Influences and Failure Analysis of the Interaction Between Melt and Gas on Double-Layer Gas-Assisted Extrusion Molding of Polymer Micro-Catheters.

Although the extrudate swelling, melt fracture, and extrusion deformation of polymer micro-catheters in traditional extrusion molding can be eliminated via the double-layer gas-assisted extrusion (DL-GAE) method, some failure problems are generated under unreasonable process conditions. To ascertain the reasons for failure in DL-GAE molding of polymer micro-catheters, the influences of the interaction between the melt and double assisted gas on the DL-GAE molding of polymer micro-catheters were experimentally and numerically studied. Meanwhile, a DL-GAE die and experimental system were designed and constructed. We analyzed the influence laws of the melt and assisted gas on the DL-GAE molding of polymer micro-catheters, as well as reasons for the molding's failure. Our studies demonstrate that under the condition of stable DL-GAE, as the melt flow rate increases, the wall thickness and diameter of polypropylene (PP) micro-catheters increase. When the melt flow rate continuously increases, the stability of the assisted gas is destroyed, resulting in the failure of DL-GAE. In addition, under synchronized pressures of a double gas-assisted layer, the diameters of the micro-catheters increase, but their wall thickness decreases. Under an individual pressure increase of the outer gas-assisted layer, surface bump defects are generated. Under an individual pressure increase of the inner gas-assisted layer, the diameters of PP micro-catheters swell prominently until they break. Therefore, although DL-GAE can eliminate extrusion problems of polymer micro-catheters, it is suggested that reasonable process parameters for the melt and double assisted gas should be satisfied and matched. This work can provide significant technical support for the DL-GAE of polymer micro-catheters during manufacture.