Continuously enhanced hoop strength of rotation-extruded polypropylene pipe via self-assembly β nucleating agent with different aspect ratio

Self-assembling beta nucleating agents (TMB-5) and self-designed rotation extrusion device were applied to optimize and control over hoop strength of polypropylene (PP) pipes. By adjusting final heating temperature, TMB-5 efficiently self-assembled into fibrous morphology with controllable aspect ratio, and acted as an oriented template to direct the epitaxial crystallization of PP, into beta-crystals with various lamellae-stacking patterns. The obtained structural information clearly demonstrated that enlarging the aspect ratio of TMB-5 could increase the ordering index and packing intensity of lamellae, moreover, impose them transforming from random arrangement to axial-orientation and then to orthogonal orientation. Among them, the anisotropic ones were further guided to align off the axial-direction of PP pipes via rotation extrusion, where the hoop drag flow caused by the mandrel rotation was superposed on the axial flow. As a result, the hoop tensile strength was enhanced monotonously from 21.3 MPa to 30 MPa for the rotation extruded PP pipes with increasing the aspect ratio of TMB-5.