Preparation Of Ultrafine Pigment Based On Cationic Copolymer Nanoparticles And Its Salt-Free Circulating Dyeing Properties For Cotton Fabrics

Textile printing and dyeing have become the main bottleneck restricting the green and low-carbon development of the industry due to the"three highs"（high water consumption,high energy consumption,and high pollution）.Low water and salt-free cyclic dyeing technology is an effective way to solve the"three highs"of printing and dyeing which is a hot research direction for the clean printing and dyeing of textiles in line with the national goal of carbon peak and carbon neutrality,and the strategic needs of the textile industry for circular sustainable development.Cellulose fibers are widely used in fields such as clothing and home decoration due to their excellent moisture absorption and natural regeneration.At present,the main synthetic dyes commonly used for cellulose fiber dyeing are reactive dyes.However,there are problems in dyeing,such as high dye promoting electrolytes,low dye uptake and fixation rates,and difficulty in wastewater treatment,which have become one of the main bottlenecks restricting the green and low-carbon development of the textile industry.Salt-free dyeing of cellulose fiber relies on the mutual attraction of positive and negative charges to promote the dyeing of colorants.The composition of the dyeing residue is relatively simple which has higher circulating dyeing value.Previous studies have shown that the strong charge attraction between cationic ultrafine pigments and cotton fabrics can adsorb and fix pigment particles on the surface of fibers,which is a green and low-carbon coloring method with the advantages of no salt,recyclable dyebath,and high uptake.However,in order to achieve zero discharge of wastewater and 100%reuse of pigments,it is necessary to prepare a highly stable cationic pigment to meet the requirements of circulating dyeing.Recently,studies in the field of colloid science have shown that amphiphilic copolymer nanoparticles can be used as solid emulsifiers and solubilizers due to their Pickering effect and anisotropic structure,which is an ideal structure for improving the adsorption and stable dispersion of organic pigments.Based on this,a series of cationic copolymer nanoparticles were first prepared by reversible addition-fragmentation chain transfer（RAFT）dispersion polymerization-induced self-assembly（PISA）method,and then adsorbed on the surface of organic pigments,and then uniformly dispersed in water system to obtain uniform and stable dispersion of nanoscale cationic pigment particles Finally,by effectively regulating the color depth,dyeing rate,color fastness,and circulating dyeing properties of cotton fabrics,a new dyeing method with excellent performance,low water,zero drainage,and no salt is established for cotton fabrics.The main conclusions are as follows:1.Synthesis and characterization of cationic copolymer nanoparticlesWith 4-cyan-4-（dodecylsulfanyl-thiocarbonyl）sulfanylpentanoic acid（CDPA）as RAFT chain transfer agent,2-（dimethylamino）ethyl methacrylate（DMA）as cationic hydrophilic monomer,ethylene glycol dimethacrylate（EGDMA）as cross-linking monomer,and benzyl methacrylate（Bz MA）as hydrophobic nucleation monomer,the affinity between copolymer nanoparticles and pigments is endowed through theπ-πinteraction between Bz MA benzene ring structure and pigments.A series of 30-300 nm cationic copolymer nanoparticles(PDMA_x-PBz MA_y-PEGDMA₁₀)（x=30-75;y=100-350）with spherical to wormlike morphology were prepared by RAFT dispersion polymerization-induced self-assembly（PISA）method.When the average degree of polymerization of hydrophilic PDMA block increased from 37 to 72,the copolymer nanoparticles were spherical,and the average particle size decreased from 62 nm to 32nm.When the average degree of polymerization of hydrophobic PBz MA block increased from 100 to 335,the morphology of copolymer nanoparticles changed from spherical to worm-like,and the average particle size increased from 50 nm to 273 nm.The electrophoresis analysis showed that the synthesized copolymer nanoparticles had amphoteric properties.When the p H value was less than 8,they were cationic;When the p H value is greater than 8,they were anionic.2.Study on preparation of ultrafine pigments and colloid properties based on cationic copolymer nanoparticlesWith C.I.Pigment Red 170 as the model pigment particle,a series of cationic copolymer nanoparticles were synthesized to disperse pigment particles.Ultrafine pigments were prepared by ultrasonic shear dispersion technology.The adsorption behavior of copolymer nanoparticles on the pigment surface was measured by UV-Visible（UV Vis）spectrophotometer.The results showed that the adsorption isotherm was Langmuir-type.Worm-like nanoparticles had stronger adsorption capacity than spherical particles.When spherical copolymer nanoparticles with an average particle size of 50 nm(PDMA₅₀-PBz MA₁₀₀-PEGDMA₁₀)was used as dispersant,the maximum adsorption capacity reached 580 mg g^-1 at 3 g L^-1;When the worm-like copolymer nanoparticles(PDMA₅₀-PBz MA₃₃₅-PEGDMA₁₀)with an average particle size of 273nm were used as dispersants,the maximum adsorption amount reached 1330 mg g^-1 at7.5 g L^-1.When the addition amount increased to 10 g L^-1,the average particle size of the ultrafine pigment reached 168 nm,and the Zeta potential reached 39.5 m V.Transmission electron microscope（TEM）observation showed that cationic copolymer nanoparticles are adsorbed on the surface of anionic pigments,and the ultrafine pigments dispersed by worm-like copolymer nanoparticles are more closely adsorbed than those dispersed by spherical nanoparticles,which can be attributed to the high anisotropy of worm-like nanoparticles,which fully cover the surface of pigments.Through aqueous electrophoresis analysis,the prepared ultrafine pigment has amphoteric properties with an isoelectric point of p H=7.Stability tests such as freeze-thaw,centrifugation,and acid-base tests have shown that cationic ultrafine pigments have excellent dispersion stability in aqueous media.3.Study on the dyeing and circulating dyeing properties of cotton fabric with cationic ultrafine pigmentsUsing cotton as a representative cellulose fiber,the dyeing properties of cationic ultrafine pigments on fabrics was studied.The salt-free dyeing process,dye adsorption kinetics curve,and color characteristics and color fastness of dyed fabrics were investigated.The results showed that the optimal salt-free dyeing process for cationic ultrafine pigments is p H=6,temperature 70℃,time 60 min,K/S value reaching 12,and dry and wet rubbing color fastness,as well as washing color fastness reaching above level 4.The ultrafine pigment dispersed by worm-like copolymer nanoparticles has faster dyeing speed and higher color depth than the ultrafine pigment dispersed by spherical nanoparticles.The balance dyeing time is shortened by 10 min,and the K/S value is increased by 4,indicating that the ultrafine pigment dispersed by worm-like copolymer nanoparticles has better dyeing performance.The main reason is that the ultrafine pigment dispersed by worm-like particles has a smaller particle size and is assembled with the fabric through electrostatic attraction to form a more compact,smooth and flat coloring layer.More importantly,cationic ultrafine pigments were used for salt-free circulating dyeing.After four cycles,the color parameters of the dyed cotton fabric showed no difference,achieving zero wastewater discharge and 100%pigment reuse.This provides a new approach for the development and practical application of green low-carbon cationic full coating salt-free circulating dyeing.