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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3. Results and discussion In Fig. 1 the single-point measurement MFR and the zero viscosity of the rheological analyses as a function of the recyclate content is shown in a semilogarithmic diagram. Materials used in pipe extrusion, such as PP-v, generally have a low MFR and high viscosity at low shear rates. With increasing recyclate content, the MFR increases linearly up to the value of the pure PP-r. Rotational measurements confirm this as it can be seen in Fig. 1 (b), the zero viscosity of the PP-v is higher compared to the PP-r and decreases linearly.

a

b

Fig. 1: (a) MFR at a temperature of 230 °C and 2.16 kg load and (b) zero viscosity at 230 °C and a shear rate of 0.003 s -1 of both material series as a function of the recyclate content.

Determining the crossover point by oscillatory measurements shows the relative changes of the molecular weight distribution and average molecular weight due to the additional PP-r. As it is illustrated in Fig. 2 (a), the increasing amount PP-r shifts the crossover point vertically to a higher angular frequency indicating a decrease of the average molecular weight. Moreover, the horizontal shift of the crossover point implies the changes of the molecular weight distribution which, however, is negligible for the investigated materials (Fig. 2 (b)). It can be concluded, that the pure PP-r have a lower molecular weight and shorter chains compared to PP-v, by blending recyclate to virgin materials the molecular weight decreases. In contrast to PP-r1, PP-r2 has a higher molecular weight and longer chains.

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b

Fig. 2. Oscillatory plate-plate rheometer measurements at a temperature of 230 °C (a) angular frequency at crossover point and (b) crossover point as a function of the recyclate content of both material series.