Polymer Competence Center Leoben (Austria)
Since several years, the European plastic pipe industry is supporting activities which reduce the carbon footprint of plastic pipes. In compliance with existing standards, by 2017 already more than 240,000 tons of recycled polyolefins and more than 110,000 tons of recycled PVC was manufactured into non-pressure pipe applications.
To fulfill desired lifetimes of non-pressure pipes of 100 years or even more, the long-term resistance of the materials against crack initiation and slow crack growth (SCG) is an essential material parameter. Especially in the context of recycled plastics, special attention must be paid to a careful assessment of the fracture mechanical long-term failure resistance. While for PE and PP several representative studies about the effect of recyclates on the crack resistance in recyclates is available, nearly no scientific studies have been reported for recycled PVC. Therefore, the current paper is focusing on the effect of repeated reprocessing on the SCG resistance of PVC.
For a quick characterization of the SCG resistance, the Cyclic Cracked Round Bar (CRB) test has been developed for PE pressure pipe grades. For the current study an initial focus was put on the applicability and sensitivity of the CRB test on PVC in general as well as on the investigation of changes in the SCG resistance after repeated reprocessing of the material. Therefore PVC-U pipe compounds with three different K values were manufactured and characterized. The generated results demonstrate the influence of the K value on the SCG resistance of the material. Furthermore, these compounds were repeatedly shredded and remanufactured up to ten times and tested after every second reprocessing step. The SCG failure curves show that even after ten reprocessing steps the SCG resistance was not influenced significantly, confirming a high insensitivity of repeated processing of PVC-U on the crack resistance.