Thermal degradation mechanism of poly(ethylene succinate) and poly(butylene succinate): Comparative study

Two aliphatic polyesters that consisted from succinic acid, ethylene glycol and butylene glycol, —poly(ethylene succinate) (PESu) and poly(butylene succinate) (PBSu)—, were prepared by melt polycondensation process in a glass batch reactor. These polyesters were characterized by DSC, ¹H NMR and molecular weight distribution. Their number average molecular weight is almost identical in both polyesters, close to 7000 g/mol, as well as their carboxyl end groups (80 eq/10⁶ g). From TG and Differential TG (DTG) thermograms it was found that the decomposition step appears at a temperature 399 °C for PBSu and 413 °C for PESu. This is an indication that PESu is more stable than PBSu and that chemical structure plays an important role in the thermal decomposition process. In both polyesters degradation takes place in two stages, the first that corresponds to a very small mass loss, and the second at elevated temperatures being the main degradation stage. The two stages are attributed to different decomposition mechanisms as is verified from the values of activation energy determined with iso-conversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures, is auto-catalysis with activation energy E = 128 and E = 182 kJ/mol and reaction order n = 0.75 and 1.84 for PBSu and PESu, respectively. The second mechanism is nth-order reaction with E = 189 and 256 kJ/mol and reaction order n = 0.68 and 0.96 for PBSu and PESu, respectively, as they were calculated from the fitting of experimental results.     

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.     

Degradation of aliphatic and aliphatic–aromatic co-polyesters by depolymerases from Roseateles depolymerans strain TB-87 and analysis of degradation products by LC-MS

The degradation activities of bacterium, Roseateles depolymerans TB-87 and its depolymerases Est-H and Est-L against aliphatic as well as aliphatic–aromatic co-polyesters, were investigated. Strain TB-87 and its enzymes exhibited an ability to degrade aliphatic and aliphatic–aromatic co-polyesters. Monomers produced as a result of degradation of aliphatic polyesters [poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA)] as well as aliphatic–aromatic co-polyester [poly(butylene succinate/terephthalate/isophthalate)-co-(lactate) (PBSTIL) by depolymerases Est-H and Est-L were investigated by liquid chromatography mass-spectrometry (LC-MS). Some common monomers like succinic acid and 1,4-butanediol were detected besides adipic acid and terephthalic/isophthalic acids as degradation products from PBSA and PBSTIL, respectively, whereas lactic acid was not detected. The succinic acid monomer was detected prior to adipic acid as a result of degradation of PBSA. The enzymes depolymerized PBS also into respective monomers. The analysis of PBSTIL degradation products revealed that enzymes easily degraded aliphatic segments as compared to aromatic segments and resulted in production of succinic acid prior to terephthalic and isophthalic acid. On the basis of these results, we speculate that both the enzymes Est-H and Est-L, attacked succinic acid segments (BS) first instead of adipic acid (BA) and terephthalic/isophthalic acid (BT or BI) segments of PBSA and PBSTIL, respectively. It is concluded from the results that R. depolymerans strain TB-87 can depolymerize aliphatic as well as aliphatic–aromatic co-polyesters; therefore, its enzymes can be applied in the process of biochemical monomer recycling.     

Characterization of a mesophilic aliphatic-aromatic copolyester-degrading fungus

We isolated 5 mesophilic microorganisms that form clear zones around the colony on an opaque medium containing the aliphatic-aromatic copolyester poly(60 mol% butylene adipate-co-40 mol% butylene terephthalate) (PBAT). Among all strains, the fungal strain NKCM1712 degraded PBAT at the fastest rate (3.5 ± 0.3 μg cm⁻² h⁻¹). Genetic and morphological analyses revealed that this strain was closely related to Isaria fumosorosea (phylum Ascomycota). Mass spectroscopic analysis revealed that the degradation products were T, AB, TB, BAB, and ABT (T, terephthalic acid unit; A, adipic acid unit; B, 1,4-butanediol unit)] in the culture of the strain that used PBAT as the sole carbon source. Furthermore, the PBAT degradation ability of this strain in terms of BOD suggested that it could utilize the PBAT degradation products as growth substrates. This is the first report of a mesophilic strain that can mineralize an aliphatic-aromatic polyester into carbon dioxide on its own.     

The enzymatic degradation of commercial biodegradable polymers by some lipases and chemical degradation of them

Biodegradable polyesters, poly(butylene succinate adipate) (PBSA), poly(butylene succinate) (PBS), poly(ethylene succinate) (PES), poly(butylene succinate)/poly(caprolactone) blend (HB02B) and poly(butylene adipate terephthalate) (PBAT), were evaluated about degradability for enzymatic degradation by lipases and chemical degradation in sodium hydroxide solution. In enzymatic degradation, PBSA was the most degradable by lipase PS, on the other hand, PBAT containing aromatic ring was little degraded by eleven kinds of lipases. In 1N NaOH solution, degradation rate of PES with ethylene unit was extremely fast, in comparison with other polyesters. Interestingly the degradation rate of PBSA in enzymatic degradation by lipase PS was faster than in chemical degradation.     

Thermal and thermomechanical properties of poly[(butylene succinate)-co-adipate] nanocomposite

In this article the thermal and thermomechanical properties of neat poly[(butylene succinate)-co-adipate] (PBSA) and its nanocomposite are reported. Nanocomposite of PBSA with organically modified synthetic fluorine mica (OSFM) has been prepared by melt-mixing in a batch mixer. The structure of nanocomposite is characterized by X-ray diffraction patterns and transmission electron microscopic (TEM) observations that reveal homogeneous dispersion of intercalated silicate layers in the PBSA matrix. The melting behavior of pure polymer and nanocomposite samples are analyzed by differential scanning calorimetry (DSC), which shows multiple melting behavior of the PBSA matrix. The multiple melting behavior of the PBSA matrix is also studied by temperature modulated DSC (TMDSC) and wide-angle XRD (WXRD) measurements. All results show that the multiple melting behavior of PBSA is due to the partial melting, re-crystallization, and re-melting phenomena. The investigation of the thermomechanical behavior is performed by dynamic mechanical thermal analysis. Results demonstrate substantial enhancement in the mechanical properties of PBS, for example, at room temperature, storage flexural modulus increased from 0.5 GPa for pure PBS to 1.2 GPa for the nanocomposite, an increase of about 120% in the value of the elastic modulus. The thermal stability of nanocomposite compared to that of neat PBSA is also examined in pyrolytic and thermo-oxidative conditions. It is then studied using kinetic analysis. It is shown that the stability of PBSA is increased moderately in the presence of OSFM.     

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.     

Microbial degradation of poly(butylene succinate) by Fusarium solani in soil environments

The use of mulch made of biodegradable plastic in agriculture is expected to help solve the problem of the enormous amount of plastic waste emission, and to save the labor of removing the mulch after harvesting crops. In this study, we isolated a microorganism possessing the ability to degrade one of the promising biodegradable plastics, poly(butylene succinate) (PBS), and investigated the degradation characteristics of the microorganism in soil environments. Fungal strain WF-6, belonging to Fusarium solani, that had not been reported could be isolated from farmland as the PBS-degrading microorganism. Strain WF-6 degraded 2.8 percent of the PBS in a 14-day experimental run in a sterile soil environment, as determined by measuring CO₂ evolution. Furthermore, we ascertained that the degradability of strain WF-6 was enhanced by co-culturing with the newly isolated bacterial strain Stenotrophomonas maltophilia YB-6, which itself does not show PBS-degrading activity. We then investigated the effects of cell density of the indigenous microorganisms in the soil environments on the degradability of the co-culture of strains WF-6 and YB-6 by inoculating these strains into non-sterilized and partially sterilized soils, which contained 10⁸, 10⁶, and 10³ CFU/g-dry solid of soil of indigenous microorganisms. The degradability strongly depended on the cell density level of the indigenous microorganisms and was remarkably diminished when the cell concentration level was the highest, 10⁸ CFU/g-dry solid. Quantitative PCR analysis revealed that the growth of strains WF-6 and YB-6 was inhibited in the non-sterile soil environment with the highest cell density level of the indigenous microorganisms.     

Probing trace Pb(2+) using electrodeposited N,N'-(o-phenylene)-bis-benzenesulfonamide polymer as a novel selective ion capturing film

A novel film modified electrode for the determination of trace lead was developed in this work. The modified electrode was prepared by the electropolymerization of N,N′-(o-phenylene)-bis-benzenesulfonamide (PBSA) as the ion capturing reagent to create the functional film. The modified electrode shows a high selectivity towards Pb²⁺ over interfering cations, e.g. Cu²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cr²⁺, and the calibration curve was linear in the concentration range of 2.0 × 10⁻⁹ to 1.0 × 10⁻⁷ M with correlation coefficient of 0.999. For 20 min accumulation, detection limit of 1.0 × 10⁻⁹ M was obtained at the signal to noise ratio of 3. Analytical availability of the modified electrode was demonstrated by the application for samples from pond water.     

Use of bioluminescent bacterial sensors as an alternative method for measuring heavy metals in soil extracts

The luminescence based bacterial sensor strains Pseudomonas fluorescens OS8 (pTPT11) for mercury detection and Pseudomonas fluorescens OS8 (pTPT31) for arsenite detection were used in testing their application in detecting heavy metals in soil extracts. Three different soil types (humus, mineral and clay) were spiked with 1, 100 or 500 μg g⁻¹ Hg²⁺ or As³⁺. Samples were taken 1, 14 and 30 days and extracted with water, ammonium acetate, hydrogen peroxide and nitric acid to represent water soluble, bioavailable, organic matter bound and residual fractions, respectively. The lowest mercury-concentration measured using biosensor (0.003 μg kg⁻¹) was considerably lower than by chemical method (0.05 μg kg⁻¹). The sensor strain with pTPT31 appeared to have a useful detection range similar to that of chemical methods. Concentration results with chemical and biosensor analysis were very similar in the case of mercury-spiked samples. Although some of the arsenite samples showed higher variation between methods, it is concluded that the bacteria can be used as an alternative traditional methods for different types of samples.     

Simultaneous determination of N-acetyl-p-aminophenol and p-aminophenol with poly(3,4-ethylenedioxythiophene) modified glassy carbon electrode

A sensitive and selective method was developed for the determination of N-acetyl-p-aminophenol (APAP) and p-aminophenol (PAP) using poly(3,4-ethylenedioxythiophene) (PEDOT)-modified glassy carbon electrode (GCE). Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical reaction of APAP and PAP at the modified electrode. Both APAP and PAP showed quasireversible redox reactions with formal potentials of 367 mV and 101 mV (vs. Ag/AgCl), respectively, in phosphate buffer solution of pH 7.0. The significant peak potential difference (266 mV) between APAP and PAP enabled the simultaneous determination both species based on differential pulse voltammetry. The voltammetric responses gave linear ranges of 1.0 × 10⁻⁶-1.0 × 10⁻⁴ mol L⁻¹ and 4.0 × 10⁻⁶-3.2 × 10⁻⁴ mol L⁻¹, with detection limits of 4.0 × 10⁻⁷ mol L⁻¹ and 1.2 × 10⁻⁶ mol L⁻¹ for APAP and PAP, respectively. The method was successfully applied for the determination of APAP and PAP in pharmaceutical formulations and biological samples.     

Bacterial polyesters grafted with poly(ethylene glycol): Behaviour in aqueous media

An easy method for grafting of poly(3-hydroxyoctanoate-co-3-hydroxyundecenoate) (PHOU) was developed. Oxidation of the pendant double bonds of PHOU into carboxyl groups to yield poly(3-hydroxyoctanoate-co-3-hydroxy-9-carboxydecanoate) (PHOD) and the esterification of the carboxyl side groups with poly(ethylene glycol) (PEG) were carried out in a single reaction solution. The grafting yield is dependent on the molar mass of the PEG graft. The maximum carboxyl group conversion (52%) was obtained with PEG M_n = 350 and decreased with increasing molar mass of PEG (19% for PEG M_n = 2000). Yields were determined by ¹H and ¹³C NMR. Short PEG grafts lowered the glass transition temperature (PHOD-g-PEG 350 −57 °C) compared to PHOD (−19 °C) and PHOU (−39 °C). This effect depends on the COOH conversion and PEG chain length. Grafting enhanced the hydrophilic character of the modified polymers making them soluble in polar solvents, such as alcohols and water/acetone mixtures. PHOD-g-PEG films were more stable towards hydrolytic degradation as PHOD films. No obvious modification of films was observed after more than 200 days at pH 7.2 and 37 °C. The molar mass of the grafted polymers decreased only slightly during this period, while PHOD films were hydrolyzed into soluble fragments.     

Characterization and biodegradability of polyester bioplastic-based green renewable composites from agricultural residues

The biodegradability, morphology, and mechanical properties of composite materials consisting of acrylic acid-grafted poly(butylene succinate adipate) (PBSA-g-AA) and agricultural residues (rice husk, RH) were evaluated. Composites containing acrylic acid-grafted PBSA (PBSA-g-AA/RH) exhibited noticeably superior mechanical properties compared with those of PBSA/RH due to greater compatibility with RH. The dispersion of RH in the PBSA-g-AA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross-linked macromolecules, between the carboxyl groups of PBSA-g-AA and hydroxyl groups in RH. Each composite was subject to biodegradation tests in an Azospirillum brasilense BCRC 12270 liquid culture medium. The bacterium completely degraded both the PBSA and the PBSA-g-AA/RH composite films. Morphological observations indicated severe disruption of the film structure after 20-40 days of incubation. The PBSA-g-AA/RH (20 wt%) films were not only more biodegradable than those made of PBSA but also exhibited lower molecular weight and intrinsic viscosity, implying a strong connection between these characteristics and biodegradability.     

Thermal diffusivity measurement of low-k dielectric thin film by temperature wave analysis

Thermal diffusivity of thin film with low dielectric constant (k), what is called low-k dielectric thin film, 0.31-1.14 μm, including hydrogen-silsesquioxane (HSQ), methyl-silsesquioxane (MSQ), and poly(arylen ether) was examined by temperature wave analysis. The phase shift of temperature wave was observable up to 100 kHz. Thermal diffusivity of HSQ was 4.7 × 10⁻⁷ m² s⁻¹, on the other hand it was not higher than 1.1 × 10⁻⁷ m² s⁻¹ for MSQ or poly(arylen ether) at room temperature. Temperature dependence of thermal diffusivity/thermal conductivity of MSQ was obtained, thermal diffusivity decreased but thermal conductivity increased in a heating scan at 30-150 °C. It was shown that the thermal diffusivity of low-k thin film was correlated with the chemical and the physical structures, the latter was formed in the spin-coating and the curing process.     

Distribution and accumulation of antimony in plants in the super-large Sb deposit areas, China

Antimony (Sb) distribution and accumulation in plants in Xikuangshan Sb deposit area, the only one super-large Sb deposit in the world, Hunan, China were investigated. Results show that soils were severely polluted with the average Sb concentrations up to 5949.20 mg kg^− 1. Sb widely occurred in 34 plants with various concentrations ranging from 3.92 mg kg⁻¹ to 143.69 mg kg^− 1, Equisetaceae family has the highest concentration (98.23 mg kg^− 1) while Dryopteridacea family has the lowest one (6.43 mg kg^− 1). H. ramosissima species of Equisetaceae family had the highest Sb average concentration of 98.23 mg kg^− 1 and P. vittata species of Pteridaceae family showed advantage of accumulating Sb from the contaminated environment (Biological Accumulation Coefficient, BAC = 0.08). Almost all species enriched Sb in their upground part such as shoot, leaf and flower (Biological Transfer Coefficient, BTC > 1), which may attribute to the high acropetal coefficient and Sb transformation from the atmosphere to the plants. P. phaseoloides and D. indicum showed predominantly accumulation of Sb in the upground part with BTC of 6.65 and 5.47, respectively.From the low bioavailable fraction in soils and weak relationship between total soil concentrations in soils and plants, it seems that the Sb bioavailability was limited and varied with different soil sites as well as plant species. Those observations would be significant to the phytoaccumulation and phytoremediation of plants and ecological and environmental risk assessment in Sb contaminated areas.     

Flow-injection post chemiluminescence determination of atropine sulfate

A new post chemiluminescence (PCL) reaction was observed when atropine sulfate was injected into the reaction mixture after the finish of CL reaction of Ce(IV) and sodium sulfite. The possible mechanism for the PCL reaction was discussed via the investigation of the CL kinetic characteristics, the CL spectra, the UV absorption spectra and the fluorescence spectra of some related substances. The flow injection PCL method for the determination of atropine sulfate was established. The relative standard deviation (R.S.D.) was 2.8% (n = 11, c = 5.0 × 10⁻⁶ g mL⁻¹). The PCL intensity responded linearly to the concentration of atropine sulfate in the range 1.0 × 10⁻⁶ to 5.0 × 10⁻⁵ g mL⁻¹ with a linear correlation of 0.9947. The detection limit was 4 × 10⁻⁷ g mL⁻¹ atropine sulfate. The method had been applied to the determination of atropine sulfate in the tablets and the results were consistent with the method of Chinese pharmacopoeia.     

An ultrasensitive post chemiluminescence reaction of ammonium in NBS-dichlorofluorescein system and its application

A strong post chemiluminescence (PCL) phenomenon was observed when ammonium was injected into the reaction mixture after the finish of CL reaction of N-bromosuccinimide (NBS) and dichlorofluorescein. Based on this, a sensitive flow injection PCL method was established for the determination of ammonium. The possible CL mechanism of the reaction was proposed based on a series of experiments. The PCL intensity responded linearly to the concentration of ammonium in the range 3.0 × 10⁻¹¹-1.0 × 10⁻⁷ g mL⁻¹ with a detection limit of 1 × 10⁻¹¹ g mL⁻¹. The relative standard deviation (R.S.D.) was 1.4% for 1.0 × 10⁻⁹ g mL⁻¹ ammonium (n = 11). This method had been applied to the determination of ammonium in samples of mineral water, tap water and river water.     

Poly(butylene terephthalate)/poly(ε-caprolactone) blends: Influence of PCL molecular mass on PBT melting and crystallization behavior

The isothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) (PBT) in binary blends with poly(ε-caprolactone) (PCL) was investigated as a function of PCL molecular mass by differential scanning calorimetry and optical microscopy. The components are miscible in the melt when oligomeric PCL (M_w = 1250) is blended with PBT, whereas only partial miscibility was found in mixtures with higher molecular mass (M_w = 10,000 and 50,000). The equilibrium melting point of PBT in the homopolymer and in blends with PCL was determined through a non-linear extrapolation of the T_m = f(T_c) curve. The PBT spherulitic growth rate and bulk crystallization rate were found to increase with respect to plain PBT in blends with PCL1250 and PCL10000, whereas addition of PCL50000 causes a reduction of PBT solidification rate. The crystallization induction times were determined by differential scanning calorimetry for all the mixtures through a blank subtraction procedure that allows precise estimation of the crystallization kinetics of fast crystallizing polymers. The results have been discussed on the basis of the Hoffman-Lauritzen crystallization theory and considerations on both the transport of chains towards the crystalline growth front and the energy barrier for the formation of critical nuclei in miscible and partially miscible PBT/PCL mixtures are widely debated.     

Accelerated degradation behaviour of poly(?-caprolactone) via melt blending with poly(aspartic acid-co-lactide) (PAL)

Poly(?-caprolactone) (PCL) has many favourable attributes for tissue engineering scaffold applications. A major drawback, however, is its slow degradation rate, typically greater than 3 years. In this study PCL was melt blended with a small percentage of poly(aspartic acid-co-lactide) (PAL) and the degradation behaviour was evaluated in phosphate buffer solution (PBS) at 37 °C. The addition of PAL was found to significantly enhance the degradation profile of PCL. Subsequent degradation behaviour was investigated in terms of the polymer's mechanical properties, molecular weight (M_w), mass changes and thermal characteristics. The results indicate that the addition of PAL accelerates the degradation of PCL, with 20% mass loss recorded after just 7 months in vitro for samples containing 8 wt% PAL. The corresponding pure PCL samples exhibited no mass loss over the same time period. In vitro assessment of PCL and PCL/PAL composites in tissue culture medium in the absence of cells revealed stable pH readings with time. SEM studies of cell/biomaterial interactions demonstrated biocompatibility of C₃H₁₀T_1/2 cells with PCL and PCL/PAL composites at all concentrations of PAL additive.     

Capillary electrophoresis-electrochemiluminescent detection of N,N-dimethyl ethanolamine and its application in impurity profiling and stability investigation of meclophenoxate

Numerous drugs are carboxylic acid derivatives containing amino group, and hydrolysis reaction of these agents often generates toxic amines. Thus, the detection of amine impurity is of great importance in drug quality control of these amino group-containing ester and amide. A capillary electrophoresis method coupled with end-column electrochemiluminescent detection based on tris(2,2′-bipyridyl)ruthenium(II) system was proposed for the analysis of N,N-dimethyl ethanolamine (DMEA, the degradation product of meclophenoxate) in the presence of its precursor. Baseline separation of DMEA and meclophenoxate can be easily achieved under the selected conditions. DMEA can be assayed within 3 min over the concentration range of 5.0 × 10⁻⁸ to 3.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 2.0 × 10⁻⁸ mol L⁻¹ at the signal-to-noise ratio of 3. The relative standard deviations of the signal intensity and the migration time were less than 5.3 and 2.5% for a standard sample containing 1.0 × 10⁻⁷ mol L⁻¹ DMEA (n = 5), respectively. The presented method has been successfully applied for the profiling of DMEA resulting from the hydrolysis of meclophenoxate in commercial formulations. A primary stability investigation of meclophenoxate in aqueous solution was also carried out at different temperatures, and the results showed that the degradation of meclophenoxate accelerated at the higher temperature.