Influence of the Stabilization System on the Rheological Behaviour of Plasticized PVC for Cables’ Insulation

The paper is devoted to the rheological study of plasticized PVC - based compositions for cables’ insulation, stabilized with three different systems (Ba laurate/Cd laurate, Sn dibutyl mercaptide, Pb bibasic stearate/Pb bibasic fosfite) in variable ratios. Starting from some measured parameters, several rheological properties - characteristic for the viscous and, respectively, elastic component of flowing - have been calculated (counter pressure, worm gear’s rotation moment, shear stress at the wall, apparent viscosity, standard viscosity and the viscosity index, output pressure from the rheological nozzle, swelling, relaxation time, first function of the normal unitary stresses, index of elasticity). The observation to be made is that the system of thermal stabilization influences strongly the rheological behaviour by both its nature and amount, which requires a careful consideration of the effects, when products of different types are to be designed. The best thermal stabilization is assured by the Pb bibasic stearate/Pb bibasic fosfite - based system. The obtained recipes have been subsequently characterized from the viewpoint of their thermal stability and, equally, of some of their electrical properties. It was observed that the system of thermal stabilization strongly influences the thermal stability as well as the electrical properties of the plasticized PVC recipes. The highest values of thermal stability, which correlated with corresponding electrical properties, have been attained for the Pb- based system. When different stabilization systems are employed, the transparent, translucent or opaque insulations may be obtained.