Abstract:

Objective Silicones having low surface energy, excellent lubricity, thermal stability, and hydrophobicity, are widely used as finishing agents for endowing the finished fabrics with softness, fluffiness, smoothness, as well as other special features. Silicones must be pre-homogenized into emulsions before application. However, higher emulsion stability means higher content of surfactants for even more than 50% of the silicone mass. Consequently, the higher content of surfactant not only increases the cost of emulsion production but also hinders the silicone adsorption onto the fabrics, resulting in the low efficiency of these additives. While the high concentration of additive residues causes COD to increase in the working liquid, the processing burden of contaminated water treatment also got increased. Hence, it is extremely urgent to develop a highly efficient and feasible stabilization system for silicones.

Method Isooctyl acrylate (EHA) and hydrophilically modified isooctyl acrylate (HPEHA) copolymer latex particles were prepared by semi-continuous seed emulsion polymerization, which were used as Pickering particles. A series of silicone oil/water (O/W) emulsions dosage co-stabilized by Pickering particles were prepared, aiming at development of stabization system with reduced dosage of surfactants. The Pickering particle co-stabilized emulsions were adopted to finish fabrics. The influence of philically modified isooctyl acrylate (PEHA) particle size, dosage, and surface hydrophilic modification on the dispersion stability of the emulsions, as well as Pickering particles on the surface friction coefficients of the finished fabrics and COD values of wastewater, were investigated.

Results PEHA and the hydrophilically modified PEHA (HPEHA) latex were dried in the first stage. The resulted latex films were analyzed with infrared spectrometer and video contact angle measuring instrument. The results demonstrated the successful hydrophilic modification of PEHA. In order to obtain a stable emulsion, the dosage of surfactant to stabilize the emulsion was as high as 21% of the mass of silicone. When synergistic stabilization system composing of 7% of 180 nm-PEHA and 5% of PEHA was applied, the silicones emulsion exhibited excellent stability, indicating high stabilization efficiency of the synergistic stabilization system. Compared to the smaller PEHA particles, PEHA with larger size showed enhanced stabilization capacity as indicated by the requirement of less PEHA. The stabilization efficiency could be further improved by application of Pickering particles with water contact angle close to 90°(for example HPEHA). In terms of the synergistic stabilization system, with the decrease of (H)PEHA particle size and increase of the (H)PEHA dosage, the droplet size of silicones emulsion decreased accordingly. When the Pickering particle size, as well as dosage, was nearly the same, the droplet size of the silicone emulsion was much smaller when replacing PEHA with HPEHA. The stabilization system also exerted significant effects on the COD values of the residual working fluid, and the slippage of the finished fabrics. When the emulsion was stabilized by surfactant alone, with the increase of surfactant dosage in the emulsion, the COD values of the residual working fluid increased sharply. It demonstrated that the method to enhance the dispersion stability of the emulsion by increasing the amount of surfactant caused a large amount of silicone to remain in the residual liquid, which not only caused the waste of additives and the burden of sewage treatment, but also caused the deterioration of the slippage of the finishing fabrics. By replacing the surfactant-stabilized system with synergistic stabilization one, the finished fabric would have a lower coefficient of surface friction and higher slippage, and the COD values of the residual working fluid would be much lower. The reason could be ascribed to the cationic HPEHA particles adsorbed on the surface of the emulsion droplet, which enhanced the positive electricity of the droplet and promoted the adsorption of the droplet to the negatively charged polyester fabric.

Conclusion Pickering particles that were adopted to stabilize silicones emulsion could be obtained by emulsion polymerization. The particle sizes and surface of Pickering particles were successfully tailor-made by emulsion polymerization recipes and post-addition of hydrophilic monomers at the final stage of reaction, respectively. When the contact angles between the Pickering particle latex films and water were close to 90°, the stabilization efficiency of the synergistic stabilization system would be significantly improved, leading to the reduction of the dosage of surfactant and Pickering particles up to 60% and 90%, respectively. With the increase in the dosage of Pickering particles, the stability of the silicone emulsions was improved, and the average droplet size got decreased. The larger Pickering particles led to the silicones emulsions with enhanced stability and increased average droplet sizes of emulsions. Compared to that in the emulsion stabilized by surfactant alone, silicone in the synergistically stabilized Pickering emulsions showed higher adsorption efficiency on fabrics, which produced fabrics with lower surface friction coefficient and waste water with lowered COD value.

Key words: silicones emulsion, Pickering emulsion, chemical oxygen demand(COD), finishing agent, friction coefficient, fabric finishing