Pulverization of rubber granulates using the solid-state shear extrusion (SSSE) process:: Part I. Process concepts and characteristics

A single screw extruder was used to pulverize rubber granulates at high shear and compression without using cryogenic fluid for cooling. This process, solid-state shear extrusion (SSSE), is based on the large compressive shear deformation of rubber granulates, which results in the storage of a large amount of strain energy and the formation of cracks. When the stored energy reaches a critical level, the granulate cannot sustain itself. As a result, the stored elastic energy is converted into surface energy through the formation of new surfaces and, in turn, pulverization occurs. The stored elastic energy is dependent on the viscoelastic response of rubber granulates to the processing condition. The independent variables of the process were identified as the degree of compression of the rubber, number of extruder passes, barrel wall temperatures, rotation rate of the extruder screw, and feed rate of the granulates. The effects of these variables on the dependent variables, such as material and screw temperatures, particle size distribution (PSD), torque, and mechanical power consumption at steady state, were systematically studied. Fine rubber particles were obtained when the granulates were compressed sufficiently, and loss of strain energy due to viscoelastic stress relaxation was minimized by significant cooling in the pulverization zone. Agglomeration of rubber particles was found to be competing with the pulverization process.