Isothermal Kinetic Analysis Research Articles

Thermal degradation of a styrenated unsatured polyester resin

The isothermal and non-isothermal degradation of a typical styrenated phthalic acid-maleic acid-propylene glycol polyester were measured. Non-isothermal and isothermal kinetic analyses were performed on the various degradation steps observed. The values of the non-isothermal and the isothermal kinetic parameters are in good agreement.

Isothermal Crystallization Studies on Neodymium Oxide Filled Nylon 6

Melt mixing of nylon 8 with neodymium oxide particles was carried out with a single-screw extruder. The crystal behaviors of plain nylon 6 and the neodymium oxide filled nylon 6 mixture were studied by means of isothermal crystallization kinetic analysis. Isothermal crystallization thermograms obtained by differential scanning calorimetry (DSC) were analyzed based on the Avrami equation. The neodymium oxide particles acted as a nucleating agent in the mixture. The overall rate of di-isothermal crystallization of the neodymium oxide filled nylon 6 mixture is higher than that of plain nylon 6. The mechanism and modes of plain nylon 6 were the same as those of neodymium oxide filled PA6 mixture.

Comparative study of the cure kinetics of an unsaturated polyester resin using different procedures

AbstractThe cure kinetics of an unsaturated polyester resin were studied by differential scanning calorimetry (DSC), and different dynamic and isothermal procedures were compared. It was established that the isothermal kinetic analysis through the isoconversional adjustment lnt = A + E/RT is the method that offers the most accurate results for unsaturated polyester resin cure kinetics. From this comparative study it was noted that the activation energy not only varies according to the degree of conversion but also according to the method used to evaluate the kinetic parameters. Furthermore, it was shown that the activation energy cannot be separated from the other adjustment parameters, so the different kinetic procedures used are not generally comparable. Different methods of evaluating the degrees of conversion α and the reaction rates dα/dt according to the experimental reaction heat were also studied. It was found that the method used has a strong influence on the values of α and dα/dt, but only a slight one on the kinetic parameters.

Isothermal kinetic analysis of solid-state reactions using plots of rate against derivative function of the rate equation

Since the advent of digital data capture and the development of quick and accurate numerical methods for data processing, the use of rate measurements ( dα dt ) for kinetic analysis of solid-state reactions has gained in popularity. Rate measurements may readily be obtained through use of isothermal derivative thermogravimetry (DTG), or from isothermal differential scanning calorimetry (DSC) (on the assumption that the evolution or absorption of heat may be used to measure the extent of reaction, α). In this paper, the feasibility and desirability of using plots of experimental dα dt values against the derivative functions for the various models for solid-state reactions is considered critically and discussed quantitatively.

On-line method for isothermal kinetic analysis

The kinetic analysis of any isothermal process is based on compliance with the equational form g( α) = kt, which requires an a priori knowledge of the final property change Δp ∞. It is therefore imperative that this equation is not applied to incomplete reactions. A new on-line method has therefore been developed here which gives analytical solutions to well known mechanisms of reaction without recourse to Δp ∞. In some cases, where Δp ∞ k appears as a product or exponential terms are to be found, computer based numerical methods have been adopted to solve the equations. The deciphering of the mechanism and the evaluation of k without waiting for the completion of a TG run has been demonstrated with a hypothetical TG curve.

Effect of the inhibitor on the curing of an unsaturated polyester resin

Differential scanning calorimetry has been used to study the influence of hydroquinone as an inhibitor on the curing of an unsaturated polyester resin using benzoyl peroxide as an initiator. The isothermal kinetic analysis was performed by isoconversional adjustment ln t = A + E/ RT. This adjustment makes it possible to predict the variations in the activation energy with the degree of conversion without the need to know the rate equations. The results obtained through this adjustment were compared with those obtained by applying an autocatalytic model. The kinetic parameters obtained by both methods permitted the simulation of the curing process inside and outside the experimental range of temperatures. From the experimental results and the kinetic analysis, it was possible to elucidate the dual mechanism of inhibition and retardation exerted by hydroquinone. With the knowledge of the inhibition mechanism, we proposed a method for using the induction times to determine the kinetic parameters associated with the decomposition of the initiator and/or the instantaneous inhibitor content in unsaturated polyester resins.

Temperature dependence of the nucleation effect of sorbitol derivatives on polypropylene crystallization

AbstractThe temperature dependence of the nucleation effect of three sorbitol derivatives on the crystallization of isotactic polypropylene (iPP) was studied by means of isothermal crystallization kinetic analysis. Isothermal crystallization thermograms obtained by differential scanning calorimetry (DSC) were analyzed based on the Avrami equation. The Avrami analysis for the nucleated iPP was carried out with DSC data collected to 35% relative crystallinity, and the rate constants were corrected assuming the heterogeneous nucleation and three dimensional growth of iPP spherulites. A semi‐empirical equation for the radial growth rate of iPP spherulites was given as a function of temperature and was used to determine the number of effective nuclei at different temperatures. The number of effective nuclei in the nucleated samples was estimated to be 3 × 102 ∽ 105 times larger than that in the neat iPP. The logarithmic numbers of the effective nuclei decreased linearly with decreasing degree of supercooling in the range of crystallization temperatures tested. The temperature dependence of the effect of the nucleating agents on iPP crystallization was given quantitatively in terms of the deactivation factor defined as a fraction of the particles that are active at a particular temperature but inert at the temperature one degree higher. The nucleation activity and its temperature dependence are considered to be cooperative effects of many factors, including the dispersion and the physical or chemical nature of the agent as well as the interaction between the agent and the polymer. It is suggested that the temperature dependence of the effect of a nucleating agent should be treated as a characteristic of a given polymer/ nucleating agent mixture.

The thermal decomposition of oxalates: Part 26. A kinetic study of the thermal decomposition of manganese(II) oxalate dihydrate

The determination of the most probable mechanism function and calculation of the kinetic parameters of decomposition of manganese oxalate have been achieved by a new kinetic analysis procedure under nonisothermal conditions in both dry and wet N 2. The isothermal kinetic analysis has also been performed in each atmosphere. Both the isothermal and nonisothermal analyses showed the most probable mechanism function is first order (Fl). The coincidence of results obtained by isothermal and nonisothermal analysis supports the idea that the proposed analysis procedure for nonisothermal conditions is a promising one.

Thermal transitions, microstructure and miscibility in ternary polyblends based on poly(vinylidene fluoride)

AbstractThe morphology, microstructure and compatibility of binary and ternary polyblends based on poly(vinylidene fluoride) have been studied by means of glass transition temperature, isothermal crystallization kinetics analysis and scanning electron microscopy in order to determine the possibilities offered by poly(vinyl acetate) for compatibilizing poly(vinylidene fluoride) and polystyrene. Calorimetric and dynamic mechanical analyses demonstrate that poly(vinyl acetate) tends to ‘compatibilize’ blends of PVF2/PS, although the results of the two analyses do not agree with each other; we presume that this is due to differences in the techniques employed.

Reliability of kinetic measurements for the thermal dehydration of lithium sulphate monohydrate.: Part 1. Isothermal measurements of pressure of evolved water vapour

The thermal dehydration of single crystal and powdered samples of lithium sulphate monohydrate, Li 2SO 4· H 2O, has been selected for detailed examination of the reliability of kinetic parameters obtained from isothermal measurements of the pressure of water vapour evolved in an initially evacuated, constant-volume apparatus. The reproducibility was examined and various methods of isothermal kinetic analysis, including integral and differential methods and the use of reduced-time scales, were compared. Arrhenius parameters derived from these experiments are compared with previously published values.

Avrami exponent of crystallization in metallic glass Cu73.8P13.8Ni8.3Sn4.1

A non-isothermal method has been developed to measure the Avrami exponent of crystallization in metallic glass based on the Johnson-Mehl-Avrami isothermal equation. An example of metallic glass Cu73.8P13.8Ni8.3Sn4.1 was studied with non-isothermal and isothermal kinetic analysis for determining the Avrami exponent,n, which are 3.5 and 3.4, respectively, and are comparable.

Kinetic study on the thermal decomposition of copper(II) oxalate

The thermal decomposition of copper(II) oxalate has been studied under vacuum using a constant-volume apparatus and a microbalance; and under dynamic atmospheres of air, nitrogen and oxygen using thermogravimetry and differential scanning calorimetry. The decomposition was found to proceed to copper metal under an inert atmosphere and vacuum; while in air and oxygen, copper(II) oxide was found to be the decomposition product. In each case the decomposition was found to be exothermic with an enthalpy change of –9 ± 2 kJ mol–1 in nitrogen and –134 ± 5 kJ mol–1 in air. Isothermal kinetic analysis showed the data to fit an Avrami–Erofeev relationship with n= 3 in each case. Arrhenius parameters are reported for each decomposition atmosphere and are compared to those of other transition-metal oxalates which appear in the literature.The presence of a preparation effect is noted, as seen with other oxysalts; however, no evidence for the formation of copper(I) oxlate has been found which has previously been speculated to be an intermediate in the 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 (sgr, sgr 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.

Kinetic analysis of the liquid-phase depolymerization of trioxane from programmed-temperature data

An experimental method for the determination of kinetic data for liquid-phase reactions under linear rise of temperature is explained for the depolymerization of trioxane. Integral kinetic analysis of the data is performed in order to determine the kinetic model and the kinetic parameters. Experiments have been carried out at different heating rates between 0.5 and 2 deg/min, leading to similar kinetic parameters. The obtained results are in agreement with the kinetic model and parameters obtained from isothermal kinetic analysis. The programmedtemperature method seems to be a useful tool for a quick determination of kinetic models, avoiding experimental work.

Effect of Lattice Anions on the Ligand Substitution Reaction of Tris(1,10-phenanthroline)metal(II) Complexes: [M(phen)3]SO4 and [M(phen)3]X2 (M: Fe(II), Co(II), Ni(II); X: Cl−, Br−, I−)

Abstract The kinetics of the ligand substitution reaction of the title complexes in the solid state have been studied using thermogravimetry (TG) and differential scanning calorimeter (DSC) techniques. For these complex salts, an exothermic peak appears in the DSC curve which correlates with a ligand substitution in which anionatobis(1,10-phenanthroline)metal(II) complexes are formed. The heats of the exothermic reaction for ligand substitution of the sulfates decrease in the order Co(II)>Ni(II)>Fe(II). Isothermal and nonisothermal kinetic analyses were carried out using the exothermic peak. Activation energies of the ligand substitution for the same counterion generally increase with the metal in the order Co(II)<Ni(II)<Fe(II) and for the same metal, Ni(II) or Fe(II), increase with the counterion in the order Cl−<Br−<I−<SO42−. However, for the cobalt complex, the activation energies are almost identical for this series of counterions. From the trends in activation parameters for the ligand substitution, we propose a dissociative mechanism for the sulfates of all complexes studied and for the cobalt complex halides studied. For the halides of the iron(II) and nickel(II) complexes studied, a mechanism involving nucleophilic attack of the halide ions is important.

Iron compounds in high oxidation states: IV . Kinetic analysis of the reaction between Na 2O 2 and FeSO 4

The isothermal kinetic analysis of sodium ferrite formation by reaction between Na 2O 2 and FeSO 4 shows that the rate-controlling step is nuclei growth. This mechanism differs from that established in the case of the BaO 2-FeSO 4 system (diffusion-controlled). The appearance of Fe 2O 3 as intermediate here might be the primary cause of this different behaviour. Non-isothermal procedures appear unsuccessful in our analysis of the reaction between Na 2O 2 and FeSO 4.

An approach to the kinetics of water desorption from A-zeolites. Part I. Isothermal and non-isothermal desorption

Desorption of water from zeolites: NaA, LiA, KA, CdA, ZnA, MgA and CaA were examined. Isothermal and non-isothermal kinetic analyses were carried out. It was found that the process of desorption can be presented as a first-order reaction. Due to the existence of several water—zeolite complexes, neither isothermal nor non-isothermal kinetic methods may be applied directly.

Steady‐State Characteristics of Oxygen Concentration Cell Sensors Subjected to Nonequilibrium Gas Mixtures

Oxygen sensors, based on membrane concentration cells, are to be used in a feedback control system on automobiles. For proper control function, the sensors should develop voltages corresponding to equilibrium oxygen partial pressures in engine exhaust, even when substantial deviations from chemical equilibrium actually exist in the bulk exhaust stream. This is accomplished through use of catalytic electrodes that are supposed to equilibrate local oxygen concentrations at the membrane surface and measure the emf developed across the concentration cell. This paper explores physicochemical factors influencing the emf across concentration cell oxygen sensors in the presence of surface reactions that are not necessarily in chemical equilibrium. Specifically, we report an isothermal kinetic analysis linking emf to (i) mass transfer between the bulk gas and boundary layers; (ii) adsorption, desorption, and chemical reaction on the catalyst/electrode surface. With nonequilibrium bulk gas mixtures, our analysis indicates that cell emf corresponds to equilibrium oxygen partial pressures when two restrictions are met: (i) mass transfer between bulk gas and surface boundary layers is slow relative to the rate of surface reactions; (ii) the reactant gases have identical mass transfer coefficients. Experimental studies of oxygen sensors with platinum catalyst/electrodes are also reported. Voltage/composition curves for systems deviate substantially from those calculated for chemical equilibrium. This reflects a relatively poor platinum catalytic efficiency for alkane oxidation. Following recent work by Takeuchi et al., a “mass transfer shift” of voltage/composition curves was observed at 600°C with the and the systems. This result, which follows from our kinetic analysis, reflects the substantially different mass transfer coefficients of the reactant gases. In a second set of experiments, gas mixtures were equilibrated chemically before reaching the sensor by passing them over a secondary platinum catalyst. Stoichiometric voltage/composition curves were obtained under these conditions.