Control over crystalline form in polypropylene pipe via mandrel rotation extrusion

In this paper, isotactic polypropylene pipes were prepared via mandrel rotation extrusion and the effects of mandrel rotation speed on crystalline form of Polypropylene (PP) pipes were investigated. The results indicated that properly high mandrel rotation speed could promote the growth of β crystal markedly in the inner surface of PP pipes, while too high mandrel rotation speed could induce the formation of α column crystal and suppress the formation of β crystal. However, only similar α spherulites appeared in the outer layer of PP pipes prepared by different mandrel rotation speed. This implied there should be different key factors impacting the crystalline form along thickness direction of PP pipes: for external layer, its “cooling rate controlled” and for internal layer, its “mandrel rotation speed controlled”. As a result, gradient crystalline structure was obtained by the compounding effects of cooling rate and mandrel rotation speed.