Preparation of cochineal/polystyrene composite colloidal microspheres and their self-assembly and coloration properties on cotton fabrics

To enhance the coloration performance and light stability of anthraquinone natural dyes on cotton fabrics, cochineal was incorporated onto the surface of cationic cross-linked polymethyl methacrylate (PMA) colloidal microspheres via electrostatic adsorption. This process led to the formation of an external surface-absorbable dye structural element (cochineal/PMA microspheres), which serves as a functional colorant. In this study, cochineal composite microspheres with uniform particle size and clear morphology were prepared by mixing cochineal with polypropylene nanospheres, which were prepared via soap-free emulsion polymerization. Their characteristics were examined using thermogravimetric analysis, infrared spectroscopy, zeta-potential analysis, and particle size distribution analysis. In addition, their dyeing properties on cotton knitted fabrics were investigated. The results show that under certain laboratory conditions, the average microspheres size increased from 112 to 192 nm, the polydispersity index (PDI) changed from 0.028 to 0.052, and the zeta potential decreased from +52.8 to +29.3 mV. With the dye concentration of 2 mg/mL, a temperature of 50°C, a mixing rate 200 rpm, and 10 minutes of adsorption, cochineal was optimally absorbed by the microspheres. The adsorption kinetics and isotherm studies indicate that the adsorption of cochineal onto polypropylene nanospheres is mainly an electrostatic interaction process. With the increasing concentration of dye microspheres, the narrower bandgap within the fabric exhibits significantly enhanced light stability. The dry rubbing fastness of the cotton knitted fabrics dyed with cochineal composite microspheres ranged from 4 to 5, while the wet rubbing fastness, staining, and color fastness to soaping all ranged from 3 to 4.