New concepts for continuous mixing of powder rubber

The development of a continuous mixing process for natural rubber (NR) powder rubber compounds using the twin screw extruder is proposed, using an appropriate screw configuration taking advantage of the various types of screw elements used for conveyance and dispersive and distributive mixing. A further target of the study was a significant increase in the output, while retaining a good quality of process behaviour and material properties. Within the given limits of machine capacity, a gradual increase of the feed rate was successfully achieved with increasing screw speed at clearly moderate mixing temperatures. A markedly high degree of dispersion of filler of >95% was obtained for all compounds produced by varying the process parameters. Consistently, rheological and mechanical measurements revealed only negligible to weak differences between the sample properties. For comparison of results, compounds based on NR in both bale and powder form were prepared by the discontinuous mixing process. (C) 2001 IoM Communications Ltd.