MELTING AND CRYSTALLIZATION OF SOLUTION CRYSTALLIZED ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE UNDER HIGH-PRESSURE

Differential thermal analysis of a ultra-high molecular weight polyethylene (UHMW-PE, Mv; 2.7×106) crystallized from a 0.1 wt% decalin solution was performed at pressures from about atmospheric pressure to 600 MPa. In the high pressure region such as 600 PMa, thick lamellae similar to extended-chain crystal are formed very rapidly in the heating process. The rapid lamellar thicknening is suggested to be due to the decrease of enthanglements. Its phase diagram was determined. The triple point in the phase diagram was about 370 MPa. The high pressure phase region of the solution crystallized sample is between those of as-polymerized powder sample and bulk sample which is melt-crystallized one after kneading in the melt. The change of phase diagram among those samples may be due to differences in entanglement density. © 1990 The Society of Polymer Science, Japan.