Effect of thermal-oxidative aging on mechanical, chemical, and thermal properties of recycled polyamide 66

Abstract

This article addresses the effect of thermal aging on unreinforced and glassreinforced recycled polyamide 66. As an accelerated test, injection-molded test bars were aged at 110, 140, and 170ЊC for up to 4000 h in air to simulate service life. FTIR spectroscopy demonstrated that the oxidative degradation primarily occurred between the surface and a depth of 0.5 mm. Furthermore, the degradation in the surface region was more pronounced with recycled as well as unstabilized materials. Reprocessing resulted in a faster increase of carbonyl groups, a decrease in melting peak temperature, and elongation at break during subsequent aging. Because of process-induced fiber shortening, however, the elongation at break of recycled reinforced samples was always at least as high as that of virgin samples for up to 4000 h of aging at 140ЊC. The decrease in melting peak temperature as determined by differential scanning calorimetry (DSC) indicated that the surface or boundary regions of the crystallites in the material are affected by aging. The loss in elongation at break for the reinforced material was shown to correlate with the reduction in melting peak temperature of material taken from the surface region of aged samples. The contribution of the degraded surface region to the properties was studied by removal of surface layers prior to testing. The degradation in the surface region was the sole cause, even of glass fiber-reinforced polyamide, for the embrittlement of aged samples. Furthermore, aging-induced changes in tensile strength and modulus were independent of the removal of the surface region, indicating that these properties are controlled by changes occurring in the bulk of the material.

Influence of Endurance tests on Space Charge Distribution of 160kV HVDC XLPE Cable

“…During the thermal endurance test, post-crosslinking might occurr simultaneously with the degradation of the XLPE, and the post-crosslinking could optimize the crystalline morphologies of the insulation, which would reduce the accumulation of the space charge. Similar results were also obtained in [11,[18][19][20]. However, it is important to point out that the thermal degradation will dominate the process when the thermal endurance time is longer or the temperature is higher.…”

Influence of accelerated aging on clay-reinforced polyamide 6

“…It seems, thus, that up to 21 days post-crystallization dominated, owing mainly to the oxidation-provoked chain scission which rendered the amorphous, previously entangled, molecules capable to crystallize [23,46]. Nevertheless, as the residence time increased further, the crystalline content steadily decreased, indicating that thermo-oxidative degradation damagingly affects the crystallite regions [33,47]. Raising the temperature of oven aging to 150 C was accompanied by more marked changes in the materials crystallinity.…”

“…The service life of a polymer in a specific environment is usually reflected by the time required for a 50% reduction in the value of an important property, such as elongation at break [47]. Turning on Fig.…”

Physicochemical origin of space charge dynamics for aged XLPE cable insulation

“…One computer was connected to the spectrometer in order to receive and analyze data. The peak near 1720 cm -1 corresponds to the absorption of a series of carbonyl group derivates, which can be used as symbol of material ageing [1,10,[25][26][27]. Meanwhile, the spectra near 2010 cm -1 is almost invariant during the cable ageing process.…”