Rheological and thermorheological assessment of polyethylene in multiple extrusion process

The relationship between rheological properties and structural changes in polyethylene chains due to the recycling of two linear low-density polyethylenes (LL-A and LL-B) has been investigated. These samples were subjected to multiple extrusion processes (9 extrusion steps). According to the results of gel content experiments, crosslinking did not occur. The results of the gel permeation chromatography indicated that the chain scission was slightly predominant during the re-extrusion, while the rheometry results clearly show the effects of long chain branching during degradation. Therefore, the degradation proceeded through both paths. Based on the rheological results and the Cole-Cole method, LL-B exhibited a higher degradation rate during the extrusion process (because of the low antioxidant content), compared to LL-A. The results of thermorheological methods including van-Gurp-Palmen and activation energy spectra indicated that the extent of thermorheological complexity was intensified with increasing the number of extrusion cycles and consequently increasing the number of long-chain branches.