Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 612-616
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drews, 1974; Fukahari and Andrews, 1978). The enhanced crack growth resistance of the water-cooled specimens relative to crystallinity may well arise from quite subtle differences in the structure of the amorphous phase which is, in some way, optimized by this particular thermal treatment. Any further comment would at this stage be purely speculative. We can only state that there is a clear decrease in crack resistance with increasing crystallinity, but that crystallinity is not the sole determining parameter. Conclusions 1. The molding conditions employed during compression molding have a substantial effect on the impact-fatigue response of UHMW LPE. In general, the faster the cooling rate during molding, the better is the impact-fatigue behavior. 2. Impact-fatigue response of UHMW LPE moldings can be correlated with internal variables. For example, quench-cooled samples which show the best impact-fatigue response also have the smallest degree of crystallinity and lamellar thickness, whereas slow-cooled samples having the poorest impact-fatigue response have the largest degree of crystallinity and lamellar thickness. Correlation with spherulite size could not be made, since attempts to measure spherulite size by laser light-scattering technique failed to reveal the presence of any definable spherulites in any of the moldings. 3. The impact-fatigue response depends on the initial notch-depth. Data reveal the presence of two critical initial notch depths, co* and co**. Above co*, the samples would fracture at the very first impact drop and below co**, the samples would sustain an indefinitely large number of drops before failure.
4. Regardless of the cooling rate employed during compression molding, all samples with shallow initial notch depths (
