The Damage And Color Fading Mechanism Of Cotton Fabric During Oxygen Bleaching Laundry

Oxygen bleaching agents are added to home laundry detergent in order to remove organic pigment stain. The chromophore of stain can be destroyed or oxidized to some easily removed micromolecule, which make the fabric whiter and brighter. However, when we remove the stain, the detergent which contains oxygen bleaching agent will produce different degree of fabric damage and color fading. Therefore, further study of the commonly used oxygen bleaching detergent's impact on fabric and dye as well as the color fading mechanism are very important, which can provide scientific basis for the fabric care.The cotton fabrics are dyed by four kinds of commonly used reactive dye first, then this research adopts the method of orthogonal experiment to test the fabric tensile strength, color change, K/S value of the fabric before and after washing. At meanwhile, adding different molar ratio, concentration of PB and TAED to the dye solution, and varying the water bath temperature, the UV-Vis spectrum of the mixture as well as the color fading mechanism can be obtain.The results show that after five consecutive washing cycles, the change of fabric tensile strength is not obvious, which reveal the critical variable have no significant impact on fabric tensile strength. However, the color change and K/S value of the fabric change remarkable, this is because dye is the important factor which affect the color change and K/S value of the fabric.Therefore, through the water bath experiment oxidation strip mechanism of four reactive dye in PB/TAED bleaching agent can be understanded. It can be concluded that decoloring rate of the chosen reactive dyes are increasing when the molar ratio changing from 5:1 to 1:2, the best molar ratio is 2:1 because PB and TAED can completely react at 2:1 and the decoloring ratio is moderate; in the condition of the molar ratio of PB and TAED is 2:1, and PB is 1 g, TAED is 0.74 g in 200 mL mixture solution, the best bleaching rate can be obtain; in the temperature of 30℃,40℃and 60℃, we can find the decolorating rate is increasing with the rise of the temperature. But the effect of changing temperature is less significant than changing the molar ratio. Through the UV-Vis spectrum, when the molar ratio of PB and TAED varying from 5:1 to 1:2, dye conjugate system is destroyed first and the absorption peak drops in visable range. The dye conjugate system is oxidized to small molecules, finally the color of the dye fades. In ultraviolet spectrum area, characteristic peak of dye skeleton structure is also gradually declined, as compared to the visible spectrum absorption peak, the decline is much smaller.With the molar ratio of PB and TAED changing from 5:1 to 1:2, the maximum absorption wavelength of C.I. Reactive Blue 194 in visable area varys from blue to light red, maybe due to the shorten of the dye conjugate. The dye C.I. Reactive Blue 160 is very sensitive to PB/TAED bleaching agent, this is because the dye conjugate system only have azo benzene rings and benzene ring, no double benzene nucleus structure. This structure is more vulnerable than other dyes we chosen. For the dye C.I. Reactive Red 141, decolouring ratio is more steady. This is because the dye molecule contain two symmetrical naphthaline-azo- naphthaline. Naphthaline is more difficult to be oxidation than benzene, so the decoloring rate is stable. The dye C.I. Reactive Red 195 only contains a naphthalene-azo-naphthalene, for this reason the conjugated system of the dye is easier to destory and decoloring rate is higher than the dye C.I. Reactive Red 141.