Effect of the Work Expended on Mixing and Extrusion on the Properties of Thermoplastic Elastomer Compounds

The effect of the processing parameters of thermoplastic elastomer compounds on their properties is studied. The compounds consist of ethylene-propylene rubber and high- or low-density polyethylene (HDPE or LDPE) mixed with extenders in equal amounts. The variations in the degree of crystallinity under different mixing modes are examined by means of differential scanning calorimetry. The variations in the molecular weight distribution (MWD) of polymeric constituents of the compounds are estimated based on the results of rheological tests. An increase in the mixing and extrusion rates affects, up to certain limits, the mechanical properties positively. The optimum preparation modes for HDPE- and LDPE-based compounds are different. A noticeable mechanical destruction of HDPE-based compounds, estimated from the MWD parameters, occurs when the work of mixing exceeds 3.4 kJ/g and is accompanied by cross-linking. Up to 7.1 kJ/g, the work of mixing improves the properties of LDPE-based compounds. The extrusion effects do not smooth out the mixing effects — both these effects add up.