Covalent bonding and photochromic properties of double-shell polyurethane-chitosan microcapsules crosslinked onto cotton fabric

The research aims at treating cotton fabrics with double-shell polyurethane-chitosan photochromic microcapsules using the coating method. FTIR indicated that an acylamino group formed between the hydroxyl of cotton fabric and amino group of the chitosan shell. The surface morphology of treated cotton fabrics revealed the compact and uniform distribution of double-shell polyurethane-chitosan microcapsules on cotton fabrics. Factors affecting the covalent bonding such as the citric acid (CA) and double-shell polyurethane-chitosan microcapsule (DSPCM) concentration were studied. The K/S value of treated fabric using 9 wt% CA increased significantly; it increased by 157.0 % compared with 5 % CA. It remained almost unchanged when the CA concentration was 11 wt%. In addition, as for 7 wt% CA-treated cotton fabric, the K/S value increased by 53.5 %. The K/S values increased by 27.29 and 42.08 %, respectively, when the concentration reached 4 and 6 wt%. The color properties of samples treated with 8 wt% concentration microcapsules increased by 44.72 %. The K/S value decreased slightly after increased launderings. It decreased by 1.73 % after 30 launderings, but did not present any changes after 40 launderings; it decreased by 8.55 % after 50 launderings. The surface morphology of treated cotton fabric samples after 50 launderings remained almost the same as the original ones. It can be speculated that the covalent bonding fastness between DSPCM and cotton fabric is good. Additionally, it possesses good thermal stability. It can be concluded that 9 % citric acid concentration and 8 % DSPCM concentration allow obtaining bright and uniform color and a quick response to UV-Vis light.