Application of natural dyes in textile industry and the treatment of dye solutions using electrolytic techniques

Abstract

Anodic oxidation of a commercial dye, methylene blue (MB), from aqueous solutions using an electrochemical cell is reported. Data are provided on the effects of eight different types of supporting electrolytes, concentration of electrolytes, initial dye concentration, current and electrolytic time on the percentage removal of methylene blue. Anodic oxidation was found to be effective in achieving the removal of methylene blue from aqueous solutions.

The optimised electrolytic conditions, for the removal of methylene blue (MB), were applied to the removal of azure A (AA), azure B (AB), azure C (AC), toluidine blue 0 (TBO), new methylene blue (NMB), dimethyl methylene blue (DMMB), thionine (TH), methylene green (MG), methyl violet (MV), Nile blue (NB), neutral red (NR), acridine orange (AO) and resorufin (RS) from aqueous solutions containing sodium chloride. Results indicated that between 84 to 100% of each dye of phenothiazine was removed during 60 minutes of electrolysis. The percentage removals for the phenothiazine dyes followed the following decreasing order: (MG ≈ MV) > (DMMB ≈ AA) > (AB ≈ AC ≈ NMB) > TBO > TH. However, the azine, acridine and oxazine dyes showed between 98 to 99% colour removal and the following decreasing order: NB ≈ NR > AO ≈ RS. Strongly electron withdrawing substituents such as nitro group or carbonyl group increases the degradation of the phenothiazine chromophore, whereas the electron donating groups such as amino and alkyl amino groups decrease the degradation.

Anodic oxidation studies were extended to the destruction of eight permitted food colours, with azo and triarylmethane chromophore, from aqueous solution containing either sodium chloride or sodium sulphate as a supporting electrolyte. Again, sodium chloride was found to be the best supporting electrolyte and between 97 to 100% colour removal was achieved after 60 minutes of electrolysis. The percentage removal for the single azo based colourants followed the following increasing order: carmoisine > sunset yellow FCF > amaranth > ponceau 411 > tartrazine. However, the binary and ternary mixtures of food colour showed the following increasing order: blue > green > yellow food colours. The extractions and applications of 54 different types of natural dyes (53 from plants and one from animal origin) are evaluated using simple techniques. The extracted natural dyes were applied in dyeing three types of textile fabrics viz: a) paj silk, b) brushed cotton twill and c) crystallized shimmering satin. The effects of two eco-friendly mordants (alum and iron) on the dyeing process were compared with the dyeing process without mordants. The colour fastness to wash and light (both natural and artificial sun light) of these natural dyes were also assessed. The results showed that out of the 54 dyestuffs studied, 32 plants are potentially able to produce marketable natural dyes. These dyes produced good colour and met minimal performance standards for colour fastness to light and washing. The addition of mordants generally increased the fastness properties. Silk gave the best performance of dyeing uptake and stability. Cotton gave the poorest fastness properties. The overall results showed that, considering molecular associations, the fastness properties were of the order: anthraquinones and tannins> indigoid > flavones> flavonols > flavanols> carotenoids> anthocyanins.

Anodic oxidation studies were extended to the destruction of ten natural dyes from aqueous solutions containing either sodium chloride or sodium sulphate as a supporting electrolyte. Anodic oxidation was effective in achieving the removal of green tea (35%), spinach (69%), Langdale yellow and turmeric (95%), carmine, saffron, henna (97%), beetroot, karkade and sumac (98%). However, TOC measurements and the UV analyses indicated that some organic intermediate compounds were formed in the presence of sodium chloride.