Prediction of processing parameters of secondary polyethylene with iron carboxylates in the preparation of prooxidants' additives

The rheological behavior of additives - pro-oxidants, representing a polymer matrix including iron carboxylates is considered in the article. The additives of prooxidants based on: high-pressure polyethylene (PVD) of PVD 158030-020, secondary linear high-pressure polyethylene (LDPE) and secondary PVD with an iron carboxylate content of 5.0% (by weight) were used as the objects of the research. The study was carried out on a high-power capillary rheometer called Smart RHEO 1000 by the firm Ceast at a temperature of 130 to 190 °C using two capillaries with a diameter d = 1 mm and a length l = 5 and l = 30 mm, respectively, in the shear rate range from 100 to 300 s-1 with a step of 50 s-1. The study showed that for all investigated pro-oxidant additives, a linear dependence of the flow curves in double logarithmic coordinates is observed in the full velocity and temperature ranges. With increasing temperature, the dependence of the effective viscosity on the shear rate decreases synchronously, that is, in the double logarithmic coordinates, the flow curves are completely invariant with respect to the construction and the geometric parameters of the capillary irrespective of the form of the polymer matrix. The unstable flow regime was noted for the additives of prooxidants based on primary thermoplastics and occurred at a shear rate exceeding 250 s-1 and a temperature below 150 °C. For a longer capillary, the viscosity and shear stress efficiency indicators were reduced, the identity with the behavior of the primary thermoplastic was manifested, consistent with theoretical representations of the behavior of the macrochain under conditions of their formation on a longer forming tool.