Bacterial Polyester Research Articles

Mechanical Properties and Higher Order Structures of the Bacterial Polyester Highly Oriented Films

Bacterial poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)(PHBH) highly oriented films were prepared by the combination of roll and uniaxial drawing processes. Compression molded films, which is rather brittle, turned to be ductile after roll drawing up to x 2, and the films were further uniaxially drawn to a draw ratio as high as 1000 %. The PHBH film with the tensile strength of 178 MPa and the modulus of 1.4 GPa were obtained. The roll drawn PHB film showed a slight crystalline orientation of Alpha-form. The orientation advanced with uniaxial draw ratio and the formation of Beta-form crystal was observed. Relations among the processing conditions, higher order structures and mechanical properties were investigated using wide-angle X-ray diffraction, differential scanning calorimetry, and tensile measurements.

Enzymatic Transformation of Bacterial Polyhydroxyalkanoates into Repolymerizable Oligomers Directed towards Chemical Recycling

The enzymatic transformation into an oligomer was carried out with the objective of developing the chemical recycling of bacterial polyesters. Poly(R-3-hydroxyalkanoate)s (PHAs), such as poly[(R-3-hydroxybutyrate)-co-12%(R-3-hydroxyhexanoate)] and poly[(R-3-hydroxybutyrate)-co-12%(R-3-hydroxyvalerate)], were degraded by granulated Candida antarctica lipase B immobilized on hydrophilic silica (lipase GCA) in a diluted organic solvent at 70 degrees C. The degradation products were cyclic oligomers having a molecular weight of a few hundreds. The obtained cyclic oligomer was readily repolymerized by the same lipase (lipase GCA) to produce the corresponding polyester in a concentrated solution. The cyclic oligomer was copolymerized with epsilon-caprolactone using lipase to produce the corresponding terpolymers having an Mw of 21,000. This is the first example of the enzymatic chemical recycling of bacterial PHAs using lipase. Poly(R-3-hydroxybutyrate) [P(3HB)] was also degraded into the linear-type R-3HB monomer to trimer by P(3HB)-depolymerase (PHBDP) in phosphate buffer at 37 degrees C. The degradation using PHBDP required a longer reaction time compared with the lipase-catalyzed degradation in organic solvent. The monomer composition of the oligomer depended on the origin of the PHBDP. The R-3HB monomer was predominately produced by PHBDP from Pseudomonas stutzeri, while the R-3HB dimer was produced by PHBDP from Alcaligenes faecalis T1. Repolymerization of these oligomers by lipase in concentrated organic solvent produced a relatively low-molecular-weight P(3HB) (e.g., Mw=2,000). Degradation of P(3HB) by lipase in organic solvent into repolymerizable cyclic oligomer and degradation of P(3HB) by PHBDP in buffer into hydroxy acid type R-3HB dimer.

Cocrystallization and Phase Segregation in Blends of Two Bacterial Polyesters

AbstractBy fractional precipitaion of bacterial copolyesters, it has been strongly suggested that the bacterial PHA copolymer normally has broad and/or multimodal chemical composition distribution (CCD). In this paper, we try to review the works on the blends of two bacterial polyesters in order to accumulate knowledge on the relation between CCD and various properties required for the practical application of bacterial copolymers. Phase structures of the blends of poly(3‐hydroxybutyrate) [PHB] and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [PHB‐HV] and crystallization kinetics of the blends of PHB‐HV and poly(3‐hydroxybutyrate‐co‐3‐hydroxypropionate) [PHB‐HP] are described.

Preparation of a Novel Artificial Bacterial Polyester Modified with Pendant Hydroxyl Groups

The Poly(hydroxyalkanoate) (PHA) chemical modifications represent an alternative route to introduce functional groups, which cannot be introduced by bioconversion. PHAs containing unsaturated chains were readily converted into polyesters containing a terminal hydroxyl group on the side chains. With the use of the borane-tetrahydrofuran complex, the pendant side chain alkenes were quantitatively transformed into hydroxyl functions. The conversion proceeded to completion without a significant decrease in molecular weight. The introduction of hydroxyl groups in the products was confirmed from Fourier transform infrared and 1H NMR analysis. The presence of repeating units containing pendant hydroxyl groups in the proportion 25 mol % caused an increase in hydrophilicity of these new PHAs because they were soluble in polar solvents such as ethanol. Besides, these reactive PHAs can be used to bind bio-active molecules or to prepare novel graft copolymers with desired properties.

Fiber Formation of Bacterial Polyesters

Fiber Formation of Bacterial Polyesters

Bacterial Polyesters: Biosynthesis, Biodegradable Plastics and Biotechnology

The discovery and chemical identification, in the 1920s, of the aliphatic polyester: poly(3-hydroxybutyrate), PHB, as a granular component in bacterial cells proceeded without any of the controversies which marked the recognition of macromolecules by Staudinger. Some thirty years after its discovery, PHB was recognized as the prototypical biodegradable thermoplastic to solve the waste disposal challenge. The development effort led by Imperial Chemical Industries Ltd., encouraged interdisciplinary research from genetic engineering and biotechnology to the study of enzymes involved in biosynthesis and biodegradation. From the simple PHB homopolyester discovered by Maurice Lemoigne in the mid-twenties, a family of over 100 different aliphatic polyesters of the same general structure has been discovered. Depending on bacterial species and substrates, these high molecular weight stereoregular polyesters have emerged as a new family of natural polymers ranking with nucleic acids, polyamides, polyisoprenoids, polyphenols, polyphosphates, and polysaccharides. In this historical review, the chemical, biochemical and microbial highlights are linked to personalities and locations involved with the events covering a discovery timespan of 75 years.

Perspectives on Modification of Aliphatic Polyesters by Radiation Processing

Aliphatic polyesters have been studied mainly for medical applications, but also for other uses. Although the properties of different aliphatic polyesters are broad, there is a need for modifications to achieve desired material properties. Plasma modification of polymers has been applied to surface modification of polymers, while the bulk of the polymer remains unchanged. High energy radiation induced processing is an established technique that is used in polymer science. Radiation is used to initiate radical polymerizations and for modifications such as degradation, cross-linking, and graft-copolymerization. In this paper article radiation processing of aliphatic polyesters is reviewed. Included are synthetic polyesters, like polyglycolide, polylactide, poly(ε-caprolactone), poly(lactide-co-caprolactone) and two commonly occurring bacterial polyesters, polyhydroxybutyrate and poly(hydroxybutyrate- co-valerate). Relevant processing parameters as well as the effects and applications of the radiation modification are presented.

Investigation of the Impact of Poly(Ethylene Glycol)-Modulation of Poly(B-Hydroxybutyrate) Syntheses on Cell Interactions of the Resulting Polymers

Poly(-hydroxybutyrate), PHB is a bacterial polyester known for its excellent bone compatibility, however, the material lacks blood and tissue compatibility. Poly(ethylene glycol), PEG,-modulated fermentation of Alcaligenes latus and Azotobacter vinelandii UWD was employed to yield copolymers consisting of PHB and PEG that exhibit diminished cell-adhesion surface properties. PEGs with molecular weights of 3400, 2000, and 400 as well as diethylene glycol, DEG, and pentaerythritol ethoxylate, PEE, were used in a concentration of 2% (w/v) for amending the fermentation broths. This modulation of the fermentation conditions did not influence polymer yields. However, the resulting copolymers had drastically reduced molecular weights, 82% less for the DEG-amended fermentation of A. latus. The reduction in molecular weight was attributed to an end-capping reaction of the nascent PHB-chain with PEG and/or early chain termination by water facilitated by the presence of the highly hydrophilic PEG-molecules. The formation of a covalent linkage was proven unambiguously by H-NMR-spectroscopic methods only for the copolymers obtained in the DEG-modified fermentations of both strains. Cell growth experiments using SK-MEL 28 and MDA-MB 231 cells were used for the evaluation of polymer-cell interaction. Copolymer films obtained from PEG-modulated syntheses showed significantly less cell adhesion with reductions in cell adhesions; up to 74% less in the two-day experiments (MDA-MB 231 on the copolymer obtained in DEG-modified fermentation of A. latus) and 48% less in the seven-day experiments (SK-MEL 28 on the copolymer obtained in PEG 400-modified fermentation of A. vinelandii UWD). In the two-day experiments, no differences in the cellinteraction was observed between the polymers obtained from two different bacterial sources, the polymers differed in their long-term, seven-day, cell interaction with copolymers obtained from A. vinelandii UWD maintaining more effective cell repulsion.

Synthesis of Graft Bacterial Polyesters for Nanoparticles Preparation

AbstractGraft copolymers of bacterial polyesters were prepared by direct condensation of poly(3‐hydroxyoctanoate‐co‐9‐carboxy‐3‐hydroxydecanoate) (PHOD) and poly(ethylene glycol) (PEG) or poly(lactic acid) (PLA). Nanoparticles from PHO, PHOD, PHOD‐g‐PEG, and PHOD‐g‐PLA were obtained by solvent displacement without stabilizer, and their stability in different aqueous media with different salt concentrations were studied. The results showed that the presence of hydrophilic PEG on the particle surface prevents the aggregation promotion by salts in aqueous solution. PHOD‐g‐PEG appears to be a promising candidate for site‐specific drug delivery systems.1H NMR spectrum of PHOD‐g‐PLA in CDCl3.magnified image1H NMR spectrum of PHOD‐g‐PLA in CDCl3.

Conformational Properties of the Bacterial Polyester Poly(3-hydroxy-5,8-decadienoate)

Molecular dynamics simulations under different conditions and rotational isomeric states calculations are performed to understand the local and global conformational properties of the bacterial polyester poly(3-hydroxy-5,8-decadienoate). The rotational isomeric state model is incorporated with Monte Carlo simulations to calculate the dimensions and the characteristic ratio of the infinitely long chain. These calculations, performed in a vacuum, predict a Gaussian distribution for the end-to-end vector with a nonzero mean and a value of 5.5 for the characteristic ratio. Molecular dynamics simulations predict the characteristic ratio of the single chain in good solvent as 23. The role of temperature on the overall dimensions and on the distribution of dihedral angles is discussed. Radii of gyration and helix formation propensities at different temperatures and in different media are compared. The chain in solution is found to have the largest persistence length with the highest helical persistence. Results are compared with experimental and theoretical studies conducted on poly(3-hydroxybutyrate), which has the same backbone structure but a different type of side chain.

Biodegradation of microbial and synthetic polyesters by fungi.

A variety of biodegradable polyesters have been developed in order to obtain useful biomaterials and to reduce the impact of environmental pollution caused by the large-scale accumulation of non-degradable waste plastics. Polyhydroxyalkanoates, poly(epsilon-caprolactone), poly( l-lactide), and both aliphatic and aromatic polyalkylene dicarboxylic acids are examples of biodegradable polyesters. In general, most aliphatic polyesters are readily mineralized by a number of aerobic and anaerobic microorganisms that are widely distributed in nature. However, aromatic polyesters are more resistant to microbial attack than aliphatic polyesters. The fungal biomass in soils generally exceeds the bacterial biomass and thus it is likely that fungi may play a considerable role in degrading polyesters, just as they predominantly perform the decomposition of organic matter in the soil ecosystem. However, in contrast to bacterial polyester degradation, which has been extensively investigated, the microbiological and environmental aspects of fungal degradation of polyesters are unclear. This review reports recent advances in our knowledge of the fungal degradation of microbial and synthetic polyesters and discusses the ecological importance and contribution of fungi in the biological recycling of waste polymeric materials in the biosphere.

Preparation and characterization of biodegradable poly-3-hydroxybutyrate-starch blend films.

Bacterial polyesters have attracted much attention as biodegradable biocompatible polymers. Poly-3-hydroxybutyrate, a microbially produced thermoplastic, has similar material properties to polypropylene. Its potential application as biodegradable and biocompatible plastics is well documented. However, due to high cost it is used mainly in biomaterials for medical applications. Materials with useful properties may result from blending bacterial polyhydroxybutyrate (PHB) with other polymers. In this paper, the compatibility of PHB with starch for improved properties and cost reduction is discussed. The thermal and mechanical properties of the blended films were studied by means of thermogravimetry, differential scanning calorimetry and an automated material testing system. The results revealed that blend films had a single glass transition temperature for all the proportions of PHB:starch tested. The nature of all combinations was found to be crystalline. The tensile strength was optimum for the PHB:starch ratio of 0.7:0.3 (wt/wt). The variation in tensile strength, Young's modulus, extension needed to break, thermal stability, glass transition temperature, melting temperature, for the different proportions of PHB:starch are discussed.

Identification of novel sulfur-containing bacterial polyesters: biosynthesis of poly(3-hydroxy-S-propyl-omega-thioalkanoates) containing thioether linkages in the side chains.

This study describes the biosynthesis of novel sulfur-containing polyhydroxyalkanoates (PHAs), which consist exclusively of hydroxypropylthioalkanoic acid containing thioether groups in the side chains. In addition, the utilization of alkylthioalkanoic acids (=thia fatty acids) by various bacteria was investigated. Based on feedings with propylthiooctanoic acid (PTO) or propylthiohexanoic acid, the metabolically engineered PHA-negative mutant PHB(-)4 of Ralstonia eutropha, which harbours plasmid pBBR1::phaC1 expressing the PHA synthase of Pseudomonas mendocina, synthesized two novel poly(3-hydroxy-S-propyl-omega-thioalkanoic) acids [poly(3HPTA)s]. A terpolyester consisting of 3-hydroxypropylthiobutyric acid (3HPTB), 3-hydroxypropylthiohexanoic acid (3HPTHx) and 3-hydroxypropyl- thiooctanoic acid (3HPTO) was synthesized from PTO, whereas a co-polyester of 3HPTB and 3HPTHx was synthesized from propylthiohexanoic acid. Fed-batch fermentation of R. eutropha PHB(-)4(pBBR1::phaC1) on PTO was done on a 26-litre scale, providing a cell density of 7.3 g l(-1), from which 45 g of the novel poly(3HPTB-co-3HPTHx-co-3HPTO) were isolated. The chemical structures of the poly(3HPTA)s were identified by gas chromatography/mass spectrometry, elemental sulfur analysis, partial pyrolysis and detailed mass spectrometric analysis, exhibiting 3HPTB, 3HPTHx and 3HPTO as constituents. These novel, hitherto undescribed, constituents of PHAs were randomly distributed in the co-polyesters.

Sustainable Bio-Composites from Renewable Resources: Opportunities and Challenges in the Green Materials World

Sustainability, industrial ecology, eco-efficiency, and green chemistry are guiding the development of the next generation of materials, products, and processes. Biodegradable plastics and bio-based polymer products based on annually renewable agricultural and biomass feedstock can form the basis for a portfolio of sustainable, eco-efficient products that can compete and capture markets currently dominated by products based exclusively on petroleum feedstock. Natural/Biofiber composites (Bio-Composites) are emerging as a viable alternative to glass fiber reinforced composites especially in automotive and building product applications. The combination of biofibers such as kenaf, hemp, flax, jute, henequen, pineapple leaf fiber, and sisal with polymer matrices from both nonrenewable and renewable resources to produce composite materials that are competitive with synthetic composites requires special attention, i.e., biofiber–matrix interface and novel processing. Natural fiber–reinforced polypropylene composites have attained commercial attraction in automotive industries. Natural fiber—polypropylene or natural fiber—polyester composites are not sufficiently eco-friendly because of the petroleum-based source and the nonbiodegradable nature of the polymer matrix. Using natural fibers with polymers based on renewable resources will allow many environmental issues to be solved. By embedding biofibers with renewable resource–based biopolymers such as cellulosic plastics; polylactides; starch plastics; polyhydroxyalkanoates (bacterial polyesters); and soy-based plastics, the so-called green bio-composites are continuously being developed.

Poly(3-hydroxyoctanoate) containing pendant carboxylic groups for the preparation of nanoparticles aimed at drug transport and release

Copolymers of poly(3-hydroxyoctanoate) (PHO) with carboxylic groups in lateral chains have been prepared by chemical modification of unsaturated bacterial polyesters. The oxidation of the pendant alkenes is complete and important loss in molecular weight of polymer was observed. The presence of repeating units containing pendant carboxy groups in the proportion of 25% has enhanced hydrophilicity of these new polymeric structures. Nanoparticles have been prepared from PHO and two functionalized derivatives, characterized by electronic microscopy and compared in view of bioactive molecules transport and release.

Thermal degradation of poly(3-hydroxyalkanoates): preparation of well-defined oligomers.

The thermal degradation of the biodegradable bacterial polyesters poly(3-hydroxybutyrate), PHB, poly(3-hydroxyvalerate), PHV, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), 0-21 mol % of hydroxyvalerate, was studied. At moderately low temperatures (170-200 degrees C), the main product is a well-defined oligomer, especially a 500-10,000 g/mol macromolecule, which contains one unsaturated end group, predominantly a trans-alkenyl end group, as well as a carboxylic end group. The process was studied regarding the effect of the copolymer composition and reaction time at 190 degrees C. During the first few hours of reaction, the thermal degradation of PHB and PHV followed a kinetic model of random scission, but eventually auto-acceleration of the pyrolysis was detected, probably due to the influence of the crotonate end groups of the oligomers formed. Ten-time scale-up experiments on a Brabender instrument were successfully undertaken.

Poly(styrene peroxide) and Poly(methyl methacrylate peroxide) for Grafting on Unsaturated Bacterial Polyesters

Poly(styrene peroxide) and Poly(methyl methacrylate peroxide) for Grafting on Unsaturated Bacterial Polyesters

Poly(styrene peroxide) and Poly(methyl methacrylate peroxide) for Grafting on Unsaturated Bacterial Polyesters

A new soluble terephthaloyl oligoperoxide (OTP) was synthesized by the reaction of terephthaloyl peroxide and 2,5-dimethyl 2,5-dihydroperoxy hexane. Thermal polymerization of vinyl monomers (styrene, methyl methacrylate) with OTP yielded poly(styrene peroxide) (PS-P) and poly(methyl methacrylate peroxide) (PMMA-P) which are used in the grafting reactions onto medium chain length unsaturated bacterial polyester obtained from soybean oily acids with Pseudomonas oleovorans poly(3-hydroxy alkanoate), (PHA). PS-g-PHA and PMMA-g-PHA graft copolymers isolated from related homopolymers were characterizated by 1H NMR spectrometry, FT-IR spectroscopy, thermal analysis and gel permeation chromatographic (GPC) techniques. Swelling measurement of the crosslinked graft copolymers were also measured to calculate qv values.

Graft Copolymerisation of Methyl Methacrylate onto a Bacterial Polyester Containing Unsaturated Side Chains

Poly(3-hydroxy alkanoate) containing unsaturated side chains was produced by feeding Pseudomonas oleovorans with soybean-soil acid (PHA-soybean). The composition of PHA-soyebean were found to be 10 mol-% of unsaturated side chains with the saturated hexanoate, octanoate and decanoate units. Methyl methacrylate (MMA) was thremally grafted on PHA-soybean in the presence of benzoyl peroxide. Fractional precipitation was used to isolate the grapht copolymer from related homopolymers. PHA content in copolymer samples was between 15 to 30 mol-%. Graft copolymer samples were kept in hydroquinone to prevent post polymerization leading to crosslinking in a day under laboratory atmospheric conditions. Copolymer characterization was performed using GPC and NMR techniques. Thermal analysis of the graft copolymer indicated the decomposition and glass transition temperatures of the PHA and PMMA segments of the graft copolymers. They also showed elongation at break in the range 10 to 21 related to the plasticizer effect of the biopolyester segments.

Free radical crosslinking of unsaturated bacterial polyesters obtained from soybean oily acids

Poly(-3-hydroxy alkanoate) containing unsaturated side chains, PHA-soybean, were produced by feeding Pseudomonas oleovorans with soybean oily acids obtained from soybean oil. Unsaturation of PHA-soybean were found to be 10 mol-% of unsaturated side chains. Main saturated part of the biopolymer was Poly(3-hydroxy octanoate) with minor hexanoate and decanoate units. PHA films were crosslinked via free radical mechanism by means of thermally or under UV irradiation in the presence of benzoyl peroxide, benzophenon, and /or ethylene glycol dimethacrylate (EGDM). Crosslinking yield of the PHA films were found to be from 81 to 93 wt.-% from the sol-gel analysis. Swelling properties of the crosslinked PHA films in chloroform and toluene were also studied. Mc values of crosslinked PHAs were also calculated using Flory-Rehner equation. The crosslinked biopolyester obtained by thermally at 60 °C with benzoyl peroxide indicated the highest crosslinking density. Glass transition temperatures (Tg) of crosslinked biopolyester samples were changed from −33 to −45 °C while that of PHA-soybean was −60 °C.