Effects of Poly(Ethylene Glycol) on the Production of Poly(β-Hydroxybutyrate) by Azotobacter vinelandii UWD

Azotobacter vinelandii UWD, ATCC 53799, an engineered strain derived from Azotobacter vinelandii UW was used in the poly(ethylene glycol) (PEG)-modulated synthesis of poly(-hydroxybutyrate) (PHB). To the best of our knowledge, this is the first report on modulating the production of PHB by amending the fermentation broth with PEG using A. vinelandii UWD. It was determined that A. vinelandii UWD is prone to back-mutation to the parent strain; hence fermentation experiments require the use of the antibiotic rifampicin. Diethylene glycol (DEG) and PEGs with molecular weights of 400, 2000, and 3400 Da and pentaerythritol ethoxylate (PEE) were used in the modulated fermentation experiments in a concentration of 2% (w/v). The molecular weight of the resulting polymers was reduced by up to 78%. No impact on the productivity of the strain was observed. Spectroscopic evidence showed that PEG-modulated synthesis resulted in the covalent attachment of the ethylene glycol moiety only when a small molecule, DEG, was used. PEGs had the same effects on the polymer formation in terms of molecular weight reduction as DEG, but no spectroscopic evidence was found for the formation of a covalent linkage between PHB and higher molecular weight PEGs.     

Radiation Effects on Blends of Poly(ε-Caprolactone) and Diatomites

Poly(-caprolactone) (PCL) was blended with diatomaceous earth (diatomite) and irradiated with -rays to introduce cross-linking between PCL molecules or both components. The unwashed diatomite containing a little of a volatile component showed high efficiency of introduction of cross-linking, whereas that with no volatile component showed low efficiency of introduction of cross-linking. Elongational viscosity, melt viscosity, and modulus of PCL/diatomite blend irradiated at various doses were significantly improved. Enzymatic degradation of the PCL/diatomite blend became faster than that of the PCL, though that of the blend irradiated became slower.     

Distribution of Poly(β-propiolactone) Aerobic Degrading Microorganisms in Different Environments

The distribution of degading microorganisms of high molecular weight poly(-propiolactone) (PPL), whose individual structural units are similar to those of poly(-hydroxybutyrate) (PHB) and poly(€-caprolactone) (PCL), was examined. Despite the fact that PPL is a chemosynthetic polymer, many kinds of PPL-degrading microorganisms were found to be distributed as resident populations widely in natural environments. A total of 77 strains of PPL-degrading microorganisms was isolated. From standard physiological and biochemical tests, at least 41 strains were referred to as Bacillus species. Microbial degradation of fibrous PPL proceeded rapidly in some enrichment cultures but was not as complete as that of PHB. Most of the isolated PPL-degrading microorganisms were determined to be PCL degraders and/or PHB degraders. Therefore, it can be assumed that mostly PPL is recognized by the microorganisms as PHB or another natural substrate of the same type as which PCL is regarded. Microbial degradation of PPL was confirmed by some Bacillus strains from type culture collections. The similarity of microbial degradation between PPL and PCL was found to be very close.     

Environmental Degradation of Biodegradable Polyesters: 3. Effects of Alkali Treatment on Biodegradation of Poly(ε-Caprolactone) and Poly[(R)-3-Hydroxybutyrate) Films in Controled Soil

The poly(-caprolactone) (PCL) and poly[(R)-3-hydroxybutyrate] (R-PHB) films with a hydrophilic surface were prepared by the alkali treatment of their as-cast films in NaOH solutions of different concentrations. The alkali-treated PCL and R-PHB films, as well as the as-cast PCL and R-PHB films, were biodegraded in soil controlled at 25°C and the effects of alkali treatment or surface hydrophilicities on their biodegradation were investigated by the use of gravimetry, gel permeation chromatography (GPC), scanning electron microscopy (SEM), and polarization optical microscopy. It became evident that the alkali treatment enhanced the hydrophilicities and biodegradabilities of the PCL and R-PHB films in soil. The biodegradabilities of the as-cast aliphatic polyester films in controlled soil decreased in the following order: PCL > R-PHB > PLLA, in agreement with that in controlled static seawater.     

Mechanical Properties and Isothermal Crystallization Behaviour of Poly(lactide)/Poly(methyl methacrylate)/α-Cellulose Composites

Polylactide (PLA)/polymethylmethacrylate (PMMA)/α-cellulose composites were fabricated using a twin-screw extruder. During fabrication, α-cellulose short fibres were incorporated for improving the toughness of the brittle PLA and a chain extender was used for reducing PLA hydrolysis. Highly transparent PLA and PMMA were blended to obtain miscible and transparent blends. For evaluating the performance of the PLA/PMMA/α-cellulose composites, a series of measurements, including tensile and Izod impact tests, light transmission and haze measurements, thermomechanical analysis, and determination of isothermal crystallisation behaviour, was conducted. Adding the chain extender considerably reduced the occurrence of hydrolytic degradation. Both the chain extender and α-cellulose short fibres increased the elongation at break and Izod impact strength of the composites. Compared with the neat PLA, including 1.0 wt% α-cellulose short fibres increased the elongation at break and Izod impact strength of the composite PLA by approximately 211 and 219 %, respectively. According to the observed mechanical performance, the optimal blending ratios for PLA and PMMA were between 90:10 and 80:20. The total light transmittance of the composites was as high as 91 %, indicating that the PLA/PMMA blend was highly miscible. The haze value of the PLA/PMMA/α-cellulose composites was lower than 32 %. Incorporating cellulose short fibres increased the number of crystallisation sites and crystallinity of the PLA/PMMA/α-cellulose composites while reducing the spherulite dimensions.     

The Impact of the Macaíba Components Addition on the Biodegradation Acceleration of Poly (Ɛ-Caprolactone) (PCL)

Journal of Polymers and the Environment - Nowadays, there is a need to obtain eco-friendly materials, especially plastics that are responsible for most of the environmental pollution. In this...     

Poly(2-ethyl-2-oxazoline) as β-Nucleating Agent for Poly(lactic acid) Blends with High Transparency and Hydrophilicity

Journal of Polymers and the Environment - This study aims to evaluate the effects of poly(2-ethyl-oxazoline) (PEOx) on the thermal properties, wettability, and optical properties of poly(lactic...     

Viscoelastic Characterization and Degradation Stability Investigation of Poly(butylene-adipate-co-terephthalate) – Calcium-Phosphate Glass Composites

Journal of Polymers and the Environment - In this work new biodegradable composite materials based on poly(butylene-adipate-co-terephthalate) (PBAT) reinforced with water-soluble calcium-phosphate...     

Synthesis of Poly(β-hydroxybutyrate) in Simulated Microgravity: An Investigation of Aeration Profiles in Shake Flask and Bioreactor

The microbial strain Azotobacter vinelandii UWD was grown under conditions of simulated microgravity in the National Aeronautics and Space Administration (NASA) Bioreactor. Bacterial growth in simulated microgravity differed significantly from that observed in conventional shake flask experiments: Cells tended to grow in a cluster-like pattern and polymer production started immediately after exposing them to conditions of simulated microgravity, and no lag time was observed. It was imperative to differentiate between the effects derived from microgravity and those imposed by the altered oxygen supply in the bioreactor. Aeration conditions were studied in both reactor types and a gas supply profile was developed for the bioreactor. This supply profile allowed for similar amounts of dissolved oxygen in the bioreactor and the shake flask in the initial stage of the fermentation and, therefore, for an evaluation of the effects of microgravity on biopolyester-producing bacteria. Since the optical density that is conventionally used as a measure for the cell growth could not be used due to the cluster-like growth pattern of the cells, it was determined that bacterial growth behavior in the bioreactor can be monitored through glucose or oxygen consumption.     

Purification of Aspergillus fumigatus (Pdf1) Poly(β-hydroxybutyrate) (PHB) Depolymerase Using a New, Single-Step Substrate Affinity Chromatography Method: Characterization of the PHB Depolymerase Exhibiting Novel Self-Aggregation Behavior

The extracellular poly(-hydroxybutyrate) (PHB) depolymerase of Aspergillus fumigatus Pdf1 was purified by a new, simple, one-step affinity chromatography method using the substrate PHB. The purified enzyme was glycosylated, with the molecular mass of 40 KD, and exhibited a novel self-aggregation behavior by means of hydrophobic interaction that was resolved by Triton X-100 (TX-100) pretreatment of enzyme and also TX-100 incorporation in the native gel. The apparent K _m value of purified enzyme for PHB was 119 g/mL and 3-hydroxybutyrate was detected as the main endproduct of PHB hydrolysis. The depolymerase was insensitive to phenylmethyl sulfonyl fluoride (PMSF), sodium azide, ethylenediaminetetraacetic acid (EDTA), and para-chloromercuric benzoic acid (PCMB), but was inactivated by dithioerythritol (DTT) and showed specificity for short chain-length poly(-hydroxyalkanoates) (PHAs) such as PHB, poly(hydroxyvalerate) (PHV), and copolymers of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV). Medium-chain-length PHA failed to get hydrolyzed. The enzyme, however, exhibited strong cross reactivity with the Comamonas sp. PHB depolymerase antibodies, but not with PHV depolymerase antibodies of Pseudomonas lemoignei. Southern hybridization and dot blot analysis of A. fumigatus Pdf1 genomic DNA with alkaline phosphatase labeled probes of P. lemoignei PHB and PHV depolymerase genes revealed no homology, although the enzyme hydrolyzed both PHB and PHV.     

Mechanical Properties and Lipase-Catalyzed Biodegradation of α-Methyl, ε-Caprolactone/ ε-Caprolactone Copolymers Obtained by Chemical Modification of Poly(ε-caprolactone)

Novel (-caprolactone)-based copolymers of different compositions were synthesized by allowing methyl iodide to react with the polycarbanion that resulted from the action of lithium diisopropylamide on poly(-caprolactone) in THF at –70°C under argon atmosphere. The copolymers were characterized by various techniques, namely ¹H nuclear magnetic resonance, size exclusion chromatography, differential scanning calorimetry, x-ray diffraction and viscoelasticimetry. They were submitted to hydrolytic and lipase-catalyzed enzymatic degradation in comparison with genuine PCL. The Young modulus depended on the degree of methylation. In contrast, loss angle and glass transition temperature did not depend on this parameter. It is shown that the lipase-catalyzed degradation of methylated PCL is much slower than in the case of genuine PCL.     

Characterization and Properties of Reactive Poly (Lactic Acid)/Ethylene–Vinyl Alcohol Copolymer Blends with Chain-Extender

A hydrophilic copolymer, ethylene–vinyl alcohol (EVOH), was incorporated into the poly(lactic acid) (PLA) matrix to improve the barrier property of PLA through twin-screw extrusion rather than the typical coextrusion process. A chain extender, poly[(ethylene)-co-(methyl acrylate)-co-(glycidyl methacrylate)] (PEMG), was used to reduce the probability of the thermal degradation of PLA during melt compounding. Biaxial stretching was used to enhance the microstructure and barrier property of PLA-PEMG/EVOH films. Experimentally, PEMG considerably reduced the probability of the thermal degradation of the PLA-PEMG sample. Biaxial stretching increased the tensile strength and decreased the value of elongation at break of the PLA-PEMG/EVOH80 (PLA/EVOH 100/80) film. Because of the efficient blending of PLA/EVOH in the twin-screw extruder, the dispersion of EVOH in the PLA matrix revealed homogeneous dispersion with a domain size of 1–5 μm. EVOH effectively improved the water vapour transmission rate (WVTR) of PLA through melt blending. Blending PLA-PEMG with EVOH substantially decreased the WVTR from 250 cc—20 μm/m²-day-atm for neat PLA to approximately 65 cc—20 μm/m²-day-atm for the PLA-PEMG/EVOH80 film, a decrease of approximately 74 % compared with neat PLA. Moreover, the WVTR decreased further from 65 cc—20 μm/m²-day-atm for the unstretched PLA-PEMG/EVOH80 film to 6.3 cc—20 μm/m²-day-atm for the film stretched at a stretch ratio of 3.5 × 3.5 and at 100 %/s, a decrease of approximately 90 % compared with neat PLA.     

Sorption of Some Rare Earth Elements from Acidic Solution onto Poly(acrylic acid–co-acrylamide/16, 16-dimethylheptadecan-1-amine) Composite

Journal of Polymers and the Environment - In this study, Acrylic acid (AA), acrylamide (AM), and 16,16-dimethylheptadecan-1-amine (PJM-T) were copolymerized using gamma irradiation with 60Co...     

Evaluation of biodegradability of poly(ε-caprolactone)/poly(ethylene terephthalate) blends

The results of an investigation aimed at evaluation of the biodegradability of blends of poly(-caprolactone) (PCL) with poly(ethylene terephthalate) (PET) as the major component are reported. Specimens of the blends, as melt extruded films and/or powders, were submitted to degradation tests under different environmental conditions including full-scale composting, soil burial, bench-scale accelerated aerobic degradation, and exposure to axenic cultures and esterolytic enzymes. Indications have been gained that blending in the melt gives rise to insertion of PCL segments in the PET chain. Copolymers thus attained acted as macromolecular compatibilizers, allowing for a complete miscibility of PCL and PET. The biodegradation detected on the blend samples was, however, well below the values expected from chemical composition and behavior of individual homopolymers under the same environmental conditions. The presence of PET as the major component in PET/PCL blends apparently reduces the propensity of PCL to be degraded, at least in the investigated composition range. The degradation data collected under different environmental conditions indicate that the full-scale composting system is the most efficient among the tested degradation procedures.     

Synthesis and biodegradation of poly(γ-butyrolactone-co-l-lactide)

Biodegradable polyesters were synthesized by ring-opening copolymerization of -butyrolactone (BL) and its derivatives withl-lactide (LLA). Although tetraphenyl tin was the main catalyst used, other organometallic catalysts were used as well.¹H and¹³C NMR spectra showed that poly(BL-co-LLA)s were statistical and that their number-average molecular weights were as high as 7×10⁴. The maximum BL content obtained from copolymerization BL/LLA was around 17%. TheT _m andT _g values of the copolymers showed a gradual depression with an increase in BL content. NoT _m was obtained for the copolymers containing more than 13 mol% BL. The biodegradability of the copolyesters was evaluated by enzymatic hydrolysis and nonenzymatic hydrolysis tests. The enzymatic hydrolysis was carried out at 37°C for 24 h using lipases fromRhizopus arrhizus andR. delemar. Hydrolyses by both lipases showed that an increase in BL content of the copolymer resulted in enhanced biodegradability. Nonenzymatic accelerated hydrolysis of copolymers at 70°C was found to increase proportionally to their exposure time. The hydrolysis rate of these copolymers was considerably faster than that of PLLA. The higher hydrolyzability was recorded for the BL-rich copolymers. The copolymerization of -methyl--butyrolactone (MBL) or -ethyl--butyrolactone (EBL) with LLA resulted in relatively LA-rich copolymers.     

The Effect of UV-B Irradiation on the Biodegradability of Poly-β-Hydroxybutyrate (PHB) and Poly-ɛ-Caprolactone (PCL)

The biodegradability of poly--hydroxybutyrate and poly--caprolactone in soil compostage before and after irradiation of the polymers for 192, 425, and 600 h in a Weather-Ometer was examined. The biodegradability tests were done in soil compostage at pH 7.0, 9.0, and 11.0 to assess the influence of this parameter on degradation. The rate of degradation was directly proportional to the soil alkalinity. Poly--hydroxybutyrate showed the greatest weight loss and aging in a Weather-Ometer did not significantly increase the biodegradation, except when the polymer was aged for 425 h and buried in soil compostage of pH 11.0.     

Crystallization behavior of predominantly syndiotactic poly(β-hydroxybutyrate)

Predominantly syndiotactic poly(-hydroxybutyrate), syn-PHB, of variable syndioregularity (syndyad fractions 0.59, 0.62, 0.64, and 0.71) and molecular weight was prepared by the dibutyltin dimethoxide catalyzed ring opening of racemic-butyrolactone (BL). The crystallization behavior of the syn-PHB polymers was investigated by DSC and X-ray diffraction analyses. DSC of films after melting and annealing showed at least one, and often two distinct melting transitions occuring over a broad (often 40°C) temperature range. These results indicate that syn-PHB chain segments of variable syndioregularity form crystalline regions with very different thermodynamic stabilities. Maximum degrees of crystallinity for melt annealed 0.64- and 0.71-syn-PHB was observed at an annealing temperature (T _c ) of 30°C. AtT _c values at 45°C and higher, crystallization of relatively lower syndioregular chain segments was apparently excluded to variable degrees dependent onT _c and sample syndiotactic dyad content. After crystallization of syn-PHB samples at elevated temperatures, ambient temperature annealing resulted in an observed lower temperature melting transition at 50°C. This result showed little to no dependence on syn-PHB syndio-regularity andT _c . Both solution precipitated 0.62-syn-PHB and 0.71-syn-PHB have WAXS patterns with poorly resolved crystalline reflections superimposed on amorphous haloes indicating low levels of crystallinity (17% and 25%, respectively) and poorly formed crystals. Isothermal crystallization monitored by DSC showed that the syn- and natural origin PHB showed fastest crystallization rates at temperatures between 50°C and 70°C and 60°C and 90°C, respectively. From the dependence of the higher melting transition onT _c it was determined that the equilibrium melting temperatures for 0.62-syn-PHB (M _n =83,700 g/mol) and a 0.64-syn-PHB (M _n =11,900 g/mol) were 157 and 154°C, respectively. An Avrami analysis of syn-PHB yielded results similar to that found for natural origin PHB indicating that crystal growth occurs by a two-dimensional mechanism.Guest Editor: Dr. Graham Swift, Rohm & Haas.     

Distribution of poly(β-hydroxybutyrate) and poly(ε-caprolactone)aerobic degrading microorganisms in different environments

To assess the capacity of the natural environment for degrading plastics, the populations of poly(-hydroxybutyrate)(PHB)-and poly(-caprolactone)(PCL)-degrading aerobic microorganisms and their ratios to the total number of microorganisms in soil samples were estimated by the plate count method with agar medium containing emulsified PHB or PCL. The numbers of the degrading microorganisms were determined by counting colonies that formed clear zones on the plate. It was found that PHB- and PCL-degrading (depolymerizing) microorganisms are distributed over many kinds of material, including landfill leachate, compost, sewage sludge, forest soil, farm soil, paddy soil, weed field soil, roadside sand, and pond sediment. Of total colony counts, the percentages of PHB and PCL degrading microorganisms were 0.2–11.4 and 0.8–11.0%, respectively. The results suggest that many kinds of degrading microorganisms are present in each environment and that specific consortia differing in biodegradation capacity are constructed.     

The degradation of gel-spun poly(β-hydroxybutyrate) “wool”

The apparent biodegradability and biocompatibility of the microbially produced polyester, poly(-hydroxybutyrate) (PHB), has been the focus of much research by a number of authors with regard to its potential for use in packaging and medical implantation devices. PHB has recently been produced by gel-spinning into a novel form, with one possible application being as a wound scaffolding device, designed to support and protect a wound against further damage while promoting healing by encouraging cellular growth on and within the device from the wound surface. This new nonwoven form combines a large volume with a low mass, has an appearance similar to that of cotton wool, and has been called wool because of this similarity. The hydrolytic degradation of this wool was investigated in an accelerated model of pH 10.6 and temperature 70°C. It was determined that the PHB wool gradually collapsed during degradation. The surface area-to-volume ratio was concluded to be a primary influencing factor. Degradation was characterized by a reduction in the glass transition temperatures and melting points and a fusion enthalpy peak of maximum crystallinity, (88%), which coincided with the point of matrix collapse.