ESR study of primary radical formation during mechanical degradation of poly(2,6-dimethyl-p-phenylene oxide) solid

Radical formation during mechanical degradation of solid poly(2,6-dimethyl-p-phenylene oxide) (PPO) was investigated by electron spin resonance (ESR). The ESR spectrum of PPO fractured at room temperature in air consisted of eight lines with a separation of about 5.5 gauss with g = 2.0043, indicating a small asymmetry. For PPO fractured in liquid nitrogen, a similar spectrum was observed at ?196°C in air or in vacuo. These spectra have been identified as belonging to a 2,6-dimethyl-substituted phenoxy radical and thus indicate the occurrence of main-chain rupture. The phenyl radical which was expected to be formed together with a 2,6-dimethyl-substituted phenoxy radical could not be detected, but at temperatures below ?46°C a small hump was observed at g = 2.034. By subtracting the spectrum observed after decay of this hump from the original one, the resulting curve was the characteristic asymmetric spectrum of a peroxy radical, which was presumably formed by the reaction between a phenyl radical and oxygen. The radical decay curve showed two stepwise-decaying regions; one located in the temperature region between about ?120°C and ?80°C where only a small number of radicals decayed, another located in the temperature region from about ?30°C to 100°C where almost all mechanically formed radicals decayed. The latter radical decay, which occurred considerably below the glass-transition temperature of PPO, was attributed to the molecular motions associated with the mechanical β^* relaxation on the basis of the activation energy and the temperature region.     

Thermoluminescence study of ZnS:Cu nanoparticles

In this paper, we report on the TL glow curves and kinetic parameters, activation energy, order of kinetics, and the frequency factor of copper-doped zinc sulfide nanophosphor under UV irradiations. The sample was prepared by the chemical precipitation method; thereafter, the TL glow curves were recorded for different doses of UV exposure at a heating rate of 10 °C/s. The synthesized nanophosphor exhibited TL glow peaks at 241, 255, and 281 °C for the heating rate 10 °C/s at different doses of 5, 10, and 15 min of UV exposure. The kinetic parameters activation energy E, the order of kinetics b, and the frequency factor S of synthesized nanophosphor of ZnS:Cu have been calculated by using a peak shape method while the trap depth was determined using different formulae. The sample was characterized by XRD (X-ray diffraction) and SEM (scanning electron microscope).     

Thermoluminescence and chemical characterization of natural calcite collected from Kodwa mines

This paper reports the thermoluminescence (TL) and chemical characterization of natural calcite collected from Kodwa mines of the C.G. Basin. The sample was irradiated with a 10-Gy dose from an Sr-90 beta source. The heating rate used for TL measurements was 6.7 °/s. The sample had a good TL peak at approximately 127 °C and the corresponding kinetic parameter were calculated. The effect of annealing temperature is also described for natural calcite. The photoluminescence excitation spectrum at ~254 nm and the corresponding emission spectrum peak at 395 nm are reported. Inductively coupled plasma–activated emission spectroscopy (ICP–AES) was conducted to determine the percentages of elements in the calcite mineral.     

Thermoluminescence study,including the effect of heating rate,and chemical characterization of Amarnath stone collected from Amarnath Holy Cave

This paper reports TL glow curve analysis and evaluation of kinetic parameter for Amarnath stone collected from Amarnath Holy Cave. TL was recorded with different heating rates (3.3, 4, 6.7, 8, and 10 ° s^?1). The samples gave good TL peaks at 310, 314, 308, 323, and 327 °C for the different heating rates. The corresponding activation energy (E) values were calculated. The peaks were indicative of second-order kinetics. Samples were characterized by XRD analysis. Inductively coupled plasma activated emission spectroscopic (ICP–AES) analysis was performed to determine percentages of elements in the natural mineral. Results from ICP–AES and XRF (X-ray fluorescence spectroscopy) studies were compared.     

Secondary retardation modes in diglycidyl ether of bisphenol A–diamino diphenyl methane networks

Thermally stimulated creep (TSCr) has been used to follow the viscoelastic behavior of some amine-cured epoxy networks below the glass transition. The investigation of the -180/+40°C temperature range has revealed two essential retardation modes characterizing localized motion of chain segments: the γ mode centered at ?155°C in all samples, and the well-known β mode observed around ?40°C in the stoichiometric network. The magnitude of the β mode was seen to decrease unexpectedly with the cross-link density, whereas its peak temperature and glass transition temperature both decreased. This evolution was confirmed by thermally stimulated currents (TSC) measurements and discussed on the basis of the antiplasticization concept. Water desorption under vacuum yielded additional information on the nature of the β mode and TSCr fractional loading experiments brought evidence that two types of relaxing units participate in β motions and furnished activation enthalpy data. © 1994 John Wiley & Sons, Inc.     

Secondary processes of poly(methyl methacrylate) and their activation energies as determined by shear and tensile creep compliance measurements

The results of measurement of the shear and tensile creep compliance of poly(methyl methacrylate) between ?150 and 75°C. are presented. The master curves show the creep behavior from essentially elastic response to the onset of the α-process. The logarithmic retardation spectra and shear loss compliance reveal two molecular processes, one process being partially obscured by the α-process and therefore not as well defined as the other. These processes manifest themselves as breaks in an Arrhenius plot of the shift factors at about ?35 and +25°C. The activation energies in the ?35 to 25°C. and 25 to 80°C. ranges are 17.8 kcal./mole and 42.2 kcal./mole, respectively. The former temperature range and activation energy corresponds to the well-known ß-process in poly(methyl methacrylate), the latter to a process which is apparently detectable using various long-time experimental techniques but whose molecular interpretation is at present obscure. The activation energy in the ?150 to ?35°C. range is about 8.7 kcal./mole.     

Electron spin resonance study of ethylene–acrolein copolymer irradiated with ultraviolet light

When ethylene–acrolein copolymer was irradiated at ?196°C with ultraviolet light, a sharp singlet spectrum with a g value of about 2.001 was predominant. This spectrum is attributed to acyl radicals, which are produced by dissociation of a hydrogen atom from an aldehyde group. At the same time it is supposed that dissociation of formyl groups also took place to give alkyl radicals, CO, and H₂. The alkyl radicals reacted with CO molecules to give acyl radicals at ?78°C under vacuum. Peroxy radicals were produced when the sample irradiated at ?196°C in the presence of air was treated at ?78°C. The sample irradiated at ?196°C was warmed to near 0°C and an apparent singlet spectrum with a g value of about 2.004 was observed. This spectrum was tentatively assigned as due to free radicals of the type      

Urea and CaCl2 as inhibitors of coal low-temperature oxidation

Thermal analysis was used to study the influence of CaCl₂ and urea as possible chemical additives inhibiting coal oxidation process at temperatures 100?C300?°C. Weight increase due to oxygen chemisorption and corresponding amount of evolved heat were evaluated as main indicative parameters. TA experiments with different heating rates enabled determination of effective activation energy E _a as a dependence of conversion. In the studied range of temperatures, the interaction of oxygen with (untreated) coal was confirmed rather as a complex process giving effective activation energies changing continuously from 70?kJ?mol^?1 (at about 100?°C) to ca. 180?kJ?mol^?1 at temperatures about 250?°C. The similar trend in E _a was found when chemical agents were added to the coal. However, while the presence of CaCl₂ leads to higher values of the effective activation energies during the whole temperature range, urea causes increase in E _a only at temperatures below 200?°C. Exceeding the temperature 200?°C, the presence of urea in the coal induces decrease in activation energy of the oxidation process indicating rather catalysing than inhibiting action on coal oxidation. Thus, CaCl₂ can only be recommended as a ??real?? inhibitor affecting interaction of coal with oxygen at temperatures up to 300?°C.     

Phase transition of layer structure of poly(p-benzenedithiol-co-p-diethynylbenzene) by heat or photon mode

Phase transition of the layer structure of poly(p-benzenedithiol-co-p-diethylbenzene) obtained in solid state polymerization was studied by a thermal treatment or UV irradiation under a nitrogen atmosphere. The peak intensities in the X-ray diffraction diagram of polymers gradually decreased with the thermal treatment time above 55°C. Below 50°C the layer structure of polymers hardly changed. The apparent activation energy for the phase transition was about 15 Kcal/mol [63 KJ/mol] at the initial stage and gradually decreased to a few Kcal/mol [ca. 2 KJ/mol]. UV light from a high-pressure mercury lamp also gradually induced the phase transition from the layer structure to an amorphous one. The pristine polymer possesses phase transition points at 75, 95 and 130°C. The exothermic transition at 75°C can be understood as the thermal destruction of the semistable layer structure. The exothermic transition at 95°C may be correspond to the cis → trans thermal isomerization of the C?°C bond in the polymer main chain. The diffuse reflectance spectrum of the pristine polymer differed from that of the amorphous polymer obtained by the thermal treatment of the pristine polymer. SEM photographs of the pristine polymer showed a particular surface structure, i.e. entangled fibrous material. TEM photographs of the pristine polymer exhibited a bright valley-and-hill structure, whereas that of the amorphous polymer obtained by thermal treatment exhibited a plain surface.     

Electron spin resonance study of poly-3,3-bis(chloromethyl) oxetane irradiated with electron beams and ultraviolet light

Poly-3,3-bis(chloromethyl)oxetane (poly-BCMO) was irradiated at ?196°C with electron beams and ultraviolet light, and observed ESR spectra were compared. A three-line spectrum (coupling constant of about 21 gauss) and a two-line spectrum (coupling constant of about 18 gauss) were observed after irradiation with electron beams in vacuo. They were attributed to free radicals and respectively. On the other hand, a three-line spectrum (coupling constant of about 20 gauss) and an asymmetric singlet spectrum were observed after ultraviolet irradiation in vacuum. They were assigned to free radicals and ? CH₂? O·, respectively. Mechanisms of radical formation were discussed in each case. When poly-BCMO was irradiated with electron beams at ?196°C in the presence of air, peroxy radicals were produced after subsequent treatment at ?78°C. The reaction between alkyl radicals and oxygen molecules was found to be diffusion-controlled.     

Volatiles Formation from Grape Must Fermentation Using a Cryophilic and Thermotolerant Yeast

Grape must fermentation performance and volatiles formation by simultaneously cryophilic and thermotolerant yeast (strain AXAZ-1), isolated from grapes in Greece, was evaluated in a wide temperature range (5?C40°C). Yeast strain was immobilized on brewer??s spent grains (BSG) and the formed biocatalyst was introduced into a Multi-Stage Fixed Bed Tower (MFBT) bioreactor. Almost complete sugar utilization from the aforementioned biocatalyst was observed in a wide temperature spectrum, ranging from 5?°C to 37?°C, while at 40?°C residual sugar was up to 29?g/l. Time to complete fermentation with the immobilized yeast ranged from 290?h at 5?°C and 120?h at 40?°C to 25?h at 33?°C. The daily ethanol productivity reached maximum (88.6?g/l) and minimum (5.6?g/l) levels at 33?°C and 5?°C, respectively. The aroma-related compounds?? profiles of immobilized cells at different fermentation temperatures were evaluated by using solid phase microextraction (SPME) gas chromatography/mass spectrometry (GC/MS). Must fermentation resulted in a high-quality fermentation product due to the low concentrations of higher and amyl alcohols at all temperatures tested. AXAZ-1 is a very promising strain for quality wine production, as it is capable of performing fermentations of high ethanol concentration and productivities in both low and high temperatures.     

Electron spin resonance study of poly-3,3-bis-(chloromethyl)oxetane irradiated with ultraviolet light

When poly-3,3-bis(chloromethyl)oxetane has been irradiated at ?196°C in a nitrogen atmosphere with ultraviolet light, a triplet spectrum is observed. After warming the sample, both a doublet and a singlet ESR spectra are observed. These spectra are attributed to and ? CH₂? O, respectively. The formation mechanism of these free radicals is discussed. It is concluded that the main process of radical formation is the dissociation of chemical bonds from the excited state of the polymer produced through the energy absorption by irregular groups acting as sensitizers. In the presence of oxygen, the radical yield at ?196°C is greater than that in nitrogen atmosphere. This is attributed to the extra absorption of light by the charge transfer complexes of polymers with oxygen molecules. It is also proposed that participation of a charge transfer complex in photooxidation of ether is important in the primary radical formation step. When a polymer sample irradiated in vacuum with ultraviolet light is treated at ?78°C for a few minutes in the presence of air, peroxy radicals form. This shows that oxygen molecules diffuse very easily into this polymer, even at this low temperature.     

ESR spectra of poly(methacrylic acid) and poly(methyl methacrylate): Reinterpretation of the 9-line spectrum

The temperature dependence of the ESR spectra of poly(methacrylic acid) and poly-(methyl methacrylate) γ-irradiated at room temperature was studied between ?196°C and +25°C. The conventional 9-line spectrum was observed throughout this range with no significant spectral change, in contrast to the propagating radical ··· CH₂? °C(CH₃)COOR found in methacrylic acid monomer or barium methacrylate dihydrate irradiated at ?196°C. In addition, the irradiation of methacrylic acid monomer with a low dose at 0°C gave the same 13-line spectrum as that of the propagating radical obtained by the irradiation at ?196°C, while prolonged irradiation at 0°C gave the same conventional 9-line spectrum as that of poly(methacrylic acid) or poly(methyl methacrylate). The conventional 9-line spectrum has a much weaker 4-line component than that of the propagating radical. The difference comes from the surrounding matrix, and the conventional 9-line spectrum is well interpreted by introducing the concept of the distribution of the conformational angle in the irregular polymer matrix. From simulation of the ESR spectrum, it was found that the intensity of the 4-line component is very sensitive to the distribution, and that the observed 9-line spectrum is well reproduced assuming a Gaussian distribution (half-height width of 5–6°) around the most probable conformation which is nearly the same as that of the propagating radical, where the conformational angles of the two C? H_β bonds to the half-filled p-orbital are 55° and 65°.     

Radiation-induced ionic polymerization of isobutyl vinyl ether in bulk

The radiation-induced ionic polymerization of isobutyl vinyl ether was investigated under conditions where the monomer was dried with molecular sieves. The investigation covered the temperature range from ?16°C to 90°C, and the dose-rate range from 10¹⁵ to 10²⁰ eV/g-sec, using both γ-rays and electrons. A very high overall activation energy of 15.9 kcal/mole was found for the process below 30°C. Above 30°C, however, the value of the overall activation energy dropped to 4.9 kcal/mole, a phenomenon which is ascribed to the solvation of the propagating carbonium ion below 30°C. The dose-rate dependence of the rate of polymerization was found to be 0.58 over the entire dose-rate range investigated. The molecular weight of the polymer was found to be far less sensitive to trace amounts of water than the rate of polymerization. The molecular weight of the polymer depended strongly on the irradiation temperature, reaching a maximum value of about 120,000 at 35°C. It is shown that at temperatures above 20°C regenerative chain transfer processes play an important role in determining the molecular weight of the polymer.     

ESR studies of some γ-irradiated organic crystals

Acrylamide, N-tert-butylacrylamide, and propionamide crystals were irradiated at ?196°C and the structures of radicals studied by ESR spectroscopy at various temperatures. The γ-irradiated acrylamide crystals show a five-line spectrum which is similar in shape to the signal obtained from the γ-irradiated propionamide crystals. Two types of radicals are produced in irradiated acrylamide and propionamide crystals at ?196°C. When the irradiated samples are kept at ?78°C the spectrum of propionamide remains the same, except in intensity. In contrast to this, the acrylamide spectrum changes to a triplet because of dimerization. Upon warming the irradiated acrylamide sample to between ?50 and ?30°C, some small new peaks become apparent on either side of the triplet. These new peaks disappear above ?20°C and the spectrum changes to a triplet because of polymerization. To observe the changes in the ESR spectra of γ-irradiated N-tert-butylacrylamide we kept the sample at various temperatures from ?196 to 100°C. From ?196°C to about room temperature the spectrum is a quintet. At and above 35°C, the spectrum changes to a triplet with shoulders on either side of the main peaks. With further warming above 80°C the spectrum changes to a broad triplet.     

Dielectric relaxations in poly(thiocarbonates)

The dielectric absorptions observed on six poly(thiocarbonates) (PTC) containing different substituents in the interphenylic carbon atom are subjected to a study. The α relaxation process associated with the glass transition temperature, which appears at the highest temperature studied, is overlapped with a strong conductive component. Between 80 and 100°C dielectric activity (β) is observed, which is related to structural relaxation phenomena. Polymers with double substitution on the interphenylic carbon atom show a γ relaxation with an activation energy of ca. 11 kcal mol^?1 while those where the carbon atom is linked to a cyclohexyl group show higher activation energies and their respective characteristics. A cryogenic absorption around ?120°C, for at least three polymers with an activation energy of about 5 kcal mol^?1, is detected. © 1994 John Wiley & Sons, Inc.     

Study on the kinetics and reactivity at the ignition temperature of Jurassic coal in North Shaanxi

Thermal analysis of seven Jurassic coal samples from North Shaanxi in West China and three permo-carboniferous coal samples from East China was studied to identify ignition temperatures in the process of the oxidation and spontaneous combustion. The experiments were carried out under non-isothermal heating conditions up to 700 °C at the heating rates of 5, 10, 15, and 20 °C min^?1 in an air atmosphere. Through the FTIR spectrometer experiments, the absorbance peaks of functional groups of coal samples were analyzed at the ignition temperatures, pre-ignition of the 10 °C, post-ignition of the 10 °C at the heating rate of 10 °C min^?1. By the differential spectrum method, the changes of functional groups were discussed with the aim to determine characteristics and reactivity of the ignition temperature around. The results showed that ignition temperatures of experimental coal samples increased with the rising heating rates, and ignition temperatures of Jurassic coals were lower than that of the permo-carboniferous coal samples at the same heating rate. Apparent activation energy of experimental Jurassic coals at the ignition temperatures was calculated by Ozawa method based on the non-isothermal and differential heating rates, ranging from 80 to 105 kJ mol^?1, which were lower than that of the eastern permo-carboniferous samples. On the basis of Pearson correlation coefficient method which can signify the degree of correlations ranging from ?1 to 1, the correlation analyses were conducted between activation energy and functional groups variation within 10 °C before and after ignition temperature. It was concluded that the key functional groups of Jurassic coals in the oxidation and ignition reaction were methyl and alkyl ether within 10 °C before ignition temperature, and carboxyl and carbonyl within 10 °C after ignition temperature.     

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.     

Dielectric relaxation in styrene-related polymers at low temperatures

The complex dielectric constants ?^* = ?′ ? j?″ of each of several members of a system of copolymers of 4-chlorostyrene and 4-methylstyrene have been measured from 1.6°K to 300°K and from 0.1 kHz to 20 kHz. The principal experimental findings are: the strength of the relaxation process which occurs near 50°K at 1 kHz varies linearly with changing copolymer composition; both the apparent activation energy (H = 2.7 ± 0.7 kcal/mole) and the shape of the relaxation curve are independent of the composition variable and of the temperature (or frequency) within the ranges studied; and the ratio of the relaxation strength of poly-4-methylstyrene to that of poly-4-chlorostyrene in the 50°K process is about 25 times the corresponding ratio for the primary relaxation process that occurs in the neighborhood of the glass-transition temperature. These findings suggest that in the 50°K process the phenyl groups relax independently of one another; that the apparent activation energy and the shape of the relaxation spectrum are determined primarily by the nature of the intrachain forces; and that the strength of the relaxation process depends primarily on effects of intermolecular forces that are governed by the molar “free volume” of the copolymers.     

Thermoluminescence from extended-chain crystals of polyethylene

Thermoluminescence (TL) has been observed in γ-irradiated extended-chain crystals of polyethylene above room temperature. The TL curve, which exhibits four peaks at 50, 90, 120, and 140°C, is different from that given by folded-chain crystals, in both shape and intensity. In particular, a shape, strong glow peak is observed at 140°C, corresponding to the melting temperature of the extended chain crystals. These results are discussed in relation to independent measurements by differential scanning calorimetry and electron spin resonance.