Basic Study of the Interaction of Thermoplastic Fluoropolymer Blends with Metal Surfaces During Extrusion

抄録

An experimental study of the flow of three thermoplastics (linear low density polyethylene (LLDPE), polystyrene (PS), and polyamide-12) containing small amounts of fluoropolymers through dies of various metals and die cross-sections is presented. It is shown using contact angle measurements that fluoropolymer is gradually deposited on the die wall for both the LLDPE and PS. In the case of the LLDPE, this results in substantial decreases in die extrusion pressure losses. Much smaller decreases in pressure losses are found for the PS. It appears that the PA12 adheres to the die wall and the fluoropolymers are dispersed in it in the form of an emulsion of fluoropolymer-PA-12 block copolymers. Experiments were also carried with aluminum dies and copper and zinc-plated dies. The results are very similar. In compression molding experiments, where there is no steady flowing stream, there seemed to be no tendency of fluoropolymers to coat the die walls. It appears that the fluoropolymer accumulates during continuous flows like debris on the wall aided by carboxyl end groups. The fluoropolymer layer induces significant slippage in the LLDPE but not the PS.