Reactive Dry-transfer Printing Of Natural Fiber Fabrics Based On Mixed Polysaccharide Thickeners

The transfer mechanism of the reactive dry-transfer printing can be stated that reactivedyes are dissolved, permeated and fixed via a steaming after giving a tight adhesionbetween transfer printing paper and unsized dry fabrics via a hot-pressing. This mechanismis different with the sublimation transfer of disperse dyes, thus there is no need to modifynatural fibers to improve their dyeability towards to disperse dyes; which is also differentwith the dissolution and transfer of dyes by the wetting method, thus the wet sizingpretreatment can be avoided. To prepare the adhesive dry-transfer printing paper, the pastecontaining high-substituted hydroxypropyl cellulose (H-HPC) acted as the hot-meltadhesive was used to modify the paper by coating. As the thermal gelation of H-HPCbrings about a decline of the paste viscosity during the process of drying coating, anotherpolysaccharide thickener without obvious thermal gelation, i.e. sodium alginate (SA),carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), guar gum (SG-9) andcarboxymethyl starch (SG-24) was mixed with H-HPC individually. To achieve thedissolution, permeation and fixation of reactive dyes, appropriate humectants and fixationalkaline agents were required in the paste.In the research of chapter two, the hot-melt property of H-HPC as well as the thermalstability and swelling ability of the six polysaccharide thickeners were mearsured first.Effects of five kinds of mixed polysaccharide thickeners, i.e. H-HPC/SA, H-HPC/CMC,H-HPC/HEC, H-HPC/SG-9and H-HPC/SG-24on the rheology of the pastes, coatingamount on the transfer printing paper and color depth of the printed fabric wereinvestigated emphatically. The results of the research showed: the hot-melt temperature ofH-HPC was about120℃. All the pastes based on H-HPC possessed a shear-thinningbehavior suitable for the paper coating, and their viscoelasticity depended on the nature ofanother thickener used, i.e. SA, CMC, HEC, SG-9and SG-24. The coating amount on the transfer printing paper might be reduced by a higher elasticity of the paste, andproportionally related to the dynamic viscosity of the paste whose viscous was higher thanelasticity. The face color depth of the prints was governed by the coating amount and thechemical nature of another thickener. The deepest color was obtained upon usingH-HPC/SA, while the sharpness was poor. The printing effects and applicability based onH-HPC/CMC were the best when comprehensively evaluating the color depth, sharpness,color fastness, handle and fabric peelable degree.The research of chapter three was focused on the rheology and morphology ofH-HPC/CMC which possessed the best transfer printing performance. Steady-shearexperiments showed: an increasing solid content contributed to a more obviouspseudo-plastic characteristic of H-HPC and CMC. CMC had a higher structural viscosityand exhibited the thinning behavior at a lower shear rate. Power-law model can be used todescribe the steady-shear curves of H-HPC and CMC. Thixotropic tests showed: thethixotropy of H-HPC was smaller than that of CMC. Dynamic frequency sweep showed:the two thickeners both displayed an increasing elasticity and a decreasing viscous with thepromotion of angular frequency or solid content, and the viscoelasticity of CMC was morestable than that of H-HPC. The compatibility of H-HPC/CMC was good under theconditions of weakly acidic, neutral, weakly alkali and different urea content viacomparing the variations in its rheology. Observing the micro-morphology of H-HPC,CMC and paste films obtained at the different dry temperatures or by the different filmforming methods using optical and atomic force microscopes found that the distribution ofH-HPC in the paste film was more uniform when drying at over80℃.In the researches of chapters four and five, the reactive dry-transfer printingperformances of silk and cotton fabrics based on H-HPC/CMC were researchedsystematically. The key impact factors on the color depth of the prints, dye penetration andfixation rate were tried to seek from the two aspects of transfer paper preparation andprinting process optimization, and the differences of the printing performance of the twofabrics were analyzed. Meanwhile, the printing effluents as well as the color characteristic and wearability of the prints respectively obtained by the dry-transfer printing andtraditional screen printing were compared. The study about the silk printing performanceshowed: color depth of the silk prints was crucially influenced by the adhesion extentimparted by H-HPC, the type of fixing alkaline agent, the hygroscopic extent of the pasteand fabric. Trichloroacetic acid (TCAA) as the fixing alkaline agent and adding ureaenhanced the color yield markedly. Dye penetration depended on the coating amount onthe transfer printing paper, the content of urea and dicyandiamide. The printed silkpossessed a deeper color, color fastness of grade3or above, clear pattern and good handlewhen the paste containing3%H-HPC,0.7%CMC,3%TCAA,5%urea,3%dicyandiamide,and0.5%SiO2was used to prepare the transfer printing paper. The biggest differencebetween cotton and silk printing performance was that cotton achieved a deeper color inthe Na2CO3/TCAA buffer fixation system with stronger alkality. The transfer printingprocess was optimized as follows: the adhesion pressure and temperature were1-3Mpa and115-125℃respectively, and the steaming temperature and duration were102-112℃and10-20min respectively. The comparisons between dry-transfer printing and screen printingshowed: COD value of the transfer printing effluent was lower than that of the screenprinting effluent, but dyes content in which was higher. COD value of the printing effluentwas mainly caused by the thickeners used. Regardless of the substrates, levelness, dyepenetration and color fastness of the prints obtained by the screen printing were higher thanthose obtained by the transfer printing, while the substrates obtained by the transferprinting had a softer handle. Both the printing methods decreased the whiteness andstrength of the silk and cotton but had practically no effect on their water-vapourpermeability.