Study On Color Fastness Performance And Fading Mechanism Of Natural Dyes On Cotton Fabric

In the background of the textile industry advocating the green concept,natural dyes have a broad development prospect in the textile industry due to their environmental friendliness and affinity to human body compared to synthetic dyes.However,the problem of poor color fastness in the production and application of natural dyes still needs to be solved.This project aims to provide methods that can improve the color fastness of natural dyes on cotton fabrics with green safety in mind.In this study,two natural dyes,namely Sodium chlorophyll copper（SCC）and Gardenia yellow（GY）,representatives of the most unstable green dyes and the most common yellow dyes,were selected for the study.The sol-gel method was used to prepare silica sol by hydrolysis of tetraethyl orthosilicate（TEOS）with ammonia,and polyvinylpyrrolidone（PVP）was used as a binder to strengthen the interaction force between silica particles and pure cotton fabrics.Different treatment methods such as PVP@SiO₂ composite coating,SCC@SiO₂ microsphere loading and antioxidant addition were used to improve the color fastness of SCC and GY on cotton fabrics,focusing on the effect of each method on the improvement of dye color fastness and handle changes,and the mechanism of action was investigated.The research contents and results are as follows:（1）Based on the silica sol-gel method,a PVP@SiO₂ composite coating treatment was realized on the fabric surface to achieve the purpose of enhancing the color fastness of SCC and GY dyed fabrics.The test results showed that,without affecting the fabric color and composite coating effect,theΔE values of treated SCC and GY dyed fabrics caused by exposure to simulated light source irradiation were reduced by 61%and 37%,respectively,when the TEOS:NH₃·H₂O volume ratio（v/v）was 1.3:1;the rating of washing colorfastness was improved to 4.0-4.5（ISO 105-CO6）;the rating of rubbing colorfastness was improved to 3.5-4.5（ISO 105-X12）;the crease resistance,drapability and bending resistance of the fabrics were reduced to different degrees.By SEM,XPS,XRD and other results,it was observed that the composite coating was successfully attached to the fabric surface and the uniformly dispersed particles on the fabric surface were SiO₂ with a diameter of about 50nm-100nm,which were amorphous crystals.（2）SCC@SiO₂ microspheres were prepared by sol-gel method,dispersed in PVP solution to form a suspension,and used as a coating to scrape on the surface of cotton fabric.At the same time,for the characteristics of GY easy to oxidize,a trace amount of antioxidant Gallic acid（GA）was added to the GY/PVP solution to prepare a dyeing solution,which was then printed onto the surface of cotton fabric by screen printing.As tested above,the results showed that theΔE values of the SCC@SiO₂ microsphere dyed fabric and GA/PVP/GY treated fabric treated caused by exposure to simulated light source irradiation were reduced by 47%and 70%,respectively,and the rating of washing colorfastness improved to 3.0-4.0 and rubbing colorfastness improved to 3.5-4.0,and the crease resistance,drapability and bending resistance of the fabric slightly decreased.By the characterization results of SEM and TEM,it was observed that both SCC@SiO₂ microspheres and GA/PVP/GY had been successfully loaded onto the fabric surface,and the SiO₂ particles wrapped SCC in the gap to form microspheres with a microsphere diameter of about 300 nm-400 nm.（3）The mechanism of the above methods on improving the color fastness of the two dyes and their color fading or change mechanism were investigated by photocurrent response,COMSOL dielectric simulation,Cyclic voltammetry,and UV-vis DRS tests.The results of photocurrent response and COMSOL dielectric simulation tests showed that SCC is photosensitive and PVP@SiO₂ coating can block the electron transfer from the photosensitive reaction and improve the color fastness of SCC.The results of CV and UV-Vis spectroscopy showed that GY has a weaker antioxidant property compared to GA,and it is presumed that the addition of trace amounts of GA can eliminate the free radicals of photosensitive products,so the GA/PVP/GY treatment method has the best effect on improving the color fastness of GY.The results of CIE LAB color space test showed that SCC mainly changed color after light exposure,and GY mainly faded.