Researches On The Light And Perspiration Stability Of Triazinylstilbene Fluorescent Brighteners On Cotton Fabrics

Owing to the high affinity to cellulose fiber, water solubility and whitening efficiency, triazinylstilbene fluorescent brighteners (TFBs) have been widely used for the finishing processof cotton fabrics. However, the fading of TFBs on cellulose matrix under simultaneous exposure to sunlight and human sweat may reduce the visual quality of garment, as well as producing numerous toxic substances which directly contact skin, leading to threaten human health. Nowadays, as a result of steady improvement of living standard, the light and perspiration stability of textiles, especially for cotton fabric commonly employed in summer, has increasingly attracted consumer attention. Moreover, domestic textiles foreign trade has been suffering from financial losses constantly attribute to the poor light and perspiration stability. Therefore, the light and perspiration stability of TFBs on cotton fabrics has become essential and important.The objective of this present work was to analyze the light and perspiration stability of six selected TFBs on cotton fabrics. The effects of substituent groups, artificial perspirations and their components on the photo-fading of TFBs were investigated primarily using the single factor analysis method. Simulating of natural exposure conditions was employedsubsequentlyto research on the environmental factors affecting the light and perspiration stability of TFBs viz. wavelength of irradiation, wet condition and atmospheric constituents. Ultimately, light-initiated degradation mechanisms of TFBs under the different perspiration conditions were proposed.The main contents and conclusions were listed as following: (1)The light and perspiration stability of TFBs on cotton fabrics were influenced by substituent groups and artificial perspirations dramatically.The light and perspiration stability of TFBs was reduced by morpholine group, while improved by the extra sulfonic groups and diethanolamine group. Among three selected standards of artificial perspiration, the alkaline sweat of ATTS standard was considered as the maximum retarding affectingfactor on the light stabilities of all the TFBs. Meanwhile, the TFB with imino group (-NH-)on triazineexhibited better light stability under the perspiration of AATCC standard than that of acidic ATTS, which was reversed in the TFB with extra sulfonic acid group on its aniline structure.(2) The light stability of TFBs was affected by perspiration components.The effect of lactic acid in perspiration on the light stability of TFB was influenced by the interaction of two factors, which was depended on its pH value. The decrease of pH value leaded to the protonation of TFBs on cotton fabrics, reducing its fluorescence intensity, while increase of pH value suppressedthe lactic acid evoked protonation of TFBs, with the lactic acid playing the counterbalance effect on the photo-oxidation of TFBs. Glucose inhibited the light induced oxidation process of TFBs by its reducibility. However, the amino acid including L-histidine monohydrochloride and DL-aspartic acid quenched the fluorescent of TFBs by competitive adsorption effect as well as accelerating generating of oxygen activation. In contrast, the sodium salt compounds in artificial perspiration, composed of sodium chloride, disodium hydrogen phosphate and sodium D-pantothenate, restrained the photo-reaction of TFBs on cellulose fibers.(3) Environmental impact on light and perspiration stability of TFBs on cotton substrate was discussed in this dissertation.The experimental results indicated that the influence of ultraviolet irradiation was more significant than visible irradiation on the light and perspiration stability of TFBs on cotton fabrics. The light stability of TFBs was susceptible to the wet environment, with the moisture accelerating the photo-fading of TFBs by photo-induced hydrolysis and cis-trans isomerism.Moreover, owing to the equilibrium of adsorption and desorption and the electron donating ability, the differences of light stability of TFBs in dry and wet conditions varied with their substitute groups. Furthermore, the study on the contribution of atmospheric constituents disclosed that the oxygen in the air involved in the photo-initiated oxidation reaction of TFBs, leading to accelerate the degradation rate.(4) The light-induced degradation process of TFBs on the surface of fibers, which is complex as well as changeable, is different from the TFBs in the interior of fibers. At the beginning of simultaneous exposing to light and perspiration, the ’Adsorb-Desorb-Dissolve-Reabsorb’dynamic procedure (ADDR) occurs. The TFBs in the interior of fibers, which have been excited by the ultraviolet light, are facilitated to take place the photo-hydrolysis and photo-isomerization reactions. While, the TFBs on the surface of cotton fabrics tend to photo-oxidization reaction. With the increasing volatilization of the moisture in perspiration, ADDR dynamic equilibrium decreases, and the dissolved TFBs tend to separate out and aggregate subsequently, resulting in photo-oxidation reaction in the interior of fibers, while photo-hydrolysis and photo-isomerization reactions still play the dominate role in the fading of TFBs. After completely volatilizing of perspiration, the ADDR process is terminated, with the TFBs in the inner fibers transferring onto the exterior of cotton fabric by capillary effect and aggregate then, leading to the fact that the photo-oxidization reaction play the dominate role in fading of TFBs in both of the interior and exterior of fibers. Interestingly, the effects of components may vary with artificial perspirations.Regarding to thealkaline artificial perspiration of ATTS standard, the reducibility of lactic acid plays the counterbalance effect on the photo-oxidation of TFB as well as glucose, and the competitive adsorption effect of L-histidine monohydrochloride is suppressed. Nevertheless, in the acidic perspirations of ATTS and AATCC standards, the reducibility of lactic acid is counteracted by its protonation effect on TFBs, reducing the light stability of TFBs significantly. Meanwhile, the competitive adsorption effect of L-histidine monohydrochloride promotes the desorption f TFBs. In addition, the aggregation induced by sodium chloride and producing of ’D-A-D’ complexes caused by compounds containing sodium play the synergistic inhibition effect on photo-fading of TFBs on cotton fabrics under both of artificial perspirations of ATTS and AATCC standards.