Saminathan Ratnapandian

Operating procedure
A fabric sample of known weight (approximately 0.2 g) is digested in concentrated acid to obtain a clear solution. This ensures that other than the metal all other organic matter has been completely destroyed. The volume of solution is brought down by boiling and then diluted with distilled water to produce a 2% w/w solution of the acid. The dilution is necessary to protect the instrument according to recommendations from the manufacturer. This dilute solution forms the sample solution.

The maximum quantity of metal that may be present in the sample solution prepared as above is calculated taking the following factors into consideration:

1. 
   the wet pick-up during padding
   
2. 
   concentration of metal salt in the padding liquor; and
   
3. 
   the ratio of atomic mass of metal to the molecular weight of the metal salt. Based on the above calculation, calibration solutions of required PPM range of concentrations are prepared by dissolving appropriate metallic salts in distilled water. As depicted in Figure 2.7, the AAS instrument aspirates the test solution, as an atomised spray, into a flame. A beam of UV light of appropriate wavelength is focused through the flame and into a detector. If the metal is present in the sample, it will absorb some of the light, thus reducing its intensity. The instrument measures the change in intensity. A computer data acquisition system converts this change into an absorbance [131].
   

Lamp

Atomised test solution

Flame

Figure 2.7 Schematic diagram of AAS

4. 
   Attenuated Total Reflectance Fourier Transform Infra-Red (ATR-FTIR) This non-destructive testing method does not involve any special sample preparation. The spectrum is obtained by measuring changes in the total internal reflection of the incident light beam caused by the sample held in close contact with one face of the reflecting crystal [132, 133]. Figure 2.8 depicts the sample position in relation to the ATR crystal and the path of the infra-red light beam.
   

Sample in contact
wave

Infrared beam
ATR crystal
To detector

Figure 2.8 Schematic diagram of ATR – FTIR

The bonds in the individual dyes and the changes to these bonds during formation of the dye-mordant and dye-mordant-cotton complex were identified by analysing the ATR – FTIR spectrum. Dye-mordant complexes were prepared according to the following procedure. Individual 50 ml solutions, at the optimal ratio indicated by padding experiments, of all four combinations of dye and mordant were prepared.
These solutions were heated at 80ºC for 20 minutes to simulate exhaust dyeing and promote formation of a dye-mordant complex. The solutions were cooled and centrifuged for 10 minutes. The solids (dye-mordant complex) that settled at the bottom of the centrifuge tubes were collected and dried at ambient temperature.

The results of AAS and ATR-FTIR were used to develop a theory that explains the observations of the padding experiments.

5. Wettability testing

The wetting properties of fabric, especially after plasma treatment, were evaluated using the drop test and wicking test according to AATCC test method 79–2007 and BS 3424 part 18, method 21A, respectively. The time required for one drop of water to be absorbed by the treated fabric was compared to that taken by the untreated fabric. A

similar comparison was done for the vertical wicking of coloured water. A 15 cm x 1.5 cm strip of fabric, marked at 1 cm intervals along the length, was clamped at the top and hung vertically. A small weight was attached to the bottom to keep the strip straight. The bottom two centimetres were immersed into distilled water coloured with blue dye. The height to which the water rose over a 15 minute period was recorded at 30 seconds, 1, 5 and 15 minutes.

6. Antimicrobial testing

This test was carried out to evaluate the effect of chitosan. A modified AATCC TM 100-2004 (clause 10.2) test method was followed to assess the antibacterial properties of dyed fabrics. Escherichia coli (E. coli) strain ATCC 11229, a gram-negative bacterium, was used as the test organism. Bacterial inoculums were prepared to obtain a suspension in an exponential growth of 10⁸ colony forming units (CFU) mL^-1 in 5 mL of modified tryptone soya nutrient broth. Fabrics dyed in the absence of chitosan were used as negative control samples.

Antibacterial tests were conducted on each sample individually as outlined by Zhang et al [134]. In brief, 1 ml of inoculum, prepared as described above, was added to a fabric swatch of 4 cm diameter in a conical flask. Immediately 100 ml of distilled water was added to the flask and this was shaken vigorously for 1 minute. From this solution, a series of dilutions were prepared as 10⁰, 10¹, 10² and 10³ times with sterile distilled water. The dilutions were then plated in triplicates and incubated for 18 hours at 37°C. After incubation, the control plates exhibiting 30--300 CFU were taken as reference.

Test plates of a similar dilution were compared. The percentage reduction of bacteria was calculated with Equation 2.2:

( X  Y ) _100%
X

Equation 2.2

where,
X= average number of bacterial colonies in the agar plate from control
Y = average number of bacterial colonies in the agar plates from fabric dyed in the presence of chitosan.

3.