Study On Preparation, Structure And Properties Of Dope Dyeing Meta-Aramid Fiber

Meta-aramid is synthesized by m-phenylenediamine and isophthaloyl dichloride through condensation polymerization. Meta-aramid fiber has excellent heat resistance, flame resistance and textile processing performance. It is often used to manufacture products as heat protective clothings, filters and fire prevention fabrics, which have many applications in military, fire protection and so on. Coloured meta-aramid fibers are often needed in these fields. The meta-aramid is difficult to be dyed due to its close molecular structure, high crystallinity and small pigment molecules can hardly get into the fiber structure.Coloured meta-aramid fibers with good dyeing depth are produced by the dope dyeing method in this study, and the chemical properties, mechanical properties of the fibers are maintained.The properties of some kinds of pigments are analyzed in this paper, including heat resistant, water resistant, acid resistant, alkali resistance properties, molecular structures, size distribution, dispersive properties and colour rendering properties. Then, three appropriate pigments are chosen from the red, blue and purple pigments which are suitable for the spinning conditions. Measurements show that the pigments have excellent thermal properties, the thermal decomposition temperatures of the pigments are all above 400℃which can meet the requirements of heat resistant applications. The average diameter of pigments are all below 2500nm, so pigments are easy to disperse in the fibers and can meet the requirements of transparency, colour gloss and colour fastness. The water resistance, acid resistance, alkali resistance and solvent resistance of the pigments are all up to 5 level. Further more, the pigments have the best dyeing depth when the processing temperature is 300℃.The die-swell behavior of dope dyed meta-aramid solution is studied in this paper. After analysis and comparison, a appropriate spinneret which is suitable for the dope dyeing spinning of meta-aramid fiber can be selected. When the solution concentration, spinning temperature and other conditions are constant, when the L/D is small, the extrusion die-swell ratio (B) declines significantly with the length and diameter ratio (L/D) increases; When the L/D is over 7, the value of B changes small with the L/D changes. What's more, the extrusion swelling ratio (B) increases with the spinning pressure increases or the temperature decreases in the process of dope dyeing spinning of meta-aramid fiber, therefore, the influence of high temperature can be reduced by increasing the spinning pressure.As-spun fibers of meta-aramid are formed by coagulating process, the properties of as-spun fibers can be controlled by controlling the coagulating conditions, such as dope concentration, coagulating temperature and coagulating time. The diffusion is studied and the diffusion coefficients are calculated through the component analysis method and computer programs. In this research, the extraction method is determined after comparing two extraction methods during the research:ultrasonic wave vibrate extraction method and soxhlet extractor extraction method. The component measure methods and experiment conditions are also determined, then the diffusion coefficients are calculated. Finally, effect of jet stretch to the coagulating performance is analyzed. The results show that, the two extraction methods have the same effect, and the ultrasonic wave vibrate extraction method is chosen due to its short extraction time. The DMAc content is measured by UV spectrophotometry. The extract is diluted 1000 times, and the absorption wavelength in the UV spectrophotometry is about 197nm. Further more, The greater the jet stretch, the greater the diffusion coefficient is, the faster the coagulation is.Fibers are prepared after wet spinning and dry heat stretching. The properties of colored fibers are studied systematically in this paper. The mechanical properties, dyeing depth of the colored fibers and the influence of sun light exposure on them are mainly studied. The results show that, fibers with the maximum breaking strength, reaching 5.73 cN/dtex, are formed with the optimal parameters of spinning process:jet stretch ratio-60%; hot water stretch 1.8 times; dry heat stretching ratio 3.The result of dyeing depth shows that, fibers have good colour gloss with heat stretching 2-3 times under temperature of 300℃. Further more, the relationship between spinning conditions and mechanical properties is fitted by an equation, and mechanical property data visualization based on the Matlab programming language is carried out. Finally, the optimal spinning process conditions are researched though the fitting equation and the mechanical property data visualization.