Abstract This article describes the general aspects of creep, stress relaxation, and yielding for homogeneous polymers. It then presents creep failure mechanisms in polymers. The article discusses extrapolative methods for the prediction of long-term creep failure in polymer materials. Then, the widely used models to simulate the service life of polymers are highlighted. These include the Burgers power-law model, the Findley power-law model, the time-temperature superposition (or equivalence) principle (TTSP), and the time-stress superposition principle (TSSP). The Larson-Miller parametric method, one of the most common to describe the material deformation and rupture time, is also discussed.
The present study provides a fundamental understanding of the mechanism of action of special new phosphate glass (P-glass) systems, having different glass transition temperatures (Tg), in polyamide 66 (PA66). Dynamic mechanical analysis (DMA) revealed that the Tg of PA66/low Tg P-glass (ILT-1) was significantly shifted to a lower Tg (65 °C), and another transition appeared at high temperature (166 °C). This was supported by a drop in the melting point and the crystallinity of the PA66/ILT-1 hybrid material as detected by differential scanning calorimetry (DSC). The dielectric spectroscopic investigation on the networks' molecular level structural variations (Tg and sub-Tg relaxations) agreed very well with the DMA and DSC findings. Contrary to intermediate Tg(IIT-3) and high Tg P-glass (IHT-1) based materials, the PA66/ILT-1 hybrid material showed an evidence of splitting the PA66 Tg relaxations into two peaks, thus confirming a strong interaction between PA66 and ILT-1 (low Tg P-glass). Nevertheless, the three different P-glass compositions did not show any effect on the PA66 sub-Tg relaxations (related to the -NH2 and -OH chain end groups' motion).
The work reported here is the first study aimed at providing a full screening of a real unsortable non-recycled post-consumer WEEE stream free of brominated flame retarded plastics, separated using on-line X-ray detection, toward its recycling. In the existing sorting lines, up to 40% of plastics from waste electrical and electronic equipment (WEEE) stream can be rejected, herein named unsortable plastics. To have the most representative homogeneous sample for physico-chemical characterizations, a sampling method was developed to overcome the heterogeneity of the investigated 500 kg batch. The batch screening on both representative samples (∼500 μm size) and 100 plastic fractions (∼20 mm size), by means of routine techniques used in the plastic industry, has allowed to quantify reliably the main polymers included in the studied batch; ∼50% styrene-based polymers, ∼15% polypropylene (PP), ∼15% polycarbonate (PC), ∼1–4% polyamide (PA), polyethylene (PE), polyvinyl chloride (PVC), poly (ethylene terephthalate) (PET), poly (methyl methacrylate) (PMMA) and ∼8% of multi-layer plastics, paints and thermosets. The identification of the ∼8.0% inorganic phase by X-ray fluorescence spectrometry revealed the presence of several additives/charges commonly incorporated in plastic materials, such as calcium carbonate and talc. The studied batch was then subjected to electron beam irradiation at 50 and 200 kGy doses, as a means of compatibilization between the batch components. The mechanical properties and thermal behavior of irradiated samples pointed out the crucial role of the residual free radical scavenger agents present in post-consumer WEEE streams, leading to significantly different properties compared to those of irradiated virgin polymer blends highlighted in the literature.
