Biaxial reinforcements for polyethylene medical-tubes via helical convergent flow

Commercialized medical-tubes prepared by axial extrusion are featured with the performance mismatching along axial and hoop directions and thus are not suitable for the complex environment in clinical applications. Here, superposing a hoop flow from rotation of mandrel and die onto axial convergent flow caused by different ratio of extrusion and taking-up speed, a helical convergent flow was constructed to prepare polyethylene (PE) medical-tubes with excellent mechanical properties. Specially, the convergent flow promoted the shish-kebab formation and reinforced molecular orientation in the tube, while the hoop flow caused by mandrel and die rotation regulated flow pattern from axial flow to helical flow to trigger the off-axis alignment. This off-axis shish-kebab structure brought out notable biaxial reinforcement on the PE tube by helical convergent flow. When rotation speed was 10 rpm with convergent flow ratio of 1.82, the axial and hoop strength increased from 32 and 20 MPa to 35.4 MPa and 34.4 MPa, respectively. This flow-manipulating strategy for performance enhancement in both axial and hoop directions is featured with simplicity and high efficiency, which is suitable for massive production of medical tube with high performance.