The influence of extent of polymerization on the thermal behavior of an epoxy-based polyether resin

A number of studies have been reported in the literature on the polymerization and thermal decomposition of epoxide resins. Lee¹ and Anderson² have both studied the thermal decomposition of epoxy resins, and they concluded that the characteristic exothermic peak (which can occur anywhere between 300° and 400°C) is caused at least partially by some reaction of the epoxide group. We have been investigating the thermal decomposition of an aromatic polyether resin which is produced by curing the diglycidyl ether of bisphenol A (Epon 825) with the catalytic agent trimethoxyboroxine (Fig. 1). DTA studies of the polyether in an inert atmosphere of N₂ showed exothermic peaks at approximately 390°, 430°, and 470°C, with the major exotherm being the one at 430°C. Our investigation has shown the important role played by low molecular weight epoxides in these exothermic reactions.     

Hydrogen chloride evolution from the heating of poly(vinyl chloride) compounds

The dehydrochlorination and the thermal decomposition of five PVC materials was studied using two techniques: a batch analytical method, combining ion chromatography and atomic absorption and continuous thermogravimetry. The temperatures studied ranged from 60°C to 120°C, over a period of almost one year (50 weeks). It was found that a very large proportion of the soluble chloride emitted early on by the PVC materials into the liquid phase is not hydrogen chloride. None of the five materials tested emitted significant amounts of HCl at temperatures lower than 105°C. The emissions at 90°C after 50 weeks ranged from <0.01 Φg/g to 23.62 Φg/g. Furthermore, one of the materials tested emitted virtually no HCl, even at 105°C, as the amount of HCl measured was almost indistinguishable from the normal background of the analytical instruments (37.30 Φg/g after 50 weeks). Numerical calculations of kinetic reaction rates and extrapolation of the results to use temperatures (40°C) indicate that properly stabilized PVC compounds will be unlikely to lose 1% of the mass of PVC as HCl until 2 billion years have passed. This number has no physical meaning as such and may be incorrect by a vast margin, but it clearly indicates that a 1% loss of HCl is unlikely to occur during the useful lifetime of a commercial product into which the PVC material has been fabricated. This is a conservative estimate, which ignores the much higher activation energy for dehydrochlorination at temperatures below the glass transition temperature (ca. 85°C). Copyright © 2005 John Wiley & Sons, Ltd.     

Preparation and performance of PANI–PVA composite film doped with HCl

The polyaniline (PANI)–poly (vinyl alcohol) (PVA) composite film doped with HCl was prepared by adopting PVA as matrix. Effects of PVA content and film drying temperature on properties of HCl–PANI–PVA composite film were studied. A comparison was made for tensile strength, elasticity, conductivity and thermal stability of PVA, HCl–PANI or HCl–PANI–PVA. PVA film presented the highest tensile strength and elasticity (150.8?MPa and 300.0%), but its conductivity was the lowest. The conductivity of HCl–PANI–PVA was the highest (1500?S?m^?1), and tensile strength and elasticity of HCl–PANI–PVA were higher than those of HCl–PANI. The order of their thermal stability is PVA?>?HCl–PANI?>?HCl–PANI–PVA before 260°C, and the order of their thermal stability is HCl–PANI?>?HCl–PANI–PVA?>?PVA after 260°C. At the same time, the structure and conductive mechanism of composite materials were characterised and analysed through infrared and scanning electron microscopy (SEM).     

Study of Chromatographic Separation of Cesium,Europium, and Cobalt on Different Types of Tungstocerate Column Matrices

Interactions of ¹³⁴Cs(I), ^152,154Eu(III), and ⁶⁰Co(II) ions from HCl acid solutions with tungstocerate(IV) gel matrices, dried at 50°C, have been individually investigated by the batch equilibration method. The selectivity sequence was found to be in the order: Cs(I) >Eu(III) >Co(II). The breakthrough capacities of 12‐tungstocerate(IV) for Cs(I), Eu(III), and Co(II) were found to be 1.00, 0.55, and 0.26 mmol/g of the sorbent, respectively. In addition, a mixture of these radionuclides [6.20 × 10^?3 M Cs(I), 3.53 × 10^?3 M Eu(III), and 1.4 × 10^?3 M Co(II)], in 150 ml of 0.02 M HCl solution was passed through 1‐g 12‐tungstocerate(IV) chromatographic column. Quantitative uptake of both ¹³⁴Cs(I) and ^152,154Eu(III) has been achieved, while only ?22% of ⁶⁰Co(II) has been retained. Then, quantitative elution of the retained fraction of Co(II) was achieved with 14 ml of 0.1 M HCl acid solution leaving Eu(III) and Cs(I) strongly retained onto the column. Quantitative elutions of Eu(III) and Cs(I) were achieved by passing 20 ml of 0.3 M HCl and 16 ml of 2 M HCl acid solutions, respectively.     

A method for correlating and extending vapour pressure data to lower temperatures using thermal data: Vapour pressure equations for some n-alkanes at temperatures below the normal boiling point

Vapour pressures for many liquids are available in the range 50–760 torr but accurate determinations at lower pressures are frequently absent. Extrapolation based on purely empirical equations is hazardous and a convenient method is proposed for extrapolating such data to lower temperatures by utilizing readily available thermal data. The method is based on thermodynamically exact relationships. It has the advantage over previous such approaches that it makes greatest use of data, such as ideal gas and liquid heat capacities at around the temperature at which the vapour pressure is required, which are likely to be available. When applied to the n-alkanes C₆–C₁₆ from the normal boiling temperature down to a reduced temperature of 0·41 the method leads to a convenient vapour equation of the form ln p⁰ = alnT + bT ? (d/T) + E.The constants in this equation have been obtained in a systematic way from the available thermal, volumetric and vapour pressure data for these alkanes. These constants, together with vapour pressures and latent heats at 25°C calculated from them, are listed. Agreement between the calculated quantities at 25°C and experimental values (where available) is good.     

Effect of γ-radiation on the thermal conductivity of polypropylene

The effect of ⁶⁰Co γ-radiation on the thermal conductivity of polypropylene (PP) has been studied over the temperature range 0–160°C. for radiation doses of 600 and 1800 Mrad. The conductivity of unirradiated specimens rises from 4.5 × 10^?4 cgs units (cal./cm.-sec.-°C.) at 0°C. to 4.8 × 10^?4cgs units at 80°C. and subsequently decreases with temperature to a value of about 3.1 × 10^?4cgs units at 160°C. Upon irradiation to 600 Mrad the thermal conductivity is lowered over the 0–150°C. temperature range. Above 90°C. the conductivity decreases with temperature and becomes relatively constant at 3.4 × 10^?4 cgs units from 120 to 160°C. Differential scanning calorimeter (DCS) measurements from 30 to 200°C. show that irradiation to 600 Mrad lowers the energy associated with crystalline melting and shifts the endotherm melting peak from about 160 to 105°C. Irradiation to 1800 Mrad results in additional lowering of the thermal conductivity over the 50–160°C. range, a further decrease in area of the endothermic peak and a shift of its maximum peak position to about 75°C. The effects of radiation on the thermal conductivity of polypropylene are compared and correlated with the observed effects of radiation on the dynamic mechanical behavior.     

Kinetics of thermal degradation studies of some new terpolymers derived from 2,4‐dihydroxypropiophenone,oxamide, and formaldehyde

The terpolymers (2,4‐DHPOF) have been synthesized by the condensation of 2,4‐dihydroxypropiophenone with oxamide and formaldehyde in the presence of 2M HCl as catalyst with varying proportions of reactants. Terpolymer composition has been determined on the basis of their elemental analysis. The terpolymer has been characterized by UV‐visible, IR, and ¹H NMR spectra. The thermal decomposition behavior of some new terpolymers was studied using thermogravimetric analysis in air atmosphere at heating rate of 10°C/min. Thermal decomposition curves are discussed with careful attention to minute details. The Freeman–Carroll and Sharp–Wentworth methods have been used to calculate activation energy and thermal stability. Thermal activation energy (E_a) calculated with the help of these methods are in agreement with each other. Thermodynamic parameters such as free energy change (ΔF), entropy change (ΔS), apparent entropy change (S*), and frequency factor (z) are also determined on the basis of the TG curves and by using data of the Freeman–Carroll method. The Freidman method evaluated the variation in the apparent activation energy changes by isoconversional (model‐free) kinetic methods. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal Insulation Characteristics of Polybenzoxazine Aerogels

Polybenzoxazine (PBO) aerogels with low densities and low thermal conductivities are prepared from Bisphenol A (BPA) benzoxazine monomers by ring‐opened polymerisation using HCl as a catalyser at 10 °C. The obtained PBO aerogels have cross‐linked and 3D network structures with the densities ranging from 0.084 to 0.526 g cm^?3. The thermal conductivities under different pressures (3–10⁵ Pa, air) and different atmospheres (N₂, Ar, and CO₂, 10⁵ Pa) are investigated. The thermal conductivities are in the range of 0.0335–0.0652 W m K^?1 under ambient pressure and 0.0098–0.0571 W m K^?1 at 3 Pa. The thermal transfer mechanism under different gas pressures is analyzed with increasing pressure. Under different atmospheres, the thermal conductivities decrease as the molecular weight of the gas increases. Compared with the traditional organic foam insulating materials of phenolic foam, polyurethane and polystyrene, which have similar apparent densities, PBO aerogels exhibit lower thermal conductivity of 0.0335 W m K^?1 than that of traditional organic foam at room temperature.     

Structural modifications of nanostructured ceria CeO2,xH2O during dehydration process

Hydrated nanostructured cerium dioxide CeO₂, xH₂O (hydrated nanoceria) has been synthesized in room conditions via a precipitation route. This hydrated nanoceria phase has been subjected to thermal decomposition in the temperature range from 25 °C to 800 °C. At least three decomposition steps have been observed in thermal and thermogravimetric analyses. Three different samples of cubic nanoceria respectively obtained at room temperature (RT-nanoceria), 80 °C (80-nanoceria) and 600 °C (600-nanoceria) have been studied by X-Ray diffraction, Raman spectroscopy and scanning electron microscopy analyses. The analyses of X-ray diffraction profiles and Raman vibrational bands have clearly shown that dehydration is accompanied by increasing crystallite size, lattice parameter contraction. The cubic structure of hydrated RT-nanoceria might be associated with a complex chemical formula unit involving Ce⁴⁺, Ce³⁺ mixed valences, oxygen vacancies, lattice and surface water and OH^? proton species.     

Effect of the thermal treatment on microstructure and physical properties of low-density and high transparency silica aerogels via acetonitrile supercritical drying

In this paper, we reported the experimental results about the effect of the thermal treatment on microstructure and physical properties of low-density and high transparent silica aerogels. From our results, with tetramethyl orthosilicate as precursor and via acetonitrile supercritical drying process, silica aerogel monolith was obtained possessing the properties as low-density (0.018 g/cm³), high surface area (923 m²/g), high optical transparency (87.9 %, 800 nm). It should be noted that high transparency of silica aerogel can be maintained up to 600 °C (91.5 %, 800 nm). The mechanical properties of silica aerogel decreased with increasing heat treated temperature to 600 °C, and silica aerogels still maintained crack-free monoliths completely and possessed high homogeneous density even after 600 °C thermal treatment. Furthermore, thermal conductivity of the monoliths at desired temperatures was analyzed by the transient plane heat source method. When the temperature flowed from 25 to 600 °C, thermal conductivity coefficients of silica aerogels changed from 0.021 to 0.065 W (m K)^?1, revealed an excellent heat insulation effect in high-temperature area. Currently, the specific process developed for low-density aerogels affected by thermal treatment has not been reported in previous literature.     

Thermal conductivities and Raman spectra of boron-doped carbon materials

Boron-doped carbons were prepared at temperatures from 1000 to 2800°C. The effect of boron doping on the thermal conductivity of carbons has been studied and discussed with the results from Raman scattering. Boron doping above 2200°C depressed the thermal conductivity of carbons and increased the intensity of the 1360-cm⁻¹ Raman band. It appeared that lowering the thermal conductivity is mainly caused by a distortion of the graphite lattice due to boron doping.     

Synthesis of zinc-containing epoxy resin

Novel epoxy resins containing zinc acrylate have been synthesized by reacting zinc acrylate with bisphenol-A and an excess of epichlorohydrin. Parameters such as epoxy equivalent weight, hydroxyl content, and hydrolyzable chlorine content have been estimated. These resins, characterized by IR, ¹H-NMR, and ¹³C-NMR, have been evaluated by thermal analysis. Curing was carried out with polyamide at 130°C for 24 h. Cured resins have improved thermal and chemical resistance. The reaction follows first-order kinetics with activation energy 86 and 34 kJ mol^?1 in the presence and absence of zinc acrylate. The role of zinc, which increases epoxidation due to formation of complex with bisphenol-A, has been discussed. © 1994 John Wiley & Sons, Inc.     

Solution of hydrochloric acid in formamide—V. Thermodynamic properties from EMF of the cell Pt,H2|HCl(m)|Hg2Cl2, Hg over a temperature range 5–55°C (278.15–328.15 K)

The emf of cells (A) Pt, H₂|HCl(m)|Hg₂Cl₂, Hg and (C). AgAgCl|HCl(m)|Hg₂Cl₂, Hg have been measured at intervals of 5°C over the temperature range 5–55°C (278.15–328.15 K) using formamide as the solvent. The molal standard potentials of Hg, Hg₂Cl₂ electrode, determined on the basis of emf data of cell (A), agree well with those derived from the emf of cell (C) using known values of E⁰_Ag-AgCl reported earlier. Based on emf data of these cells, the standard thermodynamic changes ΔG⁰, ΔH⁰ and ΔS⁰ for the cell reactions as well as the mean molal activity coefficients of HCl at rounded molalities have been determined.     

Degradation of poly(vinyl chloride). I. Kinetics of thermal and radiation-induced dehydrochlorination reactions at low temperatures

The dehydrochlorination reaction arising thermally and from exposure to γ-radiation has been followed, under vacuum, in the temperature range from 80° to 130°C by measuring the pressure of the evolved volatiles. The catalytic action of HCl, which was recently established, has been observed also at these low temperatures. In agreement with previous data, a free-radical mechanism has been accepted to be operating in the radiation-induced reaction, which has been found to be linearly dependent on dose rate and essentially independent of temperature. Assuming the thermal dehydrochlorination to proceed according to the same mechanism, its activation energy, lying within the range of values reported in the literature, represents the activation energy for the thermal process of radical formation by dissociation of normal and anomalous structures in PVC macromolecular chains. Since this value appears to be substantially constant in the temperature range from 90° to 240°C, it can be established whether the dissociation reactions of all the PVC structures are regulated by the same activation energy or, more simply, only one of these structures is concerned.     

Thermal stabilization of PVC with khaya seed oil: Thermogravimetric studies

Thermal degradation of PVC stabilized with barium and cadmium soaps of Khaya senegalensis seed oil was studied by thermogravimetry up to 500°C using a constant heating rate of 10°C min⁻¹. At temperatures below 300°C, the extents of dehydrochlorination of both the unstabilized and stabilized PVC samples were low (less than 6% conversion). It was found from the values of weight loss that HCl was the only volatile product of degradation of PVC between 170 and 200°C. The rates of dehydrochlorination at about 200°C was of the order of 10⁻²% min⁻¹, about the same order of magnitude as the values obtained from kinetic studies. The temperatures at which maximum rates of degradation were attained, t_dmax, and the temperatures at which various extents of degradation were attained were used to assess the effectiveness of the metal soaps of Khaya seed oil in stabilizing PVC against thermal degradation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1432–1438, 2000     

Platinum sulfated zirconia catalysts. Fate of chlorine during activation

The gases evolved during activation of a sulfated zirconia prepared by impregnation with chloroplatinic acid have been followed using mass spectrometry and infrared spectrometry. When the sample is heated in either helium or in air, the halogen is lost from the catalyst as HCl and Cl2. Heating the sample in hydrogen results in the loss of the halogen as HCl, and only traces as Cl2. The loss of halogen occurs over a wide temperature range (200-900°C). The data are consistent with the chloroplatinic acid being converted by loss of halide with the formation of Pt⁰. This revised version was published online in July 2006 with corrections to the Cover Date.     

Brønsted and Lewis acid catalysis with ion- exchanged clays

An acid-treated montmorillonite clay has been ion-exchanged with Al³⁺, Fe³⁺, Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺ and Na⁺. The catalytic activities of these materials have been measured in the Brønsted acid catalysed rearrangement of α-pinene to camphene, and the Lewis acid catalysed rearrangement of camphene hydrochloride to isobornyl chloride, following thermal activation at temperatures from 75 to 350°C. The surface acidities of the ion-exchanged clays have been measured using a microcalorimetric method involving ammonia adsorption, and through the infrared spectra of adsorbed pyridine. The results show that maximum Brønsted acidity is generated on thermal activation at approximately 150°C and maximum Lewis acidity at 250- -300°C. A good correlation has been found between the surface acidities and the catalytic activities of the ion- exchanged clays in both reactions. A significant result is the relatively low surface Lewis acid strength of Al³⁺- exchanged clays, for which a possible explanation is proposed.     

Thermogravimetry and differential scanning calorimetry of Kentucky bituminous coals

A detailed investigation has been made of the thermal characteristics of six Kentucky bituminous coals undergoing pyrolysis in an inert atmosphere at three different heating rates. The specific heats of the coals and the enthalpy changes characterizing their thermal degradation were measured by differential scanning calorimetry. Thermogravimetry was employed to measure the attendant weight changes, which were used to normalize the heat flow data to unit sample weight, enabling a quantitative comparison of the thermal behaviour of the several coals. The specific heats of the dry coals lie in the range 1.21–1.47 J gK^?1, 100–300 °C. The exothermic heat flow from 300 to 550 °C, where the major weight loss occurs, has been associated with the primary carbonization process, the development of the plastic state, and the onset of secondary gasification, which is responsible for coke formation. In the high pyritic sulphur coals, the endothermic pyrite/pyrrhotite transformation at ≈580 °C is clearly defined. A preliminary global kinetic analysis of the thermogravimetric data has been made, using a modified Kissinger equation at the maximum rate of weight loss. Activation energy and pre-exponential factor values of the order 198–220 kJ mol ^?1 and 2–85×10¹²s^?1 have been obtained. These compare well with the limited published values for similar coals.     

Reaction between HC1 and orthophthalates of lead in hot DOP without PVC,and stabilization in plasticized PVC

Reactions between hydrogen chloride, HCl, and either hydrocerussite, 2PbCO₃. Pb(OH)₂, or an orthophthalate of lead suspended in di(2-ethylhexyl)phthalate, DOP, at 180°C are discussed as models of what should happen during the stabilization of PVC if thermal dehydrochlorination were to yield HCl. There is a sharp contrast between the products of these model reactions and those actually found in plasticized PVC containing basic lead compounds. This is taken to show that basic lead stabilizing regimes inhibit PVC thermal dehydrochlorination, actually preventing the formation of HCl. It is proposed that these stabilizing regimes function by a free-radical mechanism which has been called “true stabilization” for ease of reference.     

Thermal decomposition and pore structure of pure and doped stannic oxide gel

The surface properties of a stannic oxide gel and its thermal dehydration products obtained both in vacuo and in the presence of air in the temperature range 100–600°C have been examined by N₂ adsorption. Phase and structural changes have been followed by differential thermal analysis and X-ray diffractometry. Complete pore structure analysis showed that samples dehydrated at or below 250°C were microporous. Above 250°C the pores were found to widen with increase of temperature, the widening occurring concurrently with the crystallisation process. Doping with cations of lower valency (Li⁺ and Al³⁺) than the host cation (Sn⁴⁺) had little effect on the pore structure and specific surface area for the low temperature samples (≤250°), whereas at higher temperatures, e.g. 600°C, it increased the specific area remarkably. The dope ions produce oxygen vacancies and hinder or retard sintering in SnO₂.