Abstract:

Objective Plant dyes have attracted widespread attention in the textile industry due to their environmental and functional health benefits. To improve the dyeing durability and functionality of fabrics treated with plant dyes, chemical crosslinking agents or mordants are often used, which is harmful to the environment and human health. It is necessary to develop eco-friendly methods of plant dyes for fabric finishing, imparting fabrics good color fastness and multifunctionality.

Method Polydopamine/chitosan (PDA/CS) modified cotton fabrics were prepared by using chitosan (CS) finishing after rapid polymerization and deposition of dopamine (DA) on the fabric surface under CuSO₄/H₂O₂ oxidation system, and then dyed with tea pigment. The structure and morphology of the fabrics before and after modification were characterized and analyzed through scanning electron microscope, Fourier transform infrared spetroscopy and X-ray photoelectron spectroscopy. The color fastness, antibacterial and UV resistance properties of different modified cotton fabrics dyed with tea pigment were compared and analyzed.

Results The effect of various factors on the dyeing performance of the modified cotton fabrics during the rapid polymerization and deposition of DA were investigated, and the better process conditions were obtained: CuSO₄ concentration of 3 mmol/L, DA concentration of 2.0 mg/mL, H₂O₂ concentration of 13 mmol/L, and deposition time of 2 h. The K/S value of the PDA/CS modified cotton fabrics after dyeing reached 6.21. The fiber morphology and structure showed that the surface of PDA modified cotton fiber was obviously covered with a layer of PDA coating, which made CS uniformly film on the fabric surface, and the surface substance of PDA/CS modified cotton fabrics was further increased after dyeing with tea pigment. The chemical structure analysis showed that the intensity of the characteristic absorption peaks near 3 342 cm^-1 of the PDA modified cotton fabrics increased significantly after CS treatment, indicating that hydrogen bonding between PDA molecules and CS molecules was generated on the surface of the cotton fabrics. The intensity of the absorption peaks of the modified fabrics after dyeing in the interval of 1 455 to 1 210 cm^-1 were increased, indicating that the tea pigments were successfully adsorbed on the surface of the modified fabrics. Elemental composition analysis showed that compared with raw cotton, there was a new Nls absorption peak at 403.4 eV in the full spectrum of PDA modified cotton fabrics, and the N element content of PDA/CS modified cotton fabrics increased from 3.84% to 4.12%. The color fastness to soaps (discoloration) of PDA/CS modified cotton fabrics after dyeing was 3-4, and the color fastness to rubbing, soaps(staining) and artificial light reached 4 or above. The UPF value reached 312, and the transmittance of UVA and UVB bands were less than 1%. In addition, the inhibition rate of Staphylococcus aureus and Escherichia coli were 91% and 90%, respectively.

Conclusion Under the CuSO₄/H₂O₂ oxidation system, DA rapidly polymerized to form PDA polymer. Cotton fabrics were composite modified by PDA and CS, and then dyed by the natural plant dye tea pigment without any chemical crosslinking agent or mordant. Modified fabrics after dyeing have good color fastness, as well as dual effects of antibacterial and anti-ultraviolet properties, which promoting the high-quality production of cotton textiles. It is expected to be developed as a short process technology for the integration of plant dye dyeing and finishing, providing a theoretical basis for the use of natural dyes in textile dyeing and finishing technology and the development of ecological textiles.

Key words: cotton fabric, polydopamine, chitosan, tea pigment dyeing, natural dye, functional finishing