Abstract
This chapter outlines the basic concepts of high-pressure crystallization in the context of basic polymer crystallization. It describes extended-chain crystals followed by a review of Hylamer and recent research on the use of high-pressure crystallization to increase the properties of irradiated ultra-high molecular weight polyethylene (UHMWPE). High-pressure crystallization refers to a type of crystallization in which a semicrystalline polymer such as UHMWPE is heated to a temperature exceeding its melting temperature, subjected to hydrostatic pressure, usually higher than 350 MPa, and then isobarically cooled to a temperature at which it is able to crystallize. High-pressure crystallization may also proceed isothermally at a temperature above the melting temperature (usually above 210°C) by increasing pressure until it reaches several hundred MPa. Such pressures are generally considered to be high because most common processing conditions, such as compression molding or ram extrusion, are conducted in a range of a few kPa up to a few MPa. High-pressure crystallization offers a novel processing route to increase the crystallinity and associated mechanical properties, such as resistance to fatigue crack propagation, resistance to creep deformation, tensile modulus, and yield strength without compromising ductility and wear resistance. The crystalline regions trap free radicals, which can lead to long-term oxidative degradation.
Published Version
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