Pbzt/Polyamide Thermoplastic Micro-Composites - An Outgrowth of Molecular Composites Development
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PBZT/POLYAMIDE THERMOPLASTIC MICRO-COMPOSITES AN OUTGROW'rH OF MOLECULAR COMPOSITES DEVELOPMENT WILLIAM C. UY AND E. R. PERUSICH E. I. du Pont de Nemours & Co., Inc., Experimental Station, P. 0. Box 80302, Wilmington, DE 19880-0302 ABSTRACT Molecular composites are dispersions of rigid-rod polymer molecules in a matrix of flexible coil polymers, formed by the coagulation of a solution containing these components. Where there is aggregation of the rigid-rod molecules, such composites are called micro-composites (MC's). These composites offer the potential for better economics and improvements in composite processing, and possibly performance, over conventional "string and glue" composites. This paper describes work performed under contract to the U. S. Air Force to develop PBZT/thermoplastic molecular composites into a viable technology. A commercially viable MC spinning and heat-treatment process has been defined based on a novel mixed solvent/quaternary solution technology developed by Du Pont. Advantages of this process include better economics, superior processing performance, and improved MC fiber tensile properties versus prior art. PBZT/polyamide MC fibers with strength/modulus of 332 ksi/29 Msi have been produced using this process. Adhesion equivalent to that obtained in conventional composites has been demonstrated. Uni-axial properties achieved to date compare favorably with conventional "string and glue" PBZT/epoxy composites although compressive and shear strengths may be limiting factors in MC applications. INTRODUCTION This work was carried out at the Advanced Structural Materials Technology Center of the Fibers Department of E. I. du Pont de Nemours & Co., Inc. This presentation is on the development of general process technology for PBZ-based molecular composites and, in particular, of PBZT-based products in thermoplastic polyamide matrix system. Du Pont involvement with PBZ* technology, the Air Force Materials Laboratory and SRI International dates back to 1981, when research focused on the neat PBZT polymer in developing spinning and heat-treatment processes for this true rigid-rod polymer from its unusually viscous as-polymerized polyphosphoric acid solution [1]. In the following year the process was refined and scaled-up [2]. In 1985 and 1987, we expanded the experimental production of PBZT fiber for the Air Force and converted a total of 160 lbs. of the polymer to heat-treated fiber in continuous 290-filament yarn. As-spun PBZT fiber has a purplish brown color while optimally heat-treated fiber has a shiny, metallic blue color. The average tensile strength and modulus values of these production yarns exceed 400 ksi/40 Msi while values as high as 614 ksi/49 Msi (Table I) have been obtained for lab-scale produced fibers. PBZ polymers in general have outstanding thermal, oxidative, and hydrolytic stability [2]. Trans-PBZT and cis-PBO, in particular, are the most important and true rigid-rod PBZ polymers [3,4]. Therefore, they are ideal as reinforcing components in molecular composites. * PBZ is th
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