Saminathan Ratnapandian

S 2R

Equation 2.1

where R is the reflectance measured at a given wavelength.
The K/S value is commonly used as a basis for evaluating dye build-up or change in colour strength. Comparison of colour strength can be made based either on the K/S values at maximum absorption wavelength (λ_max) or on the sum of K/S values across the visible spectrum when no specific peaks are identifiable. Any particular colour may

be represented by a graph of the K/S or reflectance values (across the visible spectrum) plotted against corresponding wavelength [130].

2. Fastness testing

Wash fastness was evaluated according to the AS 2001.4.15-2006 test method using an Atlas launder-o-meter. A composite sample (dyed fabric and standard multifibre fabric) was washed in a 5 g/l standard soap solution with 2 g/l soda ash at 60˚C for 30 minutes using a material-to-liquor ratio of 1:50. After washing, the sample was rinsed in hot followed by cold water and then dried at ambient temperature. The colour of the wash solution, staining of adjacent multifibre fabric and dyed fabric colour change were evaluated against AATCC grey scales for colour change and staining.

Light fastness was tested according to the AS 2001.4.21-2006 test method for a period of 48 hours. The amount of colour fading on exposure to an artificial light source (mercury vapour, tungsten filament, internally phosphor coated lamp) in comparison with simultaneously exposed blue wool standards was assessed.

Wet and dry rubbing fastness of samples was evaluated according to the AS 2001.4.3- 1995 test method using a crock meter. Dyed samples were rubbed with a standard white cotton fabric, in a dry or wet state, under specified test conditions. The staining of the cotton fabric was evaluated using standard AATCC grey scales for staining.

3. Atomic Absorption Spectrometry (AAS)

AAS was used to determine the extent to which the cotton and wool fabrics retained metal ions from the mordant in the absence and presence of the dye respectively. An increase in metal retention in the presence of dye would confirm the formation of dye- metal-textile complex.

AAS is a precise technique for quantifying metals in the parts per million (PPM) range present in a sample. It works on the principle that metals in their elemental form absorb ultraviolet (UV) light when they are excited by heat. The results are very specific because each metal has a unique characteristic absorbance wavelength. This absorption follows Beer’s Law, which states that as concentration goes up, absorbance goes up.

Hence a calibration curve for a metal may be constructed by recording the absorbance for a series of standards with known concentrations. The absorbance of an unknown
sample can be measured and the quantity of metal estimated by comparing with the calibration curve.