Preparation Of Core-shell Pigment Via RAFT Living Radical Polymerization And Its Application

Reversible Addition-Fragmentation chain Transfer polymerization is one of the living radical polymerizations. It combines the advantage of living polymerization and radical polymerization. In present work, macro-RAFT copolymers of styrene and maleic anhydride were prepared through the RAFT process. The application of macro-RAFT copolymers for organic pigment dispersion was evaluated. The effect of structure of macro-RAFT agent on stability and rheology of pigment dispersion was discussed. With living end groups, macro-RAFT agent can form new polymers via the addition of monomer at a controlled rate, which make the pigment encapsulated, composite particles with core-shell structure was prepared. The influences of additives on stability, viscosity, surface tension of prepared pigment dispersion, were analyzed. The application of pigment dispersion in pigment dyeing was evaluated.A trithiocarbonate RAFT agent was synthesized via carbon disulfide method. Controlled with synthesized trithiocarbonate RAFT agent, styrene and maleic anhydride copolymerized through the RAFT process.In basic conditions, the addition of carbon disulfide to thiol gave the thiocarbonythio salt. Without the need for isolation, the trithiocarbonate could be made to interact with bromo propionic acid. The synthesized RAFT agent was confirmed by FT-IR, mass spectrometry, 1H-NMR spectroscopy, named 2-{[(alkylsulfanyl) carbonothioyl] sulfanyl} propanioc acid. The macro-RAFT agent was copolymerized by styrene and maleic anhydride with the trithiocarbonate RAFT agent. It was characterized with FT-IR spectrum and GPC. The results showed that the average molecular weight of macro-RAFT agent decreased with increasing amount of RAFT agent, the distribution of molecular weight was much narrower. The dispersing ability of macro-RAFT agent on pigment was evaluated, including copper phthalocyanine and yellow pigment with azo structure. The effects of intrinsic viscosity, concentration, monomer ratios of dispersant on rheology and stability were discussed in detail.The particle size and distribution (PDI) had a relationship with ultrasonication time and amounts of the dispersant. With increased ultrasonication time, the particle size and PDI decreased first and increased slightly later. When the amounts of dispersant were too low or high, the particle size and PDI were larger. Also, the particle size and PDI were decreased first and increased later with increasing of intrinsic viscosity of dispersant, with intrinsic viscosity 43.78ml/g, the particle size was the smallest. There was well dispersing properties on copper phthalocyanine with the macro-RAFT copolymers. As to yellow pigment with azo structure, particle size of P.Y.14 with bisazo was smaller; P.Y. 65 and 73 with single azo were hard to be dispersed into small particles. The rheology and stability of pigment dispersion were influenced by the amounts, intrinsic viscosity, and monomer ratios of macro-RAFT copolymers. When the amount of dispersant was between 2-12%, the viscosity of pigment dispersion increased slightly with increasing amounts of dispersant. The viscosity increased sharply when the amount of dispersant exceeds 14%. The pigment dispersion was with low viscosity, when the intrinsic viscosity of dispersant was 43.78mL/g. The viscosity was higher when the intrinsic viscosity was too high or too low. The viscosity of pigment dispersion was lower with increasing shear rate, especially dispersed with dispersant that had higher intrinsic viscosity. The viscosity of pigment dispersion was higher when the dispersant had less maleic anhydride chains. The viscosity was lower as more maleic anhydride chains in the dispersant. However, too more maleic anhydride chains in the dispersant made the viscosity of pigment dispersion higher. The Zeta potential of pigment dispersion increased with the intrinsic viscosity of dispersant increasing, and the centrifugal stability increased first and then declined. The stability of pigment dispersion was influenced by the monomer ratio of the polymeric dispersant. When the ratio of St:MA was 1.5, the dispersant had appropriate ratio of hydrophilic and hydrophobic chains, and the stability of pigment dispersion was very well. PH value was another important factor that influences the stability of pigment dispersion. When the pH value was 7-8, the pigment had higher centrifugal stability. Too high acidic or basic, the particles could coagulated to each other, the stability of pigment dispersion decreased.Pigment was encapsulated with polymers by surface reversible addition-fragmentation chain transfer polymerization; core-shell pigment particles were prepared. In surface polymerization, monomers can polymerized by emulsion polymerization, starved feed emulsion polymerization, miniemulsion polymerization, and so on. In emulsion polymerization, monomers polymerized in micelle was the mainly particle nucleation, a lot of free polymer particles were formed in the aqueous phase. It appeared that it is difficult to achieve high encapsulation efficiency by emulsion technique. While, there were less nucleation in aqueous phase by starved feed emulsion polymerization and miniemulsion polymerization, much more effectively encapsulation of pigment can be made by these two methods.In preparation of core-shell pigment via starved feed emulsion polymerization, feeding rates of monomers were significant for particle nucleation mechanism and affect the encapsulation efficiency of pigment. There were much more monomers nucleate in the aqueous when the feeding rate was too fast, which made lower encapsulation ratio. However, with slowly feeding rate, the polymerization time was long. The appropriate feeding rate was about 0.04-0.05g/min. With polymer encapsulated, the pigment particle size increased, the distribution of particle size was smaller, and anther words pigment particles were much more uniform. The polymerization on pigment surface had no relationship with the structure of pigment, related to the monomer, feeding rate, temperature and so on. As to miniemulsion polymerization, the encapsulation ratio and efficiency of P.Y. 83 with polymers were larger than that of P.Y. 65. There were stronger interactions between monomers and P.Y. 83, monomers tend to adsorb better on the surface of P.Y. 83. Acrylates tend to adsorb better on the surface of azo pigment than methacrylates, while the encapsulation ratios of polyacrylates were higher. It was shown from TEM photo of pigment that pigment was encapsulated by polymers via surface RAFT polymerization. There were some pigment-free polymer particles in the pigment dispersion.The applications of core-shell pigment dispersion were evaluated, including suitability for preparation of pigment inkjet inks and dyeing properties in pigment dyeing on cotton fabrics.Additives such as polyalcohol, surfactants and n-butyl alcohol can improve rheology, moisture retention and defoaming properties of pigment dispersion. Polyalcohols such as ethylene glycol, diethylene glycol, and glycerol have no side effect on stability and particle size of pigment dispersion. The addition of polyalcohol made the viscosity of pigment dispersion increasing and surface tension decreased slightly. Surfactant peregal O made the surface tension of pigment dispersion reduction. When the concentration of peregal O was about 0.5-1%, the surface tension of pigment can be reduced to 25-35 mN/m. With this concentration, the viscosity increased little. N-butyl alcohol has well defoaming ability on pigment dispersion, and it has less effect on viscosity and surface tension of pigment dispersion.By measuring K/S values the influence of cationizing conditions on the color strengths of the modified cotton fabrics dyed with pigments were investigated, including PAE concentration, temperature and time, and pH values. The results show that when the PAE concentration was below 10% (o.w.f.), the K/S value increased nearly linearly with increasing of PAE concentration and, when the PAE concentration reached 10% the K/S value did not increase further. With increasing the pH value of cationization bath the K/S value increased first and then decreased, the maximum K/S value appeared at pH 9-10. Cotton fabrics cationized at 80oC for 20 min exhibited the best cationizing result. Cotton cationization made the cellulose fibers positively charged, and enhanced the electrostatic attraction between fibers and pigment particles. Cotton cationization improved the coloration properties, yields of pigment and brilliance of color. The color shades of dyed samples were affected by immersing in hot water, although there were on stirring during the process. After hot water immersing, K/S values and brilliance of cationized cotton were enhanced, because the distributions of pigment particles on fabrics were much more uniform under the observation through scanning electron microscopy.