Influence of Recyclates on Mechanical Properties and Lifetime Performance of Polypropylene Materials

Abstract

In Europe, the amount of plastic waste which was recycled and further processed into new products was only about 13 % in 2020. One option to process higher volumes of post-consumer recyclates into new products is blending with virgin materials. In order to investigate the effect of recyclates on rheological and structural material properties, a post-consumer polypropylene recyclate (PP-r) was added to a virgin polypropylene (PP-v) in different contents of 10 %, 25 % and 50 %, respectively. Mechanical and fracture mechanical properties were analysed and compared with initial conditions of the original virgin and recycled materials. In addition, the influence of two different recyclates (PP-r) was examined by using grades of a high (PP-r1) and low (PP-r2) melt flow rate (MRF). Results demonstrate that the blending of virgin material with recyclates had a clear influence on material properties. The MFR values increased with higher recyclate content. Tensile tests showed a reduction of the Young's modulus and the yield strength with increasing recycling content. While tensile test properties were significantly affected by a recycling content over 10 %, notched Charpy Impact strength started to change above 25 % and 50 % of PP-r1 and PP-r2, respectively. The resistance against slow crack growth (SCG) of the materials was analysed by the crack round bar (CRB) test. Results indicate that a small recyclate amount of 10 % does not significantly reduce the SCG resistance of the blend compared to the virgin material. However, the SCG resistance decreases dramatically with higher recyclate content.