Mechanical Properties versus Morphology of Ordered Polymers. Volume 2.
Abstract : Morphological techniques in conjunction with meachanical testing have been employed to elucidate the relationships between mechanical properties of rigid rod polymer fiber and file with sample microstructures and to use this knowledge to obtain the maximum in strength and modulus for these materials. The fibers and films of poly(p-phenylene benzobisthiazole) (PBT) which have been investigated were produced at Carnegie Mellon Uni and at Celanese Research Corp from liquid crystalline solutions using dry-jet-wet spin process for fibers and either shear or extrusion for films. Correlation of sample microstructure and resultant mechanical properties with processing conditions has been done to help optimize processing conditions. Spectroscopic students suggest that the polymers in solution exist in the protonated form. While most of the materials produced to date have extremely high degrees of orientation, thus, far, the key differences have been in the lateral ordering of the chains. Better laterial ordering has been observed in heat treated samples, and in particular, samples processed directly from the polymerization solvent, polyphosphoric acid, but no true 3-dimensional crystal structure is formed. It remains to be seen if this feature is a direct consequence of the chemical structure of PBT molecules or is simply the result of non-optimized processing and heat treatment conditions. The suprisingly nonlinear behavior and apparent plasticity of the as-spun fibers and the modulus increase after plastic deformation caused considerable concern. These effects are caused by microstructural element buckling due to residual stresses produced during the fiber formation process.