Anisotropy and mechanical properties of bioriented PVC pipes

A specific process devoted to the biorientation of PVC pipes is studied. It consists of the simultaneous blowing and stretching of an extruded pan: Th e tensile and impact properties of these pipes are analysed and compared to the performances of an usual extruded pipe and a blown pipe (no stretching ). The blowing significantly increases the properties of the pipes in the o rthoradial theta-direction. In the longitudinal z-direction, the tensile pr operties remain almost unchanged. Nevertheless, when impact properties are considered, the monooriented PVC exhibits very weak performances. The biori entation induced by an additional stretching makes the properties in the z- direction increase without decreasing the theta performance. Impact propert ies are significantly increased compared both to extruded pipes and blown p ipes. This improvement in the properties is related to an important modific ation of the microstructure. The molecules of the PVC are oriented and the material behaves like a laminate composed of a great number of bioriented ( theta-z) layers. The damage induced by impacts seems to be a delamination.