TG and DSC kinetics of thermal decomposition and crystallization processes

The simplen ^th order model equation combined with the Arrhenius approach of the temperature dependency of the reaction rate constant is widely used in thermal analysis. The new Mettler software package for thermal analysis, GraphWare TA72 allows to access a full model comprising the power law and the crystallization kinetics (AvramiErofe'ev). The kinetics of the following reactions are studied to illustrate some applications:

thermal decomposition of dissolved dibenzoylperoxide, (dynamic and isothermal DSC measurement)

crystallization of polyethylene terephthalate (PET) (isothermal DSC measurements).

The kinetic model applied and the accuracy of the kinetic data obtained are discussed by means of a comparison of a predicted behaviour with the kinetic data measured isothermally.     

Kinetic parameters of a cyanate ester resin catalyzed with different proportions of nonylphenol and cobalt acetylacetonate catalyst

The isothermal cure of a dicyanate ester monomer has been investigated by differential scanning calorimetry (DSC) in the presence of different quantities of a catalyst system formed by nonylphenol (NP) and cobalt (II) acetylacetonate (Co(AcAc)₂). Two sets of experiences were studied. Firstly, the NP composition was varied from 0 to 10 per hundred resin (phr) and secondly, the Co(AcAc)₂ loadings were changed at 2 phr of NP. It has been observed that the cyanate conversion increases significantly after the first addition of the metal catalyst and, also, at the same time the thermal stability improves. Moreover, the kinetic data have been fitted with a second-order equation respect to the cyanate conversion in the kinetically conversion regime. Also, both the activation energies and the kinetic order respect to the NP and the Co(AcAc)₂ have been determined.     

Thermokinetic parameters and thermal hazard evaluation for three organic peroxides by DSC and TAM III

The thermokinetic parameters were investigated for cumene hydroperoxide (CHP), di-tert-butyl peroxide (DTBP), and tert-butyl peroxybenzoate (TBPB) by non-isothermal kinetic model and isothermal kinetic model by differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III), respectively. The objective was to investigate the activation energy (E _a) of CHP, DTBP, and TBPB applied non-isothermal well-known kinetic equation to evaluate the thermokinetic parameters by DSC. We employed TAM III to assess the thermokinetic parameters of three liquid organic peroxides, obtained thermal runaway data, and then used the Arrhenius plot to obtain the E _a of liquid organic peroxides at various isothermal temperatures. In contrast, the results of non-isothermal kinetic algorithm and isothermal kinetic algorithm were acquired from a highly accurate procedure for receiving information on thermal decomposition characteristics and reaction hazard.     

Unusual recrystallization and melting behaviour in DSC scans of isotactic polypropylene samples

The unusual dependence of the melting peak temperature of the species recrystallized during DSC scans on the isothermal crystallization temperature (T _c ) is discussed for isotactic polypropylene samples. It is pointed out that such a phenomenon is not due to superheating effects; it is believed to be accounted for by assuming that the rates of the recrystallization phenomena at the same temperature are higher for samples obtained at higherT _c values.     

Nanocrystallization of anatase in amorphous TiO2

The kinetics of nanocrystallization in amorphous TiO₂ has been studied in non-isothermal conditions by DSC. It was found that this process could be well described by standard Johnson-Mehl-Avrami-Kolmogorov (JMA) model with kinetic exponent m≅1. The kinetic parameters were calculated by simultaneous analysis of experimental data taken at different heating rates. These parameters were used as a basis for prediction of crystallization kinetics in isothermal conditions. The agreement between the JMA model prediction and experimental data depends on the method of preparation of amorphous TiO₂.     

Thermal stability of styrene–(ethylene butylene)–styrene-based elastomer composites modified by liquid crystalline polymer, clay, and carbon nanotube

The thermal decomposition behaviors of styrene?C(ethylene butylene)?Cstyrene (SEBS) thermoplastic elastomer filled with liquid crystalline polymer (LCP), organomontmorillonite (OMMT), and carbon nanotube (CNT) as a heat stabilizing filler, were comparatively investigated using nonisothermal- and isothermal-thermogravimetric analyses in air. The isoconversional method was employed to evaluate the kinetic parameters (E _a, lnA, and n) under dynamic heating. For neat samples, OMMT and CNT exhibited their respective lowest and highest thermal stabilities as revealed from the lowest and the highest T _onset values, respectively. The decomposition rates of the composites containing OMMT at the temperature >250?°C were higher than those containing CNT and LCP, respectively, whereas the elastomer matrix degraded with the highest rate. The obtained TG profiles and calculated kinetic parameters indicated that the incorporation of LCP, OMMT, and CNT into elastomer matrix improved the thermal stability. Especially, the CNT- and OMMT-containing composites significantly improved the thermal stability compared with the neat matrix polymer. Simultaneously recorded DSC thermograms revealed that the degradation processes for the neat polymers and their composites were exothermic in air. From the simultaneously recorded DSC data, the enthalpy of thermal decomposition for each composite system was found to be lower than that of the neat matrix and mostly decreasing with increasing filler loading. The isothermal decomposition stabilities of the neat SEBS and its composites containing the different fillers were in agreement with those of the nonisothermal investigation.     

Crystallization kinetics of polyethylene/paraffin oil blend sheets formed by thermally induced phase separation with different molecular weights of polyethylene

Polyethylene/paraffin oil blend sheets with different molecular weights of polyethylene were prepared by thermally induced phase separation. Isothermal and non-isothermal crystallization behaviors of blend sheets were investigated by differential scanning calorimetry (DSC). Isothermal DSC curves were analyzed by Avrami equation, whereas non-isothermal DSC curves were analyzed by Jeziorny method and Mo method. Effective activation energy (ΔE) of isothermal and non-isothermal crystallization was calculated by Friedman method. Under isothermal condition, value of n in Avrami equation hovered at 2.1, and lgZ increased with the decrease of crystallization temperature. lgZ and ΔE of blend sheets with a larger molecular weight of polyethylene was smaller than that of blend sheets with smaller molecular weight. Under non-isothermal condition, value of n obtained by Jeziorny method hovered at 2.4, close to n of isothermal condition. lgZ _c increased with the increase of cooling rate and decrease of molecular weight of polyethylene. ΔE of different blend sheets were close to each other. Crystal structures of blend sheets formed under non-isothermal condition were analyzed by X-ray diffraction (XRD) analysis. XRD analysis showed that molecular weight of polyethylene and cooling rate had slight influence on crystal structure and crystallinity of polyethylene/paraffin oil blend sheet.     

Kinetics of the crosslinking reaction of nonionic polyol dispersion from terpene-maleic ester-type epoxy resin

The bulk crosslinking reaction kinetics of a novel two-component waterborne polyurethanes (2K-WPUs) composed of a bio-resin-based polyol dispersion and a hydrophilically modified hexamethylene diisocyanate tripolymer are investigated by freeze–drying and differential scanning calorimetry (DSC) technique at different heating rates. The data fit for the above two components is implemented with the nth-order kinetics equation and Málek’s mechanism function method, respectively. The kinetic parameters of crosslinking reaction are determined by the kinetic analysis of the data obtained from the thermal treatment, and then the kinetic model is built. The results indicate that the nth-order model deduced from Kissinger and Crane equation has great distinction with the experimental data, while the Málek analytic mechanism shows that the crosslinking process of the crosslinking reaction follows an autocatalytic reaction. The two-parameter (m and n) autocatalytic model (S–B model) can well describe the crosslinking reaction process of the studied 2K-WPU. The DSC curves derived from the experimental data show a good agreement with the theoretical calculation under 5–20 °C min^?1 heating rate. The results provide theoretical basis for the choice of the manufacturing process and the optimization of processing window.     

Thermal decomposition kinetics and compatibility studies of primaquine under isothermal and non-isothermal conditions

Primaquine (PQ) is the drug of choice for the radical cure of Plasmodium vivax malaria, and currently being administered in solid dosage form. In this study, the compatibility studies were carried out using differential scanning calorimetry (DSC), thermogravimetry (TG), and fourier transformed infrared (FT-IR). Non-isothermal and isothermal methods were employed to investigate kinetic parameters under nitrogen and air atmospheres using TG. The DSC investigations obtained by physical mixtures showed slight alterations in the melting temperatures of PQ with some excipients. The FT-IR confirmed the possible interactions obtained by DSC for the physical mixtures with PQ and lactose, magnesium stearate and mannitol. The results showed that the thermal decomposition followed a zero order kinetic in both atmospheres in non-isothermal method. The activation energy in both methods using nitrogen atmosphere was similar, and in air atmosphere the activation energy decreased.     

Thermokinetic analysis of two-step curing reactions in melt: Part I. Investigation of low molecular model systems

Kinetic investigations of thermo-controlled two-step reactions between an uretdione cross-linker and OH-groups are undertaken. Non-isothermal DSC measurements are chosen for the determination of the kinetic parameters (E, A, n) using of THERMOKINETICS software. The system can be described very accurately with a four-step kinetic model of consecutive reactions. On the basis of the kinetic model and parameters the realization of the first reaction step, which is the formation of the allophanate network is simulated. Finally, the result of the calculated progress of the reaction is evaluated by FT-IR and isothermal DSC measurements.     

Particle size effects on the thermal behavior of hematite

Hematite with different particle sizes was obtained through isothermal annealing and mechanochemical ball-milling methods. The hematite phase is very stable under air atmosphere. The thermal stabilities of hematite under argon atmosphere were characterized by thermal analysis studies up to 800 °C using a simultaneous DSC–TG technique. The lattice parameters a and c of hematite with different particle sizes were extracted from the Rietveld structural refinement of powder X-ray diffraction patterns. Decomposition of hematite into a lower oxidation state in inert argon atmosphere was studied by the TG experiments for the first time and the enthalpy associated with the decomposition reaction was determined from the DSC studies. Particle size has a strong effect on the thermal behavior of hematite samples. Ball-milled hematite samples with smaller particle size showed that the phase transformation was extended to higher temperature range with larger enthalpy. Hematite with larger average particle size showed higher stability under argon atmosphere.     

Methods of non-isothermal kinetic analysis by DSC curves: An investigation on lattice reorganization in copper

Various analytical methods of non-isothermal kinetics have been applied to DSC curves to determine the kinetic parameters ruling the lattice reorganization (primary recrystallization) of prestrained pure copper.The techniques by Borchardt and Daniels, and Rogers and Smith have been modified to make them suitable for complex phenomena other than nth-order reactions.The results supplied by the new formulas are consistent with the data previously obtained under isothermal conditions. The same applies to the other methods tested, provided an accurate temperature calibration be made to correct the thermal lag of the calorimetric sensors.Such a calibration is of prime importance when DSC peak shifts are analyzed as a function of heating rate.     

The kinetic deuterium isotope effect in the thermal dehydration of boric acid

The kinetic deuterium isotope effect in the thermal dehydration process from H₃BO₃ to HBO₂(III) was determined using simultaneous TG and DSC. The rate constant ratio of H₃BO₃ to D₃BO₃ obtained by the analysis of isothermal TG and DSC curves was found to be smaller than unity. Both activation energy, E, and frequency factor, A, for the dehydration of H₃BO₃ proved to be larger than those of D₃BO₃, using non-isothermal TG and DSC. The origin of the deuterium kinetic isotope effect in the thermal dehydration of boric acid is also briefly discussed.     

Isothermal crystallization of layered silicate/starch-polycaprolactone blend nanocomposites

The isothermal crystallization behavior of layered silicate/starch-polycaprolactone blend nanocomposites was studied by means of differential scanning calorimetry (DSC) measurements. The theoretical melting point was higher for the matrix than for nanocomposites. At low clay concentration, the induction time decreased and the overall crystallization rate increased acting as nucleating agent whereas at higher concentrations became retardants. Classical Avrami equation was used to analyze the crystallization kinetic of these materials. n values suggested that clay not only affected the crystallization rate but also influenced the mechanism of crystals growth. An Arrhenius type equation was used for the rate constant (k). Models correctly reproduced the experimental data.     

The effect of experimental methods and measurement conditions on values of the kinetic parameters of [Co(NH3)6]2(C2O4)3·4H2O

Using the thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O as a basis, the paper presents results which show how computed values of kinetic parameters are influenced by experimental conditions (ambient atmosphere, sample mass, linear heating rate) when using the non-isothermal methods and the Coats-Redfern (CR) modified equation. It also illustrates the influence of the experimental methods i.e. non-isothermal and isothermal (conventional) methods and also a quasiisothermal-isobaric one which can be recognised as equivalent to Constant Rate Thermal Analysis (CRTA). The results obtained have confirmed the significant influence of the experimental parameters as well as that of the experimental method used on the estimated values of kinetic parameters. The correlation between activation energy (E) and sample mass (m) or heating rate (β) is generally of a linear nature:E=a+bx     

Thermal and dynamic mechanical investigations on poly[bis(benzimidazobenzisoquinolinones)]

A series of new semi-ladder poly[bis(benzimidazobenzisoquinolinones)], obtained by the polycondensation of dinaphthalene dianhydrides and aromatic tetraamines was investigated by TG, DSC and DMA methods. The influence of polymer structure on the thermal behaviour of the poly[bis(benzimidazobenzisoquinolinones)] was examined. The polymers were found to be thermally stable with T_d > 723 K in air and T_g ranging from 585 to 701 K. A good agreement was obtained in T_g values measured by DSC and DMA methods. It was found that some cross-linking processes occurred at temperatures above T_g. Some of the isothermal ageing curves were used to find the activation energies of isothermal cross-linking and decomposition.     

Nucleation parameters for polymer crystallization from non-isothermal thermal analysis

Differential scanning calorimetry (DSC) has been used to obtain kinetic and nucleation parameters for polymer crystallization under a non-isothermal mode of operation. The available isothermal nucleation growth-rate equation has been modified for non-isothermal kinetic analysis. The values of the nucleation constant (K _g ) and surface free energies (, _e ) have been obtained for i-polybutene-1, i-polypropylene, poly(L-lactic acid), and polyoxymethylene and are compared with those obtained from isothermal kinetic analysis; a good agreement in both is seen.     

Isothermal decomposition of γ-irradiated indium acetate

The isothermal decomposition of un-irradiated (pristine) and pre-γ-irradiated indium acetate was studied in the temperature range (298–1273 K) and in air using isothermal thermogravimetric technique. The data were analyzed using various solid-state reaction models. The results showed that the kinetic of isothermal decomposition of indium acetate was governed by random nucleation reaction (Erof’ev equation A₃). The kinetics and thermodynamic parameters of the main decomposition process for un-irradiated and γ-irradiated samples were calculated and evaluated.     

TTT Cure Diagram

Curing reactions of the epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n=0) and m-xylylenediamine (m-XDA) were studied to calculate time-temperature-transformation (TTT) isothermal cure diagram for this system. Gel times were measured as a function of temperature using solubility test. Differential scanning calorimetry (DSC) was used to calculate the vitrification times. DSC data show a one-to-one relationship between T _g and fractional conversion, a independent of cure temperature. As a consequence, T _g can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from the gel times obtained using the solubility test (41.5 kJ mol^-1). This value is similar to the results obtained for other similar epoxy systems. Isoconversion contours were calculated by numerical integration of the best fitting kinetic model. This revised version was published online in July 2006 with corrections to the Cover Date.     

New polyphenylquinoxalines linked by m-terphenyl flexibilizing groups

Three new monomers with phenylglyoxyloyl groups fixed on the 4,4′-, 4,6′-, and 4,4″-positions of m-terphenyl were synthesized by different pathways. They were used to prepare a series of polyphenylquinoxalines by solution polycondensation with 3,3′-diaminobenzidine and 3,3′,4,4′-tetraaminodiphenyl ether. These polymers exhibited excellent oxidative and thermal stability as shown by thermogravimetric analysis and isothermal aging in circulating air between 300 and 450°C. Clear yellow films, cast from m-cresol solution, were used to measure their softening temperature by thermomechanical analysis (TMA). Numerical data thus obtained, indicated a thermoplastic behavior in the temperature range 300 ± 15°C. Crosslinking of the linear polymers by isothermal heat exposure under argon between 300 and 500°C was investigated by means of TMA. Molded materials were fabricated under constant pressure (996 psi) at 500–525°C with an Instron testing machine. These polymers were also used for preliminary evaluation as matrices for 181-E glass reinforced composites. Flexural values obtained after isothermal aging in air up to 400°C indicated a potential use varying from 150 hr at 350°C to 24 hr at 400°C.