Insight into hair dyeing properties and mechanisms of Maya blue-like pigments modified with different silane coupling agents

Abstract

The use of clay-based nanomaterials for human hair dyeing is an ideal method due to its high safety and minimal hair damage. However, their hair dyeing mechanisms are poorly understood. This study shows the hair dyeing properties of Maya blue-like pigment (palygorskite-indigo hybrid, MB) and its organically modified samples. The hair dyeing effect of the hybrid was determined by measuring the chromatic parameters and calculating the color difference. A series of characterizations, such as SEM, contact angle, mechanical properties, and shampoo resistance, were carried out on the hair before and after dyeing to reveal the dyeing mechanism. The results indicated that organic modification could significantly improve the hair dyeing effect of the pigment. The loading ratios of indigo, MB, 550 MB, 560 MB, 590 MB, and 1631 MB on the hair were 0.12 %, 0.54 %, 5.85 %, 3.77 %, 4.30 %, and 6.68 %, respectively. The colloidal stability of the modified pigment determined the size of particle aggregates deposited on human hair. The difference in hydrophilicity and hydrophobicity between the hybrid and hair could control the coverage of particles. Dyeing with modified pigments improved the mechanical properties and shampoo washing resistance of hair. After 10 repeated shampoo washes, the retention ratioof hair dyed with modified samples was significantly better than that of MB, still maintaining at 72–92 %. The mechanisms of action between the four silane coupling agents modified samples and hair were electrostatic attraction, covalent bonding, hydrogen bonding, and hydrophobic interaction, respectively.