Thermogravimetric studies of decomposition kinetics of six different IAC Hevea rubber clones using Flynn-Wall-Ozawa approach

The thermal degradation behaviour of rubber from six new Hevea brasiliensis clones (IAC 40, 56, 300, 301, 302 and 303) from São Paulo State, Brazil was studied by thermogravimetry using the Flynn-Wall-Ozawa approach to assess the kinetic parameters ( reaction order, activation energy and pre-exponential factor) of the decomposition process. This study indicated that the thermal behaviour is a complex multiple step process, which depends on the type of rubber Hevea clones studied. The rubber from these clones can be classified, following the order of decreasing thermal stability, as IAC 303 > 302 > 56 > 40 > 300 > 301.

Kinetic parameters for thermal decomposition of supramolecular polymers derived from flunixin-meglumine adducts

Meglumine, (2R,3R,4R,5S)-6-methylaminohexane-1,2,3,4,5-pentol, is a carbohydrate derived from sorbitol in which the hydroxyl group in position one is replaced by a methylamine group. It forms binary adducts with substances having carboxyl groups, which have in common the presence of hydrogen bonding as the main force in the stabilization of these species. During melting, adducts of meglumine with flunixin (2-[[2-methyl-3-(trifluoromethyl)phenyl]amino]pyridine-3-carboxylic acid) polymerize or self-assemble in amorphous supramolecular structures with molecular weights around 2.0 x 10(5) kDa. DSC curves, in a first heating, show isomorphic transitions where the last one at 137 A degrees C for the flunixin-meglumine adduct originated the supramolecular amorphous polymers with glass transition around 49.5 A degrees C. The kinetic parameters for the thermal decomposition step of the polymers were determined by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and heating rates of 5, 10, 15, and 20 A degrees C min(-1), the E (alpha) and B (alpha) terms could be determined and, consequently, the pre-exponential factor, A(alpha), as well as the kinetic model, g(alpha).

Non-isothermal decomposition kinetics of the interaction of poly(ethylene terephthalate) with alkyd varnish

The recycling of soft drink bottles poly(ethylene terephthalate) (PET) has been used as an additive in varnish containing alkyd resin. The PET, called to recycled PET (PET-R), was added to the varnish in increasing amounts. Samples of varnish containing PET-R (VPET-R) were used as a film onto slides and its thermal properties were evaluated using thermogravimetry (TG). Throughout the visual analysis and thermal behavior of VPET-R it is possible to identify that the maximum amount of PET-R added to the varnish without changing in the film properties was 2%.The kinetic parameters, such as activation energy (E) and the pre-exponential factor (A) were calculated by the isoconversional Flynn-Wall-Ozawa method for the samples containing 0.5 to 2.0% PET-R. A decrease in the values of E was verified for lower amounts of PET-R for the thermal decomposition reaction. A kinetic compensation effect (KCE) represented by the lnA=-13.42+0.23E equation was observed for all samples. The most suitable kinetic model to describe this decomposition process is the autocatalytic Sestak-Berggren, being the model applied to heterogeneous systems.

Kinetic parameters for thermal decomposition of microcrystalline, vegetal, and bacterial cellulose

Cellulose can be obtained from innumerable sources such as cotton, trees, sugar cane bagasse, wood, bacteria, and others. The bacterial cellulose (BC) produced by the Gram-negative acetic-acid bacterium Acetobacter xylinum has several unique properties. This BC is produced as highly hydrated membranes free of lignin and hemicelluloses and has a higher molecular weight and higher crystallinity. Here, the thermal behavior of BC, was compared with those of microcrystalline (MMC) and vegetal cellulose (VC). The kinetic parameters for the thermal decomposition step of the celluloses were determined by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and at heating rates of 5, 10, and 20 A degrees C/min, the E(alpha) and B(alpha) terms could be determined and consequently the pre-exponential factor A(alpha) as well as the kinetic model g(alpha). The pyrolysis of celluloses followed kinetic model g(alpha) = [-ln(1 - alpha)](1.63) on average, characteristic for Avrami-Erofeev with only small differences in activation energy. The fractional value of n may be related to diffusion-controlled growth, or may arise from the distributions of sizes or shapes of the reactant particles.

Composting of urban solid residues (USR) by different dispositions - Kinetics of thermal decomposition

The thermal behavior and non-isothermal kinetics of thermal decomposition of three different kinds of composting of the USR like: stack with drilled PVC tubes (ST), revolved stack (SR) and stack with material of structure (SM), from the usine of composing of Araraquara city, São Paulo state, Brazil, within a period of 132 days of composting were studied.Results from TG, DTG and DSC curves obtained on inert atmosphere indicated that the cellulosic fraction present, despite the slow degradation during the composting process, is thermally less stable than other substances originated from that process. Due to that behavior, the cellulosic fraction decomposition could be kinetically evaluated through non-isothermal methods of analysis.The values obtained were: average activation energy, E-a=248, 257 and 259 kJ mol(-1) and pre-exponential factor, logA=21.4, 22.5, 22.7 min(-1), to the ST, SR and SM, respectively.From E-a and logA values and DSC curves, Malek procedure could be applied, suggesting that the SB (Sestak-Berggren) kinetic model is the appropriated one to the first thermal decomposition step.

Kinetic of thermal decomposition of residues from different kinds of composting

Non-isothermal kinetic parameters regarding to the thermal decomposition of the ligninocellulosic fraction present in compost from urban solid residues (USR) obtained through stack covered (SC) with composted material, comes from the usine in composing of Araraquara city, São Paulo state, Brazil, and from stack containing academic restaurant organic solid residues (SAR). The samples were periodically revolved round 132 days of composting.Results from TG, DTG and DSC curves obtained on inert atmosphere indicated that the lignocellulosic fraction present, despite the slow degradation during the composting process, is thermally less stable than other substances originated during that process. The lignocellulosic fraction decomposition, between 200 and 400degreesC, were kinetically evaluated through non-isothermal methods of analysis.By using the Flynn-Wall and Ozawa isoconversional method, the medium activation energy, E-a, and pre-exponential factor, IgA, were 283.0+/-4.6, 257.6+/-1.3 U mol(-1) and 25.4+/-0.8, 23.2+/-0.2 min(-1),to the SC and SAR, respectively, at 95% confidence level.From E-a, and IgA values and DSC curves, Malek procedure could be applied, Suggesting that the SB (Sestik-Berggren) kinetic model is suitable for the first thermal decomposition step.

Titanium(IV)-EDTA complex - Kinetics of thermal decomposition by non-isothermal procedures

This work aims the evaluation of the kinetic triplets corresponding to the two successive steps of thermal decomposition of Ti(IV)-ethylenediaminetetraacetate complex. Applying the isoconversional Wall-Flynn-Ozawa method on the DSC curves, average activation energy: E=172.4 +/- 9.7 and 205.3 +/- 12.8 kJ mol(-1), and pre-exponential factor: logA = 16.38 +/- 0.84 and 18.96 +/- 1.21 min(-1) at 95% confidence interval could be obtained, regarding the partial formation of anhydride and subsequent thermal decomposition of uncoordinated carboxylate groups, respectively.From E and logA values, Dollimore and Malek methods could be applied suggesting PT (Prout-Tompkins) and R3 (contracting volume) as the kinetic model to the partial formation of anhydride and thermal decomposition of the carboxylate groups, respectively.

DECOMPOSITION RATES OF SPENT FUNGAL REFUSE OF ATTA-SEXDENS (HYMENOPTERA, FORMICIDAE) AND IMPLICATIONS FOR ESTIMATING FORAGE INTAKE BY LEAF-CUTTING ANTS

Using simulated ceramic refuse chambers, field decomposition studies were performed on the spent fungal refuse of the lead-cutting ant Atta sexdens rubropilosa. Refuse half life was estimated at 40 days, with complete decomposition at 100 days. These results suggest that the conversion-factor method used to estimate forage input into leaf-cutting ant colonies must be corrected for decomposition, or serious estimation errors will occur.

Tin(II)-EDTA complex: kinetic of thermal decomposition by non-isothermal procedures

Tin on the oxide form, alone or doped with others metals, has been extensively used as gas sensor, thus, this work reports on the preparation and kinetic parameters regarding the thermal decomposition of Sn(II)-ethylenediaminetetraacetate as precursor to SnO2. Thus, the acquaintance with the kinetic model regarding the thermal decomposition of the tin complex may leave the door open to foresee, whether it is possible to get thin film of SnO2 using Sn(II)-EDTA as precursor besides the influence of dopants added.The Sn(II)-EDTA soluble complex was prepared in aqueous medium by adding of tin(II) chloride acid solution to equimolar amount of ammonium salt from EDTA under N-2 atmosphere and temperature of 50degreesC arising the pH similar to 4. The compound was crystallized in ethanol at low-temperature and filtered to eliminate the chloride ions, obtaining the heptacoordinated chelate with the composition H2SnH2O(CH2N(CH2COO)(2))(2).0.5H(2)O.Results from TG, DTG and DSC curves under inert and oxidizing atmospheres indicate the presence of water coordinated to the metal and that the ethylenediamine fraction is thermally more stable than carboxylate groups. The final residue from thermal decomposition was the SnO2 characterized by X-ray as a tetragonal rutile phase.Applying the isoconversional Wall-Flynn-Ozawa method on the DSC curves, average activation energy: E-a = 183.7 +/- 12.7 and 218.9 +/- 2.1 kJ mol(-1), and pre-exponential factor: log A = 18.85 +/- 0.27 and 19.10 +/- 0.27 min(-1), at 95% confidence level, could be obtained, regarding the loss of coordinated water and thermal decomposition of the carboxylate groups, respectively. The E-a and logA also could be obtained applying isoconventional Wall-Flynn method on the TG curves.From E-a and log A values, Dollimore and Malek procedures could be applied suggesting R3 (contracting volume) and SB (two-parameter model) as the kinetic model to the loss of coordinated water (177-244degreesC) and thermal decomposition of the carboxylate groups (283-315degreesC), respectively. Simulated and experimental normalized DTG and DSC curves besides analysis of residuals check these kinetic models. (C) 2003 Elsevier B.V. All rights reserved.

Shunt active compensation based on the Conservative Power Theory current's decomposition

Considering the operation of shunt active compensators, such as active power filters, this paper proposes possible compensation strategies by means of the recent formulation of the Conservative Power Theory (CPT). The CPT current's decomposition results in several current components, which are associated with specific load characteristics (power transfer, energy storage, unbalances and/or non linearities). These current components are used for the definition of different compensation strategies, which can be selective in terms of minimizing particular disturbing effects. In order to validate the applicability of these new compensation strategies, simulation and experimental results for three-phase four-wire systems are presented. © 2011 IEEE.

Kinetic parameters for thermal decomposition of supramolecular polymers derived from diclofenac-meglumine supramolecular adducts

Meglumine is an aminocarbohydrate able to form supramolecular adducts with organic acids. The recognition is based on hydrogen bonds and the structures resulting from the complexation have high solubility in water. This property has been exploited by the pharmaceutical industry in the improvement of existing drugs, and the successful example of this approach involves the poorly soluble non-steroidal anti-inflammatory drugs (NSAIDs). Investigation of the thermal behavior of adduct obtained from meglumine and the NSAID diclofenac revealed that a polymer-like material is formed from the self-assembly of diclofenac-meglumine adducts in the melt. This polymer showed a high molecular weight around 2.0×105kDa. The kinetic parameters for the thermal decomposition step of the polymer were determined by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and heating rates of 5, 10, 15 and 20°Cmin-1, the Eα and Bα terms could be determined, and consequently the pre-exponential factor, Aα, as well as the kinetic model, g(α). © 2012 Elsevier B.V.