Studies on the effect of moisture content on the colour appearance of dyed cotton fabrics

Abstract

The present investigation encompasses studies conducted on the effect of different types of moisture content on the colour of dyed cotton fabrics. Different fabric-geometries, namely twill and plain structures, two each, having different pick densities and produced with the same type of yarn were considered for the study. Three direct dyes, namely C.I. Direct Red 243, C.I. Direct Yellow 106 and C.I. Direct Blue 85 were selected and seven different dye combinations produced using these dyes were utilized for dyeing the fabrics. The study reveals that the difference in colour due to moisture absorption is gradual up to 65% RH and drastic above this level. The colour difference between samples conditioned at 65% RH and those at other humidity levels is also more pronounced when the RH% is increased. Although the amount of dye on fabrics was normalized for various woven structures examined, it is found that fabric geometry plays an important role in the measurement of colour. Indeed the two twill fabrics studied exhibited higher increase in their depth of colour than plain woven fabrics at all RH levels examined. Various amounts of bulk water content in the fabrics were obtained by adjusting their wet pick up levels as an initial step. A study was also conducted to analyse the effect of hot air drying at two levels of temperature namely 50ºC and 100ºC on the colour of dyed fabrics. Fabrics were dried from 100% odwf moisture content to 40%, 30%, 20% and 10% odwf residual moisture to obtain free as well as bound moisture in them. A mathematical model was developed using first order ordinary differential equation to predict the and#8721;K/S value of the dyed fabric at any moisture content level including bone dry state. Validation of the model carried out with the dyes used in the study as well as other dyes belonging to direct and reactive classes revealed that the model performs well for both the classes of dyes at all % shades and moisture levels used except for the shades below 0.5% owm at moisture levels and#8805; 30% odwf.