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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Table 1: Blend ratios of the analysed blends.

material series

blending ratios in wt%

1 2

PP-v1/r1 PP-v1/r2

100/0 90/10 75/25 50/50 0/100 100/0 90/10 75/25 50/50 0/100

2.2. Rheological measurements Rheological properties were characterized by MFR, oscillatory and rotatory plate-plate rheometer. For the MFR measurements, according to ISO 1133, a melt index tester MF20 (CEAST, Torino, Italy) was used with a weight of 2.16 kg and a temperature of 230 °C. Of each material and blend, round discs with a thickness of 1.2 mm and a diameter of 25 mm were produced and then measured on a MCR 302 (Anton Paar GmbH, Graz, Austria) plate-plate rheometer at a temperature of 230 °C under continuous nitrogen purge. The zero viscosity was determined at a shear rate of 0.003 s -1 . For analysing the changes of the crossover point, the angular frequency (x-axis) as well as the crossover point (intersection of storage and loss modulus, y-axis) of the oscillatory measurements was evaluated for the materials and blends. 2.3. Thermal analyses For the determination of the mass change as a function of time and temperature and the mass of inorganic inhomogeneities in the recyclates, a thermo gravimetric analysis (TGA) was performed. The measurements were conducted on a TGA 800 (PerkinElmer, Waltham, USA) under nitrogen atmosphere from 35 °C to 850 °C with a heating rate of 10 K/min. The percentage of inorganic inhomogeneities was analysed by determining the residual mass at 700 °C. 2.4. Mechanical measurements Mechanical tests were carried out on injection moulded multi-purpose specimens (ISO 3167), according to ISO 527 for the tensile tests and ISO 179-2 for Charpy Impact tests. A Zwick Z010 (ZwickRoell GmbH & Co. KG, Ulm, Germany) with a 10 kN load cell and additional extensometers were used for the tensile tests. To determine the impact toughness as well as the notched impact toughness, unnotched and v-notched specimens were analysed on a Zwick HIT25P (ZwickRoell GmbH & Co. KG, Ulm, Germany) instrumented impact pendulum with a nominal working capacity of 15 J for the unnotched specimens and 2 J for the notched specimens. All mechanical measurements were conducted at ambient temperature of 23 °C. 2.5. Cracked Round Bar Test Following ISO 18489, the test specimens for the CRB test were manufactured from a compression moulded sheet and then a 1.5 mm deep sharp razor notch was introduced. Tests were all performed on a servo-hydraulic closed loop test system, MTS Table Top (MTS Systems GmbH, Germany) at a frequency of 5 Hz, a force ratio of R = 0.1, an ambient temperature of 23 °C. Applied loading stresses   were adapted to each material and blending ratio, the test duration was kept between 5 h and a maximum of one week per test specimen. Pure recyclates (PP-r) were measured between   = 7 MPa and 14 MPa and the pure virgin material (PP-v) between   = 18 MPa to 20 MPa, which correspond to a stress intensity factor  K I of 0.36 MPam 0.5 and 0.74 MPam 0.5 for PP-r and 0.95 to 1.06 MPam 0.5 for PP-v. At least five different loading stresses were performed for each grade. All fracture surfaces were examined by a Tescan Vega II Scanning Electron Microscope (SEM) (Tescan Brno, Brno, Czech Republic) to ensure brittle crack growth (Frank et al. 2012).