Research On Preparation And Properties Of Colorable/Discolorable Pigments

In traditional dye processing, active dye, direction dye and other chemicals are used. Itnot only wastes much water, but also pollutes the environment. In the thesis the pigment isprepared via dye adsorption onto titanium dioxide. By adjusting the pH value and choosingthe adsorption times the color depth of the pigment could be changed. Then the pigment ismodified by silane coupling agent KH570. Because of the catalytic capability of titaniumdioxide, the dye molecules on it can be easily decolorized under UV irradiation. And at thesame time the fixation capability of pigment on fabric can also be enhanced by modifyingwith KH570. Then the colorable/discolorable pigments are prepared. The pigments can bedecolorized under UV light radiation no matter where they are fixed. So it is veryenvironmental, non-polluted and nontoxic.The influences of pH value, adsorption times, adsorption time and dye concentration onadsorbing ability of TiO2are discussed. To analyze the first adsorption of dye molecules ontoTiO2under different concentrations, the Langmuir model, Scatchard model and Freundlichmodel are applied. What’s more, fourier transform infrared spectroscopy (FTIR), scanningelectron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy(TEM) are used to characterize the unmodified/modified pigments. The effects of couplingtime, amount of coupling agent, pH value of coupling on fixation ratio, color fastness,discoloration capability of fabrics, chromatic aberration and wearing properties have beendiscussed. In addition the scanning electron microscopy (SEM) and energy dispersivespectrum analysis (EDS) are used to characterize the colored fabric. Moreover the mechanicalproperties and discoloration properties of polymer films containing modified/unmodifiedpigments are discussed. And the pigment is fixed on the fabric with the help of a resin ofEbecrylTM5129or a fixation agent. To find out which one is better, the discolorationcapability and wearing properties of fabrics have been discussed. After that, the UV resistantagent is added in the process and the effect on discoloration property of fabrics has beendiscussed.Finally the conditions of pigment preparation are decided, which is0.32g TiO2,50ml dye solution, pH value of2(adjusting by7%HCl), twice adsorption at the concentration of1g/L and0.6g/L. By analyzing the factors of modification, the condition of modification isthat0.2g KH570is dissolved in the10mL blend solution of ethanol and water(ethanol:water=9:1) at pH value of4(adjusting by acetic acid). After30min hydrolysis,0.32gpigment is dispersed in it and then vibrated at pH value of2and temperature of65℃for2h.In the end the pigments are dried in the oven at80℃for2h and the pigments are obtainedafter washing twice. The wearing properties, color fastness, chromatic aberration anddecolorization capabilities of the pigments are all remarkable, which are made under thatcondition. And the first dye adsorption onto TiO2fits the Langmuir model in the range of lowconcentrations, implying single molecular layer chemical adsorption.It should be noticed that the decolorization properties of modified pigments are higherthan unmodified pigments no matter in the polymer films or pigment-self. The SEM picturesdemonstrated that all the pigments are nanoparticles and tend to aggregate after modification.And in the spectra of FT-IR, the peaks at2924.95cm-1,1714.91cm-1,1461.17cm-1and1289cm-1are attributed to a C-H stretching vibration of–CH3and–CH2group, stretchingvibration of C=O group and bending vibration of C-H and symmetric stretching C-O inKH570. It indicates that silane modification is successful. The crystal form of TiO2is notchanged by certifying of XRD pattern. The TEM graphs exhibit that a modified layer with athickness of about1nm is coated on the pigment. And the SEM photos of colored fabricindicate that the fabrics are covered by pigments. At the same time the EDS analysis showsthat the amount of Ti element on the fabric is high. And by analyzing the decolorizationproperty and wearing property of fabric, it is found that the fixation process with the fixationagent shows better results than EbecrylTM5129. The ultraviolet light absorber on the fabriccan adsorb the UV light in the band of UVA and UVB, but it cannot adsorb the UV light inthe band of UVC. So the color durability of pigment and colored fabric that is handled byultraviolet light absorber in daily wearing can be improved.