CONCERNING THE NEGATIVE THERMAL EXPANSION FOR EXTENDED CHAIN POLYETHYLENE

摘要

Thermal expansion coefficients have been measured on ultraoriented polyethylene fibers. Samples were prepared by a solid-state (crystalline extrusion in an Instron Capillary Rheometer at 136C, 2100 atm. and at a draw ratio of 50. The expansion coefficients between -150 and +50C, perpendicular to the fiber axis, were positive and of the order of .0001/deg C. Conversely, parallel to that direction, the observed values were both negative and small. Length changes were reversible and reproducible between -150 and+50C. Negative coefficients were attributed to the presence of highly-extended and fully aligned chains along the fiber.