Hydrostatic compression molding

Hydrostatic molding is a suitable alternative to compression molding techniques for the production of plastics that do not have the usual melt flow behavior, such as previously reviewed in the Plastic section for polytetrafluoroethylene. 

Orientation In contrast to the enzymatic hydrolytic degradation of PLLA [38, 301], orientation has a relatively small effect on neutral and alkaline hydrolytic degradation. Crystallinity, rather than biaxial orientation, seems to determine the alkaline and NHD rates of PLLA films [38]. On the other hand, Hyon and Jamshidi et al. [36, 59-61] indicated that hydrostatic molecular-oriented PLLA could retain its mechanical performance for a longer period compared to compression molded PLLA. 

ArCom XL polyethylene is produced in a multistep process that has been described in the literature [8]. Rods of GUR 1050 are isostatically molded and gamma irradiated at room temperature with a nominal dose of 50kGy. The rods are preheated to 130°C and then hydrostatically extruded with a diametral compression ratio of 1.5. The hydrostatic extrusion produces orientation of the UHMWPE and mechanically anneals the material. The rods are then stress relieved at 130°C prior to machining into components, which are terminally gas plasma sterilized. 

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