Mi-Ja Shim

Thermal degradation kinetics of PE by the Kissinger equation

Abstract Thermal degradation kinetic parameters of two forms of polyethylene were investigated by using thermogravimetric analysis and the Kissinger equation. Under the oxygen presence, polyethylene was decomposed rapidly at lower temperature by additional oxidation reaction. The thermal decomposition activation energy of low density polyethylene and cross-linked polyethylene were 146.8 kj mol−1 and 170.4 kJ mol−1, respectively.

Effect of modified rubber compound on the cure kinetics of DGEBA/MDA system by Kissinger and isoconversional methods

Abstract The cure kinetics of diglycidyl ether of bisphenol A (DGEBA)/4,4′-methylene dianiline (MDA) system with various contents of MDA-endcapped carboxyl-terminated butadiene acrylonitrile (CTBN) were studied by Kissinger and isoconversional methods. With increasing MDA-endcapped CTBN content, the exothermic heat decreased due to the diffusion control induced by rubber domain produced in the epoxy matrix, which disturbed the diffusion of functional groups, and the maximum exothermic peak value and the activation energy by Kissinger equation decreased due to the increasing content of amine group in rubber compound, which reacted with epoxy group and formed a hydroxyl group acted as a catalyst. In the isoconversional method, the activation energy decreased until minimum value in the initial stage and increased after that value. The decreasing in the initial stage was due to the autocatalytic cure reaction and the increasing after the minimum value was due to the increasing crosslink density and rubber domain.

Characteristics of polymer insulator materials:: Voltage–lifetime characteristics of DGEBA/MDA/SN system

Abstract The voltage–lifetime characteristics of the new epoxy resin system, diglycidyl ether of bisphenol A (DGEBA)/4,4′-methylene dianiline (MDA)/succinonitrile (SN), have been investigated by using non-homogeneous electrode geometry. The lifetime dependence of the applied electric field well followed the empirical Vnt=const model. The lifetime factors at 25, 70 and 100°C were 5.128, 7.533 and 14.494, respectively. The dielectric breakdown mechanism at 25°C was changed around 14xa0kV. At high temperature, the thermal stress dominated the lifetime and at the low thermal stress, the thermal decomposition and distortion by electro-mechanical stress governed the dielectric breakdown under high electric field.

Reaction mechanism of an unsaturated polyester system containing thickeners

The thickening process and curing reaction of unsaturated polyester resins were characterized by viscosity measurement and differential scanning calorimetry when a thickener was involved. Various kinetic parameters were determined by means of dynamic and isothermal experimental data and rheological process. The different values of activation energy reflected the different reaction mechanisms occurred in the curing course. Under isothermal conditions, polymerization reaction is one-order and diffusion-controlled reaction becomes significant when high concentration of thickener was applied.

Electrical tree initiation mechanism of artificial defects filled XLPE

Abstract The electrical tree initiation and propagation mechanism in XLPE (cross-linked polyethylene) with artificial voids filled with N2 gas, O2 gas or moisture was investigated. Treeing phenomena (pits, filamentary channel, voids, bridge, etc.) were observed and dielectric deterioration and breakdown mechanism were discussed. Oxidized region and rough electrode surface acted as the stress concentration point and from which electrical treeing deterioration processes were initiated after a tree inception time and started to propagate three-dimensionally toward the plane electrode. The width of the broken tree channel was 117 μm and the thickness of the tree was 1 to 30 μm. The dielectric breakdown occurred when a tree channel bridged the two electrodes.

Thermal degradation of epoxy/natural zeolite composites

The characteristics of thermal degradation of epoxy system filled with natural zeolite were studied by thermogravimetry analysis (TGA). All the epoxy composites were degraded in one stage regardless of the zeolite content. In the Freeman & Carroll equation, the activation energy at 20 phr of zeolite was lower than that at any other content of zeolite and these values decreased with the increment of heating rate. In the Kissinger equation, activation energy decreased until 30 phr of zeolite was added and the value abruptly increased at 40 phr of zeolite content. The activation energy and thermal degradation temperature showed the same tendency according to the change of zeolite content. The activation energy obtained from the Freeman & Carroll equation was larger than that from the Kissinger equation.

Effect of MDA-endcapped CTBN on the cure kinetics of epoxy system by autocatalytic cure rate expression

The cure rate of diglycidyl ether of bisphenol A (DGEBA)/4,4′-methylene dianiline (MDA) system with or without MDA-endcapped carboxyl-terminated butadiene acrylonitrile (CTBN) rubber was studied by autocatalytic cure rate expression. All the cumulative conversion curves for DGEBA/MDA system with or without MDA-endcapped CTBN (20 phr) showed s-shape and this meant that the two systems followed the typical autocatalytic reaction. The cure rate of the system with MDA-endcapped CTBN (20 phr) was faster than that of the system without MDA-endcapped CTBN (20 phr). The activation energies of k1 and k2 for DGEBA/MDA system were 54.01 kJ/mol and 44.06 kJ/mol, respectively and those of k1 and k2 for the system with MDA-endcapped CTBN (20 phr) were 47.71 kJ/mol and 40.95 kJ/mol.

Cure rate of DGEBA/MDA/GN/HQ system by differential scanning calorimetry analysis

Abstract To compare investigations of the cure kinetics of DGEBA/MDA/GN/HQ system by different methods, the fractional life method, Kissinger equation, Barrett method and integral method were used. From the fractional life method, reaction orders were between 0.77 and 0.93 but had no correlation with cure temperature, and from the Kissinger equation, the activation energy was 11.08xa0kcalxa0mol −1 and pre-exponential factor was 2.78×10 3 xa0s −1 . For the second-order reaction by the Barrett method and integral method, the activation energy was 20xa0kcalxa0mol −1 and the pre-exponential factor was 8.5×10 8 xa0s −1 . By comparison of the Barrett model with experimental data, it was found that the Barrett model was useful for predicting the cure time at a given temperature.