Analysis of thermomechanical reprocessing effects on polypropylene/ethylene octene copolymer blends

The impact of recycling by grinding and re-extrusion on the physical and mechanical properties of polypropylene (PP)/ethylene octene copolymer (EOC) blends was investigated. The considered EOC content was 0 wt. %, 10 wt. % and 20 wt. %, and the investigated number of recycling passes (extrusions) was 0, 1, 3 and 6. Up to 6 re-extrusions, an increase of the melt flow index (MFI), a slight increase of the crystallinity, a slight decrease of the decomposition temperature (Tonset), and no significant oxidation were noted. Therefore, the recycling of the blends induces thermomechanical degradation by chain scission without oxidation. Increasing the content of EOC increases the MFI and the Tonset of the PP blends. The first recycling procedure induced an increase of the Young's modulus and tensile yield stress, while for higher recycling numbers, these two parameters dropped. The EOC inclusions stabilized the tensile elongation at break up to 3 recycling procedures due to a decrease of their size and a homogenization of their shape, while that of neat PP continuously decreased with recycling numbers.