Phase transitions in ultraoriented polyethylene fibers under moderate pressures: A synchrotron X‐ray study

The effect of pressure on phase transformations of ultradrawn ultra‐high‐molecular‐weight polyethylene (UHMWPE) fibers was examined by in situ X‐ray diffraction measurements with synchrotron radiation. The mesomorphic hexagonal phase was metastable even at a relatively low pressure of about 100 bar. The effect of pressure on the melting transitions was larger than in chain‐folded structures. The existence and metastability of the hexagonal phase is the basis of compaction technology of UHMWPE fibers in composite materials.