Effects of IRM 902 aging on the mechanical thermal and chemical properties of injection molded and extruded thermoplastics.

Abstract

This study investigates the aging behavior of injection- and extrusion-processed polypropylene impact copolymer (PP), polyethylene of raised temperature (PERT), and an impact-modified polyphenylene sulfide (PPS) grade formulated for pipe fabrication. Specimens were immersed in IRM 902 reference oil at both room temperature (RT) and 95 °C. Mass uptake measurements, tensile testing, in situ punch-shear testing, differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FTIR) evaluated fluid absorption, mechanical-property retention, and thermal/chemical changes. At RT, mass uptake remained below 1%, and mechanical-property retention ranged from 89 to 113%. At 95 °C, PP showed the greatest mass uptake, reaching approximately 39% for injection-molded tensile specimens, and the largest tensile-property reduction, with modulus retention decreasing to approximately 34-36%. PERT showed intermediate behavior, while PPS showed negligible mass uptake and stable or improved mechanical-property retention. Baseline punch-shear yield strength correlated strongly with tensile yield strength ([Formula: see text]), supporting its use as a complementary indicator. However, aged tensile and punch-shear retentions were not directly comparable because tensile tests were performed ex situ, whereas 95 °C punch-shear tests were conducted in situ. DSC showed pronounced changes in PP and fabrication-route-dependent responses in PERT. The principal PPS melting transition remained stable, but cold crystallization disappeared after aging in injection-molded PPS. Its blend crystallinity increased from 17.6 to 28.7%, whereas that of extruded PPS decreased from 31.3 to 25.1%. FTIR showed no major new absorption bands after aging. Among the investigated materials, PPS exhibited the highest resistance to IRM 902 aging, followed by PERT and PP.

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