100% indigo-dyed 3/1 twill denim apparel was selected for the experiment. It was collected from the Bangladesh University of Textiles (BUTEX). The GSM of the denim was 300.

All information related to chemicals was obtained from the TDS sheet provided by the chemical company.

There are various types of chemicals used in both washing processes represented in Table 1.

Table 1. Overview of chemicals utilized in washing and their properties.

Machines used in conducting both washing processes are represented in Table 2.

Table 2. Equipment details for washing operations.

3.1.1. Desizing Treatment

Remove sized materials from yarn-dyed denim fabric.

Parameters:

Total Load: 2 kg (248 g sample + 175 g dummy fabric + additional dummy to reach 2 kg) Liquor Ratio: 1:10 (20 L water for 2 kg fabric) Chemicals:Desizing agent: 2 g/L → 40 g total Detergent: 1.5 g/L → 30 g total Process Conditions:Temperature: 60˚CDuration: 20 minutes

3.1.2. Commercial Cellulase Washing Treatment

a. Commercial Acid Cellulase (Cellzyme 2000L) Enzyme:

The treatment with acid cellulase enzyme involved the addition of 4 g/l of the enzyme to the desized denim clothing.

Figure 1 illustrates the addition of acid cellulase enzyme. During that period, the bath pH level was assessed using litmus paper, revealing a value of approximately 9.2.

Figure 2 illustrates the measurement of the solution’s pH. To sustain the pH, acetic acid was added at a concentration of 2.5 g/L.

Figure 1. Addition of commercial acid cellulose enzyme.

Figure 2. Acid Bath PH measurement.

The pH level was subsequently determined to be around 8.5. These values correspond to the real bath conditions during the applied application-oriented washing procedure. The pH determinations were made with litmus paper and are therefore only approximate. The present study is limited in that no independent verification of enzyme activity or continuous pH monitoring was performed, which is acknowledged as a limitation.

Acidic cellulose enzyme concentration: 4 g/L = 80 g total, Acetic Acid = 2.5 g/L = 50 g, Temperature: 45˚C, Duration: 30 minutes as per the standard industry benchmark to activate the acid cellulase enzyme.

The treatments were carried out under application-oriented processing conditions based on laboratory and industrial practice. Although the treatment with acid cellulase was outside the range recommended by the manufacturer, it was carried out for 30 minutes as the experimental design was application-oriented, aiming at evaluating two complete commercial cellulase washing formulations under their respective practical processing procedures. Therefore, each formulation was evaluated as a complete washing system, including the corresponding processing conditions and post-treatment operations rather than simply as a comparison between acid and neutral cellulase enzyme categories.

b. Commercial Neutral Cellulose (Biowash SL-D Ultra) Enzyme:

A neutral cellulase enzyme was applied at a concentration of 4 g/l to the desized denim garments. Figure 3 illustrates the addition of neutral cellulase enzyme. The temperature was maintained at 60˚C for a duration of 40 minutes to activate its operation as per the industrial range and technical data sheet provided by the manufacturer. The pH level was assessed using litmus paper and determined to be around 6.5. Figure 4 illustrates the pH measurement of the solution, which was determined to be 6.5.

Figure 3. Addition of commercial neutral cellulose enzyme.

Figure 4. Neutral bath PH measurement.

3.1.3. Neutralization

The neutralisation procedure is conducted to regulate pH levels. The neutralisation procedure during acid cellulase enzyme treatment was accomplished by the addition of sodium metabisulfite (Na₂S₂O₅). It’s a strong reducing and neutralizing agent to adjust the bath PH into the neutral range (shown in Figure 4) for wearable purposes in later stages. The temperature was established at 40˚C for a duration of 10 minutes. The pH level was assessed using litmus paper and determined to be 6.5.

A hot wash was conducted at 80˚C for 2 minutes following the neutralisation process.

No neutralisation step was required for the neutral cellulase enzyme treatment, as the pH was automatically maintained near 6.5 after the addition of commercial neutral cellulase. As a result, it eventually became suitable for the wearer’s skin without the addition of any neutralising agent.

3.1.4. Softening

Following the neutralization procedure, a softening treatment was conducted. Softening is performed to enhance the tactile quality of denim garments. Softening was achieved with the use of a silicone softener. The temperature was maintained at room temperature for ten minutes.

Silicone softener: 2.5 g/L = 50 g

Temperature: Ambient temperature

Duration: 10 minutes

3.1.5. Hydro-Extraction

Hydro-extraction is used to eliminate surplus water from the garments. The denim garments were subjected to a hydro-extractor machine for a duration of 7 minutes.

3.1.6. Tumble Dryer

Upon completion of the hydro-extraction drying process, drying was accomplished using a tumble dryer. The temperature was at ambient conditions.

The final output was found and is shown in Figure 5, showing neutral cellulose and acid cellulose-treated samples.

Figure 5. Commercial neutral cellulase and acid cellulase-treated sample.

The treated apparel was conditioned to moisture equilibrium as directed in ASTM D 1776. We conducted all the washing processes and testing procedures mentioned in Table 3 in the BUTEX Apparel Washing lab, Physical Testing lab, Accreditation lab, and Wet Process lab.

Table 3. Fabric testing methods with standards and equipment.

After assessment of various tests through the above-stated machines, values are recorded and illustrated through Excel.

The GSM prior to washing was 300 (Figure 6). Following the Acid Enzyme Wash, the GSM was 275; after the Neutral Enzyme Wash, the GSM was 273, as illustrated in Figure 6. The neutral enzyme has superior fading efficacy due to its structural attributes, resulting in enhanced contrast compared to the acid enzyme, which therefore leads to having slightly greater GSM reduction than the acid variant.

Figure 6. Effect of washing treatment on GSM (Acid vs. Neutral Enzyme).

Prior to washing, both the length and width were 10 cm (Figure 7). Post Acid Enzyme Wash, dimensions are 10.1 cm in length and 9.9 cm in breadth (Figure 7). Dimensions of the Neutral Enzyme Wash: length 10.3 cm, breadth 9.7 cm (Figure 7). In the longitudinal direction, warp yarn may experience stretching; hence, growth occurs instead of shrinkage. Tension applied during the processing step is removed in the widthwise direction, resulting in shrinkage.

Figure 7. Effect of washing treatment on shrinkage—pre-wash vs. post-wash (Acid vs. Neutral Enzyme).

Prior to washing, EPI was 60, and PPI was 55 (Figure 8). Post acid enzyme washing, EPI was 61, and PPI was 54 (Figure 8). Following neutral enzyme washing, EPI is 63, and PPI is 53 (Figure 8). In a neutral enzyme wash, PPI is reduced compared to acid due to more lengthwise development.

Regarding EPI, widthwise shrinking is more pronounced since the EPI of neutral is greater than that of the acid wash.

Figure 8. Effect of washing treatment on EPI and PPI—pre-wash vs. post-wash (Acid vs. Neutral Enzyme).

Prior to washing, the warp count is 10.68 Ne, and the weft count is 14.80 Ne (Figure 9). Following the acid enzyme wash, the warp count is 11 Ne, and the weft count is 16 Ne (Figure 9). Following the Neutral Enzyme Wash, the warp count is 12 Ne, and the weft count is 15 Ne (Figure 9). A marginal rise in yarn count is seen in both washes. This is attributable to the finishing technique, which renders the yarn somewhat softer.

Figure 9. Effect of washing treatment on yarn count—pre-wash vs. post-wash (Acid vs. Neutral Enzyme).

Prior to washing, the breaking strength of the warp is 515.45 N, and the weft is 263.76 N (Figure 10). Following the Acid Enzyme Wash, the breaking strength of the warp is 455.74 N and the weft is 208.94 N (Figure 10). Following the Neutral Enzyme Wash, the breaking strength of the warp is 448.76 N and the weft is 248.17 N (Figure 10). Finer yarn requires less breaking power, requiring more force for acid warp than neutral warp, and acid weft yarn has inferior breaking strength compared to neutral weft.

Figure 10. Effect of washing treatment on breaking strength—pre-wash vs. post-wash (Acid vs. Neutral Enzyme).

Figure 11. Effect of washing treatment on bending length—pre-wash vs. post-wash (Acid vs. Neutral Enzyme).

Prior to washing, the bending lengths of the warp and weft are 1.85 cm and 1.3 cm, respectively (Figure 11). Following the Acid Enzyme Wash, the bending length of the warp is 1.24 cm, and the weft is 0.994 cm (Figure 11). Following the Neutral Enzyme Wash, the bending length of the warp is 1.22 cm, and the weft is 1.096 cm (Figure 11). Acid warp yarn is coarser than neutral warp yarn, making it difficult to bend. As the bending length increases, the bending stiffness will also increase. The contrary scenario is found in the weft direction.

Prior to the wash, no color change was seen (5); subsequent to the Acid Enzyme Wash, the color change was recorded as 4 (Figure 12). The color shift following the Neutral Enzyme Wash was ¾ (Figure 12). Earlier studies have often reported more fading with acid cellulase, but in the present study, enhanced fading was observed with the commercial neutral cellulase (Biowash SL-D Ultra). This observation is consistent with the technical information of the manufacturer, which states that the product provides higher contrast denim than conventional commercial acid-stable cellulases.

Figure 12. Effect of washing treatment on grey scale rating—pre-wash vs. post-wash (Acid vs. Neutral Enzyme).

Both acid and neutral cellulase washing are potentially more sustainable than conventional stone washing because of the reduced fabric damage and no consumption of pumice stone. The use of commercial neutral cellulase (Biowash SL-D Ultra), however, provides further environmental benefits by avoiding neutralization, thus reducing the use of auxiliary chemicals and simplifying the washing process. The acid cellulase process involves pH adjustment and subsequent neutralization, resulting in increased chemical consumption and wastewater treatment requirements. Therefore, under the processing conditions investigated, the commercial neutral cellulase process presents a higher potential for sustainable denim finishing, although further environmental assessments, such as life cycle analysis, are recommended.