Investigations on the influence of multiple extrusion on the degradation of polyolefins

•Investigations of polyolefin degradation induced by thermo-mechanical stress.•Analysis of changes in molecular weights and stabilizer concentrations via HT-GPC-IR and HPLC-QTOF-MS.•Determination of molecules with odd-numbered alkane species related to HDPE via TD-GC-MS.•Determination of oxidized branched alkane species via HPLC-QTOF-MS. The importance of mechanical recycling of polymers has increased within the last decades, especially due to numerous regulations of governments all over the world. Hereby recycling quotas are enforced to pave the way towards a closed loop recycling. During its lifetime, polymers are exposed to multiple environmental factors, which can already induce degradation. However, a major factor that needs to be taken into account is the increased thermo-mechanical stress during the recycling process, which may have significant impact on the quality of recyclates as well. In the present work, polyolefins (high-density polyethylene and polypropylene) were artificially exposed to stress by continuous extrusion at varying speeds and absence or presence of stabilizers to analyze the extent to which the recycling contributes to degradation processes. These samples were analyzed for low-molecular-weight stress markers by thermodesorption gas chromatography and by high-performance liquid chromatography (both coupled to mass spectrometric detection). Depending on the extent of stress, the occurrence of odd-numbered linear alkane chains was revealed in polyethylene samples, and of oxidized branched alkanes in polypropylene samples. Correlations with molecular weight (determined by high temperature gel permeation chromatography) and with decreasing concentrations of stabilizers could be demonstrated. [Display omitted]