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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Inhomogeneities in the recyclate (organic and inorganic impurities) lead to a change in the rheological properties and cause cracking. While PP-v has no inorganic components at all, for both PP-r inorganic components were detected with a content of almost 6 % for PP-r1 and about 2 % for PP-r2. For the different blend series, as expected a linear correlation of the inhomogeneity content was measured as demonstrated in Fig. 3. Higher amount of inorganic impurities leads in a higher MFR, which indicates that the length of the molecular chains is shorter, and consequently the viscosity of the material is lower.

Fig. 3: Residual mass at 700 °C under nitrogen atmosphere and a heating rate of 10 K/min from 35 °C to 800 °C of the two material series as a function of the recyclate content.

To compare the different mechanical parameters of the tensile tests, all results were normalized with respect to PP-v (100 %). By adding a small amount of 10 % PP-r1 or PP-r2, the Young’s modulus already decreases by 10 % (Fig. 4). With increasing recyclate amount, a further linear decrease of the Young’s modulus was measured until the values of the pure PP-r with about 75 % for PP-r1 and 62 % for PP-r2 (compared to PP-v). The yield stress decreases linear, compared to the Young’s modulus the percentage decrease over the recyclate content of the yield stress is lower. Recyclates are more affecting the Young’s modulus than the yield stress of the material.

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Fig. 4. (a) Young’s modulus and (b) yield stress related to PP-v (100 %) as a function of the recyclate content for material series 1 and 2.

For Charpy measurements, even with the higher nominal working capacity of 15 J, no fracture could be generated for the unnotched specimen except for PP-r1. Therefore, only the measurements from the notched specimens were evaluated and again normalized with respect to PP-v (100 %). All tested materials failed in a brittle manner. Although both pure recyclates have quite similar notched impact toughness values of 22 % for PP-r1 and 28 % for PP-r2 compared to PP-v (see Fig. 5), the two blends series show quite different trends along their blending ratios. For