Stress stabilization of the orthorhombic and hexagonal phases of UHM PE gel-spun fibres

In highly oriented polymers, stress can stabilize fibers against melting by favoring the low-entropy fibrillar state against the high-entropy melt. The thermal stability of gel-spun ultrahigh-modulus polyethylene subjected to tensile stress is investigated. The Daresbury x-ray synchrotron radiation source and optical microscopy are utilized to follow dynamically the transformation, melting, and recrystn. of fibers under optimum conditions of controlled stress. The orthorhombic phase is stable up to 164 Deg, after which the crystals transform into a hexagonal phase which can be stable up to 179 Deg. While this is the greatest thermal stability reported for the orthorhombic phase, the question of the ultimate stability is still unanswered and is presently limited by the effectiveness of the stress transfer to the fibrils. [on SciFinder (R)]