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 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.     

Synthesis and environmental degradation of polyesters based on poly (ε-caprolactone)

Poly (-caprolactone) (PCL), poly (-valerolactone) (PVL), poly (-caprolactone-co--valerolactone) [P(CL-co-VL)], and poly (-caprolactone-co-ethylene oxide-co--caprolactone) (PCL-PEO-PCL) were synthesized by ring-opening and diol-initiated polymerization of -caprolactone and -valerolactone. The degradation of the samples by chemical hydrolysis and in a soil burial test was evaluated. It was found that PCL, PVL, and P(CL-co-VL) degrade mainly enzymatically. The rate of degradation depends on their molecular weight, chemical structure, composition, and morphology. PCL-PEO-PCL block copolymers exhibit a repelling effect to the microorganisms in the soil, which depends on the molecular weight and relative amount of PEO block in the copolymer.     

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.     

Preparation conditions and swelling equilibria of biodegradable hydrogels prepared from microbial poly(γ-glutamic acid) and poly(ε-lysine)

Biodegradable hydrogels prepared by -irradiation from microbial poly(amino acid)s are reviewed. pH-sensitive hydrogels were prepared by means of -irradiation of poly(-glutamic acid) (PGA) produced byBacillus subtilis IFO3335 and poly(-lysine) (PL) produced byStreptomyces albulus in aqueous solutions. The preparation conditions, swelling equilibria, hydrolytic degradation, and enzymatic degradation of these hydrogels were studied. A hydrogel with a wide variety of swelling behaviors has been produced by -irradiation from a mixture solution of PGA and PL.Paper presented at the 4th International Workshop on Biodegradable Plastics and Polymers, October 11–14, 1995, Durham, New Hampshire, USA.     

Degradation of poly(β-hydroxyalkanoates) and polyolefin blends in a municipal wastewater treatment facility

Six types of plastics and plastic blends, the latter composed at least partially of biodegradable material, were exposed to aerobically treated wastewater (activated sludge) to ascertain their biodegradability. In one study, duplicate samples of 6% starch in polypropylene, 12% starch in linear low-density polyethylene, 30% polycaprolactone in linear low-density polyethylene, and poly(-hydroxybutyrate-co-hydroxyvalerate) (PHB/V), a microbially produced polyester, were exposed to activated sludge for 5 months, and changes in mass, molecular weight average, and tensile properties were measured. None of the blended material showed any sign of degradation. PHB/V, however, showed a considerable loss of mass and a significant loss of tensile strength. In a second study, PHB/V degraded rapidly, but another type of microbial polymer which forms a thermoplastic elastomer, poly(-hydroxyoctanoate), did not degrade. These results illustrate the potential for disposal and degradation of PHB/V in municipal wastewater.     

Structure and Morphology of Microbial Degraded Poly(ε-caprolactone)/Graphite Oxide Composite

Biodegradation of poly(ε-caprolactone) composite with graphite oxide (GO) by the action of Bacillus subtilis (BS) was studied in this work. Nanocomposite produced in a form of thin film was exposed to nutrient cultivation medium with BS as well as to abiotic nutrient medium (control run) at 30 °C. The matrix itself was exposed to the same conditions for comparison. Biodegradation was demonstrated by the weight loss and the decrease of molecular weight during 21 days of the experiment as well as by changes in the surface morphology and structure. Both degraded and control materials were characterized by confocal laser scanning microscopy, differential scanning calorimetry, thermogravimetry, and Fourier transform infrared spectroscopy with attenuated total reflectance. The bacterial growth expressed as the measure of the optical density/turbidity in McFarland units and pH of medium were measured in situ during the experiment. Lipolytic activity of BS was determined by spectrophotometric assay. Degradation process was accompanied by the increase of matrix crystallinity degree. GO served as nucleating agent and facilitated absorption of cultivation media into the composite which led to the increase of the crystallinity degree also for control nanocomposite specimens. It was not evaluated to be promoter of biodegradation. The surface cracks formation was initiated by BS action. Large surface cracks were formed on BS-degraded composite surfaces while surface erosion was more significant on BS-degraded matrix.     

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.     

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.     

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.     

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.     

Influence of Processing Additives on the Degradation of Melt-Pressed Films of Poly(ε-Caprolactone) and Poly(Lactic Acid)

Melt-pressed films of polycaprolactone (PCL) and poly(lactic acid) (PLA) with processing additives, CaCO₃, SiO₂, and erucamide, were subjected to pure fungal cultures Aspergillus fumigatus and Penicillium simplicissimum and to composting. The PCL films showed a rapid weight loss with a minor reduction in the molecular weight after 45 days in A. fumigatus. The addition of SiO₂ to PCL increased the rate of (bio)erosion in A. fumigatus and in compost. The use of a slip additive, erucamide, was shown to modify the properties of the film surface without decreasing the rate of bio(erosion). Both the rate of weight loss and the rate of molecular weight reduction of PCL increased with decreasing film thickness. The addition of CaCO₃ to PLA significantly reduced the thermal degradation during processing, but it also reduced the rate of the subsequent (bio)degradation in the pure fungal cultures. PLA without additives and PLA containing SiO₂ exhibited the fastest (bio)degradation, followed by PLA with CaCO₃. The degradation of the PLA films was initially governed by chemical hydrolysis, followed by an acceleration of the weight change and of the molecular weight reduction. PLA film subjected to composting exhibits a rapid decrease in molecular weight, which then remains unchanged during the measurement period, probably because of crystallization.     

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.     

Biodegradation of Poly(ε-caprolactone) (PCL) Film by <Emphasis Type="Italic">Alcaligenes faecalis</Emphasis>

The biodegradation behavior of PCL film with high molecular weight (80,000 Da) in presence of bacterium Alcaligenes faecalis and the analysis of degraded polymer film have been carried out. Thin Films of PCL were prepared by means of solution casting method and the bacterial degradation behavior was carried in basal medium, in presence of bacteria with time variation after UV treatment. It was observed that after UV treatment the degradation of polymer film was increased and the degradation rate followed a three steps degradation mechanism. The degraded polymer film was analyzed by means of Differential Scanning Calorimeter (DSC), Thermo Gravimetric Analyzer (TGA) and Fourier Transform Infrared Spectroscope (FTIR). DSC results revealed that at the initial stages of the degradation up to 15–20 days, the bacterium preferentially degrades the amorphous parts of the polymer film over the crystalline zone. Thermo gravimetric analysis highlighted the low temperature stability of degraded films with extent of degradation. FTIR results showed the chain scission mechanism of the polymer chains and also supported the preferential degradation of amorphous phase over crystalline phase in the initial stages of the degradation.     

Novative Biomaterials Based on Chitosan and Poly(ε-Caprolactone): Elaboration of Porous Structures

The swelling capability of chitosan was explored in order to use water both, as volatile plasticizer and as pore-forming agent. Chitosan powder was swelled in acidic aqueous solution and melt blended with poly(ε-caprolactone) (PCL). After stabilization at 57% RH and 25 °C, samples suffered a water mass loss of around 30 wt% without dimensions variation. Despite the low miscibility of these biopolymers, quite homogeneous dispersion of chitosan within the polyester matrix was obtained. Some interactions between both biopolymers could be observed. To obtain chitosan phase with a thermoplastic-like behaviour, the plasticization effect was also studied by the addition of 25 wt% glycerol as non volatile plasticizer. The equilibrium moisture content of samples increased with the incorporation of glycerol due to its hydrophilic nature. Morphology, thermal and mechanical properties of the blends were determined after stabilization. The preparation of rich PCL blends allowed the formation of macroporous structures since samples were not contracted after water loss and stabilization. These biomaterials with such a porous structure could be used for biomedical applications.     

Hydrolytic and enzymatic degradation of poly(γ-glutamic acid) hydrogels and their application in slow-release systems for proteins

The hydrolytic and enzymatic degradation of newly developed hydrogels, produced by cross-linking purified poly(-glutamic acid) (PGA) with dihaloalkane compounds, was studied and is reported in this paper. Analysis of hydrolysis of the hydrogel as a function of pH indicated that the hydrolysis occurred slowly at neutral pH, but fast in both acidic and alkaline solutions, while the polymer could be hydrolyzed rapidly only in acidic solutions. The ester bonds were more sensitive to hydrolysis than peptide bonds. The biodegradability of the hydrogel and polymer was further confirmed when enzymatic degradation was studied by three enzymes (cathepsin B, pronase E, and trypsin), which were able to cleave both ester and peptide bonds gradually. A slow-release system for porcine somatotropin (pST) formed by using the hydrogel as matrix to entrap the hormone was evaluatedin vitro andin vivo. Results demonstrated that the hydrogel was able to release the hormone for a period of 20–30 days and indicated its potential application in slow-release systems for bioactive materials, especially macromolecules, such as peptides and proteins.     

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.     

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.     

A method for the isolation of microorganisms producing extracellular long-side-chain poly (β-hydroxyalkanoate) depolymerase

A simple method was developed for the preparation of an autoclavable, long-side-chain poly (-hydroxyalkanoate) (LSC-PHA) colloidal suspension, which was used as a substrate for enzymatic degradation and to prepare agar overlay plates for the isolation of microorganisms producing extracellular LSC-PHA depolymerase. Six cultures producing extracellular LSC-PHA depolymerase were isolated from a composted hydrocarbon-contaminated soil. All were pseudomonads or related bacteria. All (with the possible exception ofXanthomonas maltophilia) could produce LSC PHA. Except forX. maltophilia none could hydrolyze poly (-hydroxybutyrate). Screening of sevenPseudomonas strains known to accumulate LSC PHA showed that all were negative for extracellular LSC-PHA depolymerase production. It was concluded that extracellular LSC-PHA depolymerase producers are found mostly in the genusPseudomonas but that they are relatively uncommon.