RESUMO
Aqueous dispersions of nanoscale vat dyes were successfully prepared through ball milling and ultrasonication of three test dyes in the presence of dispersing agent. Critical factors included the time of ball milling and ultrasonication and the molecular structure of the vat dyes have been studied. These dispersions were characterized by morphological structures with particle size determination and quality was evaluated by shelf-life stability using digital images. The nanoscale vat dyes have been applied in dyeing and printing of cotton to evaluate the effect of nanoscale dispersion on the reducing agent account and the difference of coloration performance of a nanoscale and conventionally dispersed vat dyes. Results showed that use of sodium dodecyl sulfate (SDS) maintained a high stability of dispersion with storage. The size and stability of nanoscale dispersion were greatly influenced by molecular structure of the vat dyes. Ultrasonication was helpful in decreasing average particle size. Nanoscale vat dye dispersions gave a much higher color yield than conventional vat dyes. Fastness properties were excellent for washing effects. It is clear that coloration using nanoscale vat dye dispersions offer a number of advantages in terms of reducing agent requirement, improved appearance and also in environmental protection.