STRUCTURE PROPERTY RELATIONSHIPS OF ARAMIDS.

This paper presents results of a test program in which poly(p-phenylene terephthalamide) (PPT), commercialized in fiber form by the du Pont Company under the trademark Kevlar (all aromatic polyamides are termed Aramids). This system was chosen for analysis for two reasons: (1) the polymer is non-conventional in that it can form a liquid crystalline phase when dissolved in sulfuric acid, and (2) in fiber form the system exhibits extremely high mechanical properties (modulus up to 1000 g/d, Strength up to 30 g/d). The intent of the work was to provide understanding of the effects of liquid crystallinity on polymer processing and to isolate the microstructural features responsible for the observed property levels. In experiments, a series of PPT polymers were used. They were dissolved in 100% H//2SO//4 over a 6-20% concentration range and processed into fiber using wet spinning and dry-jet wet spinning techniques. Samples of each of the yarns produced were annealed and/or drawn in a tube furnace under nitrogen over the temperature range 200-600 degree C. Resulting yarns were tested for mechanical properties utilizing an Instron Tensile Testing machine and structurally characterized by wide and small angle X-ray diffraction, optical and electron microscopy, Differential Thermal Calorimetry and Thermal Mechanical Analysis.