Design and Analysis of a Mandrel Process to Control the Properties of Poly(p-Phenylene Terephthalamide) Films

Abstract

Kinematic and rheological considerations have been used to design and analyze the processing steps for obtaining biaxial chain orientation in poly(p-phenylene terephthalamide) (PPTA) films. A semi-quantitative approach to the mandrel design allows one to predict the type and degree of molecular orientation obtained. For the case of PPTA dissolved in H2SO4, the basic steps are extrusion of the liquid crystalline solution through an annular die followed by expansion and elongational flow over a mandrel. The mandrels used include conical, hyperbolic and ogival shapes. Molecular orientation as well as mechanical properties were found to be dependent on mandrel shape and presence. Wide angle x-ray diffraction (WAXS) techniques using White-Spruiell orientation factors and pole figures were used to characterize the films. Mechanical properties as well as the above techniques indicate a high degree of biaxial orientation can be obtained with a bias in certain film directions depending on the mandrel used. Tensile strength and Young's modulus values were found to be on the order of 30 000 psi and one million psi respectively. They also can be equally distributed in the film plane depending on mandrel shape. White-Spruiell orientation factors were as high as 0.49 and 0.5 for f1B and f2B respectively. Scanning electron microscopy was used to observe the film superstructure as a function or processing conditions. All films exhibited a skin-core structure. Uniaxially drawn films are fibillar while the biaxial films appear to be more homogeneous.