Supramolecular Structure,decomposition And Reduction Properties Of Thiourea Dioxide And Its Application In Formaldehyde-free Discharge Printing Of Polyester Fabrics

Discharge printed textile products have many attracting virtues,such as clubby colour,fine figure and clear profile,and then the technology can also develop special style printed products by controlling process parameters.However,the traditional formaldehyde hydrosulfite discharging agents and tin-containing discharge agents will release free formaldehyde and heavy metal in the producing and using process,and which are environmentally-unfriendly,instability and complicated in application.As a new environmental reductant,thiourea dioxide has limited application in discharge printing due to its low solubility and utilization effect instability although it has the potential to become a discharge agent.In addition,the compact structure of polyester fiber furtherly increases the difficulty in discharge printing of polyester fabrics.So it is of great significance to investigate the supramolecular structure,decomposition reduction mechanism of thiourea dioxide in aqueous solution and its applications in non-formaldehyde discharge printing of polyester fabrics.Our research include the following four aspects:supramolecular structure of thiourea dioxide in aqueous solution,decomposition and reduction mechanisms of thiourea dioxide,the key constrained factors of thiourea dioxide in polyester discharge printing,and the preparation and the application of the polyester environment-friendly discharge agent based thiourea dioxide.And the main results are as following:1.Density functional theory B3LYP/cc-PVDZ calculation method,Ultraviolet absorption spectrum?UV?,Raman spectrum,Ultra high performance liguid chromatography-time of flight mass spectrometry?UPLC-TOFMS?were applied to study the existence forms of thiourea dioxide in aqueous solution.The results show that thiourea dioxide is formed into II configuration with different moleculars in the aqueous solution by self-aggregation and the adsorption of[HCSO]⁺ions and[H₂NCNH]⁺ions,in which the aggregates or additions formed by II2 configuration have the largest number.2.The potential analysis showed that the electrode potential of thiourea dioxide has point of discontinuity.At 55?,its electrode potential becomes sharply decreased and when the temperature is up to 80?,the potential value is about-0.62 V,showing strong reducibility.High performance liquid chromatography shows that the decomposition rates increase with the rise of the temperatures,and the related decomposition rates are 2.20×10^-5s^-1,1.35×10^-4s^-1,8.27×10^-4s^-1,4.72×10^-3s^-11 at 50?,70?,90?,100?,respectively.Raman spectrum and UPLC-TOF-MS spectrum were applied to investigate the decompositions of thiourea dioxide at various temperatures.The related results show that thiourea dioxide begins to decompose at 55?to produce urea and sulfuric acid,in which the former will decompose into CO₂ and NH₃ and the latter will transform into S₂O₄^2-and furtherly SO₄^2-and SO₃^2-at higher temperature.3.A new viewpoint on the key factors of the application of thiourea dioxide on polyester discharge printing were proposed based on the interactions among the structure of dye molecules,the structure of fiber and the discharge agent.The results show that the asynchronism between the degree of diffusion of the discharge agent in the interior of compact structure of polyester fiber and its decomposition and reuction performance is regarded as the key factor in the polyester discharge printing of thiourea dioxide.The environmentally friendly discharge accelerator B?Ar₁-?CH₂?_n-COO-?CH₂?_m-Ar₂?can effectively improve the whiteness effect.The more difference in solubility parameter between dyes and polyester fibers,in discharge printing,the easier thiourea dioxide destroy the color as reductant,therefore,solubility parameter theory can be used to select the available disperse dyes.4.Based on the study on the structure and properties of thiourea dioxide,a non-formaldehyde discharge agent TN for polyester fabrics was prepared with thiourea dioxide as the main body,and discharge accelerator B as the auxiliary.The particle size of thiourea dioxide has been significantly reduced after grinding.The discharge accelerator B is oiliness that can construct W/O suspension emulsion system with moderate amounts of water,which can completely cut off the adduction of air,advoid the aggregation of thiourea dioxid particles,and enhance the stabilities of thiourea dioxide in store and discharge.The optimum process parameters of discharge agent TN are obtained as following:the dosage of discharge agent TN is 10-12%,steam under 102?for15 minutes.The discharge agent TN has the similar whiteness effect on polyester fabrics like discharging agent H.5.By means of theoretical prediction and practical experiments,a complete set of disperse dyes with ground color and richromatic color was developed.We can obtain good printing effect with the application of non-formaldehyde discharge agent TN and the matching disperse dyes.The ground color and richromatic color are bright and the pattern is clear.The washing fastness was above 4 grade,the dry crocking fastness and wet crocking fastness were above 3⁴ grade.