Thermal degradation behavior of poly(4-hydroxybutyric acid)

Thermal degradation behavior of poly(4-hydroxybutyric acid) (P(4HB)) was investigated by thermogravimetric and pyrolysis-gas chromatography mass spectrometric analyses under both isothermal and non-isothermal conditions. Based on the thermogravimetric analysis, it was found that two distinct processes occurred at temperatures below and above 350 °C during the non-isothermal degradation of P(4HB) samples depending on both the molecular weight and the heating rate. From ¹H NMR analysis of the residual P(4HB) molecules after isothermal degradations at different temperatures, it was confirmed that the ω-hydroxyl chain-end was remained unchanged in the residual P(4HB) molecules at temperatures below 300 °C, while the ω-chain-end of P(4HB) molecules was converted to 3-butenoyl units at temperatures above 300 °C. In contrast, the majority of the volatile products evolved during thermal degradation of P(4HB) was γ-butyrolactone regardless of the degradation temperature. From these results, it is concluded that during the thermal degradation of P(4HB), the selective formation of γ-butyrolactone via unzipping reaction from the ω-hydroxyl chain-end predominantly occurs at temperatures below 300 °C. At temperatures above 300 °C, both the cis-elimination reaction of 4HB unit and the formation of cyclic macromolecules of P(4HB) via intramolecular transesterification take place in addition to unzipping reaction from the ω-hydroxyl chain-end. Finally, the primary reaction of thermal degradation of P(4HB) at temperatures above 350 °C progresses by the cyclic rupture via intramolecular transesterification of P(4HB) molecules with a release of γ-butyrolactone as volatile product. Moreover, we carried out the thermal degradation tests for copolymer of 93 mol% of 4HB with 7 mol% of 3-hydroxybutyric acid (3HB) to examine the effect of 3HB units on thermal stability of P(4HB).     

Degradation of polycaprolactone in supercritical fluids

The degradation of polycaprolactone (PCL) was studied in subcritical and supercritical toluene from 250 to 375 °C at 50 bar. The degradation was also investigated in various solvents like ethylbenzene, o-xylene and benzene at 325 °C and 50 bar. The effect of pressure on degradation was also evaluated at 325 °C at various pressures (35, 50 and 80 bar). The variation of molecular weight with time was analyzed using gel permeation chromatography and modeled using continuous distribution kinetics to evaluate the degradation rate coefficients. PCL degrades by random chain scission in subcritical conditions (250-300 °C) and by chain end scission (325-375 °C) in supercritical conditions in toluene. The degradation of PCL in other solvents at 325 °C was by chain end scission under both subcritical and supercritical conditions indicating that the mode of scission depends on the temperature and not on the supercriticality of the solvent. The thermogravimetric analysis of PCL was investigated at various heating rates (2-24 °C/min) and the activation energy was determined using Friedman, Ozawa and Kissinger methods. It was shown that PCL degrades by random scission at lower temperatures and by chain end scission at higher temperatures again indicating that the mode of scission is dependent on the temperature.     

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.     

Thermal stability of silver sulfathiazole-epoxy resin network

The aim of this study is to evaluate the thermal stability and thermal degradation behavior of an epoxy network based on bisphenol A modified with silver sulfathiazole and crosslinked with ethylenediamine. The sample was studied by thermogravimetric analysis coupled with differential scanning calorimetry over a range of temperature between 30 and 600 °C in N₂ atmosphere and using heating rates of 5, 10, 15 and 20 °C min⁻¹. The kinetic parameters of thermal degradation process were calculated. Fourier transforms infrared spectroscopy and mass spectroscopy coupled to thermogravimetry was used to identify the volatile products resulting from the degradation of the network. The study showed that the sample is stable up to temperatures exceeding 290 °C. The major degradation volatile products identified were: ammonia, water, carbon dioxide and compounds with aromatic structure such as bisphenol A and its degradation products.     

Investigation of physicochemical properties of biooils produced from yellow poplar wood (Liriodendron tulipifera) at various temperatures and residence times

Fast pyrolysis of yellow poplar wood (Liriodendron tulipifera) was performed under different temperature ranges and residence times in a fluidized bed reactor to maximize the yield of biooil. In this study, the pyrolysis temperature ranged from 400 °C to 550 °C, and the residence time of pyrolysis products was controlled between 1.2 and 7.7 s by inert nitrogen gas flow. The results revealed that the distribution of thermal degradation products (biooil, biochar, and gas) from the woody biomass was heavily influenced by pyrolysis temperature, as well as residence time. The highest yield of biooil was approximately 68.5 wt% (wet basis), with pyrolysis conditions of 500 °C and 1.9 s of residence time. Water content of the biooils produced at different temperatures was 25-30 wt%, and their higher heating values were estimated to be between 15 MJ/kg and 17 MJ/kg. Using GC/MS analysis, 30 chemical components were identified from the biooil, which were classified into 5 main groups: organic acids, aldehydes, ketones, alcohols, and phenols. In addition, biochar was produced as a co-product of fast pyrolysis of woody biomass, approximately 10 wt%, at temperatures between 450 °C and 550 °C. The physicochemical features of the biochar, including elemental analysis, higher heating values, and morphological properties by SEM, were also determined.     

Morphology, thermal stability and visco-elastic properties of polystyrene-poly(vinyl chloride) blends

The morphology, thermal and mechanical properties of polystyrene (PS) blends with 2.5-20 wt% of poly(vinyl chloride) (PVC) have been studied. The measurement of the glass transition temperature (T_g) from the maxima of tan δ data using dynamic mechanical thermal analysis showed that the blends were incompatible and homogenously distributed only within a limited range of PVC contents in PS. The value of the storage modulus was found to increase initially but then decreased with further addition of PVC in the matrix. Distribution of the phases in the virgin and degraded blends was also studied through scanning electron microscopy. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of blends were found higher than that of pure PS which indicated the stabilizing effects of PVC on PS. The effect varies with the heating rates and the composition of the blends and the phenomenon has been explained due to changing morphology of the blends with composition and the degradation time which affect the interfacial interaction between the degrading products from the polymer components. The kinetic parameters of the degradation process calculated from a method described by Ozawa have been reported for these blends.     

Thermal degradation studies in poly(vinyl chloride)/poly(methyl methacrylate) blends

The miscibility, morphology, and thermal properties of poly(vinyl chloride) (PVC) blends with different concentrations of poly(methyl methacylate) (PMMA) have been studied. The interaction between the phases was studied by FTIR and by measuring the glass transition temperature (T_g) of the blends using differential scanning calorimetry. Distribution of the phases at different compositions was studied through scanning electron microscopy. The FTIR and SEM results show little interaction and gross phase separation. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of the first and second stage of degradation in PVC in the presence of PMMA were higher than the pure. The stabilization effect on PVC was found most significant with 10 wt% PMMA content in the PVC matrix. These results agree with the isothermal degradation studies using dehydrochlorination and UV-vis spectroscopic results carried out on these blends. Using multiple heating rate kinetics the activation energies of the degradation process in PVC and its blends have been reported.     

Kinetics of the degradation of polystyrene in supercritical acetone

The kinetic analysis of the degradation of polystyrene (PS) in supercritical acetone has been studied using the nonisothermal weight loss technique with heating rates of 3, 5 and 7 °C/min. The weight loss data according to degradation temperature have been analyzed using the integral method based on Arrhenius form to obtain the kinetic parameters such as apparent activation energy and overall reaction order. The kinetic parameters obtained from this work were also compared with those of the thermal degradation of PS in nitrogen atmosphere. From this work, it was found that the activation energies of PS degradation in supercritical acetone were 73.3-200.7 kJ/mol and lower than those of the thermal degradation in nitrogen atmosphere.     

Degradation of benzoic acid and its derivatives in subcritical water

In this research, the stability of benzoic acid and three of its derivatives (anthranilic acid, salicylic acid, and syringic acid) under subcritical water conditions was investigated. The stability studies were carried out at temperatures ranging from 50 to 350 °C with heating times of 10–630 min. The degradation of the benzoic acid derivatives increased with rising temperature and the acids became less stable with longer heating time. The three benzoic acid derivatives showed very mild degradation at 150 °C. Severe degradation of benzoic acid derivatives was observed at 200 °C while their complete degradation occurred at 250 °C. However, benzoic acid remained stable at temperatures up to 300 °C. The degradation products of benzoic acid and the three derivatives were identified and quantified by HPLC and confirmed by GC/MS. Anthranilic acid, salicylic acid, syringic acid, and benzoic acid in high-temperature water underwent decarboxylation to form aniline, phenol, syringol, and benzene, respectively.     

Comparative study on hydrolytic degradation and monomer recovery of poly(l-lactic acid) in the solid and in the melt

The hydrolytic degradation of poly(l-lactide) (PLLA) and the formation of its monomer in the solid and in the melt were investigated at 120-150 °C (in the solid), at 160 °C (in the solid up to 40 min and in the melt exceeding 40 min), and at 170-190 °C (in the melt). Such state difference caused the difference in the degradation behavior of PLLA and the behavior of lactic acid formation, although the degradation of PLLA proceeds via a bulk erosion mechanism, regardless of its state. The crystalline residues were formed at the degradation temperatures below 140 °C, but not at the degradation temperatures above 160 °C. The lactic acid yield exceeding 95% can be successfully attained for all the temperatures of 120-190 °C. The activation energy for hydrolytic degradation values of PLLA were 69.6 and 49.6 kJ mol⁻¹ for the temperature ranges of 120-160 °C (in the solid) and 170-250 °C (in the melt), respectively, and are compared with the reported values.     

Thermal degradation kinetics of polystyrene/cadmium sulfide composites

The thermal degradation kinetics of polystyrene/CdS composites were studied by thermogravimetry. The samples were heated in nitrogen, with three different heating rates: 5, 20 and 40 °C min⁻¹. We calculated kinetic parameters using KAS isoconversion method. The results showed that the maximum activation energy of thermal degradation is achieved for PS/CdS composite with about 10% of the CdS filler. Higher concentration of CdS in the composite (20%) induced acceleration of the thermal degradation, approaching the rate of degradation of the pure polystyrene matrix.     

Thermal degradation of high density polyethylene in a reactive extruder

The thermal degradation of high density polyethylene was conducted in a reactive extruder at various screw speeds with reaction temperatures of 400 °C and 425 °C. The residence time of the extruder was estimated and the molecular weight distribution of the fed plastic and reaction products was analysed using gel permeation chromatography. A continuous kinetic model was used to describe the degradation of the high density polyethylene in the reactive extruder. The breakage kernel and the scission rate model parameters were estimated from the experimental data for a variety of cases. It was found that purely random breakage and a scission rate which had a power law dependence on molecular size of 0.474 best described the experimental data.     

Physical properties of films made of copoly(ether-imide)s with long poly(ethylene oxide) segments

Polyimides having long poly(ethylene oxide), PEO, moieties in the main chain have been synthesized by a classical two-steps polycondensation method with good yield and high molecular weight. In contrast with previous works on this topic, essentially full conversion of the polyamic acid to polyimide was attained by heating at relatively low temperatures (around 160 °C).These copolyimides undergo an increase of phase separation between the PEO part and the polyimide one after a thermal annealing. This phase separation increases gas separation properties of membranes made up of these copolymers. An exhaustive study of polymer properties as a function of the thermal treatment has been carried out in order to figure out the origin of this behavior. The analysis performed included TGA, DSC, SAXS and mechanical testing.The polymers studied in this paper have medium thermal stability. In fact, degradation of the polyether chain under nitrogen takes place at temperatures above 300 °C. However, their thermal stabilities were much lower under oxidant atmosphere.     

Pyrolysis of chromated copper arsenate (CCA) treated wood waste at elevated pressure: Influence of particle size, heating rate, residence time, temperature and pressure

Lab-scale pyrolysis experiments with weathered CCA treated wood chips have been performed and the influence of particle size, residence time (10-40 min), heating rate (5-20 °C/min), temperature (330-430 °C) and pressure (0 bar, 5 bar) has been investigated. Few data, covering the pyrolysis of weathered wood was found in the literature and the literature data on pyrolysis experiments with a controlled CCA wood input, showed that results were often highly affected by experimental uncertainty. In order to reduce the uncertainty on the results, a thorough characterization of the wood input has been performed and a ratio method has been proposed which allows to study the effect of particle size on arsenic and chromium volatilization. Larger wood particles show a higher arsenic and chromium retention during pyrolysis which is attributed to the higher mass transfer resistance in these particles. Residence time has a limited effect on arsenic retentions. Increasing heating rate results in a limited increase in arsenic retentions and a more profound increase in chromium retentions. The latter is attributed to a lower average particle temperature during heating caused by the thermal lag in larger particles. Elevated pressure results in a significant increase of arsenic retentions, which is probably due to higher mass transfer resistance. Increasing temperature results in a slight decrease in arsenic retentions till 390 °C, with a sharp decrease at higher temperatures. Chromium retentions are less affected by increasing temperature, especially at higher temperatures. To conclude, a mechanism is proposed for the volatilization of chromium and arsenic during low temperature pyrolysis of CCA wood. Mass transfer resistance and the formation of As₄O₆ are crucial for the control of arsenic volatilization, while heat transfer resistance and thermal lag are more important for the control of chromium volatilization.     

Kinetics of thermal degradation and estimation of lifetime for polypropylene particles: Effects of particle size

The thermal stability and degradation behavior of polypropylene (PP) particles having diameter varying from few micrometers to nanometers were studied by thermogravimetric analysis (TGA). The PP particles of average diameter ∼20 μm, ∼10 μm, ∼5 μm, ∼1 μm and <500 nm were studied over a range of temperature from 25 to 600 °C in N₂ atmosphere and heating rates of 5, 10 and 15 °C/min. Thermal stability of PP particles initially decreases and then increases as particle size further decreases to nanometer scale. The five single heating rate techniques such as Friedman, Freeman-Carroll, Chang, Coats-Redfern and second Kissinger; and three multiple heating rate techniques such as the first Kissinger, Kim-Park and Flynn-Wall were used to compute the kinetic parameters of degradation reaction, e.g., activation energy (E_a), order of reaction (n) and frequency factor [ln(Z)]. The lifetime of macro-, micro- and nanosized PP particles was also estimated by a method proposed by Toop. It was found that the activation energy and lifetime of nanosized PP particles are moderately high compared to the microsized PP particles. Moreover, the decomposition temperature, order of reaction (n), frequency factor [ln(Z)] not only depend on the heating rate and calculation technique but also on the particle size of polymer. The results are compared with macrosized PP.     

Thermal decomposition and stability of fatty acid methyl esters in supercritical methanol

In recent years, non-catalytic supercritical processes for biodiesel production have been proposed as alternative environmentally friendly technologies. However, conditions of high temperature and pressure that occur while biodiesel is in supercritical fluid can cause fuel degradation, resulting in low yield. In this study, we performed the thermal decomposition of fatty acid methyl esters (FAMEs) in supercritical methanol at temperatures ranging from 325 °C to 420 °C and pressure of 23 MPa to investigate the degradation characteristics and thermal stability of biodiesel. The primary reactions we observed were isomerization, hydrogenation, and pyrolysis of FAMEs. The main pathway of degradation was deduced by analyzing the contents of degradation products. We found that if FAME has shorter chain length or is more saturated, it has higher thermal stability in supercritical methanol. All FAMEs remained stable at 325 °C or below. Based on these results, we recommend that transesterification reactions in supercritical methanol should be carried out below 325 °C (at 23 MPa) and 20 min, the temperature at which thermal decomposition of FAMEs begins to occur, to optimize high-yield biodiesel production.     

The effects of thermal treatment on the antioxidant activity of polyaniline

The thermal stability of chemically synthesized polyaniline (PANI) was examined, including granular (G) polyaniline powders formed conventionally in an HCl medium, and nanorod (NR) samples prepared using a falling-pH synthesis. The samples were examined before and after dedoping (dd) using thermogravimetric analysis (TGA), which showed small mass losses in the 200-300 °C temperature range, and greater mass losses due to oxidative degradation at higher temperatures. Furthermore, samples were treated thermally at 100, 125, 150, 175, 200, 250 and 300 °C for 30 min in air. SEM images did not show any pronounced effect on the morphologies of the samples from thermal treatment up to 300 °C. The ratios of the intensities (Q/B) of the predominantly quinonoid (Q) and benzenoid peaks (B) from FTIR spectroscopic analysis revealed that NR-PANI and NR-PANIdd underwent cross-linking upon thermal treatment up to 175 °C and were oxidized after treatment above 175 °C. G-PANI and G-PANIdd also underwent the same chemical changes with oxidation occurring above 200 °C. The free radical scavenging capacity of the samples was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, and was found to be independent of the spin concentrations of the samples. All samples exhibited a rapid decline in free radical scavenging capacity when exposed to temperatures above 200 °C, indicating that any polymer processing should be undertaken at temperatures less than this value to achieve high antioxidant activity.     

Dechlorination of poly(vinyl chloride) by microwave irradiation I: A simple examination using a commercial microwave oven

Poly(vinyl chloride) (PVC) was decomposed by microwave (MW) irradiation (2.45 GHz) using a commercial MW oven. The efficiency of dielectric absorption was evaluated quantitatively from the rate of temperature increase on MW irradiation. The efficiency of dielectric heating increased at temperatures above the glass transition temperature (T_g). The decomposition on MW irradiation, monitored using the weight, depended on the initial (preheating) temperature of the sample before irradiation. The degradation time profile with various initial temperatures was shifted along the time axis and was successfully superimposed on a single curve. A pure PVC film was subjected to heating at a constant temperature from 230 °C to 310 °C, and the rate of weight decrease on heating was measured. The apparent activation energy was 84.4 kJ/mol for a single monomer unit.     

Importance of control of enzymatic degradation for determination of bisphenol A from fruits and vegetables

The purpose of this study was to develop an analytical method for determination of bisphenol A (BPA) from fruits and vegetables. The present method developed for extraction of BPA from samples was based on solid-phase extraction (SPE) method and solvent extraction. Recovery results in the samples spiked with a 10 ng/ml BPA [no detection (<1 ng/g) to 77%] were lower than those in the samples with a 50 ng/ml BPA (26-96%). The fact that the low recovery results were caused by BPA degradation by enzymes is found. These problems were proved by the pH (pH ≤3) and the heating treatment (at ≥80 °C for 5 min). However, because the heating treatment at temperatures of ≥80 °C for 5 min is more difficult and time-consuming method than the pH control, we suggest that the pH control is useful to prevent BPA degradation. Good recovery results (82-101%) were obtained from all fruit and vegetable samples after pH treatment (pH ≤3). Effective elimination of impurities and a good detection limit (1 ng/g) were obtained with a method involving two SPE cartridges (OASIS HLB and Sep-Pak Florisil cartridge).