1. Introduction

Cotton is an important fibre in textiles, because of its numerous advantages which need no explanation. One of the main disadvantages of cotton is creasing after washing[1]. On creasing the cotton fabrics, the molecular chains in the amorphous region slip past each other, breaking the weak hydrogen bonds. The stretched chains then form hydrogen bonds in the stretched places and thus the fabric holds the creases. The mechanism of the crease recovery process in cotton fibres is based on introducing stable cross-links so as to prevent slippage of molecular chains[2].

Cotton fabric is usually printed with reactive dyes of low reactivity, mainly Monochlorotriazine (MCT), since these dyes exhibit high solubility, low affinity, high diffusion and high print paste stability. Printing of cotton fabric with these kinds of dyes offers the following advantages: minimum hydrolysis of the dyes during the printing process, maximum fixation on cotton fabrics, minimum staining on white grounds during the washing off process and good all-round fastness properties of the print[3].

The current procedure for printing and crease resistant finishing of cotton fabric involves the application of two processes separately and in succession. The present research work was undertaken with a view to exploring the feasibility of carrying out single step fixation of reactive printing and crease resistance finishing of cotton fabric and to investigate the effects of process parameters on single step fixation of reactive printing and crease resistance finishing of cotton fabric using design of experiment (DOE). An extensive literature review had been conducted for the identification of key factors which were systematically examined through 2³ factorial design.

2. Experimental

After a critical study of reactive printing and crease resistance finishing processes[4-21] a pre-experimental plan was developed. The 2³ factorial design were conducted to examine the significant factors affecting the single step fixation process. Potential design factors, held constant factors, nuisance factors, response variables and experiment design for the single step fixation process were outlined. The particulars of the plan are given in Table 1 and 2. The values at (-) and (+) levels of various factors were chosen based on standard practices followed in textile industry.

2.1. Pre experimental plan

2.1.1. Process Route

Initially two routes were examined for carrying out the single step fixation process for reactive printing and crease resistance finishing. The process followed in both routes is as follows;

Route 1

Crease Resistance Finish-Dry-Reactive Print-Dry-Fix- Wash-Dry

Route 2

Reactive Print-Dry-Crease Resistance Finish -Dry-Fix- Wash-Dry

2.2. Findings

It was found that in the case of Route 2 after application of print paste and drying when fabric was immersed in the liquor containing crease resistant and auxiliaries, the print bleeds and loses its localization. Therefore, Route 1 has been selected for the single step fixation process.

2.3. Experiment Design

Design of experiment (DOE) is a standard statistical technique to identify key factors and levels that influence system performance and variability. This technique is especially useful when there is the need to understand the interactions and effects of several system variables and an absence of concrete information[22]. The supplemental text material for DOE may be found in[23].

2³ factorial design was used to investigate the effect of process parameters namely: (i) Urea, (ii) concentration of crease resistant, (iii) fixation Conditions on single step fixation of reactive printing and crease resistance finishing. A 2³ two-level factorial design of 8 trials with two repetitions was run according to the design matrix in Table 3. The experiments were performed in random order. The results were analyzed using software Design Expert 7.0. The responses investigated were the colour yield and dry crease recovery angle (DCRA). The details of the experimental design arrangement are shown in Tables 1, 2 and 3.

2.4. Evaluation of Response Variables

Table 1. Potential design factors and respective levels used in in 23 factorial design

Two response variables namely, colour yield and dry crease recovery angle were selected for the evaluation of single step fixation process of reactive printing and crease resistance finishing of cotton fabric. The print-finish fabrics were conditioned (at temperature 25±1 C and relative humidity 65 ±1%) before the measurement of response variables. The samples processed with single step fixation were compared with those produced from a conventional two-step process of reactive printing and CR finishing.

Table 2. Held constant and nuisance factors for 23 factorial design

2.4.1. Color Yield Measurement

Color yield of print-finish fabrics were assessed spectrophotometrically and expressed in terms of the Kubelka-Munk (k/s) relationship. The condition for measurement was set under specular excluded with large aperture. The fabric was folded twice to ensure opacity. The k/s was calculated according to Equation 1:

(1)

Where, k is the absorption coefficient, s is the scattering coefficient and R is the reflectance of the colored samples.

2.4.2. Evaluation of Dry Crease Recovery Angle

Table 3. 23 factorial design matrix

The crease resistance properties imparted were evaluated by measuring the dry crease recovery angles (DCRA) using test standard AATCC-66 by Shirley crease recovery tester.

Table 4. ANOVA for response k/s

Table 5. ANOVA for response DCRA

3. Results and Discussion

The results from the experiment suggest that two out of three factors were significant to the response variables of single step fixation process. The significant factors are concentration of crease resistant and fixation conditions. The experimental results, ANOVA for k/s and DCRA are shown in Table 3, 4 and 5 respectively.

3.1. Assessment of the Significant Factors in Single Step Process

3.1.1. Influence of Concentration of Crease Resistant

The main factor plots of concentration of crease resistant are shown in Figure 1 and 2. Figure 1 showed that as the concentration of crease resistant increases, k/s decreases keeping other factors at average values. This was probably due to the limited number of reactive sites on cotton for reactive dye and crease resistant. As the concentration of crease resistant increases without increasing the concentration of dye the cross linking of crease resistant to cotton site will increase and hence less number of sites will be available for reactive dye, hence k/s decreases. Figure 2 supports this view. DCRA increases with the increase in concentration of crease resistant, keeping other factors at average values. This was expected as more crease resistant being cross linked to increase the crease recovery properties of fabric.

3.1.2. Influence of Fixation Conditions

The main factor plot of fixation conditions is shown in Figure 3. The plot of fixation condition showed that the dry crease recovery angle attained the maximum value for the curing mode of fixation as compared to steaming. This was highly probable because crosslinking of crease resistant is favourably happen in dry heat as compared to moist heat.

3.2. Influence of Urea

Though concentration of urea was not identified as a significant model term but the visual analysis of fabric samples showed that, in curing samples treated with 200 g/kg of urea were brighter than samples treated with 100 g/kg of urea. However, in steaming a high concentration of urea gives blurring of sharp boundaries of print design.

Figure 1. Effect of concentration of crease resistant on k/s values

Figure 2. Effect of concentration of crease resistant on DCRA values

Figure 3. Effect of fixation condition on DCRA values

4. Conclusions

2³ factorial design has been used to investigate the effect of process parameters urea, concentration of crease resistant and fixation condition on the single step fixation of reactive printing and crease resistance finishing of cotton fabric. From the statistical and graphical analyses, it was found that concentration of crease resistant and fixation conditions are significant to the considered response variables namely colour yield and dry crease recovery angle of the single step fixation process.

Furthermore, the uncertainty analyses for measurements show that the predicted values are in good agreement with experimental data and are sufficiently accurate. R² values were very high, suggesting that models accounted for most of the variability. Most of all single step fixation of reactive printing and crease resistance finishing processes offers potential benefit to the textile wet processing sector. The economic benefits include saving energy, labor and machine occupation time by shortening the process route, and increase in productivity, reduction in lead time and expectedly reducing the cost of finished fabric.

ACKNOWLEDGEMENTS

The authors acknowledge the permission given by Gul Ahmed Textile Mills Ltd, for carrying out the necessary experimental work