Crystallinity of ethylene–vinyl acetate copolymers

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Abstract

Determination of crystallinity of ethylene–vinyl acetate copolymers according to the usual x-ray diffraction method employed for polyethylene is very much hampered by the fact that these copolymers are usually largely amorphous and the Bragg reflections in their diffraction diagrams which are therefore broad and weak are drowned by the strong and dominant amorphous halo. As a consequence it is virtually impossible to carry out a realistic resolution of the total diffraction diagram into the individual Bragg reflections in the halo. In the method described in this paper this difficulty is successfully surmounted by taking advantage of the unique shape and placement of the amorphous halo with respect to the Bragg reflections in the diffraction diagrams of these copolymers. This rather fortunate situation permits a direct determination of amorphous content without having to take recourse to the cumbersome resolution of the Bragg reflections and hence one can obtain crystallinity indirectly.

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