Thermoplastic binders for solid propellants and plastic binder explosives (PBX) currently are compounded with twin screw extruders which minimize the heat history of these sensitive materials. New polyether block copolymers as energetic binders may place additional demands on the machinery used for mixing and extrusion. The utility of extruder design is being explored for mixing high-solids, heatsensitive materials. The new machine has a large rotor inside an eccentric barrel with carefully calculated clearances at various points of the annulus. A short and uniform heat history results. A gear pump and static mixers are used downstream as needed. A small 300 lb/hr lab-size unit is being tested in order to establish its potential for safer, more uniform, and more economical preparation of pbx and solid propellants. A low cost thermoplastic elastomer is being selected with melt viscosity close to that expected for newer energetic binders; and the size distribution of a selected filler is being optimized to achieve high solids content. The compounded extrudate is being examined for particle distribution, uniformity, degradation of molecular weight, and other signs of distress.
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