Dyeing properties and colour fastness of cotton and silk fabrics dyed withCassia tora L. extract

A natural colorant was extracted fromCassia tora L. using buffer solutions (pH: 2–11) as extractants. The dyeing solution (Cassia tora L. extract) extracted using pH 9 buffer solution was found to give the highest K/S values of dyed fabrics. Cotton and silk fabrics were dyed withCassia tora L. extract at 60°C for 60 min with pre-treatment of various metal salts as mordants. It was found thatCassia tora L. extract was polygenetic dyestuffs and its major components were anthraquinones. Studies have been made on the effects of the kind of mordant on dyeing properties and colour fastnesses of cotton and silk fabrics. The K/S of cotton fabrics increased in the order of the dyeing using FeSO4>CuSO4>ZnSO4>MnSO4≅Al2(SO4)3>NiSO4>none, however, the K/S of silk fabrics increased in the order of the dyeing using FeSO4>CuSO4>ZnSO4≅Al2(SO4)3>MnSO4≅NiSO4>none. It was found that the K/S values of dyed fabrics were largely affected by the colour difference (ΔE) between mordanted fabric and control fabric. However, they were not depended on the content of mordanted metal ion of the fabrics. Mordants FeSO4 and CuSO4 for cotton fabric, FeSO4, CuSO4, and Al2(SO4)3 for silk fabric were found to give good light fastness (rating 4).