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.     

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.     

Degradation of Polycaprolactone Modified with TPS or CaCO3 in Biotic/Abiotic Seawater

This paper is an investigation of the polymer degradation process in two types of seawater (with and without microorganisms) sourced from the Baltic Sea. The chosen polymeric materials were polycaprolactone modified with either thermoplastic starch (PCL/TPS?>?85%) or calcium carbonate (60% PCL/40% CaCO₃) compared directly against unmodified polycaprolactone. All samples were incubated for 28?weeks in seawater with and without microorganisms under laboratory conditions and analysed before and after the degradation process. Weight loss analysis, microscopic observations of polymer surfaces and tensile strength tests were used to determine the progress of polymer degradation. The experimental results obtained indicated, that in each of the experiments, degradation of tested polymeric samples occured. The process was more effective in seawater with microorganisms compared against systems without added microorganisms. The experiment in seawater demonstrated that modification of PCL with calcium carbonate did not encourage the degradation process; and in some circumstances inhibited it.     

Biodegradation of acrylic acid polymers and oligomers by mixed microbial communities in activated sludge

The biodegradability (mineralization to carbon dioxide) of acrylic acid oligomers and polymers was studied in activated sludge obtained from continuous-flow activated sludge (CAS) systems exposed to mixtures of low molecular weight (Mw < 8000) poly(acrylic acid)s and other watesoluble polymers [poly(ethylene glycol)s] in influent wastewater. Dilute preparations of activated sludge from the CAS units were tested for their ability to mineralize acrylic acid monomer and dimer, as well as a series of model acrylic acid oligomers and polymers (Mw 500, 700, 1000, 2000, and 4500), as sole carbon and energy sources. Complete mineralization of acrylic acid monomer and dimer was observed in low-biomass sludge preparations previously exposed to the polymer mixture, based on carbon dioxide production and residual dissolved organic carbon analyses. Extensive (though incomplete) degradation was also observed for the low molecular weight acrylic acid oligomers (Mw 500 and 700), but degradation dropped off sharply for the 1000, 2000, and 4500 Mw polymers. Radiochemical (¹⁴C) data also confirmed the low degradation potential of the 1000, 2000, and 4500 Mw materials. Degradation of two commercial poly(ethylene glycol)s at 1000 and 3400 Mw was complete and comparable to that of the acrylic acid monomer and dimer. Our results indicate that mixed populations of activated sludge microorganisms can extensively metabolize acrylic acid oligomers of seven units or less. Complete mineralization, however, could be confirmed only for the monomer and dimer material, and carbon mass balance data suggested that the true molecular weight cutoff for complete biodegradation was significantly less than the 500–700 Mw range tested.     

Biodegradability and Biodegradation of Polyesters

A variety of biodegradable plastics have been developed in order to obtain useful materials that do not cause harm to the environment. Among the biodegradable plastics, aliphatic polyesters such as: poly(3-hydroxybutyrate) (PHB), poly(ε-caprolactone) (PCL), poly(butylene succinate) (PBS), and poly(l-lactide) (PLA) have become the focus of interest because of their inherent biodegradability. However, before their widespread applications, comprehensive studies on the biodegradability and biodegradation mechanisms of these polyesters are necessary. Thus, this paper describes the degradation mechanisms and the effects of various factors on the degradation of polyesters. The distribution of polymer-degrading microorganisms in the environment, different microorganisms and enzymes involved in the degradation of various polyesters are also discussed.     

Blending Modification of PHBV/PCL and its Biodegradation by <Emphasis Type="Italic">Pseudomonas mendocina</Emphasis>

Poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) is a biodegradable polymer synthesized in microorganisms. The application of PHBV is limited by certain material disadvantages. Poly(ε-caprolactone) (PCL) possesses excellent thermodynamic and mechanical properties and was used to modify PHBV in the presence of triethyl citrate (TEC) and dicumyl peroxide (DCP), which was used as plasticizer and grafting agent, respectively. The effects of PCL and additive agents on the mechanical, thermal, amphipathic and degradability behaviors of the blends were investigated. The results showed that the mechanical properties of the PHBV blends improved by PCL incorporation and improved even further after TEC and DCP addition. The addition of DCP could not induce an increase in crystallization temperature but improved the crystallization degree of the blends. The presence of hydrophilic groups in TEC leads to an apparent increases in the hydrophilicity of the PHBV blends. A PHBV/PCL blend (40/60) with TEC (20 wt.%) and DCP (0.5 wt.%) was chosen for its good mechanical properties and hydrophilicity. The chosen ratio of the blends was also shown a preferable degradation activity by biodegradation assay using Pseudomonas mendocina. The addition of TEC and DCP has no conspicuous negative effect on the biodegradation.     

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.     

Tensile Behavior of Thermoplastic Films from Wheat Flours as Function of Raw Material Baking Properties

The production of bioplastics directly from wheat flour has been demonstrated to be reliable, but scarce knowledge is available on how flour characteristics may affect the performance of thermoplastic films. In this work, we first established the most suitable recipe and process for the production of extruded films and then we used eight single-cultivar wheat flours with different baking technological properties to assess how they affect the mechanical properties of thermoplastic films. The results have shown that flours from soft grain cultivars offered more rigid and deformable films than flours from hard grain cultivars. For similar hardness, the alveographic P/L ratio of the dough was inversely related to rigidity and directly related to deformability of plastic films, while the deformation energy of the dough (W) played a role only for great differences of it. The subsequent fabrication of blends between each of the flours that yielded the best film properties and polycaprolactone (PCL) at different proportions indicated that a wheat flour/PCL ratio (TWF/PCL) of 75/25 offered the most suitable films for further application. Our results are likely to be useful for improving the plasticization of flour, in that selection of wheat flours could be tailored on the properties desired for the bioplastic films.     

Effect of Poly(dioxolane) as Compatibilizer in Poly(ɛ-caprolactone)/Tapioca Starch Blends

The influence of poly(dioxolane) (PDXL), a poly(ethylene oxide-alt-methylene oxide), as compatibilizer on poly(ɛ-caprolactone) (PCL)/tapioca starch (TS) blends was studied. In order to facilitate blending; PCL, PDXL and TS must be blended together directly; so that PDXL is partially adhered at the TS surface as shown by scanning electron microscopy. The molecular weight effect of PDXL on the PCL/TS blends showed that mechanical properties of PCL/TS/PDXL blends from low molecular weight (M _n=10,000) and high molecular weight (M _n=200,000) PDXL were rather dependent on TS content. The enzymatic degradability of PCL/TS/PDXL blends using α-amylase increased as the TS content increased but was independent on the dispersion of tapioca starch in the PCL matrix.     

Lignin/Poly(ε-Caprolactone) Blends with Tuneable Mechanical Properties Prepared by High Energy Ball-Milling

Polymer blends between lignin, a natural, widely available, no-cost material, and Poly(ε-caprolactone) (PCL), a biodegradable polymer, have been prepared using the ‘clean’, friendly to the environment, technique of the High Energy Ball Milling (HEBM). Two kinds of lignin have been used, Straw lignin, obtained through the Steam Explosion process (SE lignin), and/or Lignosulphonated one (LS lignin). The tensile mechanical tests have shown that, at certain specific compositions, the blends, in particular those with both SE and LS lignin, have good mechanical properties. In particular, by varying the blend composition it is possible to obtain materials with tuneable properties, therefore useful for different applications. Dynamic-Mechanical-Thermal Analysis (DMTA) reveals substantial immiscibility of the blends. Experiments of UV irradiation show that lignin acts as an UV stabilizer for PCL. The effect is higher with SE lignin, likely due to its low molecular weight, which allows the short lignin chains to diffuse more easily within the amorphous regions of PCL.     

Physical properties and biodegradability of blends containing poly(ε-caprolactone) and tropical starches

In order to assess feasibility of tropical starches (sago and cassava starches) as biodegradable plastic materials, blending with poly(-caprolactone) (PCL), a biodegradable polymer, was carried out. It was confirmed that the physical properties (tensile strength and elongation) of PCL/sago and PCL/cassava blends were similar to those of PCL/corn blend, suggesting that sago and cassava starches can also be blended with PCL for production of biodegradable plastic. However, the properties of all PCL/starch blends were still low compared with those of polyethylene. Enzymatic degradability evaluation showed that lipase degradation of PCL and-amylase degradation of starch increased as the starch content in the blend increased. Burial test of the blends for 1, 3, and 5 months was carried out and the rate of degradation of the PCL/sago blend was confirmed to be slower than those of PCL/corn and PCL/cassava blends. Observation of the film blends structure by scanning electron microscope revealed that the starch was dispersed in a PCL continuous phase. Furthermore, changes in the film surface before and after enyzme treatments were observed.     

Biosynthesis of poly-(R)-3-hydroxyalkanoate: An emulsion polymerization

Poly-(R)-3-hydroxyalkanoates (PHAs) are bacterial storage polyesters, which are accumulated by a wide variety of microorganisms as a reserve of carbon and energy. Currently, these biopolymers are receiving much attention because of their potential application as biodegradable and biocompatible plastics. The polymer appears as submicron intracellular granules. The biosynthesis of these granules has been studied extensively but many observations remain inexplicable. This paper draws an analogy between the process of emulsion polymerization and that of granule formation. This analogy may explain many of the unknown features of granule formation and may also lead to useful applications of granules as latex products.     

Determination of Microorganisms’ Attack on Some Flexible Polymers by Using Soil Burial Test Method

Many controversial issues have recently been associated with plasticized poly(vinyl chloride) (pPVC) used in building applications, mainly for flooring. One of them has to do with the health impact of some plasticizers and thermal stabilizers based on heavy metal compounds. Recent advances in the synthesis of polyolefins based on metallocene catalysts can yield similar flexibility for formulations as is now available for those based on pPVC. Polyolefin copolymers are considered to be possible replacements for pPVC. The soil burial test has demonstrated that highly filled polyolefin elastomer formulations having a significant percentage of post-consumer polyolefins (up to 60% in laboratory conditions) have interesting properties from the biodegradation point of view. They are more resistant to microorganisms’ attack than plasticized flooring formulations based on PVC that are currently used, even in a very harsh environment as soil, where complex mixtures of microorganisms are present. The effect of microorganisms’ attack after soil burial was evaluated by visual examination, weight loss, water absorption and changes in mechanical properties.     

TPS/PCL Composite Reinforced with Treated Sisal Fibers: Property, Biodegradation and Water-Absorption

Sisal fibers bleached with sodium-hydroxide followed by hydrogen peroxide treatment were incorporated in a thermoplastic starch/ε-polycaprolactone (TPS/PCL) blend via extrusion processing. These samples with smooth and homogenous surfaces were examined for their property, biodegradability and water absorption. Scanning electron microscopy revealed that the fibers were well dispersed in the matrix. In addition, it was found that the fibers and matrices interacted strongly. Blends with 20 % (dry weight-basis) fiber content showed some fiber agglomeration. Whereas blends with 10 % fibers showed increased crystallinity and lower water absorption capacity. The CO₂ evolution study showed that the thermoplastic starch samples without any additives had the highest rate and extent of degradation whereas the neat PCL samples had the lowest degradation rate. Addition of fiber to the TPS/PCL blend exhibited the degradation rates and extents that were somewhere in between the pure TPS and neat PCL. This work demonstrates that TPS/PCL composites reinforced with bleached sisal has superior structural characteristics and water resistance and thus, can be used as polymeric engineering composites for different applications.     

The Effects of Additives on the Biodegradation of Polycaprolactone Composites

Because environmental pollution caused by plastic waste is a major problem investigations concerning biodegradable packaging are important and required. In this study, the biodegradation of PCL composite films with organic (glycerol monooleate and oleic acid) and inorganic additives (organo nano clay) was investigated to understand which additive and the amount of additive was more effective for biodegradation. The relationship between the degree of crystallinity and the effect of additives on the biodegradability of polycaprolactone (PCL) was examined. PCL composite films were prepared using organo nano clay (0.1–0.4–1–3 wt%) and oleic acid (1–3–5 wt%) or GMO (1–3–5 wt%). The 35 films prepared with PCL (P), clay (C), oleic acid (O), or glycerol monooleate (G) are coded as P_C#wt%_O (or G)#wt%. The composite films, P_C0.4_O5 contains 0.4 wt% clay and 5 wt% oleic acid and the P_C3_G1 contains 3 wt% clay and 1 wt% glycerol monooleate. The biodegradation of PCL films in simulated soil was studied for 36 months. The films were periodically removed from the simulated soil and film thicknesses, weight losses, visual changes, crystal structures, and a functional group analyses were performed. PCL composite films are separated into three groups, depending on degradation time, (1) films that degraded before 8 months (fast degradation), (2) films that degraded around 24 months (similar to neat PCL), and (3) films that take longer to degrade (slow degradation). The films in the first group are PCL films with 1 and 3 wt% clay additive and they begin to biodegrade at the 5th month. However, a composite film of PCL with only 0.4 wt% clay and 5 wt% GMO addition has the shortest degradation time and degraded in 5 months. The films in the last group are; P_G3, P_G5, P_C0.1, P_C0.1_O1, and P_C0.1_O5 and they took around 30 months for biodegradation. It was observed that increasing the organo nanoclay additive increases the biodegradability by disrupting the crystal structure and causing a defective crystal formation. The addition of GMO with organo nano clay also accelerates biodegradation. The addition of organo nano clay in an amount as small as 0.1 wt% acts as the nucleating agent, increases the degree of crystallinity of the PCL composites, and slows the biodegradation period by increasing the time.     

Biobased Contents of Organic Fillers and Polycaprolactone Composites with Cellulose Fillers Measured by Accelerator Mass Spectrometry Based on ASTM D6866

The biobased contents of raw materials such as starches, sugar, chitin, or wood powders for biomass plastics were measured using Accelerator Mass Spectrometry (AMS) based on ASTM D6866. AMS measures the isotope carbon ratio of ¹⁴C to ¹²C and ¹³C in graphite derived from sample powders. The biobased contents of starches, sugar or chitin were almost 100% which means that they are fully biobased. The biobased contents of the wood powders were over 140% due to the effect of the post 1950s ¹⁴C injection due to nuclear testing. Poly(ε-caprolactone) (PCL) composite samples were prepared using the polymerization and direct molding method. The starting compound was the ε-caprolactone monomer liquid combined with cellulose and inorganic fillers using aluminum triflate as a catalyst at 80 °C for 6 or 24 h. PCL cylinder-shaped composite samples with a homogeneously dispersed cellulose filler were prepared with M_n = 4,600 (M_w/M_n = 2.9). The biobased content of the PCL composite with 50 wt% cellulose filler (51.67%) measured using AMS was slightly higher than the carbon ratio of cellulose in the starting powder samples (41.3 mol%). This is due to the higher biobased content (112.70%) of the cellulose filler used in this study. The biobased content of the polymer composite powders by AMS was found not to be affected by the presence of inorganic fillers, such as talc.     

Synthesis of copolyesters containing poly(ethylene terephthalate) and poly(ε-caprolactone) units and their susceptibility toPseudomonas sp. lipase

Copolyesters containing poly(ethylene terephthalate) (PET) and poly(-caprolactone) (PCL) were synthesized from PET and PCL homopolymers by transesterification reaction at 270°C in the presence of catalyst. The copolyesters were characterized by¹³C-NMR and differential scanning calorimetry (DSC). The degradation behavior of PCL byPseudomonas sp. lipase in buffer solution (pH 7) and tetrahydrofuran (THF) was investigated by gel permeation chromatography (GPC) and¹H-NMR. From these experiments, it was found thatPseudomonas sp. lipase acted endoenzymatically on PCL. Using this lipase, degradation tests for PET/PCL copolyesters whose PCL content was below 50% by weight were also performed in buffer solution (pH 7). However, evenPseudomonas sp. lipase with high degradation activity on PCL did not easily degrade the PCL unit in PET/PCL copolyesters.     

Lignin-based Carbon Fibers: Effect of Synthetic Polymer Blending on Fiber Properties

Carbon fibers have been produced from hardwood lignin/synthetic polymer blend fibers. Hardwood kraft lignin was thermally blended with two recyclable polymers, poly(ethylene terephthalate) (PET) and polypropylene (PP). Both systems were easily spun into fibers. A thermostabilization step was utilized prior to carbonization to prevent fusion of individual fibers. For the lignin-based carbon fibers, careful control of heating rate was required. However, PET–lignin blend fibers can be thermostabilized under higher heating rates than the corresponding homofibers. Carbon fiber yield decreased with increasing incorporation of synthetic plastic. However, carbon fiber yield obtained for a 25% plastic blend fiber was still higher than that generally reported for petroleum pitch. Blend composition also affected surface morphology of the carbon fibers. Immiscible lignin–PP fibers resulted in a hollow and/or porous carbon fiber; whereas carbon fiber produced from miscible lignin–PET fibers have a smooth surface. Synthetic polymer blending also affected the mechanical properties of the fibers, especially MOE; lignin-based carbon fiber properties improved upon blending with PET.     

Biodegradation Properties of Poly-ε-caprolactone,Starch and Cellulose Acetate Butyrate Composites

Blending starches with polymers such as poly-ε-caprolactone (PCL) has been used as a route to biodegradable plastics. The addition of starch has a significant effect on all physical properties including toughness, elongation at break. On blending cellulose acetate butyrate (CAB) with starch and PCL, improvements in most physical and mechanical properties were observed. This is may be due to CAB acts as a compatibilizer between PCL and starch due to the presence of both hydroxyl groups (in starch and CAB) and ester carbonyls (in PCL and CAB). The presence of different compounds affects the way in which other components degrade. For example the structure of CAB within a starch and PCL combination might make the degradation rate different to that when starch was only mixed with PCL. To check whether this was the case, three combinations of different blends were used to calculate the rate of degradation of each of them separately. These degradation rate constants were then used to predict the theoretical degradation which was checked against the experimental value for other different combinations.     

Biodegradation of Electrospun Poly-(ɛ-caprolactone) Non-woven Fabrics by Pure-Cultured Soil Filamentous Fungi

The biodegradation of electrospun nano-fibers of poly(-caprolactone) (PCL) was initially investigated with respect to the environmental application of PCL non-woven fabrics, using pure-cultured soil filamentous fungi, Aspergillus oryzae, Penicillium caseicolum, P. citrinum, Mucor sp., Rhizopus sp., Curvularia sp., and Cladosporium sp. Three kinds of non-woven PCL fabrics with different mean fiber diameters (330, 360, and 510 nm) were prepared by changing the viscosities of the pre-spun PCL solutions (150, 210, and 310 cPs, respectively). All of the pure-line soil filamentous fungi tested grew on the two fiber materials. Electron microscopy was used to observe the biodegradation processes revealing remarkable growth of two fungi, Rhizopus sp. and Mucor sp., along with the accompanying collapse of the nano-fiber matrices. In the biochemical oxygen demand (BOD) test, the biodegradation of the 330 nm PCL nano-fibers by Rhizopus sp. and Mucor sp. exceeded 20 and 30% carbon dioxide generation, respectively. The biodegradability of the PCL non-woven fabrics decreased with the mean fiber diameter and the 330 nm PCL nano-fiber that was made from 150 cPs solution (concentration, 7 wt%) exhibited the highest biodegradability. These results might offer some clues for the applications of the PCL non-woven fabrics having the controlled biodegradability in the environmental uses.