Chemical and thermal analysis of the biopolymers in thyme (Thymus vulgaris)

Thyme (Thymus vulgaris) has been known, long time ago, for its aromatic properties. It contains essential oils and polymers such as cellulose (mixture of hemicellulose and cellulose) and lignin. The thyme, studied in this work, was gathered from the same place, in the period from November 1999 to October 2000. The chemical analysis (water, total ash, essential oils, extractive substances, cellulose, holocellulose and lignin) can be used roughly in the characterisation of the four periods that correspond to the four seasons of the year. The cellulose level was found to be more than lignin level in the wet periods (growth of the plant). The opposite was found in the dry periods. The total ash and essential oil levels were found to be high during the period of high pluviometry. The thermal decomposition of cellulose and holocellulose was found to fit well with the first-order kinetics. The activation energy, under air flow, was 185 and 196 kJ mol⁻¹ for cellulose and holocellulose, respectively. The maximum decomposition rate and thermal analysis heating rate of lignin were found to have a direct linear relationship.     

Comparative thermal analysis study of two biopolymers, starch and cellulose

The degradation of cellulose and starch samples in air and nitrogen has been investigated by thermal analysis techniques. The techniques employed were differential thermal analysis, rising temperature and temperature jump thermogravimetry. Rate data were obtained from these experiments and Arrhenius parameters calculated from these values. This data was used to determine the mechanism by which the cellulose and starch samples degraded. The Arrhenius parameters were also calculated. The behavior of starch and cellulose upon thermal analysis were compared and are reported.E _act for corn starch was found to be 474 kJ mol^–1 and for a cellulose 242 kJ mol^–1.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Pyrolytic characteristics and kinetics of pistachio shell by thermogravimetric analysis

Pyrolytic characteristics and kinetics of pistachio shell were studied using a thermogravimetric analyzer in 50?C800?°C temperature range under nitrogen atmosphere at 2, 10, and 15?°C?min^?1 heating rates. Pyrolysis process was accomplished at four distinct stages which can mainly be attributed to removal of water, decomposition of hemicellulose, decomposition of cellulose, and decomposition of lignin, respectively. The activation energies, pre-exponential factors, and reaction orders of active pyrolysis stages were calculated by Arrhenius, Coats?CRedfern, and Horowitz?CMetzger model-fitting methods, while activation energies were additionaly determined by Flynn?CWall?COzawa model-free method. Average activation energies of the second and third stages calculated from model-fitting methods were in the range of 121?C187 and 320?C353?kJ?mol^?1, respectively. The FWO method yielded a compatible result (153?kJ?mol^?1) for the second stage but a lower result (187?kJ?mol^?1) for the third stage. The existence of kinetic compensation effect was evident.     

Thermogravimetric analysis of cellulose insulation and determination of activation energy of its thermo‐oxidation using non‐isothermal,model‐free methods

The aim of the work was to determine the effect of heating rate on initial decomposition temperature and phases of thermal decomposition of cellulose insulation. The activation energy of thermo‐oxidation of insulation was also determined. Individual samples were heated in the air flow in the thermal range of 100°C to 500°C at rates from 1.9°C min^?1 to 20.1°C min^?1. The initial temperatures of thermal decomposition ranged from 220°C to 320°C, depending on the heating rate. Three regions of thermal decomposition were observed. The maximum rates of mass loss were measured at the temperatures between 288°C and 362°C. The activation energies, which achieved average values between 75 and 80.7 kJ mol^?1, were calculated from the obtained results by non‐isothermal, model‐free methods. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

Kinetics of the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O

The thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages thermal decomposition have been evaluated. The R_N and/or A_M models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods are very close. The calculated activation energies were in air: 96 kJ mol^–1 (R_1.575, stage I); 101 kJ mol^–1 (Ain1.725 stage II); 185 kJ mol^–1 (A _2.9, stage III) and in argon: 66 kJ mol^–1 (A _1.25, stage I); 87 kJ mol^–1 (A _1.825, stage II); 133 kJ mol^–1 (A _2.525, stage III).     

Oxidation kinetics of timahdit and tarfaya moroccan oil shales

Organic matter evolution and kinetics of combustion of Tarfaya and Timahdit oil shales have been examined by thermogravimetry (TG) and by differential thermal analysis (DTA). An agreement is observed between both techniques where it was found that combustion of organic matter occurs in two steps. Kissinger's method applied on experimental results gives an activation energy of the same magnitude for the first step of both oil shales (103 kJ mol^–1) whereas the second is 148 kJ mol^–1 for Timahdit and 118 kJ mol^–1 for Tarfaya.The changes in specific surface area during thermal combustion of Timahdit and Tarfaya oil shales have been studied by thermogravimetric gas sorption balance and correlated with experimental results obtained on TG/DTA in air. For Timahdit oil shale oxidation products, specific surface areas calculated from nitrogen adsorption data shows a slight increase during the temperature domain of 280 to 430°C and after this temperature, they increase sharply. However, data obtained with Tarfaya oil shales shows a significant increase at the temperature of maximum oxidation of the first stage of combustion of organic matter.This revised version was published online in November 2005 with corrections to the Cover Date.     

Pyrolysis kinetics of polypropylene

The pyrolysis of oil shale and plastic wastes is being presently considered as an alternative means of partial substitution of fossil fuels to generate the necessary energy to supply the increasing energy demand and as well as new technology to reduce the negative environment of plastic wastes. However, Knowledge of pyrolysis kinetics is of great imponrtance for the design and simulation of the reactor and in order to establish the optimum process conditions. In this study, the thermal decomposition of polypropylene, oil shale and their mixture was studied by TG under a nitrogen atmosphere. Experiments were carried out for various heating rates (2, 10, 20, 50 K min⁻¹) in the temperature range 300–1273 K. The values of the obtained activation energies are 207 kJ mol⁻¹ for polyethylene, 57 kJ mol⁻¹ for the organic matter contained in the oil shale and 174 kJ mol⁻¹ for the mixture. The results indicate that the decomposition of these materials depends on the heating rate, and that polypropylene acts as catalyst in the degradation of the oil shale in the mixture.     

Thermogravimetric Analysis of Cobalt(II)-dothiepin Complexes

The complexes of cobalt(II) with dothiepin (DOT) hydrochloride have been studied for kinetics of thermal degradation by thermogravimetric analysis (TG) and derivative thermogravimetric studies (DTG) in a static nitrogen atmosphere at a heating rate of 10° C min⁻¹. A general mechanism of thermal decomposition is advanced involving dehydration and decomposition process for both organic and inorganic ligands. The thermal degradation reactions were found to proceed in three steps having an activation energy in the range 6.75–170 kJ mol⁻¹. Thermal decomposition kinetics parameters were computed on the basis of thermal decomposition data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal behaviour, compatibility study and decomposition kinetics of glimepiride under isothermal and non-isothermal conditions

In the present work, the thermal decomposition of glimepiride (sulfonylurea hypoglycemic agent) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). Isothermal and non-isothermal methods were employed to determine kinetic data of decomposition process. The physical chemical properties and compatibilities of several commonly used pharmaceutical excipients (glycolate starch, microcrystalline cellulose, stearate, lactose and Plasdone®) with glimepiride were evaluated using thermoanalytical methods. The 1:1 physical mixtures of these excipients with glimepiride showed physical interaction of the drug with Mg stearate, lactose and Plasdone®. On the other hand, IR results did not evidence any chemical modifications. From isothermal experiments, activation energy (E _a) can be obtained from slope of lnt vs. 1/T at a constant conversion level. The average value of this energy was 123 kJ mol^–1. For non-isothermal method E _a can be obtained from plot of logarithms of heating rates, as a function of inverse of temperature, resulting a value of 157 and 150 kJ mol^–1, respectively, in air and N₂ atmosphere, from the first stage of thermal decomposition.     

Molecular structure,conformational mobility,vibrational spectra,and thermochemistry of peroxyacetic acid: an ab initio and density functional study

The structure of the peroxyacetic acid (PAA) molecule and its conformational mobility under rotation about the peroxide bond was studied by ab initio and density functional methods. The free rotation is hindered by the trans-barrier of height 22.3 kJ mol^–1. The equilibrium molecular structure of AcOOH (C _s symmetry) is a result of intramolecular hydrogen bond. The high energy of hydrogen bonding (46 kJ mol^–1 according to natural bonding orbital analysis) hampers formation of intermolecular associates of AcOOH in the gas and liquid phases. The standard enthalpies of formation for AcOOH (–353.2 kJ mol^–1) and products of radical decomposition of the peroxide — AcO^· (–190.2 kJ mol^–1) and AcOO^· (–153.4 kJ mol^–1) — were determined by the G2 and G2(MP2) composite methods. The O—H and O—O bonds in the PAA molecule (bond energies are 417.8 and 202.3 kJ mol^–1, respectively) are much stronger than in alkyl hydroperoxide molecules. This provides an explanation for substantial contribution of non-radical channels of the decomposition of peroxyacetic acid. The electron density distribution and gas-phase acidity of PAA were determined. The transition states of the ethylene and cyclohexene epoxidation reactions were located (E _a = 71.7 and 50.9 kJ mol^–1 respectively).     

Temperatures and kinetics of anatase to rutile transformation in doped TiO<Subscript>2</Subscript> heated in microwave field

The influence of aliovalent ions such as Mn, Cr, Fe, Mo, and V on the temperature and kinetics of anatase to rutile phase transformation in TiO₂ heated in microwave field was studied in this work. The results indicated that heat treatment method and dopants considerably affected the anatase-to-rutile phase transition temperature and kinetics of transformation. The activation energy for anatase to rutile transformation of TiO₂ derived from the isothermal data was found to be 328.4 kJ mol^–1, which was considerably reduced by the addition of dopants in TiO₂ matrix. The activation energy for Mo, Mn and V doped samples was 252.0, 101.3 and 96.4 kJ mol^–1, respectively.     

Investigation of accidental explosion of raw garbage composting system

Cellulose, chitosan and piroxicam were investigated by TG and DSC at heating up to 215°C, and by X-ray powder diffraction before and after the heating. Dehydration of cellulose and chitosan comes to the end near 160°C. Thermal decomposition of chitosan starts at the final stage of its dehydration, and the mass losses after these two reactions overlap with one another. Enthalpy of dehydration is 47.1±2.4 kJ mol^–1 of water for cellulose and 46.2±2.0 kJ mol^–1 for chitosan. Thermal decomposition of chitosan is an exothermic process. Crystal structure of cellulose after heating remains unchanged, but that of chitosan contracts. Piroxicam melts at 200.7°C with the enthalpy of melting 35 kJ mol^–1. Heat capacity of the liquid phase is greater than that of the solid phase by approximately 100 J mol^–1K^–1. Cooled back to ambient temperature, piroxicam remains glassy for a long time, crystallizing slowly back into the starting polymorph.     

Kinetic studies on the oxidation of uranium(IV) in nitric acid solution

The kinetics of oxidation of U(IV) in nitric acid solution by nitrous acid and air oxygen have been studied. The effects of concentrations of U(IV), nitric acid, hydrogen ion and nitrous acid in aqueous solution or oxygen in gas on the oxidation rate have been examined. The oxidation rate increases with increasing temperature and the activation energies are 47 kJ mol^–1 for nitrous acid and 91 kJ mol^–1 for oxygen. The mechanisms for both oxidation reactions are discussed.     

Effect of oxygen on the thermal decomposition of poly(vinylidene fluoride)

Thermogravimetric studies have been made of successive stages of the thermal decomposition of poly(vinylidene fluoride) during programmed heating, at low and high heating rates, in nitrogen, air and oxygen. A single-stage (probably chain-stripping) mechanism operates in nitrogen; it is second order in polymer and has a high activation energy (approx. 180 kJ mol^?1). The presence of oxygen in the atmosphere drastically changes the behaviour of the reaction which becomes zero order with respect to the polymer. TG and DTG charts of reaction in nitrogen and in air differ mainly in the appearance of the carbon burn-off reaction. However the kinetic activation parameters of the reaction in air are very similar to those of the much more complex three-stage reaction in oxygen. The effects of the high heating rates are noticeable predominantly in that the separate stages become much less easy to distinguish and the temperature of initial breakdown is lowered, although the temperature at which 1% of the mass has been lost remains essentially unchanged.     

Thermal degradation of a composite solid propellant examined by DSC

The thermal decomposition of ammonium perchlorate (AP)/hydroxyl-terminated-polybutadiene (HTPB), the AP/HTPB solid propellant, was studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius parameters were estimated according to the Ozawa method. The calculated activation energy was 134.5 kJ mol^-1, the pre-exponential factor, A, was 2.04×1010 min^-1 and the reaction order for the global composite decomposition was estimated in 0.7 by the kinetic Shimadzu software based on the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for comparison. These results are discussed here. This revised version was published online in August 2006 with corrections to the Cover Date.     

The thermal dehydration and decomposition of Ba[Cu(C2O4)2(H2O)]·5H2O

The thermal behaviour of Ba[Cu(C₂O₄)₂(H₂O)]·5H₂O in N₂ and in O₂ has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311±30 kJ mol^–1 (or 52±5 kJ (mol of H₂O)^–1). The overall enthalpy change for the decomposition of Ba[Cu(C₂O₄)₂] in N₂ was estimated from the combined area of the peaks of the DSC curve as –347 kJ mol^–1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the -time curves could be described by the three dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125±4 kJ mol^–1 and (1.38±0.08)×10¹⁵ min^–1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2.The values ofE _a andA were 206±23 kJ mol^–1 and (2.2±0.5)×10¹⁹ min^–1, respectively, for the fast process, and 259±37 kJ mol^–1 and (6.3±1.8)×10²³ min^–1, respectively, for the slow process.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Degradation behavior and kinetic study of ABS polymer

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.     

Decomposition of Bio-polymers of Some Mediterranean Plants During Heating

Forest fires are a plague for all countries in the world. Many factors can induce them. The organic matter (‘fuel’) in the plant, is often responsible for the start of the fire. The bio-polymers and mainly the cellulose decompose at about 300°C with flammable evolved gas. This decomposition is first order, and the activation energy is about 180 kJ mol⁻¹ . On the other hand, the degradation of the lignin seems more complex, but we observed on many samples, a linearly decomposition of the lignin vs. the heating rate (in the interval close to the start of the forest fire, 300 to 3000°C h⁻¹ ). The decomposition of the plant during the heat is mainly dependent on the cellulose level. This degradation is also slightly dependent on the lignin level mainly if the lignin present in this plant is less stable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal behavior study and decomposition kinetics of salbutamol under isothermal and non-isothermal conditions

The thermal decomposition of salbutamol (β₂ — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage of the thermal decomposition process. For isothermal experiments the average values were E _act=130 kJ mol⁻¹ (for standard sample) and E _act=252 kJ mol⁻¹ (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min⁻¹). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min⁻¹). The calculated values were E _act=134 kJ mol⁻¹ (for standard sample) and E _act=139 kJ mol⁻¹ (for pharmaceutical sample).