Characterization and Selection of Polymer Materials for Binary Munitions Storage. Part 2. Characterization of LLDPE Resins.
ARMY MATERIALS AND MECHANICS RESEARCH CENTER WATERTOWN MA
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This work is aimed at determining the materials properties required for storage of DF methylphosphonic difluoride over extended periods of time at temperatures as high as 70 C. Earlier studies showed the most likely mode of failure to be environmental stress cracking of the polyolefin container, rather than chemical or oxidative attack. The most promising candidates in terms of resistance to environmental stress cracking are ethylene copolymers with a small alpha-olefin comonomer content. The comonomer, typically butene-1 or hexene-1, introduces short side chain branches which disrupt the regularity of the crystal morphology, presumably leading to a greater proportion of intercrystalline ties. An X-ray diffraction method was developed for measuring the amount of short chain branching which offers greater accuracy than the previous infrared absorption method. Characterization of short chain branching by such a method, along with molecular weight characterization by gel permeation chromatography and crystallinity determination by density, were deemed essential to quality control of resins for the intended application.
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