Environmental stress cracking resistance of HDPE and PP packaging: evaluation of failure time in real-world studies versus accelerated studies

Abstract

Environmental stress cracking (ESC) is a phenomenon that affects the quality of rigid plastic packaging when exposed to stressful situations in the presence of aggressive agents, resulting in cracks and fractures (failures). High-density polyethylene (HDPE) and polypropylene (PP) are the most widely used polymers in rigid plastic packaging for packing a wide variety of chemically active products and formulations that can affect their mechanical performance, resulting in the loss of the packaged product and environmental damage due to the potential contamination of terrestrial and aquatic environments. To predict the resistance of these packaging materials, accelerated ESC resistance tests are performed using elevated temperatures compared to ambient temperature. However, these tests do not provide a correlation between the observed results and the actual lifespan of the packaging materials. Considering that plastic materials are sensitive to temperature variations, the objective of this study was to evaluate the possibility of establishing a correlation between the outcomes of the accelerated tests and the actual durability of the plastic material, including using calculations via a specific methodology for accelerated studies. The evaluation period was 365 days, and from the findings of this study, it was possible to conclude that the correlations between the test results and temperatures are specific to each package, since they depend on its physical and manufacturing characteristics, and cannot be used generically. Thus, the international methodologies used for accelerated testing should only be employed to assess the susceptibility of plastic packaging to rupture and its resistance to the stress and stacking conditions to which they will be subjected.