Plate out in extruded SantopreneTM thermoplastic vulcanisate - formation and structure

Plate-out is defined, in the context of this research, as a hard deposit that can be found adhered to the surface of screw, barrel and die resulting in the loss of output performance and ultimate extrude quality. It is typically is seen as a coloured deposit, ranging from white through to brown that can occur at any time in the process. Plate-out occurs randomly with SantopreneTM TPV products within a manufactured lot, or from lot-to-lot without any changes to the base formulation or manufacturing procedures or practices. The aim of the research was firstly to understand the influences of various elements of the extrusion process and any interactions on the formation of plate-out. The second aspect of the research was to investigate whether deposited plate-out had in itself any form and structure. Two experimental routes were taken. The first was a university based small scale laboratory extrusion study; the second complementary approach was industrially based; involving the ExxonMobil Newport manufacturing plant supported by the company analytical laboratories based in Brussels. The programme of work explicitly excluded in depth analysis of the chemistry involved in the manufacture of SantopreneTM TPV, this remaining proprietary to the company. The results of the study of the effects of the processing variables conclude that plate-out formation is complex and no single variable removed or reduced it. With a combination of lower process temperature, longer residence times and higher melt compression there is an increased likelihood that plate-out will form. For the film type deposit which contains novolac resin and zinc chloride, the onset of migration of these materials is seen to occur in the transition zone. This is believed to be the tie-layer precursor to plate-out deposition further along the screw. Two types of plate-out were identified, a powdery deposit and a film deposit. Both contained clay filler, stannous chloride, zinc oxide but the film deposit also contained traces of novolac resin and zinc chloride. The plate-out was confirmed to have its own distinct cross sectional structure.