Synthesis of Poly(para-phenylene terephthalamide) and Preparation of Short Fibers: Effect of Sodium Sulphate on the Fibers

Kevlar is one of the fibers which is used in heavy industrial productions suchas, shipping, military and weaving for reinforcement of composites. Initialpolymer of Kevlar or poly(para-phenylene terephthalamide) is an orientedliquid crystal polymer. Existence of aromatic group in the main chain leads to formationof rigid-rod molecules in the polymer, high strength and high modulus in it is fibers.Impurities in the polymer lead to decrease in fibers performance. In this research,poly(para - phenylene terephthalamide) was synthesized from polycondensation ofphenylene diamine and terephthaloyl dichloride in n-methyl pyrrolidone and calciumchloride (NMP-CaCl2) solution. Fourier transform infrared spectroscopy (FTIR) andX-ray diffraction (XRD) tests were carried out to characterize chemical bonds andcrystalline plates of the polymer, respectively. Concentrated sulfuric acid is a solventof poly(phenylene terephthalate) therefore, this polymer was dissolved in concentreatedsulfuric acid (96%) and the polymer solution was injected into the cylindricaltank contain water. Sulfuric acid was transferred into water and the polymer wassolidified. After solidification, tensile force of vortex led to orientation of rigid-rodpolymer molecules in direction of water rotation and long fibers were formed fromthe polymer. The fibers were broken to short fibers by the same force of vortex. Theshort fibers were dried. SEM images showed the regular particles on the surface offibers. Results of FTIR and XRD proved that the regular particles are sodium sulphatesalt. The effect of sodium sulphate salt as an impurity on the short fibers was studied.