Results and discussion
3.1. Effect of dyeing conditions
Dyeing silk fabrics in the mangrove bark extract dye solution showed that increasing temperature increased the color strength (K/S value). Based on Fig. 2, the maximum color strength was obtained at 90◦C. The color of the dyed silk fabric was reddish- brown.
The effect of dyeing time on K/S values is shown in Fig. 3. A longer dyeing time means higher color strength (K/S values) until dye exhaustion attains equilibrium, and there is no significant increase after further increases in dyeing time. The optimum time for dyeing the silk fabrics was obtained at 60 min.
The effect of pH value on K/S values is illustrated in Fig. 4. The maximum dye uptake was observed at pH 3. Dye uptake increased from the initial pH 3 until pH 5, and then decreased at higher pH values. In the alkaline solution, reaction with hydroxide ions (OH− ) converts the ammonium ion (NH3 + ) to amino (NH2) groups and the fiber contains more carboxylate ion (COO−) (Mongkholrattanasit et al., 2011b; Broadbent, 2001). Thus,