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

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 ( $$\:{R}^{2}=0.991$$ ), 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. Compared IRM 902 aging responses of injection-molded and extruded PP, PERT, and impact-modified PPS at room temperature and 95 °C. Combined mass uptake, tensile, punch-shear, DSC, and FTIR measurements to assess fluid uptake and associated mechanical, thermal, and spectroscopic responses. At 95 °C, injection-molded PP showed the greatest mass uptake and tensile-property loss, whereas PPS showed negligible uptake and stable or improved mechanical properties. Baseline punch-shear and tensile yield strengths showed a strong empirical correlation within the tested baseline dataset, supporting punch-shear testing as a complementary measurement.