By using a shearing-drawing two-dimensional compound stress field die developed by the authors

two-dimensional self-reinforcement polypropylene random copolymer(PP-R C180) pipes were extruded.The tensile strength

molecule orientation and crystal melting were studied.The results indicate that the molecule degree of order is improved by shear-inducement of shearing-drawing two-dimensional compound stress field.The orientation of molecule is easier along the circular and axial directions of PP-R C180 pipes respectively.The heat resistance and crystallization velocity are kept

and even improved.The degree of crystallinity is reduced.The self-reinforced PP-R C180 pipes show different crystallization structure and morphology.-phase is induced in the self-reinforced pipes.The tensile strength is improved too.The crystallinity decreases from 44.96% of conventional pipes to 40.03% of self-reinforced pipes.The best axial tensile strength of self-reinforced pipes is 25.49 MPa

but that of the conventional pipes' is 23.35 MPa. And that the circular tensile strength increases from 22.71 MPa of conventional pipes to 26.54 MPa of self-reinforced pipes at the most and the improvement is 16.9%.At the same time

the melting point of self-reinforced pipes is kept

even higher than that of the conventional pipes'.Moreover

the circular tensile strength of self-reinforced pipes is higher than the axial tensile strength and it rather satisfies the requirement of pipes.