Oriented and thermal crystallization of poly(ethylene terephthalate)

The oriented and thermal crystallization of amorphous poly(ethylene terephthalate) (PET) films was investigated in terms of the morphological aspects. When the amorphous PET films were stretched up to the desired draw ratios in a hot water bath at 62, 72, and 80 °C, the birefringence of the specimens increased with increasing draw ratio (λ). This tendency becomes most significant when the specimen was drawn in the bath at 62 °C. The storage modulus of the specimen drawn at 62 °C was higher than those of the specimens drawn at 72 and 80 °C. The exothermic peak in the DSC curves was observed clearly for the specimen drawn up to λ=4 in the hot water bath at 80 °C, while the peak did not appear for the specimen drawn up to λ=4 at 62 °C. Under an H_v polarization condition, light scattering patterns from the specimens drawn in the hot water bath showed four lobes at small azimuthal angles and four sharp streaks at large azimuthal angles. Such a profile was independent of the drawing temperatures from 62 to 80 °C. Based on the observed H_v patterns, a model was proposed by assuming the existence of a row-nucleated sheaf-like structure whose rows were preferentially oriented at a particular angle with respect to the stretching direction. The patterns calculated by using the above model were rather close to the patterns observed. This agreement implies that row-nucleated sheaf-like texture arises with lamellar overgrowth.

     

Effect of neutralization and cross-linking on the thermal degradation of chitosan electrospun membranes

Thermal degradation of as-electrospun chitosan membranes and samples subsequently treated with ethanol and cross-linked with glutaraldehyde has been studied by thermogravimetry (TG) coupled with an infrared spectrometer. The influence of the electrospinning process and cross-linking in the electrospun chitosan thermal stability was evaluated. Up to three degradation steps were observed in the TG data, corresponding to water dehydration reaction at temperatures below 100 °C, loss of side groups formed between the amine groups of chitosan and trifluoroacetic acid between 150 and 270 °C and chitosan thermal degradation that starts around 250 °C and goes up to 400 °C. The Kissinger model was employed to evaluate the activation energies of the electrospun membranes during isothermal experiments and revealed that thermal degradation activation energy increases for the samples processed by electrospinning and subsequent neutralization and cross-linking treatments with respect to the neat chitosan powder.     

Polymers of carbonic acid. XXVII. Macrocyclic polymerization of trimethylene carbonate

2,2-Dibutyl-2-stanna-1,3-dioxepane (DSDOP) was used as cyclic initiator for the polymerization of trimethylene carbonate (TMC). The polymerizations were either conducted in concentrated chlorobenzene solution at 50 and 80°C or in bulk at 60 and 120°C. With monomer/initiator ratios ≤100 the conversion was complete within 2 h at 80°C and within 12 h at 50°C. Variation of the reaction time revealed that the rapid polymerization is followed by a relatively rapid (backbiting) degradation even at 80°C. The polymerizations in bulk at 60°C were somewhat slower than those at 80°C in solution, but the influence of degradation reactions was less pronounced. With optimized reaction time the number average molecular weight (M_n) roughly parallels the monomer/initiator ratio and M_n's up to 100,000 were obtained. In contrast to a classical living polymerization broader polydispersities (1.5–1.7) were found. In the case of 5,5-dimethyltrimethylene carbonate rapid degradation and chain transfer reactions prevented the formation of high molecular weight polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2179–2189, 1999     

Differential pulse polarographic study of the degradation of cephalexin: Determination of Hydrogen Sulphide and other Degradation Products

Differential pulse polarography (d.p.p.) is used to study the degradation of cephalexin. Hydrogen sulphide, evolved during the degradation of cephalexin solutions, was removed continuously in a stream of nitrogen and determined periodically. Other electroactive degradation products were observed by d.p.p. of the degraded sample solutions. The degradation mechanism is highly dependent on pH, the initial concentration of cephalexin, temperature, the particular buffer used, and the presence of dissolved oxygen. The formation and degradation of the diketopiperazine derivative formed by intramolecular aminolysis, particularly at neutral pH, can be followed by means of its polarographic peak at -0.9 V (pH 7.4). Approximately half the total sulphur originally present in cephalexin is liberated as hydrogen sulphide at pH 7.4 at 37°C. Increasing the degradation temperature to 80°C and sweeping out the hydrogen sulphide with nitrogen increases the yield of a major product which gives a peak at -1.26 V. At pH 8.5 (80°C. 100 μg cephalexin ml^-1) the percentage of the sulphur evolved as hydrogen sulphide increases with time, and a peak appears at -0.96 V (probably 2-hydroxy-3-phenyl-6-methylpyrazine) which increases as the peak at -1.26 V becomes smaller. Other products formed under different conditions (concentration, pH, temperature) are reported. At pH 3 (80°C) only 8% conversion via intramolecular aminolysis and 5% evolution of total sulphur is indicated after four hours.     

Extraction of Co-Products from Biomass: Example of Thermal Degradation of Silymarin Compounds in Subcritical Water

In an effort to increase revenues from a given feedstock, valuable co-products could be extracted prior to biochemical or thermochemical conversion with subcritical water. Although subcritical water shows significant promise in replacing organic solvents as an extraction solvent, compound degradation has been observed at elevated extraction temperatures. First order thermal degradation kinetics from a model system, silymarin extracted from Silybum marianum, in water at pH 5.1 and 100, 120, 140, and 160 °C were investigated. Water pressure was maintained slightly above its vapor pressure. Silymarin is a mixture of taxifolin, silichristin, silidianin, silibinin, and isosilibinin. The degradation rate constants ranged from 0.0104 min⁻¹ at 100 °C for silichristin to a maximum of 0.0840 min⁻¹ at 160 °C for silybin B. Half-lives, calculated from the rate constants, ranged from a low of 6.2 min at 160 °C to a high of 58.3 min at 100 °C, both for silichristin. The respective activation energies for the compounds ranged from 37.2 kJ/gmole for silidianin to 45.2 kJ/gmole for silichristin. In extracting the silymarin with pure ethanol at 140 °C, no degradation was observed. However, when extracting with ethanol/water mixtures at and 140 °C, degradation increased exponentially as the concentration of water increased. An erratum to this article can be found at     

Syntheses and degradations of fluorinated heterocyclics II. Perfluoroalkyl and perfluoroalkylether-1,2,4-oxadiazoles

3-Perfluoroalkylether-5-perfluoro-n-heptyl-1,2,4-oxadiazole and 3,5-bis(perfluoroalkylether)-1,2,4-oxadiazole were synthesized and characterized. The 3,5-bis(perfluoroalkylether)-1,2,4-oxadiazole was subjected to thermal, thermal oxidative, and hydrolytic degradations at 235 and 325°C and was found to be stable under these conditions as evidenced by practically quantitative recovery of the test samples. In the presence of Jet-A-fuel at 235°C a low degree of degradation,～4%, was observed. 3,5-Bis(perfluoro-n-heptyl)-1,2,4-oxadiazole was found to be stable to attack by water at 325°C; however in air in the presence of Jet-A at 235°C the extent of degradation was in excess of 10%.     

Silymarin extraction from milk thistle using hot water

Hot water is attracting attention as an extraction solvent in the recovery of compounds from plant material as the search for milder and “greener” solvents intensifies. The use of hot water as an extraction solvent for milk thistle at temperatures above 100°C was explored. The maximum extraction yield of each of the silymarin compounds and taxifolin did not increase with temperature, most likely because significant compound degradation occurred. However, the time required for the yields of the compounds to reach their maxima was reduced from 200 to 55 min when the extraction temperature was increased from 100 to 140°C. Severe degradation of unprotected (plant matrix not present) silymarin compounds was observed and first-order degradation kinetics were obtained at 140°C.     

Mass spectral and pyrolysis/gas-chromatographic studies of the monomer and polymer of bis(p-toluenesulfonate) of 2,4-hexadiyne-1,6-diol

The thermal degradation of the monomer and polymer of bis(p-toluenesulfonate) of 2,4-hexadiyne-1,6-diol has been investigated. Decomposition during the latter stages of solid-state thermal polymerization at 80°C and of 100% polymer at 112°C was observed by mass spectrometry and the decomposition fragments identified. Mechanisms for this low-temperature degradation are suggested. Pyrolysis of the monomer and polymer between 400 and 1000°C was studied by gas chromatography and mass spectrometry. The principal pyrolysis products are triacetylene and p-toluenesulfonic acid. The fragmentation routes leading to and derived from these products are discussed.     

Studies on enhancing the keeping quality of peach (Prunus persica Bausch) Cv. Elberta by gamma-irradiation

The effect of gamma-irradiation on keeping quality of peach fruit was studied. The fruit, after harvesting at proper maturity stage, was irradiated in the dose range of 1.0–2.0 kGy, stored under ambient (temp. 25±2 °C, RH 70%) and refrigerated (temp. 3±1 °C, RH 80%) conditions and evaluated periodically for firmness, total soluble solids (TSS), anthocyanins, water-soluble pectic fractions, loss in weight and decay percentage. The anthocyanin evaluation of the fruits revealed that irradiation enhanced the colour development under both the storage conditions. The gamma-irradiation dose range of 1.2–1.4 kGy proved effective in maintaining higher TSS concentration, reducing weight loss and significantly (p⩽0.05) delaying the decaying of the fruit by 6 days under ambient conditions and by 20 days under refrigerated storage conditions.     

Transport properties of alternative fuel microemulsions based on sugar surfactant

Electrical conductivity of fuel microemulsion composed of diesel, pentanol, water, and sucrose laurate as surfactant was investigated over a wide range of water contents varying from 0 to 90?wt% and temperature varying from 10°C to 50°C. Conductivity measurements were performed on samples, the composition of which lie along the one-phase channel using a conductivity meter. Activation energy of conduction flow was evaluated. The hydrodynamic radius as a function of temperature in the aqueous phase-rich region (90?wt%) was measured using the dynamic light scattering (DLS) method. The microstructure of the microemulsion was further investigated by NMR diffusometry by which the self-diffusion coefficients for water were determined at 25°C. Electrical conductivity increases with water content up to 40?wt% and the percolation threshold was observed, and then stabilizes between 40 and 80?wt% then decreases. Percolation threshold temperature at constant composition was monitored as 36°C for water contents below 80?wt% and as 34°C for water contents above that. As predicted by the conductivity measurements, the determined self-diffusion coefficients of water confirmed the structural transition from discrete W/O droplets to bi-continuous phase and finally to O/W droplet microemulsion.     

A 31P NMR Study of the Stability of Carboxyifosfamide and Carboxycyclophosphamide,Two Metabolites of Ifosfamide and Cyclophosphamide

Abstract

Ifosfamide (IF) and cyclophosphamide (CP) are two phosphorated anticancer agents used in the treatment of solid tumours. Several phosphorated metabolites, among them carboxyifosfamide (CXIF) and carboxycyclophosphamide (CXCP), were detected and quantified by ³¹P NMR in urine from patients treated with IF or CP. In agreement with other authors [1], we observed a great inter-patient variability in the urinary excretion of CXIF in patients treated with IF [2]. This variability was attributed to a genetic polymorphism of aldehyde dehydrogenase, the enzyme responsible for the formation of CXCP or CXIF [1,3]. Since CXCP and CXIF are unstable, we thought that the inter-individual variability could also be due to a degradation during the storage of urine samples. A ³¹P NMR study of the stability of CXIF and CXCP in urine as a function of time, pH (7 and 5.5) and storage temperature (25°C, 8°C, ?20°C, ?80°C) demonstrated that (i) CXCP and CXIF are more stable at pH 7 than at pH 5.5, (ii) CXCP is more stable than CXIF at both pH, (iii) the degradation decreases with temperature but still occurs at ?20°C and even ?80°C. For an accurate quantification of these compounds, the storage of urine samples must be done at ?80°C immediately after collection and not exceed 1 month at pH 7 whereas, at pH 5.5, the assay must be carried out in the few days following the sampling. To identify the degradation products of CXCP and CXIF, the time course of hydrolysis (between pH 2 and 7) of these compounds was monitored by ³¹P NMR. The structure of each compound formed was determined by mass spectrometry and ¹H and ¹³C NMR after their isolation (except compound A too unstable to be isolated). The results are reported in the following schemes.     

Degradation of poly(3-hydroxybutyrate) and its blends during treatment with UV light and water

The degradation of films of poly(3-hydroxybutyrate) and its blends with ethylene-propylene rubber during their treatment with water and UV radiation at 20 and 90°C is studied. Changes in the structural characteristics of both components during degradation are investigated via DSC, IR spectroscopy, and optical microscopy. It is shown that pure poly(3-hydroxybutyrate) features the highest weight loss during degradation in distilled water at 20°C. In the case of the blends, the most significant changes in the structures of the components are observed for the 50: 50 (wt %) sample.     

Role of temperature during ageing under gamma irradiation of filled EPDM: consequences on mechanical properties

Filled EPDM materials have been processed and aged by gamma radiation at ambient temperature and at 80 °C to study the influence of the fillers presence in the material degradation. The acceleration of the polymer degradation by the ATH fillers, evidenced when irradiation is performed at 25 °C, is also effective at 80 °C. In addition, in the case of silica‐filled EPDM, the creation of strong filler‐matrix bonds, already reported for irradiation at 25 °C, is also thermally activated; this enables to this material to keep its integrity at high irradiation dose, whereas the irradiated ATH‐filled EPDM is so degraded that it flows. Thus, the introduction of fillers in the polymer has an impact on its resistance to irradiation, whatever the temperature at which the irradiation is performed. Moreover, the consequences of the degradation on the evolution of the mechanical properties of the composite are very dependent on the filler nature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1319–1328, 2010     

Structural change of water by gelation of curdlan suspension

Phase transition of water restrained by curdlan suspension annealed at a temperature from 20 to 110°C was investigated by differential scanning calorimetry (DSC). The melting temperature of water restrained by annealed curdlan discontinuously decreased at around 60°C, while the amount of bound water calculated from enthalpy of melting increased at 60°C, regardless of water content. Using a highly sensitive DSC, curdlan suspension with various concentrations was studied. It was found that an endothermic transition was observed at ca. 58°C in a wide range of concentrations. The transition observed at 60°C is thermo-reversible and both temperature and transition enthalpy are constant even after gel formation. Well equilibrated suspension at a temperature lower than 60°C formed no gel.     

Gelation kinetics of PAM/PEI system

Excess water production in oil and gas wells causes serious productivity and environmental problems in the oilfield. A mixture composed of a polymer, cross-linker, and water is usually injected into the reservoir to block unwanted water by forming a three-dimensional structure. This transition process from solution to gel is a function of temperature, time, salinity of mixing water, and concentration of the various components. The gelling solution was prepared by mixing polyacrylamide (PAM) with distilled water, and then polyethylenimine (PEI) was added as a cross-linker. The injection process was simulated and investigated by differential scanning calorimeter (DSC) over the temperature range of 80–120 °C. The DSC dynamic scan showed two consecutive peaks. An endothermic peak was observed at low temperature due to PAM alkaline hydrolysis which ends at around 60 °C. Another exotherm was observed at ~70 °C which corresponds to the onset of cross-linking of PAM and PEI. It was found that high temperatures lead to high release of heat due to gelation. The effect of salts on the cross-linking was also examined. More delay in cross-linking was observed in the case of NH₄Cl compared to NaCl. The gelation kinetics was modeled using a rate process model that relates fractional gelation with time. Further, Avrami model, usually used to study crystallization kinetics, was also used to model the gelation process. Kinetic parameters were obtained from the two different models, and the results showed good agreement with experimental data. The presence of salts in seawater leads to a drop of 60–80 % in the rate constant without influencing the order of the gelation reaction.     

Thermal degradation of aramids: Part I—Pyrolysis/gas chromatography/mass spectrometry of poly(1,3-phenylene isophthalamide) and poly(1,4-phenylene terephthalamide)

The thermal degradation reactions of poly(1,3-phenylene isophthalamide) or Nomex (I) and poly(1,4-phenylene terephthalamide) or Kevlar (II) aramids have been investigated in the temperature range 300–700°C by pyrolysis/gas chromatography/mass spectrometry. The initial degradation products below 400°C of (I) are carbon dioxide and water. At 400°C benzoic acid and 1,3-phenylenediamine are detected. Benzonitrile, aniline, benzanilide, N-(3-aminophenyl)benzamide as well as carbon monoxide and benzene are evolved in the range 430–450°C. The yields of these products increase rapidly in the range 450–550°C. Isophthalonitrile is observed at 475°C and hydrogen cyanide is detected above 550°C, as are other secondary products such as toluene, tolunitrile, biphenyl, 3-cyanobiphenyl and 3-aminobiphenyl. Pyrolysis of (II) below 500°C evolves only water and trace amounts of carbon dioxide. At 520–540°C the following degradation products have been detected: 1,4-phenylenediamine, benzonitrile, aniline, benzanilide and N-(4-aminophenyl)benzamide. These products as well as carbon dioxide and water increase appreciably between 550°C and 580°C; benzoic acid, terephthalonitrile, benzene and 4-cyanoaniline are also detected in this temperature range. Above 590°C, hydrogen, carbon monoxide, hydrogen cyanide, toluene, tolunitrile, biphenyl, 4-aminobiphenyl and 4-cyanobiphenyl are evolved. Degradation reactions consistent with the formation of these products, which involve initial heterolytic cleavage of the amide linkage for (I) and initial homolytic cleavage of the aromatic NH and amide bonds for (II), are described.     

Migration of Additives from Poly(vinyl chloride) (PVC) Tubes into Aqueous Media

The stability and migration product of medical PVC tubes plasticized with polyadipates were investigated by ageing in phosphate buffer at pH 1.679 and water at different temperatures. Changes in the PVC tubes were studied by water absorption, weight loss, Fourier infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The low molecular weight migration product that was released was extracted and silylanized before gas chromatography/mass spectroscopy (GC/MS) identification and quantification. After 70 days, the weight loss was less than 0.5% and only a small amount of adipic acid migrated when a tube was aged at 37°C in water and phosphate buffer (pH 1.679), and at 70°C in water after 56 days. However, when aged at 70 and 110°C, gradual deactivation of heat stabilizer after 21 days of ageing in buffer solution and separation of plasticizer from PVC matrix occurred. When the tube was aged at 110°C, significant degradation of both polyadipates and PVC were observed. Adipic acid and 1,4-butanediol monomers and oligomers of polyadipate were the major migration products from polyadipates in the water ageing solution, while only a relatively high amount of adipic acid was identified as the main product in the buffer ageing solution.     

Rheological and DSC changes in poly(vinyl alcohol) gels induced by immersion in water

Poly(vinyl alcohol) (PVA) gels were prepared by freezing and thawing aqueous solutions at temperatures from ?20 to 15°C. The temperature was varied periodically by use of a computer. The endothermic DSC peak was observed for the PVA gels at about 60°C for five specimens of different degrees of saponification (DS). Another endothermic peak was also observed in the range 67–80°C, and this peak shifted to higher temperature with increasing DS. These endothermic peaks shifted to lower temperature on immersion of the PVA gels in water. The dynamic Young's modulus E′ at room temperature was also decreased by immersion of PVA gels in water; E′ decreased monotonically with increasing temperature for PVA gels without immersion in water, while it increased up to a certain temperature and then decreased with increasing temperature for PVA gels in water. The X-ray diffraction showed a characteristic crystalline pattern for PVA gels of higher DS, and this peak was intensified by stretching the gel.     

Copper carboxylate formation in the thermal oxidative degradation of atactic polypropylene on copper oxide films

The thermal oxidation of atactic polypropylene on CuO_0.67 surfaces in air was studied using IR reflection-absorption spectroscopy. Degradative losses of primary, secondary, and tertiary alkyl hydrogens were observed. At 60 and 73°C, carboxylic acids are the primary degradation products, while at 85 and 100°C, copper carboxylate formation predominates and CuO_0.67 is decomposed. The distinct change in the oxidative mechanisms between 73 and 85°C apparently is related to an irreversible thermal transition in the atactic polypropylene films, which may favor carboxylate production by increasing the permeability of the films to oxygen and water vapor.     

Untersuchung der Bedingungen zur Gewinnung wasserfreien Zinksulfats

The three component system, zinc sulphate-sulphuric acid—water has been investigated in the region of high sulphuric acid concentrations at 15, 25, 35, 45, 60, and 80°C. In all cases a region of existence of anhydrous zinc sulphate was found. The conditions for obtaining anhydrous zinc sulphate by thermal dehydratation have been studied. The endothermic effect due to the conversion monohydrate—anhydrous salt was observed in the temperature interval from 220 to 290°C. The exact transition temperature depended on the conditions of preparation of the zinc sulphate monohydrate sample. The experimental data obtained by the physico-chemical investigation of the system permitted the determination of the equilibrium pressure of water vapour for the conversion monohydrate—anhydrous salt at 25.0°C.