Authors:Sanjiv Arora, Rajeev Bagoria, and Mahender Kumar
Alpha-tocopherol (vitamin E) is the most widely used antioxidant for edible oils. The present investigation presents its effect
on the thermal degradation behavior of edible oils (sunflower, soybean, and their blend) through the use of dynamic thermogravimetry.
The study is based on the comparison of activation energies of decomposition process which were subsequently calculated using
preferred and reliable multiple-heating rate methods viz. Kissinger, Friedman, Ozawa–Flynn–Wall, and Coats–Redfern (modified).
It is concluded that the role of alpha-tocopherol as antioxidant at higher temperature is nearly accomplished.
Authors:H. P. de Oliveira, J. Rieumont, C. Nogueiras, D. Souza, and R. Sánchez
between other small molecules. Its thermal degradation was studied using different experimental methods, such as differential scanning calorimetry, thermogravimetry, and thermal volatilization analysis; the thermal degradationbehavior of poly
Authors:R. K. Singh Raman, F. C. Parida, and A. S. Khanna
Although liquid sodium has proved to be a technologically superior and economically viable coolant in the heat-exchange circuits of fast reactors, it is fraught with the serious problems of fire hazards in the event of accidental leakages into the ambient air. For the rapid and effective suppression of sodium fires, sodium bicarbonate has emerged as a potential extinguishant. This paper attempts a description of the thermal decomposition behaviour of sodium bicarbonate fine powder in vacuum on the basis of thermogravimetry and differential thermal analysis. The analog percentage mass change data, transformed into dimensionless extents of reaction and calculated rates of reaction, are then analysed by a generalized computational technique. The results indicate that the most probable rate-controlling step is a process of three-dimensional contraction of the bicarbonate particle surface, with activation energyE=82.94 kJ mol−1 and frequency factorA=34.73×106 s−1. The decomposition temperature of sodium bicarbonate shows an upward trend with increasing heating rate.
Authors:H. Polli, L. Pontes, A. Araujo, Joana Barros, and V. Fernandes
The degradation kinetics of the ABS terpolymer (acrylonitrile-butadiene-styrene) was investigated by means of thermogravimetric
analysis. The samples were heated from 30 to 900°C in nitrogen atmosphere applying three different heating rates: 5, 10 and
20°C min−1. The Vyazovkin model-free kinetic method was used to calculate the activation energy (E) of the degradation process as a function of conversion and temperature. Between 20 and 80% of conversion, E was calculated
and the figures were: for ABS GP, E is 204.5±11.5 kJ mol−1 (medium value); for ABS HI, E is 239.0±9.8 kJ mol−1; for ABS HH, E is 242.4±5.4 kJ mol−1.
Authors:L. Barral, J. Cano, J. López, I. López-Bueno, P. Nogueira, C. Ramírez, and M. Abad
A study of an epoxy-cycloaliphatic amine system has been realized using a thermogravimetric technique (TG). Isothermal and
non-isothermal (dynamic) methods were employed to determine the kinetic data of this system.
Five methods were used for determining the activation energies of this system in the dynamic heating experiments. In two of
them (Flynn-Wall-Ozawa, and Kissinger) it is not necessary to have a prior knowledge of the reaction mechanism of the degradation
behaviour for this system. In the other ones (Coats and Redfern, Horowitz and Metzger, and Van Krevelen et al.) it is necessary
to know this reaction mechanism, besides Criado et al. method was used for determining it.
The results have shown that good agreement between the activation energies obtained from all methods can be achieved if it
is assumed that the degradation behaviour of this system is of sigmoidal-rate type.
Thermal degradation studies were carried out of copolymer phenyl methacrylate-styrene in the presence of aluminum isopropoxide
to assess the stability and alteration of degradation mechanism using thermogravimetry-differential thermogravimetry (TG-DTG)
in inert atmosphere and under vacuum using thermal volatilization analysis (TVA). After collecting the condensable volatile
degradation products from TVA experiments and separating them by sub-ambient TVA, investigation and identification were effected
out by IR spectroscopy and gas chromatography-mass spectrometry (GC-MS) techniques. The degradation products from the blends
consisted of some additional products, i.e., isopropanol, phenol, methacrylic acid, ethyl benzene, benzene and a cyclic compound
apart from similar products obtained from the degradation of pure copolymers. The mechanism of newly formed degradation products
has been discussed in detail.
The thermal degradation of graft copolymers of both polysaccharides (guar gum and xanthan gum) showed gradual decrease in mass loss. Pure guar gum degraded about 95% but pure xanthan gum degraded about 76% up to 1173.15 K, while graft copolymers of guar gum and xanthan gum degraded only 65–76% up to 1173.15 K. Acrylic acid grafted guar gum and xanthan gum showing two-step degradation with formation of anhydride and ketonic linkage during heating, same pattern of degradation was found for xanthan gum-g-methacrylic acid. Guar gum-g-acrylamide degraded in single step and xanthan gum-g-acrylamide started to degrade above 448.15 K and it is a two-stage process and imparts thermal stability due to the formation of imide linkage with evolution NH3. Guar gum-g-methacrylamide degraded in three steps due to the loss of NH3 and CO2 successively. 4-vinyl pyridine grafted both polysaccharides show single step degradation due to loss of pyridine pendent. N-vinyl formamide grafted guar gum and xanthan gum started to degrade at about 427.15 K, showed two-stage degradation process with the evolution of CO and NH3 molecules while guar gum-g-(N-vinyl-2-pyrrolidone) degraded into two steps by the loss of pyrrolidone nucleus. Gum-g-2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) showed two-step degradation processes in two successive degradation steps, while xanthan gum-g-AMPS has started degradation at about 427.15 K and completed in five degradation steps. Overall, it was found that the grafted polysaccharides are thermally more stable than pure polysaccharides.
The thermogravimetry of a series of 50/50 mixtures of polypropylene, acrylonitrile/butadiene/styrene, polyvinyl chloride and
polyurethane polymers have been studied as representative of the major polymeric materials found in automobile shredder residues.
The weight loss behaviour of these polymeric mixes have been compared with the results calculated from the individual polymeric
components. This comparison of the thermogravimetry curves and the calculated kinetic parameters indicates that interactions
occur between the individual polymers when heated together. The extent of these interactions are dependent upon the polymeric
mixtures being considered, but in most cases the changes in the degradation kinetic parameters were not large.
The influence of untreated and treated fique fibers on the crystallization process and thermal degradation of different thermoplastic
matrix composites has been evaluated. The fique fibers have been treated with different chemicals according with the type
of thermoplastic matrix employed. Additionally, a copolymer of poly(propylene) with maleic anhydride (MAPP) has been used
as compatibilizer. The treatments introduce an increment on the thermal stability of fique fibers respect to untreated fibers.
Crystallization is affected by the presence of fique fibers showing important differences for each type of composites. Fiber
presence has an important influence on the matrix morphological characteristics, as observed by dynamical mechanical analysis.