Study On Spinning Process Of Homopolycondensation Heterocyclic Aramid Fiber

Homopolycondensation heterocyclic aramid fiber is an important member of heterocyclic aramid polyamide fiber family.Homopolycondensation heterocyclic aramid polyamide fiber has wide application in the fields of aerospace industry,protective equipments,high-performance composite materials and braids as it owns more excellent heat resistance and mechanical properties than PPTA(poly(p-phenylene telephthalamide))fiber.Homopolycondensation heterocyclic aramid can dissolve in the polymerization system and be spinned directly to form fiber for using of 5(6)-amino-2-(4-aminophenyl)benzimidazole(DAPBI)as monomer,which results the destroys of macromolecular symmetry structure and improves the flexibility of the chains.This study focused on the spinning process fiber preparation as well as the structure and properties of homopolycondensation heterocyclic aramid fiber.Thermodynamic conditions for coagulation of homopolycondensation heterocyclic aromatic solution were studied by the way of cloud point titration.The results showed that this method owned good reproducibility and high precision and the coefficient of variability was less than 3%.Compared with other no-solvent,water was a strong coagulant for its low coagulation value and the value was 16.35mL/25mL.The solubility of the polymer was better in DMAc than that in NMP.The coagulation value enhanced from 7.32mL/25mL to 34.52 mL/25mL with the increasing of the concentration of coagulation bath from 0%to 50%and the critical coagulation concentration remain unchanged.The coagulation value reduced and its critical coagulation concentration increased with the increasing of the molecular weight.But the coagulation value enhanced and its critical coagulation concentration reduced with rise in the titration temperature and the increase of the content of salinity in the titrating solution.These showed the solubility property of the polymer was improved.Homopolycondensation heterocyclic aramid fiber was prepared by wet-spinning processing.We studied on the effects of molecular weight and the coagulation conditions on the structure and mechanical property of homopolycondensation heterocyclic aramid fiber.The degree of crystallization and orientation enhanced with the increasing of the molecular weight,as well as its mechanical property.The optimum process conditions were as follow:coagulation bath temperature was 20?,coagulation bath concentration was 20%,the spinneret draw ratio was-30%and wet draw ratio was1.3 times.These were determined by the result of scanning electron microscope(SEM),the intensify and X-Ray Diffraction(XRD)etc.The strength and modulus of the as-spun fiber under optimum conditions was 4.74cN/dtex and 125.79 cN/dtex.Finally,we focused on the heat treatment process and its influence on the structure and performance of homopolycondensation heterocyclic aramid fiber.The best heat treatment conditions were under nitrogen atmosphere,temperature of 400? and draw ratio of 1 time by Dynamic thermomechanical analysis(DMA),Thermogravimetry(TG)and mechanical property test.The chemical structure of the molecular chain did not change after heat treatment,but the degree of crystallization and orientation improved.Especially the improvement of orientation caused the mechanical property of homopolycondensation heterocyclic aramid fiber increasing greatly.At the same time,the glass transition temperature also increased from 282.36? to 327.52?.The thermal gravimetric analysis under different heating rates and atmospheres showed that the thermal degradation of fiber was serious under air atmosphere and the residual rate was nearly equalto zero,while the residual rate was relatively high without oxidation.The active energy(E)of decomposition of homopolycondensation heterocyclic aramid fiber was 218.91KJ/mol and 223.15KJ/mol by Fridemen and Kissinger methods respectively.