A study of parameters interfering in oxidative induction time (OIT) results obtained by differential scanning calorimetry in polyolefin (original) (raw)
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Investigation of parameters affecting the test results of oxidation induction time of polyolefins
International Journal of Plastics Technology, 2018
Oxidation induction time test is as an accelerated procedure and a qualitative evaluation performing to measure, thermal stability of polyolefins with using of Differential Scanning Calorimetry method. This can be interpreted as an indicator of the thermal stability of polyolefins, used in an oxidation environment. The results of test depend on various factors. Despite the widespread use of it in many different bases, studies about these factors and their impacts have not been significant. In ahead study, these factors were in two main groups, Ι-Sample conditions includes amount of the sample, the place of sample, sample geometry and ΙΙ-Test and instrument conditions includes heating rate, type of crucible, Oxygen gas flow rate, isothermal temperature and instrument temperature stabilization time. By choosing a High Density Polyethylene sample and conducted tests with preparation, together with statistical analysis by Yates algorithm and application of Minitab along with Design Expert software's, the impact of above factors were investigated. Among the factors related to the conditions of the test sample, specimen geometry and location of its choice and among the ones related to test conditions, heating rate, isothermal temperature and instrument temperature stabilization time were identified important and with significant impacts.
Two approaches to kinetic analysis applied to the prediction of antioxidant activity
Kinetics and Catalysis, 2006
Differential scanning calorimetry (DSC) followed by mathematical data processing can be used instead of the conventional method of long term thermal aging in predicting the activity of antioxidants in polyolefins. In this method, a regression relationship is established between the oxidation initial temperatures measured by DSC (X data) and the oxidation induction period values determined by thermal aging (Y data). Two approaches, called hard and soft, are employed in the construction of models. In the first case, nonlinear regression analysis is used in combination with successive Bayesian estimation. The second approach combines partial least squares regression and simple interval calculation. Use of a common data set makes it possible to compare these approaches and to draw inferences as to the cases in which one or the other is preferable.
Revista de Chimie, 2001
Utility of polymeric material is a major contribution to the production of waste, particularly in Pakistan. An easy escape to it is the damping in the land which is not commendable for an environmental point of view. On the other hand, the aging of polymer is analogous to its burial conditions under the soil in the absence of light. Therefore, in this research report, two different brands of polyethylene carrying bags were investigated. One sample was obtained from Pakistan abbreviated as sample "Y" while the other from Canada abbreviated as "E". In order to accelerate the degradation process and to observe the impact of aging in a shorter span of time, these samples were heated at an elevated temperature (80°C) in an oven for the period of 20 days. The samples were characterized before and after aging with an interval of 2 days by applying different techniques like FT-IR, SEM, DSC, and thermogravimetric analysis (TGA). Carbonyl peak at 1715 cm-1 was observed only in the case of sample "E" displaying carbonyl index value as 28.45 % after 20 days of aging. The SEM images before and after aging revealed that the degradation took place at preferential sites in case of sample "Y" and at numerous sites in case of sample "E". The results of percent crystallinity obtained by DSC showed an increasing pattern with aging for both the samples and was high in case of sample "E." The activation energy determined by using Flynn-Wall-Ozawa showed a decreasing pattern for both the samples with aging. It concluded that the thermal aging initiates the process of degradation which was then accelerated by heating in TGA oven. The order of reaction was slightly decreased after aging for both the samples and was found to be independent of the heating rate.
Radiation Physics and Chemistry (1977), 1985
In part one of this series the effects of a phenolic, an amine and a thioester antioxidant on the thermo-oxidative stability of irradiated and unirradiated low-density polyethylene was reported. In this paper the effects of combined phenolic and thioester stabilizers are described. Isothermal thermogravimetric analysis was used to study the systems. Pronounced synergism was observed with the induction periods, the time when the initial weight loss begins and the 5% weight loss. At about 50% of each stabilizer increases greater than twofold were observed both with the unirradiated and irradiated polymers. The rate constants for oxygen uptake were decreased. However, the rates of degradation at 5% weight loss fell between the values of the two pure stabilizers with no pronounced synergism in either case. In the absence of oxygen little effect of either antioxidant or their mixtures was observed. The corresponding activation energies were somewhat higher, however, with the irradiated samples containing antioxidants. Dynamic thermogravimetry was used for this study. A kinetic analysis indicated that there were somewhat different modes of degradation at lower-and highertemperature ranges.
A Kinetic Analysis of the Thermal-Oxidative Decomposition of Polypropylene
Journal of Fire Sciences, 2000
The kinetics of the thermal-oxidative decomposition of poly propylene (PP) was studied by a conventional thermogravimetric technique in pure nitrogen and various concentrations of oxygen ranging from 5-21%. The kinetic model that accounts for the effects of oxygen concentration was proposed to describe the thermal decomposition of PP. The thermogravimetric analysis curve and its derivative have been analyzed using the differential and integral methods with modification of the Friedman and Coats-Redfern methods. The activation energy, the pre-exponential factor, and the reaction order for unreacted material and oxygen concentration have been determined. When oxy gen was present, the activation energy was reduced significantly.
A differential scanning calorimetry method to study polymer photoperoxidation
Polymer Testing, 2001
A main challenge in the field of polymer aging is the detection of extremely small amounts of peroxide formed in the primary steps of oxidation. This is a necessary condition to be able to predict physical changes and to remedy the resulting loss of properties. All experiments carried out to assess the properties of peroxide species are generally based on direct or indirect chemical titration. However, all of these techniques are limited by the molecular accessibility of chemical reagents in the macromolecular medium. As the decomposition of these species is known to be strongly exothermic, we used differential scanning calorimetry (DSC) measurements to quantify the level of peroxides formed from the photo-oxidation carried out under accelerated conditions. This method appears to be more sensitive than chemical titration in the detection of small amounts of peroxide structures. Moreover, it gives additional information such as their thermal range and kinetics of decomposition.
Estimation of Bias in the Oxidative Induction Time Measurement by Pressure DSC
Astm Special Technical Publication, 1997
Oxidative induction time (OIT) is defined as the time to the onset of oxidation of a test specimen exposed to an oxidizing gas at an elevated isothermal test temperature. In standard DSC, the oxidizing purge gas is initiated once the specimen has stabilized at the isothermal test temperature. In Pressure Differential Scanning Calorimetry, however, the test specimen is often exposed to the oxidizing atmosphere as the apparatus is heated from ambient to the isothermal test temperature. This approach creates a bias in the measurement due to undetected oxidation on heating. An expression, based upon the Arrhenius equation, is derived and then numerically integrated to obtain an estimation of the bias introduced into the OIT measurement by exposing the test specimen to oxygen at room temperature. The bias is dependent on the activation energy of the reaction and on the heating rate. The bias is found to be less than 1.2 minute for the most common heating rates, and is less than 3 minutes for the most extreme sets of experimental conditions. The bias is found to be small when compared to experimental repeatability of the OIT measurement and to the mean of OIT values. For this reason, it may be ignored in all but the most extreme cases of low activation energy, very slow heating rates, very low OIT values and high test temperatures. The ease-of-use benefits, achieved by exposing the test specimen to the reactive gas from the start of the experiment are likely to out weigh the small bias effect in most OIT measurements whether under Pressure DSC or standard DSC conditions. A precursory study shows the same mathematical treatment can be used to estimate bias in other isothermal studies of kinetic phenomena such as isothermal polymer crystallization and isothermal reaction kinetics such as thermoset cure.