Processing Rubber Compounds with Polymeric Dispersions of Rubber Chemicals by Automated Pellet Feeding Technology

Abstract

Abstract This paper describes the cross-fertilization of plastics technology and the processing of rubber compounds in particulated form, employing an extruder as a mixing device. Stress-strain and rheometer test data established that pelletized compounds based on CR, CSM, EPDM, and SBR are successfully extruder-mixed with their respective curative systems predispersed in polymeric binders and pelletized. Since all ingredients in both types of pellets are in dispersed form, only good blending is required, not intensive, high shear mixing. X-ray radiography confirms that intimate mixing of the pellets was obtained by tracing the progress of incorporation of zinc oxide into a CR compound. The need to modify the extruder screw used in this experimental work by insertion of pins to create an improved mixing action is demonstrated. A screen pack at the breaker plate provides the necessary backpressure to further improve the degree of mixing. With other types of mixing screws, not necessarily made with pins, the screen pack may be eliminated. A process is suggested to manufacture extruded items by metering, blending, and extruder-mixing base and curative pellets. The cost of a second pass Banbury mix can be obviated resulting in the virtual elimination of scorched and bin-aged batches while maintaining the cleanliness of the strained base compound.