Effect of the inner wall cooling rate on the structure and properties of a polyethylene pipe extruded at a high rotation speed

Role of Melt Plasticizing Temperature in Morphology and Properties of PE100 Pipes Prepared by a Rotational Shear System

To increase the maximum internal pressure that a polyethylene (PE) pipe can withstand, a novel rotational shear system (RSS) was constructed in this study to fabricate PE pipes with enhanced hoop strength by applying hoop shear on the pipes using a rotational mandrel. The microstructure and morphology with the influences of melt plasticizing temperature on PE pipes processing under rotational shear were investigated indirectly using small-angle X-ray scattering and wide-angle X-ray diffraction (SAXS/WAXD) measurements. In the SAXS patterns, equatorial streaks and meridional scattering peaks were clearly observed in all three samples prepared at different melt plasticizing temperatures, 215, 235, and 255 °C. Their presence indicated that shish-kebab crystals form in rotational shear. Compared to those at the low melt temperature, the increase in the melt temperature enhanced the amount and the dimensions of shish formed. However, the shish also relaxed faster at the high melt temperature. This behavior was attributed to the enhancement of the molecular chain's athletic ability. The hoop tensile strength and the heat resistance of the pipes peaked at the melt plasticizing temperature of 235 °C, 75.2 MPa, 102.4 °C, up 1 MPa, 0.2 °C (compared to the 215 °C) and 7.8 MPa, 3.2 °C (compared to the 255 °C). The axial strength increased with an increase of melt plasticizing temperature. However, the increase of melt plasticizing temperature worsens the inherent good tensile toughness of PE100 pipes as the axial elongation at break decreases.

Critical formation conditions for β-form hybrid shish-kebab and its structural analysis

Critical formation conditions for β-form hybrid shish kebab and its unique condensed state structure.

Effect of the Mandrel Rotation Speed and Inner Wall Cooling Rate on the Performance and Structure of Polypropylene Block-Copolymer Pipe

Polypropylene block-copolymer (PP-B) pipes were prepared using a self-designed rotational extrusion processing system. The experimental results showed that though the crystal morphology in the prepared PP-B pipes did not change compared to conventional extrusion, the molecular chains in amorphous region apparently deviated from the axial direction. As a result, in comparison with the conventional extrusion pipes, the mechanical properties in hoop direction and the resistance to crack growth of rotation extrusion PP-B pipes were greatly improved. Furthermore, both the two mechanical properties improved monotonously with increasing mandrel rotation speed and inner wall cooling rate.