Adsorption behavior and kinetics of lac dyeing on poly(ethyleneimine)-treated bamboo fibers

Bamboo fibers (BFs) were surface modified using alkali (controlled BFs) and alkali followed by poly(ethyleneimine) (PEI) as a pre-treating agent (PEI-treated BFs). Attenuated total reflection-FTIR, morphological observation, and thermal decomposition analysis were used to indicate the surface changes of the controlled- and the PEI-treated-BFs. The adsorption behavior and kinetics of lac dyeing on the controlled- and the PEI-treated-BFs were comparatively investigated. The dye adsorption rate at initial stage was found to be slightly affected by dyeing temperatures. At equilibrium, the highest amount of adsorption for both controlled- and PEI-treated BFs systems was found under dyeing at low temperature (30 °C) indicating that the dyeing systems were controlled by exothermic process. The PEI-treated BFs exhibited remarkable improvement in dyeability. The surface morphology and FTIR spectra of the PEI-treated BFs dyed with lac indicated the presence of electrostatic interaction between cationic sites of PEI and anionic sites of lac dye. The experimental data of both controlled- and PEI-treated-BFs dyeing systems fitted well to the Langmuir isotherm, whereas the adsorption kinetics could be described by pseudo-first-order model. The natural dye/natural fiber dyeing based eco-friendly systems investigated in this work are beneficial for the requirement of high adsorption capacity with less energy consumed during dyeing process.