Systematic methodologies to surveil and evaluate the early imperceptible thermal degradation of EPDM composite

Abstract

Without knowledge and resultful surveillance of the early degradation of polymers, it is challenging to realize the high reliability of high-end equipment and the screening and grading of waste plastics. Their reliability evaluation and lifetime prediction are also unfulfillable for a lack of sensitive characterization techniques. This work, taking commercial ethylene propylene diene monomer (EPDM) composite as an example, explores a variety of multi-scale evaluation methods to identify its early thermal aging behaviors and molecular mechanisms, including various spectroscopic technology, swelling-equilibrium tests, scanning electron microscope (SEM), thermal analysis, contact angle tests and mechanical properties. Only some methods can give the perceptible indicators of the slight thermal degraded EPDM, namely fluorescent probe technology, infrared spectroscopy for gas mixtures, swelling-equilibrium tests and specific mechanical properties. Other methods are inferior in early aging identification. Both fluorescent probe technology and infrared spectroscopy for gas mixtures can recognize the thermal degradation induced products within 5 h at a temperature lower than 120 °C, while elongation at break can reflect the damage of EPDM within 5 h at 60 °C. Based on the time-temperature superposition principle, the master curve of the thermal aged EPDM is constructed using the data of elongation at break, which predicts that 50% retention of elongation at break occurs after 10.5 years at 30 °C. We further propose a new aging evaluation methodology to reflect the aging degree comprehensively, which is based on the standardized sequence numbers obtained from the above sensitive characterization methods.