Determination of degradation apparent activation energy values of polymers

The isothermal degradation of three aromatic polyetherketones was studied in an inert environment at various temperatures in the range 683-803 K. In the first degradation stage (mass loss D￡20%) a linear increase of D as a function of heating time (t) was observed and the corresponding kinetic D=D _o+bt equations at various temperatures were directly drawn by smoothing the experimental TG data. The b values, which represent the mass loss rates during degradation, increased as a function of temperature according to Arrhenius-type equations, from which degradation E _a values were determined, which appear in agreement with those from literature methods. Some differences observed were discussed and interpreted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Degradation of Natural Polymers

The thermal degradation of sodium hyaluronate, xanthan and methylcellulose was evaluated by thermogravimetric and infrared analysis. Kinetic parameters such as activation energy and pre-exponential factor were determined considering the Ozawa and Freeman–Carroll methods. The results suggest changes in the degradation mechanism with the fraction of mass loss for both the studied polysaccharides. The activation energy values determined by the Freeman–Carroll method are higher than those obtained by the Ozawa method under the same conditions, probably because in the first method a first order reaction was assumed and the thermal history effects were eliminated since only one TG curve was used to determine the kinetic parameters. Low thermal stability was observed for polyanions e.g. sodium hyaluronate (Na-Hy) and xanthan(XT) in comparison with methylcellulose (MC) which is a neutral polysaccharide. By infrared spectroscopy, it was observed that at low temperatures there occured only the scission of the exocyclic groups for both polysaccharides and that the scission of strong links in the backbone occurred at high temperatures, in agreement with the kinetic parameters determined for the degradation reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal stability of flexible polyurethane foams containing modified layered double hydroxides and zinc borate

Abstract

Flexible polyurethane foams (FPUFs) have been modified to contain layered double hydroxides (LDHs) by dihydrogen phosphate (H₂PO₄ ^?). The thermal stability of the prepared foams has been characterized using thermogravimetric analysis (TGA) at 5, 10, 20, 30, and 40?°C/min heating rates. The experimental data indicate that the temperature range for the two pyrolysis stages of FPUF is about 212–350?°C and 350–565?°C, respectively. Integral programmed decomposition temperature (IPDT) has been calculated according to the measured data, which was found that the IPDT of the modified FPUF was increased to 526?°C. Additionally, the thermal stability of FPUF composite has been also evaluated by the activation energy (E) on the basis of the pyrolysis kinetics of FPUF composites during thermal decomposition using Coats–Redfern integral method. These results manifest that the presence of intercalated LDHs enhances the thermal stability of FPUF.     

Thermogravimetric analysis of composites obtained from sintering of rice husk-scrap tire mixtures

Summary The disposal of used automotive tires has caused many environmental and economical problems to most countries. We propose the use of rice husk as filler for increasing the value of recycled tire rubber. Thermal degradation of both components and their sintering mixtures is presented in this paper. Thermal decomposition of rice husk occurs in various steps in the temperature range between 150 and 550°C. This complex process is the result of the overlapping of thermal decomposition of the three major constituents common in all lignocellulosic materials, i.e., hemicellulose, lignin and cellulose. Hemicellulose is degraded at temperatures between 150 and 350°C, cellulose from 275 to 380°C and lignin from 250 to 550°C. The degradation process of major constituents of scrap tires or their composites is observed at temperatures between 150 and 550°C. For composites, the addition of rice husk (maximum 25%) produces an increase in the mass loss rate. This effect is higher as the amount of rice husk increases. However, the degradation initial temperature of elastomeric matrix is not affected with addition of rice husk. Apparent kinetic parameters were also studied by the isoconversional Friedman method. We observed that the addition of rice husk produces a decrease in apparent activation energy for low conversions (up to 0.6). For higher conversions this decrease was not so clearly observed.     

Thermal Degradation of Polyvinyl Chloride

The thermal degradation of a sort of polyvinyl chloride was investigated. Complex processes for polyvinyl chloride degradation were evidenced. The kinetic analysis of dehydrochlorination and of subsequent processes was carried out. A change of mechanism was detected when dehydrochlorination goes to completion. The values of non-isothermal kinetic parameters determined by various methods are in a satisfactory agreement. The obtained results allowed some clarifications concerning the thermal degradation steps. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dynamic and Isothermal Thermogravimetric Degradation of Poly(vinyl Chloride)/Chlorinated Poly(ethylene) Blends

The thermal degradation of poly(vinyl chloride)/chlorinated poly(ethylene) (PVC/CPE) blends of different compositions was investigated by means of dynamic and isothermal thermogravimetric analysis in flowing atmosphere of nitrogen. Kinetic parameters (the apparent activation energy E, and pre-exponential factor Z) were calculated after Flynn-Wall-Ozawa method for the first stage of dynamic degradation of PVC/CPE blends, and after Flynn method for the isothermal degradation. In both cases, there is the compensation dependence between the values E and logZ. The values of compensation ratios as well as the characteristics of TG and DTG curves, confirm the stabilizing effect of CPE on PVC dehydrochlorination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Degradation of Polychloroprene Rubber Under Isothermal and Non-Isothermal Conditions

The results of a kinetic investigation of the non-isothermal degradation and the isothermal degradation of the residual deformation under constant deflection for polychloroprene rubber are presented. A relationship was derived between the degree of non-isothermal conversion and the value of the investigated mechanical property. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Degradation Kinetics of Polyurethane/Organically Modified Montmorillonite Clay Nanocomposites by TGA

Polyurethane (PU) has been prepared by using polyether polyol (jagropol oil) and 1,6- hexamethylene diisocyanate (HMDI) as a cross-linker. The organically modified montmorillonite clay (MMT) is well-dispersed into urethane matrix by an in situ polymerization method. A series of PU/MMT nanocomposites have been prepared by incorporating varying amounts of nanoclay viz., 1, 3, 5 and 6 wt %. Thermogravimetric analysis (TGA) of the PU/MMT nanocomposites has been performed in order to establish the thermal stability and their mode of thermal degradation. The TGA thermograms exhibited the fact that nanocomposites have a higher decomposition temperature in comparison with the pristine PU. It was found that the thermal degradation of all PU nanocomposites takes place in three steps. All the nanocomposites were stable up to 205°C. Degradation kinetic parameters of the composites have been calculated for each step of the thermal degradation processes using three mathematical models namely, Horowitz–Metzger, Coats–Redfern and Broido's methods.     

Thermal analysis of new,artificially aged and archival linen

The thermal degradation of new, and artificially aged fine Ulster linen and archival linen specimens from 19th century paintings were compared using thermogravimetric analysis and differential scanning calorimetry. Thermal degradation data from new and artificially aged linen were found to be similar in nature. Archival specimens showed a decreased major degradation temperature, an increase in char remaining at the end of the experiment and some evidence of a depressed glass transition temperature. These indicate natural ageing through chain scission. Evidence of a two-stage degradation process was observed in some archival specimens suggesting that an unknown additive was present. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal stability and degradation behavior of hydroxyethyl methacrylate-poly(lactide) polymers

Hydroxyethyl methacrylate (HEMA)-Poly(L-lactide) (PLA) polymers, with different molar ratios of HEMA/lactide (1/4 and 1/8), were synthesized by ring-opening polymerization. The thermal degradation behavior and kinetic parameters of these obtained HEMA-PLA polymers were analyzed by thermogravimetric analysis (TGA) and Pyrolysis-Gas chromatography/Mass spectrometry (Py-GC/MS). It was found that the activation energies of thermal degradation of the polymers increased as the residue weight was decreased, indicating that the mechanism of thermal decomposition changes during the process progress. The results showed that the random chain scission proceeded at lower temperature, and subsequently the specific chain scission did so. Moreover, the results revealed that thermal stability of PLA was increased by the copolymerzation of HEMA. In addition, Py-GC/MS analysis showed that the main decomposed products obtained from the HEMA-PLA polymers were HEMA, lactide, dimer, trimer and tetramer.     

Thermal analysis of smithsonite and hydrozincite

Thermogravimetric analysis of synthetic smithsonite and hydrozincite, two secondary minerals of zinc, was used to determine their relative thermal stability. Thermal decomposition of smithsonite occurs at 293°C and hydrozincite at 220°C showing that the carbonate mineral is more stable than the hydroxy-carbonate mineral hydrozincite. Hot stage Raman spectroscopy confirms the decomposition of smithsonite and hydrozincite by 300 and 250°C, respectively. Thermogravimetry shows that a small amount of hydrozincite is formed during the synthesis of smithsonite. No evidence is found for the separate loss of the carbonate and hydroxyl units from hydrozincite.     

Thermal stability and decomposition of pharmaceutical compounds

Thermal analysis of fusion and decomposition processes were carried out on recently synthetized pharmaceutical compounds in order to establish thermal stability criteria. This study was carried out using thermogravimetry, TG, and differential scanning calorimetry, DSC. Degradation and fusion temperatures have been produced as thermal data with the aim of to study the thermal stability of the compounds. Relationship is found among stability and a series of effects of structure of the compounds. The compounds which present an amide functional group in the central molecule are more stable because they have a comparatively higher fusion and degradation temperature. In addition, the stability of this type of compounds depends on the position of the electrophilic substitution (in ortho, meta or para). Likewise, the groups linked to the aromatic ring with high electronic density give stability, and therefore are able to delocalize the charge in a greater spacial interval. Therefore, criteria for the selection of substituents have established that improve the stability of compounds     

Kinetics Analysis of the Thermal Decomposition of Poly(Butylene Adipate) Ionomers by Thermogravimetry (TG) and Derivate (DTG) Analysis

Kinetics analysis and thermal decomposition study of poly(butylene adipate) ionomers (PBAi) synthesized using the dimethyl 5‐sulfoisophthalate sodium salt (DMSI) of the diacid monomer were carried out by thermogravimetry (TG) and derivate (DTG) analysis. The decomposition kinetic parameters (activation energy, frequency factor) were calculated. The activation energy values of the PBAi‐2, PBAi‐3 and PBAi‐5 ionomers were respectively found as 164.51, 141.91 and 78.07 kJ/mol. The influence of DMSI content on the decomposition of the ionomers was investigated. The activation energy values decrease with increasing the content of DMSI. This suggests that increasing the content of DMSI makes the thermal decomposition of the ionomers easier.     

丙烯酸化环状磷腈/环氧丙烯酸酯光固化体系热降解动力学研究

以TGA为手段, 进行了丙烯酸化环状磷腈/环氧丙烯酸酯光固化体系热降解动力学的研究, 同时与加入粉末状环状磷腈混合体系进行了对照. 采用Kissinger, Flynn-Wall-Ozawa和Friedman三种方法计算了固化膜降解反应活化能, 证明了磷腈结构的引入, 使得体系在高温阶段的活化能有所提高, 表明降解变得困难, 热稳定性得到提高. 而反应型丙烯酸化环状磷腈相对粉末状环状磷腈混合体系具有更高的降解活化能.     

Comparison of isothermal and dynamic methods for the determinationof activation energy by thermogravimetry

Several dynamic methods for estimating activation energies have been developed. This development has arisen largely as a matter of convenience and the desire to minimize analysis time. While these methods generally afford values which are somewhat similar, the agreement among values from various methods is never outstanding. Further, the values obtained are often, at best, only approximations of the values obtained by the traditional isothermal approach. To better ascertain the utility of dynamic methods for the determination of activation energies, the activation energy for the thermal degradation of a standard vinylidene chloride/methyl acrylate (five-mole percent) copolymer has been generated by a variety of methods. The degradation of this polymer is an ideal reaction for evaluation of the various methods. At modest temperatures (<200°C), the only reaction that contributes to mass loss is the first order evolution of hydrogen chloride, i.e., there is only one significant reaction occurring and it is not impacted by competing processes. The best values (most reproducible; best correspondence to values obtained by titrimetry and other methods) are those obtained by plotting the natural logarithm of rate constants obtained at various temperatures vs. the reciprocal of the Kelvin temperature. Various dynamic methods yield values which are less reproducible and which approximate these values to a greater or lesser degree. In no case is the agreement good.     

TG studies of a composite solid rocket propellant based on HTPB-binder

Thermal decomposition kinetics of solid rocket propellants based on hydroxyl-terminated polybutadiene-HTPB binder was studied by applying the Arrhenius and Flynn-Wall-Ozawa's methods. The thermal decomposition data of the propellant samples were analyzed by thermogravimetric analysis (TG/DTG) at different heating rates in the temperature range of 300-1200 K. TG curves showed that the thermal degradation occurred in three main stages regardless of the plasticizer (DOA) raw material, the partial HTPB/IPDI binder and the total ammonium perchlorate decompositions. The kinetic parameters E _a (activation energy) and A (pre-exponential factor) and the compensation parameter (S _p) were determined. The apparent activation energies obtained from different methods showed a very good agreement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Behavior of Hexogen Phlegmatized with Montan Waxes

Hexogen can be used pressed only if its crystals are covered by some polymeric material [1], either natural or artificial. Montan waxes, as natural polymeric materials, were used for the phlegmatization. The melting process of seven types of waxes was analyzed by differential scanning calorimetry. The thermal decomposition processes of hexogens and phlegmatized hexogens were investigated by dynamic differential scanning calorimetry and dynamic thermogravimetric analyses. Kinetic parameters of the decomposition processes of hexogens were evaluated by using data obtained from differential scanning calorimetric curves. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal degradation and decomposition of jute/vinylester composites

Thermal analysis of jute fibre reinforced vinylester resin with 30 vol% of fibre were performed by TG/DTG under dynamic conditions. The fibres were treated with alkaline solution at different temperatures and the final composition (cellulose, hemicellulose and lignin) of the fibre was determined by chemical analysis. Apparent activation energies were determined using a variety of conventional thermogravimetric methods. Two peaks were found in the composite differential curves: the first peak close to 327 and the second peak at 408°C. The apparent activation energy values for the second peak decreased when fibre were treated. The addition of the jute fibres produced a slightly decrease in the thermal stability of the composites.     

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.     

Thermal Stability of Some Textile Dyes

The effect of thermal treatment at 25–800°C on the structure of some textile dyes (rhodanine' derivatives) has been investigated. The general formula of these dyes are;[(R)–C₆H₄–C₃NS₂O–C₅H₄N–CH=CH–C₆H₄N(CH₃)₂]; 2-[p-dimethylamino-styryl]-6-[5-(3-aryl)-rhodanine]-1,2-dihydropyridine and its derivatives, R=H (I), o-OCH₃ (II), p-OCH3 (III) and p-OH (IV). The techniques employed were TG, IR, UV, NMR and elemental analysis. The results showed that the thermal stability of these dyes depends on the nature of the substituent (R) alkyl radical present and its position in the benzene ring. On the basis of the application of a non-isothermal kinetic equation, it was found to be a first order reaction. Some kinetic and thermodynamic parameters for the thermal decomposition process in each stage have been evaluated by the application of two different calculation methods. To support the above results a simple quantum study was reported. This revised version was published online in August 2006 with corrections to the Cover Date.