Evaluation of thermal behavior of latex membranes from genetically improved rubber tree (Hevea brasiliensis)

Thermal stability, thermal decomposition process, residual mass, temperature of glass transition (T_g) and temperature dependence of storage modulus (E’), were determined for latex membranes prepared from six clones of Hevea brasiliensis: IAC 331, IAC 332, IAC 333 and IAC 334 grown at experimental plantations of Instituto Agronômico de Campinas (IAC) in Votuporanga, São Paulo State, Brazil. Latex membranes from GT1 and RRIM 600 Asian matrix clones were used as references. The thermal behavior of latex membranes from genetically improved rubber trees was characterized using thermogravimetry/derivative thermogravimetry (TG/DTG), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The thermal behavior of latex from clones studied in the present work showed similar features of the clones previously reported (IAC 40, IAC 300, IAC 301, IAC 328, IAC 329 and IAC 330), with mass loss in four consecutive steps, except IAC 333, which showed an additional mass loss step.     

Use of Methods of Thermal Analysis in Studying Ceramic Materials on the Basis of Al2O3, ZrO2, Si3N4, SiC and Inorganic Binder

By thermoanalytical methods TG, DTG, DTA there have been investigated the processes occurring during the formation of ceramic materials on the basis of Al₂O₃, ZrO₂, Si₃N₄, SiC,and inorganic binder. IR spectroscopy has been an additional research method. It's been determined that with the use of H₃PO₄ as the binder for ceramic materials, the mechanisms of thermal decomposition are connected with the following processes: 1. removal of weakly tied and crystallized water in the temperature range of120–230°C, the removal being characterized by the endothermic effect, 2. interaction of the initial powder components of the ceramic materials with orthophosphoric acid conditioned by a strong exothermic effect on the DTA curve in the range of 230–530°C, 3. overlapping of endo- and exo-effects, testifying to a complex mechanism of thermal transformations, 4.oxidizing of the non-reacted silicon at the temperature of 720(760)°C, an increase of mass is observed on the TG curve as a result of the formation of SiO₂ – crystoballite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Analysis of Polymer-silicate Nanocomposites

The thermal behavior of epoxy-smectite nanocomposites (hybrids) is examined by non-isothermal thermogravimetry (TG, DTG and DTA) in air atmosphere. It has been shown that the thermal stability of hybrids is much greater than that of epoxy resin and strongly depends on both the smectite loading and the type of the gallery cations of organically modified smectites. The kinetics of degradation of nanocomposites is significantly influenced by the presence of smectites and proceeds in three stages. Stage I is attributed to the effect of quaternized ammonium ion exchanged smectite, as stages II and III are associated with the decomposition of the bulk epoxy resin. Because of the interfacial interactions and thesilicate-polymer multilayered nanoscale organization, the nanocomposites act as excellent heat insulator and mass transport barrier, which shift the thermal decomposition peaks towards much higher temperatures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Feasibility Study of Crude Oil Fields by Thermal Analysis Techniques

This paper investigates the minimum oil content necessary for self-sustained combustion, which is introduced as a criterion for the selection of suitable reservoirs for in-situ combustion processes. Differential scanning calorimetry was used to determine the heat values of oil-limestone mixtures. The minimum temperature required for the total consumption of the fuel was obtained by thermogravimetry (TG/DTG). The minimum amount of oil necessary to sustain combustion was calculated from these two parameters and compared with the oil content of the reservoir. Reservoirs with an oil content greater than or equal to this minimum value were considered feasible. It was seen that the fields examined are generally not suitable for in-situ combustion processes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Amino Acid-Pillared Layered Double Hydroxide and Montmorillonite Thermal Characteristics

Zn-Al hydrotalcite (HT) and Na-montmorillonite (Na-mont) were pillared by the deprotonated and the protonated forms of L-tyrosine, respectively. Pillaring was successful as the increased basal spacings due to intercalation attest. L-Tyr-HT proved to be thermally less stabile than HT, while that of L-Tyr-mont did not change compared to Na-mont. DTG curves showed more mass loss steps for the hosts than for the intercalated compounds. The extra steps belonged to the decomposition of the amino acid derivatives. FT-IR spectra of the samples pretreated in vacuum in the 293-773 K temperature range also showed that intercalation was successful and L-Tyr-HT is more temperature sensitive than L-Tyr-mont. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal behavior of polystyrene synthesized in the presence of carboxymethyl cellulose

Summary Study of the decomposition kinetics is an important tool for the development of polymer recycling in industrial scale. In this work, parameters such as activation energy, frequency factor and reaction order, were measured under dynamic conditions. Flynn-Wall-Ozawa, Van Krevelen, Horowitz-Metzger, Coats-Redfern, Madhusudanan and Vyazovkin methods were used to determine the kinetic parameters. The analysis of the results obtained by the Coats-Redfern method shows that the thermal degradation process of LDPE and HDPE corresponds to a phase boundary controlled reaction (mechanism R2). This method shows that the reaction order values of LDPE and HDPE are about 0.7 and 0.6, respectively.     

Thermal Behaviour of Metal Complexes of 6-(2-Pyridylazo)-3-acetamidophenol

The present work aims chiefly to study the thermal behaviour of complex compounds with general formula: [M(HL)xH₂O](A)yH₂O (where HL=C₁₃H₁₁N₄O₂=6-(2-pyridylazo)-3-acetamidophenol (PAAP), M=Cu(II), Zn(II), Cd(II) and Fe(III) x=1, 3; y=2, 5) while A=CH₃COO^– (Ac), Cl₂. The second formula is [M(H₂L)xH₂O]Cl₂yH₂O, (where H ₂ L=C₁₃H₁₂N₄O₂ (PAAP), M=Ni(II), Co(II) x=3; y=4, 6). The compounds were identified by elemental analysis, FT-IR spectra and TG/DTG,DTA methods. It was found that during the thermal decomposition of complex compounds water molecules of crystallization are released in the first step. In the next step the pyrolysis of organic ligand takes place. Metal oxide remained as a solid product of the thermal decomposition. Mass spectroscopy has been used for the determination of the thermal decomposition on the intermediate products. It was found that the thermal stability of the studied compounds increases as the ionic radii decreases. The activation energy E, the entropy change S ^*, the enthalpy H ^* change and Gibbs free energy change G ^* were calculated from TG curve.This revised version was published online in November 2005 with corrections to the Cover Date.     

Spectral signs of reaction between dihydric phenols and boric acid

We have studied the vibrational spectra and thermal curves (DTA, DTG, and TG) for the products of reaction between total shale phenols and boric acid, and also the polymer matrix of a gas-filled alkyl resorcinol polymer modified by mixtures of boric acid and aluminum oxide. Based on analysis of the IR absorption spectra, we show that the reason for the change in the physicochemical properties of the foam polymer is complex formation between the polymer and the additive. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 260–263, March–April, 2006.     

Synthetic,spectroscopic and thermal aspects of some heterochelates

The present article describes the synthesis, structural features and thermal studies of heterochelates of the type [M(SB)(benen)(H₂O)]·nH₂O [where H₂SB=(Z)-2-(2,2,2-trifluoro-1-(5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)ethylideneamino)benzoic acid, benen=bis(benzylidene)ethylenediamine and M=Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and VO(IV)]. The Schiff base (H₂SB) have been characterized on the basis of elemental analysis, IR, ¹H and ¹³C NMR. The heterochelates have been characterized on the basis of elemental analyses, magnetic measurements, solid state conductivity measurements, IR, reflectance spectra, and thermal studies. The FAB mass spectrum of [Co(SB)(benen)(H₂O)] has been carried out. The kinetic parameters such as order of reaction (n) and the energy of activation (E _a) have been reported using Freeman-Carroll method. The pre-exponential factor (A), the activation entropy (ΔS ^#), the activation enthalpy (ΔH ^#) and the free energy of activation (ΔG ^#) have been calculated.