with the increase of CNT content as shown by the weight loss measurements. SEM analysis of PHBV/CNT nanocomposites after biodegradation process showed increased amount of CNT exposed at the matrix surface suggesting the possibility of CNT recovering after the biodegradation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48020.     

Effect of graft modification with poly(N‐vinylpyrrolidone) on thermal and mechanical properties of poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

Poly(N‐vinylpyrrolidone) (PVP) groups were grafted onto poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) backbone to modify the properties of PHBV and synthesize a new novel biocompatible graft copolymer. The effect of graft modification with PVP on the thermal and mechanical properties of PHBV was investigated. The thermal stability of grafted PHBV was remarkably improved while the melting temperature (T_m) was almost not affected by graft modification. The isothermal crystallization behavior of samples was observed by polarized optical microscopy and the results showed that the spherulitic radial growth rates (G) of grafted PHBV at the same crystallization temperature (T_c) decreased with increasing graft yield (graft%) of samples. Analysis of isothermal crystallization kinetics showed that both the surface free energy (σ_e) and the work of chain‐folding per molecular fold (q) of grafted PHBV increased with increasing graft%, implying that the chains of grafted PHBV are less flexible than ungrafted PHBV. This conclusion was in agreement with the mechanical testing results. The Young's modulus of grafted PHBV increased while the elongation decreased with increasing graft%. The hydrophilicity of polymer films was also investigated by the water contact angle measurement and the results revealed that the hydrophilicity of grafted PHBV was enhanced. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) particles in O/W emulsion

In the present paper, we investigate the preparation of polymeric particles based on the biodegradable polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). A new technique for PHBV particle preparation has been developed. This method utilizes the thermoreversible gelation of PHBV in toluene. Particles have been obtained by the secondary dispersion technique in a three-step procedure: (a) preparation of PHBV solution in toluene; (b) preparation of O/W emulsion by ultrasound followed by the gel formation in toluene/PHBV droplets; and (c) toluene extraction. In the present study we investigated the influence of the stabilizer type and its concentration in the aqueous phase, ultrasound power, and PHBV concentration in toluene on the size and stability of the formed droplets as well as the final PHBV particles. It has been found that PEO/PS block copolymers are the best stabilizers for the present system as compared to conventional tensides such as SDS or CTAB. It has been found that PEO/PS block copolymers allow obtaining PHBV particles with a regular shape and controlled dimensions after toluene extraction. The minimal size of the PHBV particles obtained by this technique was ca. 100 nm. The obtained particles exhibit a relatively broad particle size distribution and the particle shape is strongly affected by the block copolymer composition, ultrasound power and the way of toluene extraction.     

Synthesis and characterization of multi‐block copolymers containing poly [(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] and poly(ethylene glycol)

Various problems, including high crystallinity, high melting temperature, poor thermal stability, hydrophobicity and brittleness, have impeded many practical applications of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (PHBV) as an environmentally friendly material and biomedical material. In the work reported here, multi‐block copolymers containing PHBV and poly(ethylene glycol) (PHBV‐b‐PEG) were synthesized with telechelic hydroxylated PHBV as a hard and hydrophobic segment, PEG as a soft and hydrophilic segment and 1,6‐hexamethylene diisocyanate as a coupling reagent to solve the problems mentioned above. PHBV and PEG blocks in PHBV‐b‐PEG formed separate crystalline phases with lower crystallinity levels and lower melting temperatures than those of phases formed in the precursors. The crystallite dimensions of the two blocks in PHBV‐b‐PEG were smaller than those of the corresponding precursors. Compared to values for the original PHBV, the maximum decomposition temperature of the PHBV block in PHBV‐b‐PEG was 16.0 °C higher and the water contact angle was 9° lower. In addition, the elongation at break was 2.8% for a pure PHBV fiber but 20.9% for a PHBV/PHBV‐b‐PEG fiber with a PHBV‐b‐PEG content of 30%. PHBV‐b‐PEGs can overcome some of the disadvantages of pure PHBV; it is possible that PHBV might be a good candidate for the formulation of environmentally friendly materials and biomedical materials. Copyright © 2010 Society of Chemical Industry     

Fabrication and improved performance of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) for packaging by addition of high molecular weight natural rubber

The packaging industry is searching for alternative materials to attain environmental sustainability. Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate (PHBV) is a semicrystalline polymer that meets this sustainability goal since it is bioderived and biodegradable. However, its brittle nature and relatively high water permeation and transmission rates make it unsuitable for packaging applications. In addition, PHBV has poor mechanical, thermal, and rheological properties above 160 °C, limiting its use in cast sheets and thermo‐formed packaging applications. To improve these properties, new blends of PHBV with high molecular weight natural rubber at 5, 10, 15, and 25% by weight were fabricated, and physico‐chemical properties of the blends were characterized. The rubber in the blends aided in the following: increased thermal stability since the complex viscosities of the blends were improved by one log over pure PHBV at 170 °C, created more uniform melting peaks attesting to improved homogeneity, decreased water permeation to a level similar to that of traditional thermoplastics; increased the elongation at break, and stabilized the Young's modulus. Therefore, these blends can potentially be used in‐place of traditional, petroleum‐based thermoplastics in cast sheets and thermoforms. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43937.     

Comparison of covalent and noncovalent interactions of carbon nanotubes on the crystallization behavior and thermal properties of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

In this study, multiwalled carbon nanotubes (MWCNTs) were dispersed into a poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) matrix, in which PHBV was either covalently attached to the nanotubes through an esterification reaction between the carboxylic groups of functionalized MWCNTs and the hydroxyl groups of PHBV with toluene diisocyanate as a coupling agent or physically mixed to result in only noncovalent interactions. The structure, crystallization behavior, and thermal properties of the resulting nanocomposites were studied. We found that the crystallization of PHBV grafted onto the MWCNTs (PHBV‐g‐MWCNTs) was markedly hindered and exhibited an exothermic peak caused by cold crystallization, whereas the nonisothermal crystallization of PHBV was enhanced because a heterogeneous nucleation effect appeared in the PHBV/MWCNTs. Moreover, the maximum decomposition temperature of the PHBV‐g‐MWCNTs was improved by about 14.4°C compared with that of the PHBV/MWCNTs and by about 23.7°C compared with that of the original PHBV. Furthermore, the PHBV‐g‐MWCNTs exhibited the wider melt‐processing window than the PHBV/MWCNTs and original PHBV. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4299–4307, 2013     

Biodegradation of PHBV/GNS nanocomposites by Penicillium funiculosum

Biodegradable polymer nanocomposites are an essential alternative to minimize the generation of polymeric solid waste that shows short shelf life and difficult degradation. In this study, nanocomposites based on poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) were prepared by the incorporation of different contents, 0.25, 0.50, 0.75, and 1.00 wt % of graphite nanosheets (GNS), using a solution casting method. The investigation of the PHBV samples biodegradation was made using filamentous fungi (Penicillium funiculosum) in solid medium. Characterization of the material was performed by weight loss, differential scanning calorimetry, carbonyl index determined by Fourier transformed infrared spectroscopy, contact angle, roughness, and scanning electron microscopy. Results revealed that PHBV/GNS nanocomposites can be totally degraded in the presence of Penicillium funiculosum; however, it will be necessary high incubation period. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44234.     

The morphology and degradation behavior of electrospun poly(3‐hydroxybutyrate)/Magnetite and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/Magnetite composites

Electrospinning of biodegradable poly(3‐hydroxybutyrate) (PHB)/magnetite and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/magnetite composites in 2,2,2‐trifluoroethanol (TFE) and chloroform are investigated to develop nonwoven nanofibrous structure. Ultrafine PHB/magnetite fibers are obtained and the resulting fiber diameters are in the range of 690–710 nm and 8.0–8.4 µm for the polymer dissolved in TFE and chloroform. The surface of PHB composites fiber fabricated in chloroform contains porous structures, which are not observed for the sample of PHB composites fiber dissolved in TFE. The fiber diameters for PHBV5/magnetite composites are in the range of 500–540 nm and 2.3–2.5 µm, depending on the use of TFE and chloroform. The average diameters of PHBV5/magnetite composite fibers are smaller than those of PHB/magnetite composites fiber. All electrospun PHB/magnetite and composite fibers are superparamagnetic. The degradation behaviors of PHB/magnetite and PHBV5/magnetite composite fibers were investigated using Caldimonas manganoxidans. For the fabricated composite fibers, it is found that the degradation rate increased with the increasing loading of magnetite nanoparticles. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41070.     

Influence of particle size and glassy carbon content on the thermal,mechanical, and electrical properties of PHBV/glassy carbon composites

Glassy carbon (GC) constitutes a promising carbonaceous material that can be employed as an antistatic agent in the development of antistatic packaging used in the electronics industry. Thus, the present work aims at developing biodegradable and antistatic packaging from poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) reinforced with different GC contents (0, 0.5, 1.0, 2.5, and 5.0 wt%) and different GC particle size (<45 μm and > 75 μm) using extrusion processing. differential scanning calorimetry analysis shows that the addition of GC decreases the degree of crystallinity (X_c) of PHBV, which can explain the reduction of its stiffness. Impedance spectroscopy results reveal that the use of GC contents greater than 2.5 wt% (GC > 75 μm) makes possible the obtainment of a material with an electrical resistivity small enough to be used in antistatic packaging. It can be concluded that GC is an interesting alternative of antistatic agent for electrically dissipative packaging.     

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/clay nanocomposites for replacement of mineral oil based materials

Due to the short‐running of mineral oil and the increasing waste problem, biopolymers become more and more important. However, they still suffer from disadvantages, and in many cases, their properties are still insufficient to replace mineral oil based plastics. In this study, the biobased and biodegradable polymer poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) is reinforced by different clay types and their effect on the properties profile is investigated. Natural as well as organomodified montmorillonite and bentonite are dispersed by melt mixing within the PHBV matrix. Thermal stability, crystallization behavior, and dynamic mechanical properties as well as the materials morphology is analyzed. Dispersion state of the nanoclay is found to be crucial for the improvement of the material performance and well dispersed organomodified clays reveal to simultaneously improve different properties of PHBV matrix. POLYM. COMPOS., 34:1033–1040, 2013. © 2013 Society of Plastics Engineers     

Bio-based blends from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and natural rubber for packaging applications

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a promising bioplastic but has limited packaging applications due to its brittleness and poor processability. Incorporation of highly viscous high-molecular-weight natural rubber (HMW-NR, gel extracted from NR) into PHBV can improve these properties. HMW-NR is not commercially available, impeding commercialization of the PHBV/rubber blends. Therefore, an organic peroxide was used to selectively crosslink NR to increase its viscosity during its melt blending with PHBV. The PHBV/NR blends were fabricated through a two-step extrusion process using a twin-screw extruder. The blends contained two phases with crosslinked rubber being dispersed in PHBV, and had clear rubber loading-dependent differences in performance. The thermal stability and melt strength of the blends were enhanced over pristine PHBV, indicating improved processability. The flexibility and toughness of the blends were improved by 59 and 20%, respectively, compared with pristine PHBV, and were comparable to commercial petroleum-based plastics. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47334.     

Microscopy and microbeam X-ray analyses in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with amorphous poly(vinyl acetate)

Double ring-banded spherulites of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV with 12 wt% 3HV) blending with 30 wt% amorphous poly(vinyl acetate) (PVAc) were examined using polarized light optical microscopy (POM), scanning electron microscopy (SEM), atomic-force microscopy (AFM) and micro-beam X-ray diffraction. A ring-banded spherulite of PHBV/PVAc 70/30 blend was linearly scanned across the bands in 5 μm steps by means of micro-beam X-ray diffraction. Solvent-etching and fracturing were utilized for probing the interior lamellar textures of the blend samples. Detail interior lamellar orientations in bulk film of PHBV three-dimensional ring-banded spherulites were revealed. SEM and micro-beam X-ray diffraction results suggest that the PHBV lamellar orientation gradually change along the radial growth direction with right-handed rotation sense. The blending effect in band pattern (width and regularity) of PHBV/PVAc blend was discussed.     

The effects of PHBV-g-MA compatibilizer on morphology and properties of poly(3-hydroxybutyrate-Co-3-hydroxyvalerate)/olive husk flour composites

The paper provides some experimental data on the effects of a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) grafted maleic anhydride (PHBV-g-MA) used as the compatibilizer for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/olive husk flour (OHF) composites prepared by melt compounding. The natural filler was added to PHBV at various contents, i.e. 10, 20, and 30 wt%, while the amount of PHBV-g-MA was 5 wt% based on neat PHBV. Morphology, contact angle measurements, water absorption (WA), mechanical, viscoelastic, and barrier properties of the various composites were investigated with and without the compatibilizer. The study showed through scanning electron microscopy that the addition of PHBV-g-MA to PHBV/OHF composites resulted in better and finer dispersion of the filler in the matrix, even at a higher content ratio, indicating improved affinity between the components. This is in agreement with the decrease in both surface energy and WA. Furthermore, tensile and dynamic mechanical measurements indicated a reinforcing effect of OHF in PHBV composites, being more pronounced in the presence of PHBV-g-MA. The barrier properties against oxygen and water vapor were also improved for the compatibilized composites.     

Understanding external plasticization of melt extruded PHBV–wheat straw fibers biodegradable composites for food packaging

The objective of this work is to get further knowledge on the external plasticization mechanisms of melt extruded polyhydroxyl‐3‐butyrate‐co?3‐valerate (PHBV) when combined with wheat straw fibers (WSF). Different types of biodegradable substances, all authorized for food contact according to the European regulation, i.e., acetyltributyl citrate (ATBC), glycerol triacetate (GTA) and (PEG) at different molecular weights, were tested at different percentages (5, 10 and 20 wt %). Thermal and mechanical characterization of PHBV/plasticizer blends showed that a significant plasticizing effect was obtained using hydrophobic substances such as ATBC and GTA, with an increase of the elongation at break from 1.8% up to about 6% for an additive content of 10 wt %. However, the incorporation of WSF in plasticized PHBV led to a dramatic decrease in the elongation at break of composites, neutralizing the increase of this parameter by the addition of the plasticizers. The stress at break of plasticized films was also significantly decreased by the introduction of fibers. Such a loss of ductility was mainly explained by the occurrence of microscopic defects in the materials induced by the presence of fibers and to a poor adhesion at the fiber/matrix interface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41611.     

Natural polyphenol tannic acid reinforced poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) composite films with enhanced tensile strength and fracture toughness

Novel fully biodegradable composites were successfully prepared by solution casting. The mechanical properties, chemical structure and intermolecular interaction, the melting and crystallization behaviors, and crystalline morphologies of the Tannic acid (TA)/PHBV composites were investigated. Uniaxial tensile mechanical testing results show that both tensile strength and fracture toughness were enhanced. Fourier transform infrared (FTIR) results confirm the intermolecular hydrogen bonding interactions in composites. Differential scanning calorimetric (DSC) studies show that there is a significant increase in T_g and T_cc, and a decrease in melting temperature of TA/PHBV composites. The crystal growth behaviors and crystalline morphologies results were showed that with the addition of TA component, the size of PHBV spherulites reduces, and the number of PHBV spherulites increases significantly. POLYM. COMPOS., 36:2303–2308, 2015. © 2014 Society of Plastics Engineers     

Improvement of thermal properties of biodegradable polymer poly(3‐hydroxybutyrate) by modification with acryloyloxyethyl isocyanate

Poly(3‐hydroxybutyrate) (PHB) is one type of polyhydroxyalkanoates often used as a biomedical material due to its biodegradable and biocompatible nature. However, the mechanical and thermal properties of PHB must be improved before it can be used in a wider variety of biomedical applications. To improve the thermal properties of biodegradable PHB, various reaction conditions were studied. Results demonstrate that reacting PHB with acryloyloxyethyl isocyanate (AOI), a monomer with dual functional groups, produces a modified PHB material with markedly improved thermal properties. The 10% thermal decomposition temperature for PHB modified with 5% AOI was 297°C, which was 26.8°C higher than original PHB. The T_g also increased from 4°C to around 30°C for AOI‐modified materials. Additionally, due to the poly(ester‐urethane) structure and hydrogen bonding of polymer materials, the mechanical properties also improved. Thus, this modified PHB biodegradable polymer may have greater application as a biomedical material due to its enhanced thermal and mechanical properties. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers