Plastic Pipes Conference Association # 2023 Lake Buena Vista
Mario Messiha, Jessica Hinczica, Márton Bredàcs, Alwin Huisjes, Florian Arbeiter, Gerald Pinter
BSTRACT Engineering structures, such as operating plastic pipes, are often submitted to unexpected influences that may shorten their lifetime. An increasing understanding about the processes that govern these sudden failures has been attained in the last decades. This has led to a remarkable improvement of pipe performances by enhancing the material’s slow crack growth (SCG) resistance (e.g. from PE63 to PE100RC). Still a great deal of uncertainty is associated with the use of non-virgin grades. This is mainly, because of the unknown effects of impurities that are found in recycled materials. The effects on lifetime relevant properties with regard to contaminants can be divided into three categories:
- polymeric contaminants of a different kind (e.g. PE in PP)
- polymeric contaminants of the same kind (e.g. PE-LD in PE-HD, PP-R in PP-H)
- non-polymeric contaminants (e.g. inorganic particles)
In that context, effects of non-polymeric impurities were studied in this work by mixing virgin polypropylene (v-PP) grades with actual polypropylene recyclates (r-PP) into different compositions (v-PP/r-PP in %: 100/0, 90/10, 75/25, 50/50 and 0/100). Subsequently, these materials were tested via internal pressure pipe tests. A profound dependency of contamination content on final failure time (tf) could be demonstrated, thereby. Additionally, a deeper analysis of fractured pipe samples revealed a clear correlation between the maximum size of incorporated inorganic impurities and tf. This indicates, that two seemingly identical pipe samples, with regard to content of recycled material, can still have vastly different resulting failure times, based on the size of the introduced critical contaminant. Results show, that it is not only necessary to understand the influence of the content and distribution of recyclates on the resulting lifetime of pipes, but more importantly the maximum introduced defect size as well. Consequentially, pipe manufacturers should choose recycled grades carefully, and only after knowing about the feedstock of origin, treatment- and mechanical sorting history.
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