A study of direct gas injection foam extrusion of polyolefins for a wire coating application.

摘要

A low density foamed jacketing material is used on submarine communication cables. The buoyancy layer of the submarine's high speed buoyancy cable antenna (HSBCA) must be a lightweight foam material with a density of 0.30 g/cc or less to promote increased speed/depth performance over the existing cable jacketing. Previous research has been done using chemical foaming agents and some types of physical foaming agents. This research investigated the possible use of direct gas injection foaming using a twin screw extruder. The inert gases nitrogen and carbon dioxide were used as the physical blowing agents. The carbon dioxide process involved injecting the carbon dioxide at supercritical conditions, while the nitrogen was injected as a compressed gas. Both talc and an endothermic chemical blowing agent were investigated as possible nucleating agents.; Overall the research shows that the nitrogen gas injection system, equipped with a water bath using the "zero-air gap" technique, performed better than the CO2 injection system with air cooling of the extrudate. The high density polyethylene samples were foamed down to 35-40% of the original density. These samples also had a skin which was formed during processing which prevents water absorption and increases tensile properties.