Thermodynamic and kinetic studies of the adsorption behaviour of the natural dye cochineal on polyamide 66

Abstract

The adsorption behaviour of the natural dye cochineal on polyamide 66 was studied at different pH values. The thermodynamic and kinetic parameters such as standard affinity (−Δμ˚), changes in enthalpy (ΔH˚) and entropy (ΔS˚), diffusion coefficient and activation energy of the diffusion, were determined for pH values of 3 and 6. Results indicated that the experimental data fitted appropriately with the Nernst isotherm. Furthermore, the partitioning ratio and −Δμ˚ decreased significantly with increasing temperature, and it was revealed that the adsorption of cochineal onto polyamide was an exothermic process. The −Δμ˚ value of polyamide dyed at pH 3 was higher than that dyed at pH 6. This is related to higher numbers of electrostatic and non‐electrostatic interactions between cochineal and polyamide at pH 3, whereas at pH 6 non‐electrostatic hydrophobic interactions between cochineal and polyamide are dominant. At pH 6 comparatively higher negative values for ΔH˚ and ΔS˚ were obtained. The diffusion coefficient increased with rises in temperature. The polyamide dyed at pH 3 had a higher diffusion coefficient at every temperature than the polyamide dyed at pH 6. The dyeing rate for polyamide at pH 3 was higher than at pH 6 and reached equilibrium in a shorter time. Furthermore, a lower activation energy of diffusion was obtained at pH 3 compared to pH 6.

Cationization of cotton with ovalbumin to improve dyeing of modified cotton with cochineal natural dye

“…These data suggested that the mechanism of adsorption of the pseudo second-order model was predominant and that the overall rate of adsorption of cochineal dye was probably controlled by the chemisorption process due to the electrostatic attraction between the dye and the fiber. This is consistent with other studies that described the adsorption of the cochineal dye in compounds having amine groups, such as wool 28,43 and polyamide, 6 and in the marine sponge Hippospongia communis that has protein composition. 44…”

“…The small amount of dye adsorbed in the dyeing of untreated fabric can be attributed to the formation of non-electrostatic interactions as hydrogen bonds between the hydroxyl groups present in the dye and cellulose and also by the attraction of Van der Waals forces. 6,38…”

“…This result is consistent with other studies using cochineal dye in dyeing cotton, 41 wool, 2,28,42 and polyamide. 6…”

“…Negative values for thermodynamic parameters were reported in cochineal dyeing of wool, silk, and polyamide. 2,5,6…”

“…The main coloring compound present in the body of this insect is carminic acid, which consists of an anthraquinone derivative, with anionic character mainly due to a large number of hydroxide groups. 2,5,6 Its chemical structure is shown in Figure 1.

Figure 1.Chemical structure of carminic acid.

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