Preparation And Dyeing Mechanism Of Spandex Easily Dyed With Acid Dye

Conventional polyurethane fiber（spandex）has been widely used in clothing.Adding a small amount of spandex to textiles can greatly improve the elasticity,wear resistance and other mechanical properties of textiles.But it is difficult to be colored into a deep hue with acid dyes.Therefore,textiles containing spandex fiber have the problem of"whitening"in the process of wearing,which affects the appearance and wearing experience.This work proposed to use dicyclohexyl methane-4,4’-diisocyanate（HMDI）and N-tertiary butyl diethanolamine（TBDEA）,1,4-（2-hydroxyethyl）piperazine（BHOPA）as raw materials to synthesize polyurethanes,respectively named poly（HMDI–TBDEA）and poly（HMDI-BHOPA）.The modified polyurethane fibers,MPUF and BPUF,were prepared by adding them into the spinnin g solution of conventional polyurethane fiber（CPUF）to enhance dyeability towards acid dyes.Poly（HMDI-TBDEA）or Poly（HMDI-BHOPA）introduced tertiary amine groups to MPUF or BPUF,which were protonated under acidic conditions and colored by electrostatic adsorption of acid dye anions.The larger molecular space structure of TBDEA or BHOPA destroyed the ordered arrangement of hard segments in polyurethane and increased the accessible area of acid dyes.The synthesis of poly（HMDI-TBDEA）and poly（HMDI-BHOPA）was verified by the NMR spectroscopy(¹H and ¹³C NMR)and gel permeation chromatography（GPC）.CPUF,MPUF and BPUF were characterized by differential scanning calorimetry（DSC）,thermogravimetric analysis（TG）,X-ray diffraction（XRD）and mechanical properties tests.The dyeing kinetics and thermodynamics of CPUF,MPUF and BPUF were studied.It was found by thermal analysis and XRD analysis that poly（HMDI–TBDEA）and poly（HMDI–BHOPA）were in their broad space structure and asymmetry,and helped to reduce the proportion of orderly arrangement of hard segment.With the addition of poly（HMDI-TBDEA）or poly（HMDI-BHOPA）,the three kinds of spandex exhibited roughly the same elastic recovery and the elongation at break,and the breaking strength were reduced.Zeta potential tests showed that the tertiary amine groups in poly（HMDI-TBDEA）or poly（HMDI-BHOPA）could be protonated to enhance the positive charges on MPUF and BPUF under acidic conditions.It was found by studying the dyeing kinetics and thermodynamics of CPUF,MPUF and BPUF that Elovich model had high applicability to the dyeing kinetics curves of three types of spandex at different temperatures and p H.The Freundlich adsorption isotherm model and Langmuir adsorption isotherm model were used to fit the adsorption isotherms of acid dyes.The data of the adsorption isotherm showed different fitting results at different p H and temperature.It could be concluded based on the model fittings of adsorption kinetics and adsorption isotherm model,that there were two ways to bind acid dyes to CPUF.One was the acid dye site formed by the protonation of ammonia lipid group in acidic conditions,and the fiber was dyed by electrostatic interaction.The other was that acid dyes were adsorbed on the soft segments of spandex by van der Waals forces and hydro gen bonds.In addition to the above two dyeing methods,there were also some dyeing sites for acid dye formed by protonation of tertiary amino group on poly（HDMI-TBDEA）or poly（HDMI-BHOPA）under acidic conditions.In the thermodynamics of dyeing,the two combination methods showed different strength relationships under the conditions of different p H and temperature,but when the acidity of dyeing solution was gradually increased,the electrostatic interactions gradually became the dominant forces for dyeing.