Search Results
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.
Abstract
This article continues our study published earlier on the application of the oxidative induction test to a wide variety of medical polymers. In a series of thermoplastic olefin elastomers (TPO), the extrapolated induction time on the Arrhenius plot was found to coincide with published results based on oven aging mechanical studies extending to much lower temperatures and times as long as nearly a year. This agreement indicates the potential of the OIT for long term durability prediction. For medical flexible PVC compounds, the traditional measure of extent of degradation by color formation was found to correlate to measured oxidative induction times. Furthermore, three distinct regimes were also detected, where in the first phase, little color changes can be detected. In a longer time, lower temperature study, effect of room temperature fluctuations was clearly detected, emphasizing the need for good environmental control for sensitive detections. These and other recent results will be presented to illustrate the utility of this versatile test.
Biodiesel from soybean oil, castor oil and their blends
Oxidative stability by PDSC and rancimat
measurement and the oxidative induction time (OIT) is obtained in the isothermal curve. Both are related to the onset of the exothermic peak characteristic of the oxidative process. A recent work invested the relationship between the Rancimat technique
Abstract
This biomaterials overview for selecting polymers for medical devices focuses on polymer materials, properties and performance. An improved understanding of thermoplastics and thermoset properties is accomplished by thermal analysis for device applications. The medical applications and requirements as well as the oxidative and mechanical stability of currently used polymers in devices are discussed. The tools used to aid the ranking of the thermoplastics and thermosets are differential scanning calorimetry (DSC), thermogravimetry (TG), thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) as well as a number of key ASTM polymer tests. This paper will spotlight the thermal and mechanical characterization of the bio-compatible polymers e.g., olefins, nylon, polyacetals, polyvinyl chloride and polyesters.
temperature range from 25 to 500 °C. The isothermal curves were obtained in oxygen atmosphere, using the same conditions of pressure, flow rate and heating rate at the temperature of 100 °C. The oxidation induction time (OIT) values were obtained from the
Abstract
Degradation of polymeric materials used in nuclear power plants (NPP), especially polymeric cable insulation materials, in the course of their service can be monitored by measuring their properties by DSC, mainly oxidative induction time — OIT. The studied materials were in-laboratory aged by applying main stressors that act in NPP — ionising radiation and temperature. The dependence of OIT on radiation and thermal degradation of polymeric material was determined. The OIT values have been compared to elongation at break as a property that directly reflects the functionality of the studied material. The comparison of monitored OIT of real cable samples taken from NPP with dependencies on how the OIT values change with the elongation at break, makes possible to establish the extent of cable degradation. This method can be considered as a suitable and effective technique for lifetime assessment not only of cable insulations but also of many other plastics.
Oxidation induction time and oxidation onset temperature of polyethylene in air
Testing Gimzewski’s postulate
Abstract
Oxidation induction times (OIT) and oxidation onset temperatures (OOT) of a low density polyethylene melt were evaluated in air using DSC. Good regression fits to OOT data were obtained using global values for the activation energy (E) that are specific for each antioxidant but assumed independent of concentration. Gimzewski’s postulate that OIT and OOT correspond to the same level of antioxidant depletion was tested by attempting to predict OIT values from OOT generated model parameters. The deviations between predicted and experimental OIT values were comparable in magnitude to the inherent scatter in the data. However, regression of the dynamic OOT data yielded statistically significant lower values for the activation energy than are obtained by direct regression of isothermal data.
Abstract
Oxidation thermal parameters on samples of polypropylene (PP) stabilized with hydroxytyrosol were determined. For comparison purposes, α-tocopherol and a synthetic phenolic commercial antioxidant (Irganox 1076), were also analyzed. Oxidation induction time (OIt) and oxidation induction temperature (OIT) were determined by differential scanning calorimetry (DSC). The addition of hydroxytyrosol 0.1 mass% to PP was enough to obtain efficient stabilization during processing. Certain decrease in stabilizing properties of natural antioxidants was observed for compression moulded materials at high temperatures. However, these samples were still efficiently stabilized in comparison to the pure material. Hydroxytyrosol showed good performance as polypropylene antioxidant and it might be considered as promising alternative to the use of phenolic synthetic compounds.
Abstract
A characteristic index for the oxidation stability this is the oxidation induction time (OIT) which is defined by the time between the start of oxygen exposure and the onset of oxidation. Pressure DSC is required to increase oxygen concentration in order to achieve faster reactions at lower temperatures. OIT measurements of reference engine oils have been used to study the influence of oxygen pressure in the range from 0.1 to 10 MPa. A power law relationship was derived to describe this correlation between OIT and oxygen pressure. From this a quantitation factor is proposed to represent the influence of stabilizer. The exponent describes the sensitivity of the oxidation reaction of the oil towards the oxygen pressure and the term 'inherent stability' is proposed for that.. This relationship characterizes in more details the oxidation behavior. Extrapolation to higher pressures indicates, that the stabilization effects of additives can be overcome by the inherent stability. This signifies, that the ranking of the oils can be affected by the oxygen pressure.
Summary The CEC L-85-T-99 pressure differential calorimetry (PDSC) test was developed in Europe for ACEA E5 specification for heavy duty diesel oils. This test differentiate between base oils, additives, indicates synergies between antioxidants and correlates with other oxidation tests. Occasionally, the PDSC test can have difficulties to provide a true value for the OIT, which can vary between samplings. This work gives evidence of such case and concludes that variability in results is caused by variability in the oil rather than in the test itself. It appeared possible that certain oils might not be fully homogenous and this could produce a problem for representative PDSC sampling.
