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 she ar and compression without using cryogenic fluid for cooling. This process, solid-state shear extrusion (SSSE), is based on the large compressive shea r deformation of rubber granulates, which results in the storage of a large amount of strain energy and the formation of cracks. When the stored energ y reaches a critical level, the granulate cannot sustain itself. As a resul t, the stored elastic energy is converted into surface energy through the f ormation of new surfaces and, in turn, pulverization occurs. The stored ela stic 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 p asses, barrel wall temperatures, rotation rate of the extruder screw, and f eed rate of the granulates. The effects of these variables on the dependent variables, such as material and screw temperatures, particle size distribu tion (PSD), torque, and mechanical power consumption at steady state, were systematically studied, Fine rubber particles were obtained when the,granul ates were compressed sufficiently, and loss of strain energy due to viscoel astic stress relaxation was minimized by significant cooling in the pulveri zation zone. Agglomeration of rubber particles was found to be competing wi th the pulverization process. (C) 2001 Elsevier Science B.V. All rights res erved.