Preparation And Properties Of Ultrafine Pigment For Dope Dyeing Of Lyocell Fibers

Dope dyeing can reduce the dyeing and finishing processes of fibers and it is energy-saving as well as environmentally-friendly because it avoids the waste water in conventional dyeing. Carbon black is the main colorant of dope dyeing. In order to prepare the waterborne ultrafine carbon black which is suitable for dope dyeing of Lyocell fibers, several kinds of ultrafine carbon black dispersion were prepared by directly dispersing method and miniemulsion polymerization method, respectively, and their preparation processes were optimized. Dispersion stability of ultrafine carbon black and encapsulated carbon black in both NMMO solution and Lyocell spinning solution were further investigated. The effects of adding ultrafine coating carbon black to the rheological propertiy of NMMO solution and Lyocell spinning solution were also discussed.The results prove that sanding machine is better dispersing equipment for directly dispersing carbon black. The optimum preparing conditions is as follows: rotating at 1800 r·min-1 for 90 minutes. NNO, NP-10 and 710 have better dispersing effects on carbon black as the small molecules anionic dispersant, the non-ionic dispersant and the polymeric dispersant, respectively. MMA is a more suitable comonomer compared with St and BA in preparation of encapsulated carbon black. The optimal encapsulation conditions are that the weight ratio of MMA to carbon black, weight ratio of APS to comonomer, reaction temperature and reaction time are about 25%, 2.0%, 80oC and 2h respectively. Particle size of encapsulated carbon black is 157.4nm. The analysis approaches of FT-IR, XRD, TEM, TGA and DLS indicate that there is polymer coating on the surface of carbon black. It is found out that the changing rate of particle size is only 2.58% when encapsulated carbon black is placed at 80 oC for 24h. Compared with polymerization before and directly dispersion ultrafine carbon black, thermal stability, centrifugal stability and freeze-thaw stability of encapsulated carbon black are greatly improved.In the study of dispersion of carbon black dispersoid in lyocell spinning solution, it is discovered that encapsulated carbon black and ultrafine carbon black using NNO and 710 as dispersant don't lead to the phenomena of obvious flocculation and sedimentation. NMMO solution is a shear thinning fluid and its viscosity obviously decreased obviously after adding ultrafine carbon black. However, the rheological properties are unchanged. The dispersion stability of encapsulated carbon black in NMMO solution is better than that of NNO and 710. Encapsulated carbon black had uniform particle size distribution in lyocell spinning solution. Large particle size agglomeration occurred when NNO ultrafine carbon black or 710 ultrafine carbon black was added into lyocell spinning solution. The latter obviously couldn't be used as colourant in dope dyeing of lyocell fibers. Lyocell spinning solution is a shear thinning fluid, so the viscosity decreased obviously with adding encapsulated carbon black, increased gradually with the further increase of encapsulated carbon black. However, the rheological property of Lyocell spinning solution is unchanged. Encapsulated black/ Lyocell spinning solution has a good viscosity stability. The change rate of viscosity was not more than 5% after placing for 48 hours. With the increase of encapsulated carbon black, K/S value of cellulose films increased dramatically but then became stable.