Study On Dyeing And Anti-ultraviolet Properties Of Madder Natural Dye

With people's increasing pursuit of environmental protection and health,natural dyes have once again received attention from people due to their own unique cultural,aesthetic,and environmental significance.Natural dyes not only enable fabrics to enjoy the elegant colors conferred by nature,but also realize the recycling of resources and reduce the environmental pollution caused by chemical dyes.In this paper,one of the natural dyes,Madder,was selected as the research object.A series of detailed studies were carried out on its physicochemical stability,the dyeing performance of cotton and nylon fabrics,and the dyeing process and functionality.In this paper,Madder was placed in liquors of different temperatures,pH,metal ions,oxidants and reducing agents.The absorbance values of dye liquors before and after treatment were measured,thus as an indicator for evaluating various stabilities.The final conclusions were drawn as follows:Below 100°C,the Madder dye liquor had good thermal stability and redox stability.And the state of the Madder dye solution changed with the pH value of the dyeing solution and the type of added metal ions,so its pH stability and metal ion stability were relatively poor.Using EDTA as a chelating agent,the standard working curve of Madder dyes in the presence of both EDTA and Fe²⁺was plotted to study the dyeing mechanism of cotton fabrics,with Fe²⁺pre-mordanting,dyed with Madder dyes.Conclusions drawn from the fitting of different models were:The dyeing rate curve in the dyeing process was finally consistent with the Quasi-secondary model.And the adsorption isotherm best fitted the Langmuir adsorption model,and was more consistent with the Freundlich model.It showed that there was not only localization adsorption due to Coulomb force between the pre-mordanted cotton fabrics and dyes,but also the non-localized adsorption due to Van der Waals force and other intermolecular force.The equilibrium adsorption capacity reached a maximum at 80°C and the dyeing enthalpy value was 21.0787KJ·mol^-1,indicating that the dyeing process was endothermic and the dyeing entropy was 0.0938 KJ·mol^-1·K^-1.Based on the results of thermodynamic and kinetic analysis,the single factor test and orthogonal test were used to optimize dyeing process of natural Madder dye on cotton fabrics with Fe²⁺pre-dyeing.It was found that when the amount of Madder dye was 1%o.w.f,the mordant FeSO₄ amount was 3%,the pre-media temperature and time was 70°C and 50 min,and the dyeing temperature and dyeing time was 80°C and 50 min,the dyeing effect was best.In addition to the light fastness of the pure cotton fabrics dyed in this process,all the other fastness was relatively good and could reach 3-4 levels.The standard working curve of natural Madder dye under weak alkaline conditions was drawn to study the dyeing mechanism of natural Madder dye direct dyeing nylon fabric under weak alkaline conditions.It was shown from the fitting of different models that the dyeing rate curve of the dyeing process conformed to the Quasi-secondary-level model,and the adsorption isotherm most conformed to the Nernst adsorption model.It illustrated that the combination of Madder dye and nylon fiber was mainly based on Van der Waals force and hydrogen bonding.And when temperature was below 100°C,the equilibrium adsorption capacity of the dye increased and the dyeing affinity decreased with increasing the dyeing temperature.The dyeing enthalpy value was-21.5330 kJ·mol^-1,indicating that the dyeing process was an exothermic reaction.The dyeing entropy was-0.0501 KJ·mol^-1·K^-1,showing that the affinity was relatively high and the orientation of the dye on the fiber was relatively small.Box-Behnken experimental design and response surface analysis were used to study the effect of dyeing temperature,dyeing time,dyeing pH and dyeing density on the dyeing uptake rate of nylon fabrics when natural Madder dye was used to directly dyeing nylon fabrics.The variance analysis data of the quadratic model indicated that the degree of effect of the Madder directly dyeing on nylon was ranked as follows:dyeing pH>dyeing concentration>dyeing temperature>dyeing time.And a higher dye uptake could be achieved by lowering the dyeing pH to near-neutrality,lowering the dyeing concentration of Madder,and increasing the dyeing time.The response surface analysis experiments showed that the best dyeing process was:the dyeing temperature was 95°C,the dyeing time was 160 min,the dyeing pH was 7.00,and the dyeing concentration was 2.0%o.w.f.The nylon fabric dyed under this dyeing process had relatively poor acid,alkali and perspiration resistant fastness,while the remaining other fastness was better.Finally,the effects of Madder dye and Fe²⁺dosage on the anti-ultraviolet and light-fading properties of different fabrics were investigated.Results showed that the UV resistance of the dyed cotton fabrics improved with increasing the dosage of Madder dye and Fe²⁺.And Fe²⁺had a positive effect on the improvement of light fastness of dyed cotton fabrics.And increasing the amount of Madder dye was also beneficial to the improvement of UV resistance of dyed nylon fabrics.