Synthesis And Spinning Performance Of Chlorinated Poly(Para-phenylene Terephthanlamide) In Different Solution System

Para-aramid fibers possess excellent mechanical property, thermal and chemical stability etc.However, aromatic polyamide with rigid chain has poor solubility. poly(para-phenyleneterephthanlamide)(PPTA) could only be dissolved in fuming sulfuric acid, thus it needs higherrequirements for the spinning technology and equipments and it is disadvantageous to theindustrialized production of PPTA fibers. In this thesis, chloride substituent groups wereintroduced into the main chain of PPTA in order to improve its solubility. Chlorinated PPTA(Cl-PPTA) solution was prepared by low-temperature solution polycondensation and therheological behaviors of different solutions were studied. The Cl-PPTA solution was directlyspun into fibers by one-step wet-spinning. The structure and properties of resultant Cl-PPTAfibers were studied and compared with that of commercial PPTA fibers.Firstly, Cl-PPTA was synthesized by low-temperature solution polycondensation betweenterephthalylchloride (TPC) and2-chloro-1,4-phenylenediamine (Cl-PPD) in the solvent system ofN-methyl-2-pyrrolidone (NMP) and LiCl (or CaCl2). The effects of the molar concentration ofmonomer, initial reaction temperature, molar ratio of TPC/Cl-PPD, cosolvent content and reactiontime on the inherent viscosity of resultant Cl-PPTA were investigated. The optimumpolymerization conditions were obtained in different solution systems. In NMP/CaCl2system, theoptimal Cl-PPD concentration was0.35mol/L, initial reaction temperature was-5℃, molar ratioof TPC/Cl-PPD was1.001, cosolvent content was4%and the optimal reaction time was20min. InNMP/LiCl system, the optimal Cl-PPD concentration was0.25mol/L, initial reaction temperaturewas-15~-8℃, the molar ratio of TPC/Cl-PPD was1.001, cosolvent content was3~4%and theoptimal reaction time was30min. In comparison, it was much easier to get higher molecularweight of Cl–PPTA in NMP/LiCl system than that in NMP/CaCl2system, and the Cl-PPTA withinherent viscosity of2.38dL/g was produced under the optimum condition. The molecularstructure of Cl-PPTA was characterized by fourier transform infrared spectrometer (FTIR). Thecharacteristic absorption peaks of Cl-groups were found on the FTIR spectrum of resultantCl-PPTA and other absorption peaks were completely the same as that of commercial PPTA fibers.This proved that the target polymer of Cl-PPTA was synthesized.Secondly, the steady and dynamic rheological behaviors of different Cl-PPTA solutions werestudied by Anton Paar-MCR senior rotary rheometer. The effects of the solution temperature,polymer concentration and molecular weight on apparent viscosity, storage modulus, loss modulus, and loss angle tangent were discussed. The non-Newton exponent, viscous activation energy andvisco-elasticity transition point (gel point) were obtained. The results indicated that Cl-PPTAsolution was a shear thinning pseudo-plastic fluid. The solution viscosity decreased with theincrease of solution temperature, while it increased with the increase of solution concentration orCl-PPTA molecular weight. The non-Newton exponent of solutions increased with the increase ofsolution temperature, while it decreased with the increase of solution concentration or Cl-PPTAmolecular weight. Compare with the NMP/LiCl system, Cl-PPTA solution of NMP/CaCl2systemwas more sensitive to the changes of temperature, and its viscous flow activation energy was alsohigh. TheG and G of Cl-PPTA solution increased with the increase of solutionconcentration or Cl-PPTA molecular weight, and they decreased with the increase of solutiontemperature.The gel point moved to higher angular frequency with the increase of solution temperature. Theangular frequency corresponding to the gel point had few changes at relatively high temperature inNMP/LiCl system and its change was not obvious at relatively low temperature in NMP/LiClsystem.Finally, the Cl-PPTA solution was directly spun into fibers by one-step wet-spinning method.The structure and properties of resultant Cl-PPTA fibers were characterized using scanningelectronic microscopy (SEM), tensile testing, sonic velocity orientation, X-ray diffraction (XRD),thermogravimetric analysis (TGA),,and the limited oxygen index (LOI) measurements. Theresults showed that compared with the fibers made from the NMP/CaCl2system, the Cl-PPTAfibers produced from NMP/LiCl system were more smooth and dense in their morphologicalstructure, and they also had higher tensile properties. After heat treated under high temperature,the tensile properties fibers were improved obviously with improved sonic velocity orientation andcrystallinity. In addition, the thermal stability and flame retardant performance of resultantCl-PPTA fibers were greatly higher than that of commercial PPTA fibers. The Cl-PPTA fibers’weightlessness rate were lower than that of PPTA fibers before400℃. Compared with commercialPPTA fibers, the limit oxygen index of Cl-PPTA fibers in NMP/CaCl2and NMP/LiCl system wereincreased by31.4%and37.9%, respectively.