synthesis of poly(para-phenylene terephthalamide) and preparation of short fibers: effect of sodium sulphate on the fibers

Kevlar is one of the fbers which is used in heavy industrial productions such as, shipping, military and weaving for reinforcement of composites. Initial polymer of Kevlar or poly(para-phenylene terephthalamide) is an oriented liquid crystal polymer. Existence of aromatic group in the main chain leads to formation of rigid-rod molecules in the polymer, high strength and high modulus in it is fbers. Impurities in the polymer lead to decrease in fbers performance. In this research, poly(para - phenylene terephthalamide) was synthesized from polycondensation of phenylene diamine and terephthaloyl dichloride in n-methyl pyrrolidone and calcium chloride (NMP-CaCl2) solution. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) tests were carried out to characterize chemical bonds and crystalline plates of the polymer, respectively. Concentrated sulfuric acid is a solvent of poly(phenylene terephthalate) therefore, this polymer was dissolved in concentreated sulfuric acid (96%) and  the polymer solution was  injected  into  the cylindrical tank contain water. Sulfuric acid was transferred into water and the polymer was solidifed. After solidifcation,  tensile  force of vortex  led  to orientation of  rigid-rod polymer molecules  in direction of water rotation and  long fbers were formed from the polymer. The fbers were broken to short fbers by the same force of vortex. The short fbers were dried. SEM  images showed  the regular particles on  the surface of fbers. Results of FTIR and XRD proved that the regular particles are sodium sulphate salt. The effect of sodium sulphate salt as an impurity on the short fbers was studied.