Fatigue crack growth resistance under superimposed mechanical-environmental loads of virgin and recycled polystyrene using cracked round bar specimens

• Method development and consolidation for FCG resistance under superimposed mechanical-environmental loads testing of CRB specimen. • Improvement of the FCG resistance under superimposed mechanical-environmental loads for all materials in ethanol environment. • Enhancement of the FCG resistance under superimposed mechanical-environmental loads through super-cleaned recycling process • Fracture surface investigation of brittle, quasi-brittle and ductile failed fracture zones. The service life of polymers is significantly influenced by the load conditions and environmental factors. Prolonged contact with harsh environments increases the tendency to crazing and leads to a shortened service life. In this study, the fatigue crack growth (FCG) resistance under superimposed mechanical-environmental loads of polystyrene (PS) under different environments such as air and food simulants (ethanol, acetic acid, and water) is investigated by cyclic testing. Both virgin and recycled PS (from yogurt cups) were tested to evaluate the effects of food simulants. In addition, the effects of key specimen preparation steps and test settings were analyzed. This included a test frequency dependency analysis, an investigation of the influence of different blades to create the initial notch, and an immersion time test in the different food simulants to investigate the saturation of the specimens. The research highlights the influence of food simulants on the polymeric materials and the impact of a super-cleaning recycling process of polystyrene for food packaging. Cyclic tests in ethanol environment showed an improvement of the FCG resistance for all materials, likely due to the plasticizing effect of ethanol. The super-cleaning recycling process enhanced the FCG resistance in air and ethanol environment, except for the polystyrene post-consumer recyclate in air, where super-cleaning reduced the FCG resistance at lower maximum loads.