Isolation and characterization of poly(butylene succinate)-degrading fungi

We isolated 12 poly(butylene succinate) (PBSu)-degrading fungi from various soil environments. Among the isolates, the NKCM1706 strain exhibited the fastest degradation rate for the PBSu film (10.5 μg cm⁻² h⁻¹). Phylogenetic analysis revealed that this strain is closely related to Aspergillus fumigatus (internal transcribed spacer (ITS) identity, 100%). Further, this strain exhibited PBSu-hydrolytic activity in the presence of poly(?-caprolactone) (PCL), PBSu, and poly(butylene succinate-co-adipate) (PBSA). On adding this strain into the soil sample, the PBSu degradation rate accelerated approximately sixfold, suggesting that this strain plays a crucial role in PBSu degradation in actual soil environments. In addition to PBSu, the NKCM1706 strain could degrade PBSA, poly(ethylene succinate) (PESu), poly(3-hydroxybutyrate) (P(3HB)), and PCL.     

Thermal degradation kinetics of the biodegradable aliphatic polyester, poly(propylene succinate)

The preparation of the biodegradable aliphatic polyester poly(propylene succinate) (PPSu) using 1,3-propanediol and succinic acid is presented. Its synthesis was performed by two-stage melt polycondensation in a glass batch reactor. The polyester was characterized by gel permeation chromatography, ¹H NMR spectroscopy and differential scanning calorimetry (DSC). It has a number average molecular weight 6880 g/mol, peak temperature of melting at 44 °C for heating rate 20 °C/min and glass transition temperature at −36 °C. After melt quenching it can be made completely amorphous due to its low crystallization rate. According to thermogravimetric measurements, PPSu shows a very high thermal stability as its major decomposition rate is at 404 °C (heating rate 10 °C/min). This is very high compared with aliphatic polyesters and can be compared to the decomposition temperature of aromatic polyesters. TG and Differential TG (DTG) thermograms revealed that PPSu degradation takes place in two stages, the first being at low temperatures that corresponds to a very small mass loss of about 7%, the second at elevated temperatures being the main degradation stage. Both stages are attributed to different decomposition mechanisms as is verified from activation energy determined with isoconversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures is auto-catalysis with activation energy E = 157 kJ/mol while the second mechanism is a first-order reaction with E = 221 kJ/mol, as calculated by the fitting of experimental measurements.     

Fungal degradation of poly(ethylene succinate)

Twenty fungi, which all formed a clear zone around the colony on a poly(ethylene succinate) (PESu)-containing medium, were isolated from various environmental samples. Mesophilic strain NKCM1003, with the highest PESu hydrolytic activity among all the isolates, degraded a PESu film at the rate of 21 ± 2 μg/cm²/h when it was aerobically incubated at 30 °C on a medium containing PESu as the sole carbon source. SEM observations showed that the strain gradually degraded the film starting from the amorphous regions of the surface. Phylogenetic analysis revealed that the strain was closely related to the species Aspergillus clavatus. Zymogram analysis suggested that the secreted enzyme with PESu hydrolytic activity is a P(3HB) depolymerase. The strain also utilized the enzymatic products of PESu, permitting it to grow well. These results indicate that the strain NKCM1003 plays an important role in the PESu-degrading process in the field.     

Biodegradable poly(alkylene succinate) blends: Thermal behavior and miscibility study

New binary blends composed of poly(ethylene succinate) and poly(propylene succinate) or poly(ethylene succinate) and poly(butylene succinate) were prepared. Both PESu/PPSu and PESu/PBSu systems belong to semicrystalline/semicrystalline pairs. The miscibility and crystallization behavior was investigated using differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), and polarizing light microscopy (PLM). Blends of PESu and PPSu exhibited a single composition dependent glass transition temperature over the entire range of composition, indicating that the system is miscible. The melting point depression of the high melting temperature component, PESu, was analyzed according to the Nishi‐Wang equation. A negative polymer–polymer interaction parameter was obtained, indicating that the blends are thermodynamically miscible in the melt. The two components crystallized sequentially when the blends were cooled rapidly to a low temperature. DSC traces of PESu/PBSu blends after quenching showed two distinct composition dependent glass transition temperatures between those of the neat polymers, showing that the polymers are partially miscible. The amorphous PESu/PBSu blends in the intermediate compositions showed three cold‐crystallization peaks, indicating the influence of mixing. The crystallization rates of PBSu were reduced and those of PESu were increased. WAXD showed reduced crystallinity and peak broadening in the patterns of the blends of intermediate compositions, while no spherulites could be detected by PLM. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 584–597, 2006     

Investigation of thermal degradation mechanism of an aliphatic polyester using pyrolysis-gas chromatography-mass spectrometry and a kinetic study of the effect of the amount of polymerisation catalyst

The thermal degradation mechanism of the aliphatic biodegradable polyester poly(propylene succinate) (PPSu) and the effect of the polymerisation catalyst (tetrabutyl titanate, TBT) were studied using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and TGA analysis. It is found from mass ions detection, that the decomposition takes place, mainly, through β-hydrogen bond scission and secondarily by α-hydrogen bond scission. At low pyrolysis temperatures (360 and 385 °C) gases as well as succinic anhydride, succinic acid and propanoic acid are mainly produced while allyl and diallyl succinates are formed in smaller quantities. At high temperatures (450 °C) the behaviour is inverted. Using the isoconversional methods of Ozawa and Friedman it is founded that PPSu degrades by two consecutive mechanisms. According to this analysis the first mechanism that takes place at low temperatures is autocatalysis with an activation energy of about E = 110-120 kJ/mol. The second mechanism is a first-order reaction with E of 220 kJ/mol, and corresponds to the extended β- and α-hydrogen bond scissions. These activation energies are slightly dependent on the catalyst amount and are shifted towards lower values with an increase of TBT content from 3 × 10⁻⁴ to 3 × 10⁻¹ mol TBT/mol succinic acid (SA).     

Thermal decomposition of poly(propylene sebacate) and poly(propylene azelate) biodegradable polyesters: Evaluation of mechanisms using TGA, FTIR and GC/MS

The synthesis, characterization and thermal behavior of two biodegradable aliphatic polyesters poly(propylene azelate) (PPAz) and poly(propylene sebacate) (PPSeb) are described in the present work. The thermal degradation of both polyesters was studied using thermogravimetric analysis (TG) by the determination of their mass losses during heating. From the thermogravimetric curves it can be seen that both polyesters are thermally stable materials since PPAz has its highest decomposition rate at 411.3 while PPSeb at 413.6 °C. From the variation of activation energy (E) with increasing degree of conversion it is found that the polyester's decomposition proceeds with a complex reaction mechanism with the participation of at least two different mechanisms. To evaluate these mechanisms the TG, FTIR and a combination of TG-gas chromatography-mass spectrometry (TG/GC-MS) methods were used. From mass ions detection of formed decomposition compounds, it was found that the decomposition of both polymers takes place, mainly, through β-hydrogen bond scission and secondarily through α-hydrogen bond scission. The main decomposition products are aldehydes, alcohols, allyl, diallyl, and carboxylic acids.     

Performance of biodegradable microcapsules of poly(butylene succinate), poly(butylene succinate-co-adipate) and poly(butylene terephthalate-co-adipate) as drug encapsulation systems

Poly(butylene succinate) (PBSu), poly(butylene succinate-co-adipate) (PBSA) and poly(butylene terephthalate-co-adipate) (PBTA) microcapsules were prepared by the double emulsion/solvent evaporation method. The effect of polymer and poly(vinyl alcohol) (PVA) concentration on the microcapsule morphologies, drug encapsulation efficiency (EE) and drug loading (DL) of bovine serum albumin (BSA) and all-trans retinoic acid (atRA) were all investigated. As a result, the sizes of PBSu, PBSA and PBTA microcapsules were increased significantly by varying polymer concentrations from 6 to 9%. atRA was encapsulated into the microcapsules with an high level of approximately 95% EE. The highest EE and DL of BSA were observed at 1% polymer concentration in values of 60 and 37%, respectively. 4% PVA was found as the optimum concentration and resulted in 75% EE and 14% DL of BSA. The BSA release from the capsules of PBSA was the longest, with 10% release in the first day and a steady release of 17% until the end of day 28. The release of atRA from PBSu microcapsules showed a zero-order profile for 2 weeks, keeping a steady release rate during 4 weeks with a 9% cumulative release. Similarly, the PBSA microcapsules showed a prolonged and a steady release of atRA during 6 weeks with 12% release. In the case of PBTA microcapsules, after a burst release of 10% in the first day, showed a parabolic release profile of atRA during 42 days, releasing 36% of atRA.     

Synthesis and characterization of biodegradable aliphatic copolyesters with poly(ethylene oxide) soft segments

A series of multiblock poly(ether-ester)s based on poly(butylene succinate) (PBS) as the hard segments and hydrophilic poly(ethylene oxide) (PEO) as the soft segments was synthesized with the aim of developing degradable polymers which could combine the mechanical properties of high performance elastomers with those of flexible plastics. The aliphatic poly(ether-ester)s were synthesized by the catalyzed two-step transesterification reaction of dimethyl succinate, 1,4-butanediol and α,ω-hydroxyl terminated poly(ethylene oxide) (PEO, = 1000 g/mol) in bulk. The content of soft PEO segments in the polymer chains was varied from about 10 to 50 mass%. The effect of the introduction of the soft PEO segments on the structure, thermal and physical properties, as well as on the biodegradation properties was investigated. The composition and structure of these aliphatic segmented copolyesters were determined by ¹H NMR spectroscopy. The molecular weights of the polyesters were verified by gel permeation chromatography (GPC), as well as by viscometry of dilute solutions and polymer melts. The thermal properties were investigated using differential scanning calorimetry (DSC). The degree of crystallinity was determined by means of DSC and wide-angle X-ray scattering. A depression of melting temperature and a reduction of crystallinity of the hard segments with increasing content of PEO segments were observed. Biodegradation of the synthesized copolyesters, estimated in enzymatic degradation tests in phosphate buffer solution with Candida rugosa lipase at 37 °C was compared with hydrolytic degradation in the buffer solution. The weight losses of the samples were in the range from 2 to 10 mass%. GPC analysis confirmed that there were significant changes in molecular weight of copolyesters with higher content of PEO segments, up to 40% of initial values. This leads to conclusion that degradation mechanism of the poly(ether-ester)s based on PEO segments occurs through bulk degradation in addition to surface erosion.     

Synthesis, characterization and thermal degradation mechanism of three poly(alkylene adipate)s: Comparative study

Three high molecular weight aliphatic polyesters derived from adipic acid and the appropriate diol - poly(ethylene adipate) (PEAd), poly(propylene adipate) (PPAd) and poly(butylene adipate) (PBAd) - were prepared by two-stage melt polycondensation method (esterification and polycondensation) in a glass batch reactor. Intrinsic viscosities, GPC, DSC, NMR and carboxylic end-group measurements were used for their characterization. Mechanical properties of the prepared polyesters showed that PPAd has similar tensile strength to low-density polyethylene while PEAd and PBAd are much higher. From TGA analysis it was found that PEAd and PPAd have lower thermal stability than poly(butylene adipate) (PBAd). The decomposition kinetic parameters of all polyesters were calculated while the activation energies were estimated using the Ozawa, Flynn and Wall (OFW) and Friedman methods. Thermal degradation of PEAd was found to be satisfactorily described by one mechanism, with activation energy 153 kJ/mol, while that of PPAd and PBAd by two mechanisms having different activation energies: the first corresponding to a small mass loss with activation energies 121 and 185 kJ/mol for PPAd and PBAd, respectively, while the second is attributed to the main decomposition mechanism, where substantial mass loss takes place, with activation energies 157 and 217 kJ/mol, respectively.     

Miscibility and enzymatic degradation studies of poly(ε-caprolactone)/poly(propylene succinate) blends

In the present study the miscibility behaviour and the biodegradability of poly(ε-caprolactone)/poly(propylene succinate) (PCL/PPSu) blends were investigated. Both of these aliphatic polyesters were laboratory synthesized. For the polymer characterization DSC, ¹H NMR, WAXD and molecular weight measurements were performed. Blends of the polymers with compositions 90/10, 80/20, 70/30 and 60/40 w/w were prepared by solution-casting. DSC analysis of the prepared blends indicated only a very limited miscibility in the melt phase since the polymer-polymer interaction parameter χ₁₂ was −0.11. In the case of crystallized specimens two distinct phases existed in all studied compositions as it was found by SEM micrographs and the particle size distribution of PPSu dispersed phase increased with increasing PPSu content. Enzymatic hydrolysis for several days of the prepared blends was performed using Rhizopus delemar lipase at pH 7.2 and 30 °C. SEM micrographs of thin film surfaces revealed that hydrolysis affected mainly the PPSu polymer as well as the amorphous phase of PCL. For all polymer blends an increase of the melting temperatures and the heat of fusions was recorded after the hydrolysis. The biodegradation rates as expressed in terms of weight loss were faster for the blends with higher PPSu content. Finally, a simple theoretical kinetic model was developed to describe the enzymatic hydrolysis of the blends and the Michaelis-Menten parameters were estimated.     

Thermal and mechanical properties of mandelic acid‐copolymerized poly(butylene succinate) and poly(ethylene adipate)

Phenyl side chains were introduced to poly(butylene succinate) and poly(ethylene adipate) by the polymerization of the respective monomers in the presence of mandelic acid. The increasing content of the phenyl side chains decreased the melting temperature and the crystallinity but increased the glass‐transition temperature of the aliphatic polyesters. The phenyl side branches reduced the crystallinity of poly(butylene succinate) more significantly than the ethyl or n‐octyl side branches did. The tensile strength, elongation, and tear strength of poly(ethylene adipate) decreased with an increase in the content of mandelic acid units. However, the increasing content of mandelic acid units enhanced the elongation and tear strength of poly(butylene succinate) considerably without a notable deterioration of tensile strength. The biodegradability of the copolyesters was increased as a result of the introduction of more mandelic acid units due to the decrease in the crystallinity. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1504–1511, 2000     

Nonisothermal crystallization kinetics of biodegradable poly(butylene succinate‐co‐propylene succinate)s

Poly(butylene succinate) (PBSu) and two poly(butylene succinate‐co‐propylene succinate)s were synthesized via the direct polycondensation reaction. The copolyesters were characterized as having 7.0.and 11.5 mol % propylene succinate (PS) units, respectively, by ¹H NMR. A differential scanning calorimeter (DSC) and a polarized light microscope (PLM) adopted to study the nonisothermal crystallization of these polyesters at a cooling rate of 1, 2, 3, 5, 6, and 10 °C/min. Morphology and the isothermal growth rates of spherulites under PLM experiments were monitored and obtained by curve‐fitting. These continuous rate data were analyzed with the Lauritzen?Hoffman equation. A transition of regime II → III was found at 95.6, 84.4, and 77.3 °C for PBSu, PBPSu 95/5, and PBPSu 90/10, respectively. DSC exothermic curves show that all of the nonisothermal crystallization occurred in regime III. DSC data were analyzed using modified Avrami, Ozawa, Mo, Friedman, and Vyazovkin equations. All the results of PLM and DSC measurements indicate that incorporation of minor PS units into PBSu markedly inhibits the crystallization of the resulting polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1299–1308, 2010     

Crystallization kinetics and morphology of biodegradable poly(butylene succinate‐co‐propylene succinate)s

The crystallization behavior of biodegradable poly(butylene succinate) and copolyesters poly(butylene succinate‐co‐propylene succinate)s (PBSPS) was investigated by using ¹H NMR, DSC and POM, respectively. Isothermal crystallization kinetics of the polyesters has been analyzed by the Avrami equation. The 2.2‐2.8 range of Avrami exponential n indicated that the crystallization mechanism was a heterogeneous nucleation with spherical growth geometry in the crystallization process of polyesters. Multiple melting peaks were observed during heating process after isothermal crystallization, and it could be explained by the melting and recrystallization model. PBSPS was identified to have the same crystal structure with that of PBS by using wide‐angle X‐ray diffraction (WAXD), suggesting that only BS unit crystallized while the PS unit was in an amorphous state. The crystal structure of polyesters was not affected by the crystallization temperatures, too. Besides the normal extinction crosses under the POM, the double‐banded extinction patterns with periodic distance along the radial direction were also observed in the spherulites of PBS and PBSPS. The morphology of spherulites strongly depended on the crystallization temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 420–428, 2007     

Synthesis and characterization of biodegradable poly(butylene succinate-co-butylene fumarate)s

A series of aliphatic biodegradable polyesters modified with fumaric residues was synthesized by transesterification in the melt of dimethyl succinate, dimethyl fumarate and 1,4-butanediol. The amount of unsaturation, originating from the fumaric acid residues in the polyesters chains was varied from 5 to 20 mol%. The molecular structure and composition of the polyesters were determined by ¹H NMR spectroscopy. The effects of the content of fumaric residues on the thermal and thermo-oxidative properties of the synthesized polyesters were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. The degree of crystallinity was determined by DSC and wide angle X-ray scattering. The degrees of crystallinity of the unsaturated copolyesters were reduced, while the melting temperatures were higher in comparison to poly(butylene succinate). Biodegradation of the synthesized copolyesters was estimated in enzymatic degradation tests using a buffer solution with Rhizopus arrhizus lipase at 37 °C. Although the degree of crystallinity of the copolyesters decreases slightly with increasing unsaturation, the biodegradation is not enhanced suggesting that not only the chemical structure and molecular stiffness but also the morphology of the spherulites has an influence on the biodegradation properties. The highest biodegradability was observed for the copolyesters containing 5 and 10 mol% of fumarate units.     

Preparation, characterization and hydrolytic degradation of poly[p-dioxanone-(butylene succinate)] multiblockcopolymer

A series of poly[p-dioxanone-(butylene succinate)] (PPDOBS) copolymers were prepared from p-dioxanone (PDO), 1,4-butanediol and succinate acids through a two-step process including the initial prepolymer preparation of poly(p-dioxanone)diol (PPDO-OH) and poly(butylene succinate)diol (PBS-OH) and the following copolymerization of the two kinds of prepolymers by coupling with hexamethylene diisocyanate (HDI). The molecular structures of the prepared PPDO-OH, PBS-OH and PPDOBS were characterized by hydrogen nuclear magnetic resonance spectroscopy (¹H NMR). The crystallization of the copolymers was investigated by using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). It has been shown that the crystallization rate and the degree of crystallization increases with the increase of the weight fraction of poly(butylene succinate) (PBS) blocks in the copolymers. In phosphate buffer solution with pH 7.4 at 37 °C for 18 weeks, the hydrolytic degradation behaviors of the copolymers were studied. The changes of retention weight, water absorption, pH value, and surface morphologies with the degradation time showed that the hydrolytic degradation rate of PPDOBS could be controlled by adjusting the weight fraction of poly(p-dioxanone) (PPDO) and PBS blocks in the copolymers. The changes of the thermal properties of PPDOBS during the degradation were also investigated by DSC.     

Biodegradability of poly(butylene succinate) (PBS) composite reinforced with jute fibre

Poly(butylene succinate) (PBS)/jute composites were prepared, and the effects of fibre content, diameter, surface modification and arrangement forms on the biodegradability were evaluated by compost-soil burial test. The weight losses of PBS/jute composites are higher than that of pure PBS film and bulk jute fibre, and decreased with increasing fibre content. The weight loss of PBS/10% jute composite after 180 days is 62.5%. In the case of the effect of fibre diameter, the weight loss is found to decrease with decreasing fibre diameter. For the effect of fibre surface modification, the order of higher weight loss is PBS/untreated jute > PBS/alkali treated jute > PBS/coupling agent treated jute. Furthermore, the composite of PBS/woven fabric has the highest weigh loss, followed by that of PBS/nonwoven fabric and PBS/bulk jute fibre, respectively.     

Thermo-oxidative processes in biodegradable poly(butylene succinate)

Aliphatic polyesters have acquired significant interest as environmentally friendly thermoplastics for a wide range of applications, and understanding their degradation behaviour has relevance both for processing and end uses. We have investigated the thermal and thermo-oxidative degradation processes occurring in synthetic and commercial poly(butylene succinate) (PBSu). Thermal oxidation was performed in atmospheric air using extremely thin polymer films at 170 °C for up to 6 h. The oxidized compounds were analyzed by size exclusion chromatography (SEC), NMR spectroscopy, and Mass Spectrometry (MALDI-TOF MS). A measurable reduction of the molar mass of the polyesters was soon apparent, promoting the formation of PBSu oligomers with different end groups. MALDI mass spectrometry combined with the use of extremely thin polyester films provided a virtual magnifying glass to obtain exhaustive information on the structure of the oxidation products. An α-H abstraction mechanism has been unambiguously ascertained to be the primary step in PBSu oxidation. The oxidized polymer chains originating from the decomposition of the hydroperoxide intermediate by radical rearrangement reactions had not been revealed before. The latter products subsequently undergo chain scission processes, which can be accurately traced from the chemical species identified in our work. Thermal degradation experiments were also performed under nitrogen at 240-260 °C. The new species identified in the MALDI spectra support a decomposition pathway taking place through a β-hydrogen-transfer mechanism, followed by the production of succinic anhydride from succinic acid end molecules via a back-biting process.     

Effect of molecular weight on thermal degradation mechanism of the biodegradable polyester poly(ethylene succinate)

A series of aliphatic polyesters, in particular poly(ethylene succinate), having different molecular weights, were synthesized from succinic acid and ethylene glycol, following the melt polycondensation process. Intrinsic viscosities (IV), GPC, DSC, ¹H NMR and carboxylic end group measurements were used for their characterisation. From thermogravimetric analysis, it was concluded that the molecular weight of polyesters achieved during polycondensation are strongly related to thermal stabilities of initial oligomers. In order to synthesise high molecular weight polyesters, the number average molecular weight of oligomers must not be lower than 2300–3000 g/mol, since thermal decomposition begins at temperatures lower than 200 °C. However, even in that case, polycondensation temperatures must not exceed 230–240 °C. From TGA studies, it was found that sample having different molecular weights could be divided into two groups characterized by different thermal stability. In the first group, belong samples with intrinsic viscosity of IV = 0.08 dL/g and in the second one all the other samples (IV > 15 dL/g). From kinetic analysis of thermal degradation, it was found that degradation of all polyesters takes place in three stages, its one corresponding to a different mechanisms. Degradation of samples with low molecular weight is more complex that that of polyesters having high molecular weights. The values of the activation energy and the exponent n for the two groups of samples—with different molecular weight—are similar, regarding the first two mechanisms, while there is an alteration in the case of the third mechanism.     

Synthesis and characterization of poly(butylene succinate) and its copolyesters containing minor amounts of propylene succinate

High molecular weight poly(butylene succinate) (PBSu), poly(propylene succinate), and PBSu-rich copolyesters were synthesized using an effective catalyst, titanium tetraisopropoxide. The compositions of the copolyesters were determined in three ways from ¹H and ¹³C NMR spectra, and good agreement between the results was obtained. The analysis of the carbonyl carbon spectra indicates a random distribution of the comonomers. Thermal properties were studied using a differential scanning calorimeter and a thermogravimetric analyzer. No significant difference exists among the thermal stabilities of these polyesters. However, the window between the glass transition and the melting temperatures becomes narrower with the increase in the concentration of propylene succinate in the copolymers. Additionally, the cold crystallization ability reduces considerably. Wide-angle X-ray diffractograms of isothermally crystallized copolyesters also follow the same trend.     

Multiblock copolymers composed of poly(butylene succinate) and poly(1,2-propylene succinate): Effect of molar ratio of diisocyanate to polyester-diols on crosslink densities, thermal properties, mechanical properties and biodegradability

In order to study the relationship between structure and properties, multiblock copolymers composed of poly(butylene succinate) (PBS) and poly (1,2-propylene succinate) (PPSu) have been synthesized by chain-extension at various molar ratios of hexamethylene diisocyanate (HDI) to polyester-diols, which have been abbreviated as R-values in this paper. Molecular weights of soluble fractions, gel fractions and crosslink densities have been determined. Thermal properties, mechanical properties and biodegradability have been studied and correlated with R-values. Crystallization of copolymers becomes difficult with increasing R-value. Tensile strength, flexural strength and flexural modulus tend to increase with increasing R-value up to 1.2, and vary little when R-value increases from 1.2 to 1.3, then decrease with further increase in R-value. Impact strength achieves a maximum value at R-value of 1.3. Biodegradation rate reaches a minimum value when R-value is 1.1. Biodegradation has been studied systematically by attenuated total reflectance Fourier transform infrared (ATR-FTIR), ¹H NMR and SEM.