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The effect of coagulants on the microstructure and mechanical properties of lyotropic fiber-forming polymers
Abstract
The effect of coagulant on the mechanical properties and microstructure of three lyotropic fiber-forming polymers, poly(p-phenylene benzobisthiazole) (PBZT), poly(p-phenylene terephthalamide) (PPTA) and poly(p-phenylene benzobisoxazole) (PBO) was studied. Previous research found that the imbalance between tensile and compressive/shear properties in these high-modulus fibers is due to a low degree of lateral interaction between microfibrillar elements. In this work, coagulants were chosen which could have strong specific molecular interactions with some portion of the polymer chain; the goal of this research was to increase compressive and shear properties by creating lateral physical crosslinks among the polymer chains. Results from these coagulation studies show that macroscopic properties such as compressive strength and torsion modulus are dependent on the coagulant; these interactions are strong enough to significantly affect mechanical and structural properties of the fiber. For oxygen-containing lyotropic polymers, the cations present in the coagulant may be important in determining the occurrence of specific interactions. As-spun PBZT fiber coagulated in iodine/ethanol solution with a spin/draw of 3 had a shear modulus of 1.14 GPa and tensile strength of 2.2 GPa; fiber coagulated in ethanol had respective values of 0.63 GPa and 1.8 GPa. Wide-angle X-ray scattering (WAXS) studies showed that I$\sb3\sp-$ and I$\sb5\sp-$ anions were present within the fiber, and that there was some disruption of the standard PBZT unit cell. PPTA fiber was coagulated into water, ethanol, iodine/ethanol and aqueous solutions of alkali salts. Coagulation in water produced PPTA fiber with the highest tensile, shear and compressive properties. The shear and/or compressive properties of PPTA fibers could be decreased without a corresponding change in crystal structure; these properties seem to be based on an element of microstructure above that of the unit cell. PBO fibers were coagulated in many of the same coagulants; mechanical properties were unaffected. Coagulation in aqueous potassium iodide produced fiber containing oriented potassium iodide crystals within the fiber.
Subject Area
Materials science|Plastics
Recommended Citation
Rakas, Margaret Ann, "The effect of coagulants on the microstructure and mechanical properties of lyotropic fiber-forming polymers" (1990). Doctoral Dissertations Available from Proquest. AAI9022734.
https://scholarworks.umass.edu/dissertations/AAI9022734