PSI - Issue 42

Jessica Hinczica et al. / Procedia Structural Integrity 42 (2022) 139–146 Hinczica et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Notched impact toughness (Fig. 5) and the SCG resistance (Fig. 6) following a similar trend for material series 1 and 2. A higher decrease of the SCG resistance of material series 2 only occurs with an addition of 50 % PP-r2. Whereas for material series 1 the SCG resistance already decreases at 25 % PP-r1. Comparing only the pure recyclates, a lower molecular weight as well as the higher presence of inorganic impurities results to a significant lower SCG resistance. Compared to Charpy Impact tests is the CRB test a slower test method, this test duration and the previous results show that the CRB test is a more sensible test method to analyse the influence of recyclates. After testing, all CRB specimens were analysed with SEM in order to investigate changes in the fracture surface appearance. The images were taken on areas of similar loading conditions with respect to the stress intensity factor. The top line of Fig. 7 images a representative fracture surface of a failed CRB specimen for the material series 1 and the bottom line for material series 2. All fracture surfaces of the specimens show brittle failure, which is essential for the comparability of the results. It is visible that the size of fibrils decreases with higher amount of PP-r. This might be an effect of changes in the average molecular weight as well as of the increasing amount of inorganic impurities in PP-r1 and PP-r2. Due to the higher molecular weight of PP-r2, compared to PP-r1, the fibrillation of the pure material is stronger.

PP-v1r1-7525

PP-v1r1-9010

PP-v1r1-5050

PP-r1

PP-v1

Increasing recyclate content

PP-v1r2-7525

PP-v1r2-9010

PP-v1r2-5050

PP-r2

PP-v1

Fig. 7. Fracture surface analysis via scanning electron microscope after CRB test for material series 1 (top line) and material series 2 (bottom line) at a magnification of 2000 x. 4. Conclusion The aim of the presented study was to evaluate different testing methods to analyse the influence of recyclates on virgin materials. For this purpose, rheological measurements (MFR and Plate-Plate rheometry), thermo-gravimetric analysis, mechanical measurements (tensile tests and notched Charpy Impact tests) and a fracture mechanical test (CRB test) were performed. Many phenomena influence the properties of recyclates and blends. In this case, the focus is on the influence of molecular weight and inorganic impurities on the analysed methods. Rheological measurements of both material series showed similar trends, PP-r has a lower molecular weight compared to PP-v. Despite the different properties of pure recyclates, a linear correlation of the viscosity was observed for both material series. Also, the results of the tensile tests show a linear behavior between the Young’s modulus/yield stress and the recyclate content. In comparison, notched Charpy Impact tests and CRB tests showed different trends, depending on the rheological properties and the inorganic impurities of the pure recyclate. Inorganic impurities as well as lower molecular weight lead to a significant lower SCG resistance. These influences are also visible on the SEM images. Due to the higher amount of impurities the fibrillation is weaker. The higher the molecular weight, detected for PP-v and PP-r2, the stronger the fibrillation. With these two analysed influences the trends of the different measurements, especially the notched impact toughness and the SCG resistance, can be explained.