The results of non-isothermal kinetic analysis of the thermooxidative degradation in air and oxygen of an unsaturated polyester
resin are presented. It has been shown that the thermooxidative degradation in oxygen occurs at lower temperatures than the
thermooxidative degradation in air. The kinetic parameters of the thermooxidative degradation depend on the heating rate and
the oxygen pressure. Two straight lines of InAvs. E (A is the preexponential factor andE is the activation energy), characteristic for the compensation effect, have been obtained for the thermooxidative degradation
in air and in oxygen respectively. The difference between the intercepts of these straight lines can be explained by dependence
of the pre-exponential factor on the oxygen pressure.
Effects of nano-metal powders (aluminum and nickel) addition on the thermooxidative degradation of binder PEG in air atmosphere
from 20 to 350°C were studied by TG/DTA and in-situ FTIR. TG/DTA results showed that the addition of nano-Al slowed down the
degradation process of PEG in the early period but accelerated the process in the late period; the addition of nano-Ni made
the PEG degradation process begin as soon as melted. The in-situ FTIR results showed that nano-Ni promoted the thermooxidative
degradation of PEG in air, and made the degradation process of PEG complete much earlier.
Results obtained on the thermooxidative degradations of LDPE (low-density polyethylene) and NBR (nitrile-butadiene rubber)
are presented. The activation energies for the thermooxidations leading to solid products were estimated. For LDPE, the activation
energies obtained from non-isothermal data are in satisfactory agreement with those obtained from isothermal data. For NBR,
the isothermal activation energy is ≉16% higher than the non-isothermal one. This difference is due to the morphological changes
undergone by NBR during its heating at the rather high temperatures at which isothermal measurements were performed.
Authors:J. M. Salla, J. M. Morancho, X. Ramis, and A. Cadenato
Summary Thermogravimetry was used to study the kinetics of isothermal degradation of an epoxy thermoset powder coating in a nitrogen atmosphere and in oxidizing atmospheres of air and pure oxygen. An integral isoconversional procedure was used to analyse how the activation energy varies depending on the degree of conversion and depending on the atmospheres used. In the case of degradation in a nitrogen atmosphere, in addition to the activation energy, the kinetic triplet was completed using an Avrami reaction model and the pre-exponential factor. With this atmosphere, the conclusion was reached that the isothermal and non-isothermal kinetics are equivalent. It was shown that the thermooxidative degradation process is more complex and consists of a two-stage process. The first stage of degradation is similar whether nitrogen, oxygen or air are present. Chain scission occurs and it seems that there is formation of thermally more stable compounds. The second stage of degradation, involving several phenomena, occurs only in the presence of oxygen or air and leads to the total disappearance of the organic material by thermooxidation. These stages are very similar under non-isothermal or isothermal conditions.
The thermooxidative degradation of poly(vinyl chloride) (PVC), chlorinated polyethylene (CPE) and PVC/CPE blend 50/50 was
investigated by means of dynamic and isothermal thermogravimetric analysis in the flowing atmosphere of air. To estimate the
thermooxidative stability of the samples the characteristics of thermogravimetric (TG) curves were used. Kinetic parameters
(the apparent activation energy E and preexponential factor Z) were calculated after isoconversional method for the first
stage of dynamic degradation where dehydrochlorination (DHCl) of PVC and/or CPE is the main degradation reaction. Despite
the chemical resemblance, the degradation mechanisms of CPE and PVC are different, as a consequence of differences in microregularity
of the corresponding polymer chains. The addition of Ca/Zn carboxylates as well as the ratio of Ca and Zn carboxylates have
considerably different influence on the investigated polymers.
Results are presented on: (a) the nonisothermal degradation of nitrile-butadiene rubber (NBR) from TG, DTG and DTA data; (b) the accelerated isothermal thermal degradation of NBR at 80°, 90° and 105° from the change in weight versus time data; (c) the accelerated isothermal thermal degradation of NBR at 80°, 90° and 105° from the change in relative elongation at break with time.
The accelerated thermal degradation of low-density polyethylene (LDPE) was studied in air at atmospheric pressure and temperatures
of 70, 80, 90 and 100C. The changes in elongation at break, traction resistance and density as a result of accelerated thermooxidative
degradation were followed. Thermal analysis curves (TG, DTG and DTA) of non-aged and thermally aged LDPE were recorded, and
the thermal analysis results were compared with those relating to the variations in the elongation at break, the traction
resistance and the density as a consequence of accelerated thermal aging.