Activation energies for the thermodegradation process of an epoxy-diamine system

The study of the degradation of a polymer is important because it can determine the upper temperature limit, the mechanism of a solid-state process, and the life-time for this system. Since the behavior of thermosets is affected by the selection of the curing cycle, it is important to investigate the changes which take place during the thermal degradation of these materials when a change on the sequence of time and temperature is introduced during the curing reaction. In this work, the thermal degradation of two epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) cured through different sequences of time and temperature was studied by thermogravimetric analysis in order to determine the reaction mechanism of the degradation processes, and also to check the influence of the curing cycle on this mechanism. Values obtained using different kinetic methods were compared to the value obtained by Kissinger’s method (differential method which do not require a knowledge of the n-order reaction mechanism), and to that obtained through Flynn–Wall–Ozawa method in a previous work.     

Kinetics study of thermal oxidative degradation of ABS containing flame retardant components

The thermal oxidative degradation kinetics of pure acrylonitrile–butadiene–styrene (ABS) and the flame-retarded ABS materials with intumescent flame retardant (IFR) were investigated using Kissinger, Flynn–Wall–Ozawa, and Horowitz–Metzger methods. The results showed that the degradation of all samples included two stages, the activation energy at the first stage decreased by the incorporation of these flame retardant components, while increased at the second stage. The activation energy order of the flame-retarded ABS samples at stage 2 illustrates the relationship between the composition of IFRs and their flame retardancy, FR materials with appropriate acid agent/char former ratio has higher activation energy and better flame retardancy.     

Effect of compatibilization on thermal degradation kinetics of HDPE-based composites containing cellulose reinforcements

Dynamic thermogravimetric analysis under nitrogen flow was used to investigate the thermal decomposition process of high-density poly(ethylene) (HDPE)-based composites reinforced with cellulose fibers obtained from the recycling of multilayer carton scraps, as a function of the cellulose content and the compatibilization. The Friedman, Flynn–Wall–Ozawa, and Coats–Redfern methods were used to determine the apparent activation energy (E _a) of the thermal degradation of the cellulose component into the composites. E _a has been found dependent on the cellulose amount and on the cellulose/polymer matrix interfacial adhesion. In particular, it has been evidenced an increase of the cellulose thermal stability as a consequence of the improved interfacial adhesion between the components in NFR composites.     

Synthesis and non-isothermal degradations of the bridged diacetato–diamido–diamine–uranyl complex

The new bridged diacetato–diamido–diamine–uranyl complex {2[(UO₂)(H₂N)(H₃N)(OOCCH₃)]} was prepared and characterized by elemental analysis, IR measurement as well as TG and DTA analysis. The kinetic parameters; activation energy (E_a), pre-exponential factor (A) and the order of decomposition (n) were calculated from TG curves using Coats–Redfern and Flynn–Wall–Ozawa methods. The mechanism of decomposition has been established from TG and DTA data. The data obtained agree quite well with the expected structure and show that the complex finally decomposes to form UO₃. A general mechanism describing the formation of bridged complex {2[(UO₂)(H₂N)(H₃N)(OOCCH₃)]} is proposed.     

New Regional Editor

Thermal decomposition of an agrowaste, namely banana trunk fibers (BTF) were investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG) up to 900 °C at different heating rates (from 5 to 100 °C/min). The BTF was subjected to modification by means of various known chemical methods (mercerization, acetylation, peroxide treatment, esterification, and sulfuric acid treatment). Various degradation models, such as the Kissinger, Friedman, and Flynn–Wall–Ozawa were used to determine the apparent activation energy. The obtained apparent activation energy values (149–210 kJ/mol) allow in developing a simplified approach to understand the thermal decomposition behavior of natural fibers as a function of polymer composite processing.     

Thermal kinetic studies on the decompositions of cefuroxime lysine in different atmospheres and heating rates

The thermal decomposition of a new antibiotic agent, cefuroxime lysine, was investigated by thermogravimetry analysis/derivative thermogravimetry and differential scanning calorimetry (DSC) methods in anoxic and oxidative environments. The influence of heating rates (including 5, 10, 15, and 20 °C/min) on the thermal behavior of cefuroxime lysine was revealed. By the methods of Kissinger and Flynn–Wall–Ozawa, the thermal kinetic parameters of activation energy and pre-exponential factor for the exothermic processes under non-isothermal conditions were calculated using the analysis of corresponding DSC curves.     

Non-isothermal decomposition kinetics of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized using egg white solution route

The thermal decomposition kinetics of nickel ferrite (NiFe₂O₄) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different heating rates. The activation energy (E _α) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS), which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe₂O₄ precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm.     

A comparative thermogravimetric study of waterlogged archaeological and sound woods

Waterlogged archaeological woods Pinus pinaster and Fagus sylvatica L. were analyzed by using TG technique. Degradation processes ascribable to the holocellulose decay were evidenced at nearly the same temperature for sound and archaeological samples. The residual matters at 600 and 900 °C of the sound woods are much lower than those of archaeological waterlogged woods in agreement with the presence of inorganic materials encapsulated during the burial into the marine environment. It was proposed a new protocol to rapidly calculate the maximum water content parameter, which is related to the wood degradation state. TG experiments at variable heating rates were performed to obtain kinetic parameters for the degradation process. The Flynn–Wall–Ozawa and Friedman approaches allowed us to calculate the activation energy, which is significantly different for the sound and the archaeological woods.     

Kinetic parameters determination in non-isothermal conditions for the crystallisation of a silica-soda-lead glass

Two integral isoconversional methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose) and the invariant kinetic parameters method (IKP) were used in order to examine the kinetics of the non-isothermal crystallisation of a silica-soda-lead glass. The objective of the paper is to show the usefulness of the IKP method to determine both the activation parameters and the kinetic model of the investigated process. Thismethod associated with the criterion of coincidence of kinetic parameters for all heating rates and some procedures of the evaluation of the parameter from Johnson–Mehl–Avrami–Erofeev–Kolmogorov (JMAEK) equation led us to the following kinetic triplet: activation energy, E=170.5±2.5 kJ mol^–1 , pre-exponential factor, A=1.178±0.350·10 10 min^–1 and JMAEK model (A _m) m=1.5.     

Thermal behavior of loratadine

Simultaneous thermogravimetry (TG) and differential thermal analysis (DTA) techniques were used for the characterization the thermal degradation of loratadine, ethyl-4-(8-chloro-5,6-dihydro-11H-benzo[5,6]cyclohepta[1,2-b]pyridin-11-ylidine)-1-piperidinecarboxylate. TG analysis revealed that the thermal decomposition occurs in one step in the 200–400°C range in nitrogen atmosphere. DTA and DSC curves showed that loratadine melts before the decomposition and the decomposition products are volatile in nitrogen. In air the decomposition follows very similar profile up to 300°C, but two exothermic events are observed in the 170–680°C temperature range. Flynn–Wall–Ozawa method was used for the solid-state kinetic analysis of loratadine thermal decomposition. The calculated activation energy (E _a) was 91±1 kJ mol^–1 for α between 0.02 and 0.2, where the mass loss is mainly due to the decomposition than to the evaporation of the decomposition products.     

Thermal decomposition kinetics of some aromatic azomonoethers

The non-isothermal kinetic parameters corresponding to the decomposition of 4-[(4-chlorobenzyl)oxy]-4’-nitro-azobenzene were evaluated. The kinetic analysis was performed by means of different multi-heating rates methods: isoconversional (‘model-free’) methods (Flynn–Wall–Ozawa) and invariant kinetic parameters method (IKP) associated with the criterion of the independence of activation parameters on the heating rate. The values of the obtained non-isothermal kinetic parameters are in satisfactory agreement.     

Kinetics of thermo-oxidative degradation of polypropylene/aluminum trihydroxide/organo Fe-montmorillonite nanocomposites

In the article, the thermal oxidative degradation kinetics of pure polypropylene/aluminum trihydroxide (PP/ATH) and PP/ATH/organo Fe-montmorillonite (Fe-OMT) nanocomposites were investigated using Kissinger, Friedman and Flynn–Wall–Ozawa methods. The results showed that thermal oxidative degradation of PP/ATH/Fe-OMT nanocomposites to PP/ATH were complex reaction: the whole process of thermal oxidative degradation were composed with the decomposition of ATH, the cracking and charring of the backbone chains of PP, and the oxidative degradation of char, which the curses of energy mutative with the process of thermal oxidative degradation. The control steps were different in each degradation stage. The activation energy was high in the original degradation stage. It was due to the molecular structure and may closely relate with onset temperature. In the intermediate process, the activation energy was low. In the last stage of the degradation, the activation energy was graveled because the carbon may be oxidized. In the whole process of thermal oxidative degradation, the activation energy of PP/ATH/Fe-OMT nanocomposite was higher than that of PP/ATH.     

Kinetic studies of urban solid residues and leachate from sanitary landfill

Urban solid residues are constituted of food remaining, grass leaves, fruit peelings, paper, cardboard, rubber, plastic, etc. The organic fraction formed represents about 50% during the decomposition yields biogas and leachate, which are sources of pollution. Residue samples were collected from the landfill in different and cells from several ages and the corresponding leachate, both after treatments, were submitted to thermal analysis. Kinetic parameters were determined using Flynn–Wall–Ozawa method. The linear relation between the two kinetic parameters (ln A and E) was verified for organic residue urban’s samples, but not for leachate’s sample. The occurred difference can be attributed to the constituents present in leachate.     

The preparation of inorganic/organic hybrid nanomaterials containing silsesquioxane and its reinforcement for an epoxy resin network

A series of new inorganic/organic hybrid nanomaterials were prepared through the reaction of cage octa(γ-aminopropylsilsesquioxane) with n-butyl glycidyl ether. The structures and properties of these hybrid materials were characterized by Fourier transform infrared spectroscopy, ²⁹Si nuclear magnetic resonance (NMR), ¹H-NMR, and mass spectrometry spectra. The hybrid materials were used for improving mechanical and thermal properties of epoxy resin E-51. The results showed that appropriate amount of addition of the hybrids could enhance the fracture elongation ratio and impact strength. The tensile strength decreased with the addition of the hybrids. The thermal properties such as glass transition temperature, antioxidant index, decomposition temperature, and Vicat softening temperature were obviously improved. Scanning electron microscope observation displayed a rough structure inside the cured epoxy resin by the addition of the hybrids. Kinetic study indicated that the curing process was continuous with average activation energy of 48.06 kJ/mol which was based on Kissinger and Flynn–Wall–Ozawa models.     

Thermal degradation kinetics of g-HA/PLA composite

Thermal degradation behaviors of a composite constituted by poly(l-lactide) (PLA) and hydroxyapatite nanoparticle that was surface-grafted with l-lactic acid oligomer (g-HA) in a nitrogen atmosphere were studied using thermogravimetric analysis (TGA) and compared with PLA. The kinetic models and parameters of the thermal degradation of PLA and the g-HA/PLA composite were evaluated by the invariant kinetic parameters (IKP) method and Flynn–Wall–Ozawa (FWO) method based on a set of TGA data obtained at different heating rates. It was shown that the conversion functions calculated by means of the IKP method depend on a set of kinetic models. The g-HA particle slowed down the thermal degradation of PLA polymer matrix.     

Thermal behaviour of some industrial and food dyes

Thermal behavior of four food dyes, i.e. tartrazine, crysoine, azorubine and amarant was studied under non-isothermal conditions, in dynamic air atmosphere and at heating rates of 5, 10, 15 and 20°C min^–1. The TG data were correlated to the FTIR spectra of each sample, before and after the thermal decomposition. Kinetic study by processing the TG data was performed. The main conclusion of this study is that the non-parametric kinetic method allows a separation of the steps of a complex process and that the values of the activation energy obtained by this method agree satisfactory with that of Flynn–Wall–Ozawa estimation.     

Study on the pyrolysis of Moroccan oil shale with poly (ethylene terephthalate)

Investigations into the pyrolytic behaviours of oil shale, poly (ethylene terephthalate) (PET) and their mixture have been conducted using a thermogravimetric analyzer. Experiments were carried out dynamically by increasing the temperature from 298 to 1,273 K with heating rates of 2–100 K/min under a nitrogen atmosphere. Discrepancies between the experimental and calculated TG/DTG profiles were considered as a measurement of the extent of interactions occurring on co-pyrolysis. The maximum degradation temperature of each component in the mixture was higher than those the individual components; thus an increase in thermal stability was expected. The kinetic processing of thermogravimetric data was carried out using Flynn–Wall–Ozawa (FWO) method.     

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of kinetics and thermodynamics of the dehydration reaction of AlPO<Subscript>4</Subscript> · H<Subscript>2</Subscript>O

The kinetics and thermodynamics of the thermal dehydration of aluminum phosphate monohydrate, AlPO₄ · H₂O were studied using thermogravimetry (TG-DTG-DTA) at four heating rates in dry air atmosphere. The activation energies of the dehydration step of AlPO₄ · H₂O were calculated through the methods of Friedman (FR) and Flynn–Wall–Ozawa (FWO) and the possible conversion function has been estimated through the Achar and Li–Tang equations. The independent activation energies on extent of conversions and the better kinetic model of the dehydration reaction for AlPO₄ · H₂O indicate single kinetic mechanism and the F _2.05 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”, respectively. The positive values of ΔH^# and ΔG^# for the dehydration reaction show that it is endothermic and non-spontaneous process and it is connected with the introduction of heat. The kinetic and thermodynamic functions calculated for the dehydration reaction by different techniques and methods were found to be consistent.