Long-term heat aging

Long-term heat-aging tests on Tefzel 280 are in progress. It is expected that its continuous-use temperature will be above 150°C. 

For long-term heat ageing, property retention depends on the property and grades considered, notably the heat stabilizers used. For a heat-sensitive characteristic such as elongation at break, the values for a given polyethylene after ageing at 120°C are roughly ... 

For long-term heat ageing, property retention depends on the property and grades considered, notably the heat stabilizers used. 

For peroxide cross-linking, organic peroxides, such as dicumyl, di-t-butyl, and benzoyl peroxides, are used in amounts 1 to 3 phr (parts per hundred parts of rubber). Typical cure cycles are 5 to 10 min at temperatures 115 to 170°C (239 to 338°F), depending on the type of peroxide used. Each peroxide has a specific use. A postcure is recommended to complete the cross-linking reaction and to remove the residues from the decomposition of peroxide. This improves the long-term heat aging properties.62... 

Impurities in natural sources can result in poor color, lower retention of physical properties on long-term heat aging, and reduction in electrical properties with the presence of electrolytes. Therefore, fine precipitated ATH and magnesium hydroxide are favored as particle size can be controlled to a nominal 1 pm size with low surface area and they contain very low impurity levels. Magnesium hydroxide production processes, by manufacturer, have considerably more variation than ATH but both metal hydrates are considered products by process, which in many cases results in the need to qualify alternate sources or in some cases to reformulate around filler selection. 

Table I also compares the heat stabilities of 60- and 120-mil plaques at 140 °C. The relative order of stabilities has changed slightly. The stability of Resin A in the thicker sections has equalled or surpassed the stability of the long term heat aging Resin B. Resins E, C, and H have improved their position, displacing I, the most stable resin in the 25-mil sheets, which is now third best in the 60-mil plaques and only fourth best in the 120-mil plaques.

Hindered phenols are used preferentially for processing and long-term heat aging of PO where their very low-discoloring properties are advantageous (Pospisil, 1998 Zweifel, 1998 Pospisil, 1993). Phenolic antioxidants are effective also for thermal stabilization of styrene-based polymers. Low amounts are used in PET and aliphatic PA. Common concentrations in plastics range between 0.025 and 0.3 %. 

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