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Abstract
Attempts are made to use kinetics parameters from thermal decomposition experiments at high temperatures to predict service lifetimes of polymeric materials at lower temperatures. However, besides the obvious measurement and extrapolation errors (which can be considerable), there are two fundamental reasons why quantitative long range extrapolations can not be made for complex condensed phase systems. They are: 1) Arrhenius kinetics parameters can not be extrapolated through phase transitions or softening temperatures; 2) Arrhenius kinetics parameters can not be extrapolated through the ceiling temperature region. Satisfactory lifetime prediction methods can be developed only after a thorough analysis of the causes of service failure. A real method has been taken from literature to illustrate the correct procedures.
The temperature of initial decompositionT id was determined from TG and DTG curves of mass loss during thermooxidative polymer decomposition in an environmental air atmosphere. The values ofT id were applied for comparison of the thermal stabilities of several polymers, e.g. PC-A, PBT, PET, PPO and PVC. Both the activation energies of initial decompositionE id and the preexponential termsA id of the Arrhenius equation were calculated by using the Kissinger approach. The initial mass loss is proposed as a criterion for calculation of the time to failuret f from the known values ofE id andA id, and hence for a prediction of the lifetime of polymer materials.
Abstract
The paper deals with the study of thermal degradation of some new and old paper supports. The experimental data allows the prediction of the dependence between the half time and the temperature at which the paper support must to be kept.
Abstract
A common scepticism towards the application of many product formulations results from the fact that their long-term stability is difficult to predict. In the present study we report on a new approach of kinetic analysis of the oxidation reactions of natural rubbers with and without stabiliser in an oxygen atmosphere at moderate temperatures using CL measurements carried out on a newly-developed instrumentation. The kinetic parameters of the oxidation process, calculated from the chemiluminescence’s signals by means of the differential isoconversional method of Friedman, were subsequently applied for the simulation of the rubber aging under different temperature profiles. The presented results are the first stage of research by using the chemiluminescence method to measure the oxidative aging of rubber and predicting the life time of rubber items.
Abstract
A DSC instrument modified to incorporate a chemiluminescence (CL) detector has been used to make simultaneous measurements of heat flow and light emission for oxidising polymer samples. Comparison of heat flow and light emission from unstabilised polypropylene shows a linear relation between heat flow and square root of intensity, giving indirect confirmation of the Russell mechanism for CL emission. Measurements of oxidation induction times (OIT) for stabilised samples show excellent correlation of the two techniques. The advantage of the CL method in being insensitive to thermal transitions in the sample is illustrated by a study of poly(ethylene terephthalate), whilst the very high sensitivity of CL detection is illustrated by its ability to detect peroxides at levels which are not detected by DSC. Finally, the limitations of the OIT approach in lifetime prediction by Arrhenius extrapolation are emphasised.
]. Lifetime prediction of polymeric materials undergoing thermooxidative decomposition is currently done by measuring OIT or OOT at elevated temperatures. Then an extrapolation is done to obtain the induction period at the actual use or storage temperature of
. Flynn JH Dickens B . Application of new kinetic techniques to lifetime prediction of polymers from weight-loss data . Abstr Pap ACS. 1978 ; 176 : 14
