Study On Morphological Structure And Properties Of Self-Reinforcement Polyolefine Pipes In Two-direction Extruded In Complex Stress Fields

Polyolefine pipes are applied generally as profile. But the strength around the hoop of generic polyolefine pipes is too low to endure much high inner pressure; increasing thickness of pipe wall is a regular way to meet needs of use in engineering. If we add the thickness of wall pipe, there would be many problems. Firstly much more plastics would be wasted; In the second, pipe under processing would be difficult to cool, so, stabilization of shape of pipe would be difficult.Until now, many people made research on the reinforcement technology of pipe to obtain bi-directional reinforcement polyolefine pipes. But among those researches, there were few reports on self-reinforcement polyolefine pipes. On the bases of previous researches we have made a complex stress die which has an annulus-shearing element and an axis-stretching element. And the self-reinforcement polyolefine pipes have been successfully made through this extrusion die. The most prominent peculiarity of this die was that we could freely adjust the size of compound element of die in order to turn out different caliber pipes. Another characteristic of this die was changing mandrel rotating into sleeve rotating. This paper made detailed research on the change of Polyolefine crystallographic structure, melt behavior and morphology structure in complex stress field and conclusions were listed as following:1) On condition that few HMWHDPE1158 (high molecular weight HDPE) was added into general HDPE6098, the pipe extruded in complex stress field was provided good properties. At the point of 15r/min (mandrel rotating speed), the circumferential strength of pipe was 34.27Mpa and axial strength was 28.84MPa.As compared with general pipe, its circumferential strength had been improved about 36% and axial strength had been increased 8%. In the same way, when few HMWHDPE1158 was added into general HDPE6100M, it was shown that bi-directional self-reinforcement pipe made in complex stress field had beenachieved.2) Different kinds of HDPE6100M/HMWHDPE1158 compounding were extruded through the die, and circumferential and axial strengths of pipes were studied respectively. It was obviously shown that properties of pipe made from the mixture of HDPE and few HMWHDPE1158 was better than that made from the blend of HDPE and 40%HMWHDPE1158, which indicates the addition of few HWMHDPE to HDPE contributes to inducing HDPE6100M molecular orientation and crystallization along the stress direction.3) Melting peak by DSC of general HDPE pipe extruded in complex stress field didn't change, while melting peak of the pipe of general HDPE blended with few HMWHDPE1158 drifted to high temperature, which showed the wafer thickened. Besides, the heat of melting of the latter increased. All of these indicated that the shearing stress field could make polymer HMWHDPE1158 easily to be line-nucleus and induced polymer of general HDPE crystallize around the nucleus.4) The aggregate structure of shear-induced crystallization reinforcement pipe extruded in complex stress field had been studied by SEM, it was shown that there were much more orientation lamellar crystal in order.5) Through series of experiments, it was obvious that the bi-directional strength of the pipe of HDPE blended with few HMWHDPE1158 could be increased largely in complex stress die. Shear-induced crystallization mechanism plays a key role in this reinforcement. As a result of shear stress field applied by extrusion die, the polymer of HMWHDPE1158 was firstly stretched and come into being stabilized line-nucleus; secondly, nucleus would induce general HDPE to crystallize in the form of duplicated lamellar crystal around the nucleus. Theselamellar crystals were ranged in order.