Denim is a warp faced, indigo dyed, firm 2/1 or 3/1 twill weave fabric which is currently considered as a top fashion product for people of all ages especially to the youth due to its durability, fashionable and aesthetic look. Denim garment business gets supreme pace because of its indefinite variety of wash effects [1]. Washing is considered as one of the most widely used finishing treatments due to its appearance and comfortability to the wearers [2]. Denim washing process has a great impact on the environment which is why sustainability has become a major concern in recent times. A sustainable wash method by reducing wash baths will be able to reduce consumption of chemicals, water and time, which will enhance the denim community as well as washing industries all over the world [3]. L. Heikinheims et al. [4] worked on denim fabrics with Trichoderma Reesei Cellulases where he found Purified cellulase EG II is most effective at removing color from denim, producing a good stone washing effect with the lowest hydrolysis level. Arkady P. Sinitsyn et al. [5] experimented on application of microassays for investigation of cellulase abrasive activity and back staining where they want to present model microassays for testing the denim-washing performance and indigo deposition on garment pocketing fabric. A Sadeghian Maryan et al. [6] worked on introducing organo-montmorillonite instead of using pumice stone during washing to achieve old look appearance. In this study, desizing and softening operation was optimized. RM Tyndall [7] investigated on refining the smoothness and exterior look of cotton fabrics and garments by treatment with cellulase enzymes. They compared the use of cellulase alone and cellulase in combination with stones with regular stone washing. Naima Abdelfattah Haleb et al. [8] investigated the tactile properties of denim fabric in variance of four different types of washing i.e. caustic rinse at 60˚C, washing at cold bath for 30 min, washing at 60˚C for 60 min and stone wash. Ali Sadeghian Maryan et al. [9] researched on one step treatment with amylase or cellulose or laccase for a cleaner production of denim garment. They found that, the obtained color on the samples treated with the three enzymes had not been differed significantly with the bio-desized garment treated with cellulose or laccase and cellulase/laccase. Chi-Wai Kan [10] examined on CO₂ laser treatment as a clean process for treating denim fabric and a carbon dioxide (CO₂) laser was used for the color-fading treatment of denim fabrics. They observed that the color fading effect induced by CO₂ laser in denim fabrics was more effective than conventional cellulase treatment, if the processing parameters can be controlled carefully. A. Sadeghian Maryan et al. [11] synthesized silver nanoparticles in denim fabrics by silver nitrate reduction at cellulosic chain in presence of starch and/or glucose at alkali media. Ayanna Card et al. [12] studied the effects of repeated home laundering on the physical properties of washed denim fabric. Murat Tarhan et al. [13] studied the performance properties of denim fabric after applying several fading method i.e. sand blasting, laser and washing. Majid Montazer et al. [14] investigated the effect of different enzymatic treatment i.e. acid cellulases, neutral cellulases and combination of laccases with cellulases on denim garment. Martin Ortiz-Morales et al. [15] investigated on a comparative study of laser fading characteristics of denim fabric in variation of different types of laser. Abdur Rahman Telli et al. [16] researched on three types of denim yarn i.e. cotton fibers, recycled cotton fibers obtained from yarn wastes, and fibers produced from recycled PET bottles to produce denim fabric followed by enzyme and stone washing to find out washing performance based on several physical and mechanical properties of denim fabric. C.W. Kan et al. [17] studied the effect of repeated home laundering on stretch denim fabric. In this research they evaluated various performance properties of stretch denim fabric. Nazli Uren et al. [18] proposed recommendations to improve tactile comfort of denim fabric and also explored the competence of denim fabric in terms of low stress mechanical properties and sensory evolution. Shou Xiang Jiang et al. [19] illustrated an advanced textile design that is an amalgamation of laser engraving and foil lamination on denim fabric.

Several researchers have studied on the methods of washing but there is a research deficiency on process optimization of denim garment washing. This research work is performed by applying potassium permanganate spray on unwashed garments avoiding separate desizing process as well as maintaining same bath fixing, softening, pH control process which improves the water, chemical and time consumption successively creates a low cost denim garment which is cost effective and environment friendly.

In conventional process at Table 4, there are more steps like individual desizing bath which have been skipped in sustainable washing. In sustainable washing, Potassium Permanganate was sprayed on the garments after dry process & then cellulase enzymatic treatment was done. By this process 1 neutral bath was saved. But in conventional process potassium permanganate was sprayed after base wash. Hence 2 additional neutral bath were required after potassium permanganate & bleaching treatment. After bleaching treatment only 1 rinse was

applied in leu of 2 rinses in case of sustainable washing. On the other hand, in conventional process fixing, softening and pH control were executed in separate bath but in sustainable washing all of prior mentioning operations were combined in a single bath. So finally, one desizing step, one neutral step, six rinsing steps, softening & pH control were skipped in sustainable washing process which was common steps in conventional washing process.

Tear and Tensile Strength

Typically, the tear strength was evaluated according to ASTM-D2261 method. The sample of 7.5 × 20 cm was inserted between one fixed jaw and another moveable jaw. Then 4.5 lb pressure was applied to warp direction and 4 lb pressure was applied to weft direction. Meanwhile moveable jaw is started to move by 300 mm/min. Jaw’s motion is continued until sample is torn out. A computer is compiled to the instrument with relevant software which gives required reading of tearing strength. According to Figure 1, the tear strength for both warp & weft direction is comparatively good in sustainable washing process because less fibre degradation and less fabric friction happens in sustainable washing process.

Typically, the tensile strength was evaluated according to ASTM-D5034 standard. Here Crosshead speed of 10 mm/min and gauge length of 50 mm were maintained. The load was continuously applied to the 10 × 15 cm denim sample till it is fractured. The load and the corresponding extensions were recorded by the computer. According to Figure 2, the tensile strength for both warp & weft direction is comparatively good in sustainable washing process because less fibre degradation and less fabric friction happens in sustainable washing process.

Color Fastness to Rubbing

Table 5 shows that color fastness to dry rubbing for both conventional & sustainable process is very good to excellent and wet rubbing grade shows significant staining. Although some processes have eliminated in sustainable wash process but identical result is achieved in both type of wash indicates the corroboration of sustainable wash.

Colorfastness to Perspiration

Table 6 and Table 7 show that the result of color fastness to perspiration in acid medium is same for both conventional and sustainable wash process which affirms no impact on colorfastness to perspiration for sustainable wash as there is no additional chemical or process is imparted in sustainable wash that validates the approach of sustainable wash technique.

Colorfastness to Water

Table 8 defines that for both conventional and sustainable wash process, color fastness to water is same. That means, the Colorfastness to water is not dependent on process elimination. In both process bleach process is done to match the shade. So there is no possibility of change of color fastness to water.

Colorfastness to Wash

Table 9 shows that in both conventional and sustainable wash process, color

Here, 5 = Excellent, 4 = Good, 3 = Fair, 2 = Significant staining, 1 = Deep staining.

change and color staining rating is same i.e. the colorfastness to wash is not changed for process skipping in sustainable wash.

CMC value of washed garments for shade matching

At Table 10, sample of sustainable wash process is compared with conventional processed garments in two different light sources i.e. D65 and F11. Table 10 shows value of CMC DE, DL*, Da*, Db*, DC* and DH* lies below 1. As a result, CMC decision is passed and shade is accepted for light source D65 and F11.

pH, BOD and COD value of denim garments after washing

According to guideline for the Assessment of Effluent, Dept. of Environment, Ministry of Environment and Forest, Bangladesh, June 2008 [20]: acceptable Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) range are 0 - 50 ppm and 0 - 200 ppm respectively. In comparison between two type of washing process, BOD and COD value is satisfactory for sustainable washing method. In conventional washing process, pH is not properly controlled that’s why every step of washing bath shows higher pH value where as in case of sustainable washing technique, pH is controlled in early enzyme step. As a result, sustainable washing technique has become a proven environment friendly washing method (Table 11).

Shrinkage Test

Figure 3 shows that, in conventional washing process, the shrinkage% for both warp and weft direction is more in comparing with sustainable washing process. The reason of higher shrinkage in conventional process is its prolong washing time. So it is well defined that sustainable washing technique is more expected to avoid higher shrinkage of wash garment.

Fabric weight (GSM) Test

Figure 4 shows that the GSM of unwashed fabric is 368 gm/m² and after completion of washing, increment percentage of GSM is found as 9.2% and 6.5% for conventional and sustainable washing method respectively. Here sustainable

washing method is appreciated due to less increment percentage of fabric GSM which will reduce fabric consumption.

Cost calculation

Cost calculation is performed considering weight of garments 60 kg for 120 pcs garments. (Table 12 and Table 13)

Total save at sustainable process = 3480 − 3191 = 289 Tk. or $3.40 per lot (120 pcs)

Per dozen saving = 28.9 Tk. or $0.34 (1 US dollar = 85 Tk.)

Table 14 shows that, in sustainable washing method, almost 730 lots more denim garments can be washed in per year per machine by following sustainable washing technique which saves 730 × TK.289 = TK.210970 = $2482. Total water saving per lot in sustainable process is 5800 L which saves 5800 × 730 × TK.024 = TK.101616 = $1195 per year per machine. In sustainable process 47% water and 19% time is saved in per lot garments which makes this sustainable process more effective.

Visual Comparison

See Figure 5.

Cost of 1 liter water = 0.024 Tk (Source: Denimach washing ltd).

We gratefully acknowledge the help rendered by Department of Textile Engineering, Mawlana Bhashani Science and Technology University and Denimach washing ltd, Bangladesh to conduct research work successfully.

The authors declare no conflicts of interest regarding the publication of this paper.

Siddiquee, Md.A.B., Gulam Moula, A.T.M., Saha, J.K., Khan, Md.H.K., Kaisar, Z. and Roy, A. (2022) Sustainable Denim Washing by Process Optimization. Journal of Textile Science and Technology, 8, 149-162. https://doi.org/10.4236/jtst.2022.84012