Morphologies and enzymatic degradability of melt-crystallized poly(3-hydroxybutyric acid-Co-6-hydroxyhexanoic acid)

The films of poly[(R)-3-hydroxybutyric acid-co-10mol% 6-hydroxy-hexanoic acid] (P[(R)-3HB-co-6HH]) were prepared by melt-crystallized method at various crystallization temperatures. The morphologies and properties of melt-crystallized films were characterized by means of x-ray diffraction, differential scanning calorimetry, optical microscopy, and scanning electron microscopy. All of the melt-crystallized films showed the banded spherulite morphology. The enzymatic degradation of melt-crystallized films was carried out at 37 °C in an aqueous solution (pH 7.4) of PHB depolymerase from Alcaligenes faecalis. The rate of enzymatic erosion was strongly dependent on the crystallinity of films, and the highest rate was as large as 2.15 mg·h⁻¹·cm⁻². After enzymatic degradation, the banded morphology of P[(R)-3HB-co-6HH] spherulites was visible, suggesting that PHB depolymerase predominantly hydrolyzes polymer chains on the edges of crystalline lamellar stacks.     

Adsorption effects of poly(hydroxybutyric acid) depolymerase on chain-folding surface of polyester single crystals revealed by mutant enzyme and frictional force microscopy

Adsorption effects of poly(hydroxybutyric acid) (PHB) depolymerase from Ralstonia pickettii T1 on various polymer single crystals were studied using a catalytically inactive mutant of PHB depolymerase by means of transmission electron microscopy (TEM), atomic force microscopy (AFM), and frictional force microscopy (FFM). Six types of polymer single crystals, poly[(R)-3-hydroxybutyric acid] (P(3HB)), poly[(R)-3-hydroxybutyric acid-co-6 mol% (R)-3-hydroxyvaleric acid] (P(3HB-co-6 mol% 3HV)), poly[(R)-3-hydroxybutyric acid-co-8 mol% (R)-3-hydroxyhexanoic acid] (P(3HB-co-8 mol% 3HH)), poly(l-lactic acid) (PLLA), poly(d-lactic acid) (PDLA), and polyethylene (PE), were prepared to examine the influence of an ester bond and stereoregularity of a polymer on the enzymatic adsorption. The numbers of PHB depolymerase enzymes adsorbed on P(3HB) and P(3HB-co-6 mol% 3HV) single crystals were determined as 171 and 183 enzymes/μm² by AFM, respectively. AFM observation revealed that the concentration of PHB depolymerase enzymes adsorbed onto PLLA and PDLA single crystals is much higher compared to those on a P(3HB) single crystal, whereas the concentration of enzyme adsorbed onto PE and P(3HB-co-8 mol% 3HH) single crystals is much less. In addition, the single crystals of each polymer were characterized by TEM and FFM before and after enzymatic treatment by mutant for 1 h at 37 °C. The surface properties of P(3HB), P(3HB-co-6 mol% 3HV), and P(3HB-co-8 mol% 3HH) single crystals were changed by the enzymatic adsorption, whereas the internal structures were not affected. On the basis of these results, the properties of the binding domain of PHB depolymerase to polymer chain-folding surfaces have been discussed.     

Environmental Degradation of Microbial Polyhydroxyalkanoates and Oil Palm-Based Composites

This paper investigates the degradation of polyhydroxyalkanoates and its biofiber composites in both soil and lake environment. Time-dependent changes in the weight loss of films were monitored. The rate of degradation of poly(3-hydroxybutyrate) [P(3HB)], poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-23?mol% 4HB)] and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) [P(3HB-co-9?mol% 3HV-co-19?mol% 4HB)] were investigated. The rate of degradation in the lake is higher compared to that in the soil. The highest rate of degradation in lake environment (15.6?% w/w week^?1) was observed with P(3HB-co-3HV-co-4HB) terpolymer. Additionally, the rate of degradation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-38?mol% 3HV)] was compared to PHBV biofiber composites containing compatibilizers and empty fruit bunch (EFB). Here, composites with 30?% EFB displayed the highest rate of degradation both in the lake (25.6?% w/w week^?1) and soil (15.6?% w/w week^?1) environment.     

Mechanical properties, structure analysis and enzymatic degradation of uniaxially cold-drawn films of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate]

Poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] (P(3HB-co-4HB)) films were prepared by uniaxial cold-drawing from an amorphous preform at a temperature below, but close to the glass transition temperature. Molecular and highly-ordered structures and physical properties of cold-drawn films were investigated by tensile testing, wide-angle X-ray diffraction and small-angle X-ray scattering. Enzymatic degradation of P(3HB-co-4HB) films was performed using an extracellular polyhydroxybutyrate depolymerase purified from Ralstonia pickettii T1. Tensile strength, elongation to break and Young’s modulus of P(3HB-co-4HB) with cold-drawn ratio 1200% reached 290 MPa, 58% and 2.8 GPa, respectively. X-ray fibre diagrams of cold-drawn P(3HB-co-4HB) films showed a strong reflection on the equatorial line, indicating a planar zigzag conformation (β-form) together with 2₁ helix conformation (α-form). The β-form seems to contribute to the high tensile strength, and a new mechanism of generation of the β-form is proposed. The enzymatic degradation rate increased with increasing draw ratio, and increased greatly with increasing 4HB content.     

Degradation of commercially important polyhydroxyalkanoates in tropical mangrove ecosystem

This paper presents the degradation trends of selected polyhydroxyalkanoate (PHA) films in a tropical mangrove environment. The biodegradability of homopolymer poly(3-hydroxybutyrate) [P(3HB)] and its co-polymers, poly(3-hydroxybutyrate-co-5 mol% 3-hydroxyvalerate) [P(3HB-co-5 mol% 3HV)] and poly(3-hydroxybutyrate-co-5 mol% 3-hydroxyhexanoate) [P(3HB-co-5 mol% 3HHx)], was investigated along with P(3HB) films containing 38 wt% titanium dioxide (TiO₂) [P(3HB)-38 wt% TiO₂]. The degradation of these formulations was monitored for 8 weeks at three different zones in an intermediate mangrove compartment along Sungai Pinang, adjacent to a famous fishing village on south of Penang Island. The degradation rate was observed both on the surface and in the sediment and was expressed in percentage of weight loss. The microbial enumeration done using sediment from the different zones indicated similar colony-forming unit (CFU) counts even though differences were noticed in the degradation profile of the various films in the respective zones. The results obtained revealed that co-polymers disintegrated at similar or higher rate than the homopolymer, P(3HB). However, the incorporation of TiO₂ into PHB films caused the degradation rate of P(3HB)-38 wt% TiO₂ composite film to be far slower than all the other PHA films. The overall rate of degradation of all PHA films placed on the sediment surface was slower than those buried in the sediment. Microscopic analyses showed that the surface morphology of P(3HB-co-5 mol% 3HHx) was more porous compared to P(3HB) and P(3HB-co-5 mol% 3HV) films, which may be an important factor for its rapid degradation.     

Microbial synthesis,physical properties,and biodegradability of polyhydroxyalkanoates

Poly((R)-3-hydroxybutyrate), P(3HB), is produced by Alcaligenes eutrophus from fructose or butyric acid. The kinetics and mechanism of P(3HB) biosynthesis are presented. Four types of copolymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly (3-hydroxybutyrate-co-3-hydroxypropionate), poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly (3-hydroxybutyrate-co-4-hydroxybutyrate), are produced by several bacterial strains from various carbon substrates. These microbial polyesters are biodegradable thermoplastics whose physical properties can be regulated by varying the molecular structure and composition of copolymers.     

Crystallization behaviors and morphology of biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Crystallization behaviors and spherulitic morphology of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] with different 4-hydroxybutyrate (4HB) molar fraction were investigated by differential scanning calorimetry and polarized optical microscopy. Crystallization behaviors of P(3HB-co-4HB) are significantly affected by 4HB molar fraction. The melting temperature (T _m), glass transition temperature (T _g), and crystallinity (X _c) decrease with the increase of 4HB molar fraction. Banded spherulites are observed in poly (3-hydroxybutyrate) (PHB) and P(3HB-co-4HB) copolymers. The band spacing decreases with the increase of 4HB molar fraction. The morphology and growth rate of the spherulites strongly depend on 4HB molar fraction and the crystallization temperatures. The introduction of 4HB unit can inhibit the emergence of cracks in PHB spherulites.     

Characterization and enzymatic degradation of microbial copolyester P(3HB-co-3HV)s produced by metabolic reaction model-based system

The two types of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s [P(3HB-co-3HV)s] were produced by Paracoccus denitrificans ATCC 17741 using two different feeding methods. The produced P(3HB-co-3HV)s were fractionated and the copolymer sequence distributions were analyzed by ¹H and ¹³C NMR spectroscopy. It was found that the P(3HB-co-3HV) samples produced by conventional feeding method were statistically random copolymers. The sequence distributions of P(3HB-co-3HV) samples produced by optimization method were different from random P(3HB-co-3HV)s. The thermal properties and melting behaviors were analyzed by differential scanning calorimetry (DSC). These results demonstrated that P(3HB-co-3HV) samples produced by optimization method are close in nature to P(3HB-co-3HV)s rich in long-sequence of block 3HB units, but less in 3HV random regions. The enzymatic degradation profile of P(3HB-co-3HV) films was investigated in the presence of 3-hydroxybutyrate depolymerase from Pseudomonase lemoignei. The degradation process was observed by monitoring the time-dependent change in the weight loss of copolymer films. The surface erosion of copolymer films was qualitatively monitored by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The highest degradation rate of 2.6% per day was observed for random P(3HB-co-38%3HV) produced by conventional method. In comparison, the hydrolysis degradation rates of random P(3HB-co-3HV)s were about one time faster than those of P(3HB-co-3HV)s produced by optimization method.     

Engineering of pha operon on Cupriavidus necator chromosome for efficient biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from vegetable oil

Cupriavidus necator H16C_Ac, previously constructed for production of poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate) [P(3HB-co-3HHx)] from soybean oil, was further engineered aiming to increase 3HHx composition in the copolyester. PHA synthase gene derived from Aeromonas caviae on the H16C_Ac chromosome was replaced by a gene encoding the N149S/D171G mutant and this recombination enhanced PHA productivity as well as slightly increased 3HHx composition. Manipulation of phaA_Cn locus partially reduced the amount of 3HB unit concomitantly with relative increase of 3HHx composition, whereas deletion of phaB1_Cn resulted in drastic decline of 3HB unit in P(3HB-co-3HHx). Insertion of phaJ_Ac encoding (R)-specific enoyl-CoA hydratase from A. caviae into pha operon significantly enlarged 3HHx fraction without negative effects on the cell growth and polyester accumulation. Consequently, efficient production of P(3HB-co-3HHx) with 3HHx composition of 5.7-9.9 mol% was successfully achieved from soybean oil by the engineered strains.     

Bioconversion of Glycerine Pitch into a Novel Yellow-Pigmented P(3HB-co-4HB) Copolymer: Synergistic Effect of Ammonium Acetate and Polymer Characteristics

Glycerine pitch waste generated from oleochemical industry was exploited as a carbon source for poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) copolymer production by a novel, yellow-pigmented bacterium Cupriavidus sp. USMAHM13 to improve the economics of microbial polyhydroxyalkanoate production and to establish a feasible waste management approach. Medium optimization using response surface methodology through shake-flask fermentation had led to the accumulation of P(3HB-co-51%4HB) copolymer using a combination of glycerine pitch (10 g/l), 1,4-butanediol (8.14 g/l), and ammonium acetate (2.39 g/l). P(3HB-co-4HB) copolymers with 4HB monomer compositions ranged from 3 to 40 mol% were obtained through batch fermentation in a bioreactor using different concentrations of ammonium acetate. The copolymers exhibited a wide range of material properties depending on the monomer composition and type of carbon sources. P(3HB-co-40%4HB) was a typical random copolymer, whereas other P(3HB-co-4HB) produced were blend copolymers. Carotenoid pigment which was produced simultaneously with the polymer production was found to have negligible effect on the mechanical and thermal properties of the P(3HB-co-4HB) copolymer films.     

Biosynthesis and biocompatibility of biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Poly(3-hydroxybutyrate), PHB, and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), P(3HB-co-4HB), consisting of 0-94% mole fraction of 4HB content, were produced in high content by Cupriavidus necator strain A-04. The carbon sources used for PHB production included sugars made locally in Thailand: refined sugarcane, brown sugarcane, rock sugar, toddy palm sugar and coconut palm sugar. The switching of the ratios of carbon to nitrogen, together with the ratios of fructose to 1,4-butanediol, were applied to P(3HB-co-4HB) production in fed-batch cultures. Optimal P(3HB-co-4HB) production was achieved with 112 g biomass and 73 g P(3HB-co-4HB) with 38% mole fraction of 4HB content. Next, P(3HB-co-4HB) with a 0, 5, 24, 38 and 64% mole fraction of 4HB content were purified and prepared as plastic films. The mechanical properties and biocompatibility of these films were tested and compared with commercial PHB, polystyrene (PS) and polyvinylchloride (PVC) prepared without additives. The results demonstrated that PHB had thermal and mechanical properties similar to those of commercial PHB. The P(3HB-co-4HB) polymers possessed melting temperature and glass transition temperature values higher than those reported previously. The mechanical properties were compared with those of PS and PVC. The in vitro biocompatibility was assessed using L929, human dermal fibroblast and Saos-2 human osteosarcoma cells. The cytotoxicity results and scanning electron micrographs showed that P(3HB-co-4HB) films have good surface characteristics and can promote cell attachment, proliferation and differentiation. Combined with their good mechanical properties, P(3HB-co-4HB) polymers possess potential usefulness for biomaterial applications in artificial skin tissue support and orthopedic support.     

Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from cottonseed oil and valeric acid in batch culture of Ralstonia sp. strain JC-64

A Ralstonia sp. strain JC-64 that is capable of accumulating poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P[3HB-co-3HV]) from cottonseed oil and valeric acid was isolated. By using a high limiting-nitrogen (HLN) mineral medium as the medium for the second stage of the fermentation process and by adding the two carbon sources at different times, a range of copolymers with 12–62 mol% of 3HV were produced from a series of HLN mineral mediums containing different compositions of cottonseed oil and valeric acid by Ralstonia sp. JC-64. The melting temperature (T _m ) of polyhydroxybutyrate from cottonseed oil was 174°C and that of P(3HB-co-3HV) with the highest 3HV-mol fraction (62%) was 81°C.     

Infrared Spectroscopy and X-Ray Diffraction Studies of C?H…O Hydrogen Bonding and Thermal Behavior of Biodegradable Poly(hydroxyalkanoate)

Infrared (IR) spectra and wide-angle X-ray diffraction (WAXD) patterns of poly(3-hydroxybutyrate) (PHB) and its copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), P(HB-co-HHx) (HHx = 12 mol%) were measured over a temperature range of 20 °C to higher temperatures (PHB, 185 °C, HHx = 12 mol%, 140 °C) to explore their structure change and thermal behavior and molecular interaction. The WAXD measurements revealed that the a lattice parameter increases significantly with temperature, while the b lattice parameter varies a little in the crystalline PHB and P(HB-co-HHx). It seems that the intermolecular interaction between the CO group of one helical structure and the CH₃ group of the other helical structure decreases along the a axis of crystalline PHB and P(HB-co-HHx) with temperature. The temperature-dependent IR spectral variations were analyzed for the CH stretching, CO stretching, CH₃ deformation, and C O C stretching variation regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It was found from the anomalous frequencies of the CH₃ asymmetric stretching and CO stretching bands of PHB and P(HB-co-HHx) and the X-ray crystallographic structure of PHB that there is an intermolecular interaction (C H…OC hydrogen bond) between the CO group and the CH₃ group combining two helical structures in PHB and P(HB-co-HHx). In this review paper we discuss the role of the C H…OC hydrogen bonding and the crystal and lamella structure of PHB and P(HB-co-HHx) (HHx = 12 mol %) in comparison with the structure of Nylon.     

Biosynthesis and Characterization of Poly (3-hydroxybutyrate-<Emphasis Type="Italic">co</Emphasis>-3-hydroxyvalerate-<Emphasis Type="Italic">co</Emphasis>-4-hydroxybutyrate) Terpolymer with Various Monomer Compositions by <Emphasis Type="Italic">Cupriavidus</Emphasis> sp. USMAA2-4

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) [P(3HB-co-3HV-co-4HB)] terpolymer was produced using Cupriavidus sp. USMAA2-4 via one-step cultivation process through combination of various carbon sources such as 1,4-butanediol or γ-butyrolactone with either 1-pentanol, valeric acid, or 1-propanol. Oleic acid was added to increase the biomass production. The composition of 3HV and 4HB monomers were greatly affected by the concentration of 1,4-butanediol and 1-pentanol. Terpolymers with 3HV and 4HB molar fractions ranging from 2 to 41 mol.% and 5 to 31 mol.%, respectively, were produced by varying the concentration of carbon precursors. The thermal and mechanical properties of the terpolymers containing different proportions of the constituent monomers were characterized using gel permeation chromatography (GPC), DSC, and tensile machine. GPC analysis showed that the molecular weights (M _w) of the terpolymer produced were within the range of 346 to 1,710 kDa. The monomer compositions of 3HV and 4HB were also found to have great influences on the thermal and mechanical properties of the terpolymer P(3HB-co-3HV-co-4HB) produced.     

Real-time enzymatic degradation study of poly[(R)-3-hydroxybutyric acid] copolymer thin film by atomic force microscopy in buffer solution

In situ observation of lamellar crystals during the enzymatic degradation by poly(hydroxybutyrate) (PHB) depolymerase is carried out on the thin films of poly[((R)-3-hydroxybutyric acid)-co-(16 mol-%-(R)-3-hydroxypentanoic acid)] using atomic force microscopy in buffer solution. Erosion of lamellar crystals and formation of splintered morphology along the crystal growth direction are directly observed during the course of the enzymatic degradation process. The changes in lamellar morphologies caused by enzymatic degradation are discussed in terms of lamellar crystal growth process.

AFM images of a P[(R)-3HB-co-(R)-3HV] thin film before and during enzymatic degradation.     

Enhancement of Stress Tolerance in the Polyhydroxyalkanoate Producers without Mobilization of the Accumulated Granules

Poly(3-hydroxybutyrate) [P(3HB)], a polymer belonging to the polyhydroxyalkanoate (PHA) family, is accumulated by numerous bacteria as carbon and energy storage material. The mobilization of accumulated P(3HB) is associated with increased stress and starvation tolerance. However, the potential function of accumulated copolymer such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] remained unknown. In this study, Delftia acidovorans DS 17 was used to evaluate the contributions of P(3HB) and P(3HB-co-3HV) granules during simulated exogenous carbon deprivation on cell survival by transferring cells with PHAs to carbon-free mineral salt medium supplemented with 1 % (w/v) nitrogen source. By mobilizing the intracellular P(3HB) and P(3HB-co-3HV) at 11 and 40 mol% 3HV compositions, the cells survived starvation. Surprisingly, D. acidovorans containing P(3HB-co-94 mol% 3HV) also survived although the mobilization was not as effective. Similarly, recombinant Escherichia coli pGEM-T::phbCAB _Cn (harboring the PHA biosynthesis genes of Cupriavidus necator) containing P(3HB) granules had a higher viable cell counts compared to those without P(3HB) granules but without any P(3HB) mobilization when exposed to oxidative stress by photoactivated titanium dioxide. This study provided strong evidence that enhancement of stress tolerance in PHA producers can be achieved without mobilization of the previously accumulated granules. Instead, PHA biosynthesis may improve bacterial survival via multiple mechanisms.     

Biosynthesis and characterization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer from wild-type Comamonas sp. EB172

Poly(3-hydroxybutyrate) [P(3HB)] homopolymer and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] copolymer was produced by Comamonas sp. EB172 using single and mixture of carbon sources. Poly(3-hydroxyvalerate) P(3HV) incorporation in the copolymer was obtained when propionic and valeric acid was used as precursors. Incorporation of 3HV fractions in the copolymer varied from 45 to 86 mol% when initial pH of the medium was regulated. In fed-batch cultivation, organic acids derived from anaerobically treated palm oil mill effluent (POME) were shown to be suitable carbon sources for polyhydroxyalkanoate (PHA) production by Comamonas sp. EB172. Number average molecular weight (M_n) produced by the strain was in the range of 153-412 kDa with polydispersity index (M_w/M_n) in the range of 2.2-2.6, respectively. Incorporation of higher 3HV units improved the thermal stability of P(3HB-co-3HV) copolymer. Thus the newly isolated bacterium Comamonas sp. EB172 is a suitable candidate for PHA production using POME as renewable and alternative cheap raw materials.     

Infrared Spectroscopy and X-Ray Diffraction Studies on the Structure and Thermal Behavior of Biodegradable Polyhydroxyalkanoates

The structure and thermal behavior of new types of bacterial copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); P(HB-co-HHx) (HHx=2.5, 3.4, and 12 mol %) have been explored by means of wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), and infrared (IR) spectroscopy. The WAXD pattern of P(HB-co-HHx) (HHx=12 mol %) copolymer measured at room temperature has revealed that it has an orthorhombic system (α=β=γ=90°) with a=5.76Å, b=13.20Å, c=5.96Å (fiber repeat), which is identical to that of poly(3-hydroxybutyrate) (PHB). It has been found from the temperature-dependent variations of the WAXD pattern that only the a lattice parameter shows the thermal expansion, while the b lattice parameter changes little with temperature in the crystalline P(HB-co-HHx) (HHx=12 mol %). This observation suggests that there are inter and intramolecular interactions between C=O groups and alkyl groups along the a axis and that interactions are broken little by little with temperature. IR spectra were measured for the four kinds of polymers over a temperature range from 30°C to high temperatures (200°C; PHB, 180°C; P(HB-co-HHx) (HHx=2.5 mol %), 180°C; P(HB-co-HHx) (HHx=3.4 mol %), 150°C; P(HB-co-HHx) (HHx=12 mol %)). Temperature-dependent IR spectral variations were analyzed for the CH, C=O, and C-O-C stretching band regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It has been found from the IR study that the strength of interaction between the C=O group and the CH₃ (or CH₂) group is similar among the four polymers and that the population of C=O groups that are not involved in the interaction becomes higher with the increase in HHx. Both WAXD and IR studies have revealed that the crystallinity of P(HB-co-HHx) (HHx=12 mol %) decreases gradually starting from relatively low temperature (about 60°C) while that of PHB remains high up to 170°C.     

Characterization of biosynthesized P(3HB-co-3HA)s swellable in organic solvents

Polyhydroxyalkanoate (PHA) copolymers consisting of (R)-3-hydroxybutyrate (3HB) and medium-chain-length (R)-3-hydroxyalkanoate (3HA), P(3HB-co-3HA), are usually solved in chloroform. However, we found that some of the P(3HB-co-3HA) aged for more than 1 month under ambient conditions were not solved in chloroform, but instead swelled when the 3HA fraction was over 14 mol%. On the basis of differential scanning calorimetry and wide-angle x-ray diffraction analyses, we predicted that swellable P(3HB-co-3HA) contained numerous P(3HB) microcrystals, which may form physical crosslinks between adjacent PHA polymer chains.     

Tribological and Mechanical Properties of Poly[(R)-3-hydroxybutyric acid] Grafted with Vinyl Compounds: Insight into Possible Application

Biodegradable graft copolymers were prepared by gamma radiation-induced graft polymerization of two vinyl monomers, vinyl acetate and vinyl alcohol, onto poly[(R)-3-hydroxybutyric acid]. Success of the grafting reaction was verified by Fourier-transform infrared and nuclear magnetic resonance spectroscopy. Thermal remolding was used to create membranes from the copolymers. We determined tribological and mechanical properties of the membranes obtained. The lowest elongation at break in tensile testing is seen for P(3HB) and the highest for P(3HB-g-VA). Up to 5 N or so, the highest scratch resistance is exhibited by P(3HB-g-VA). Piezoelectric behavior is seen for P(3HB-g-VA) while P(3HB-g-VAc) and plain P(3HB) showed no electric response. Explanation of the piezoelectric behavior in terms of molecular structures is provided.