Abstract
Eye-catching, aesthetic fashions often suppress its untold dark story of unsustainable processing including hazardous wet treatment. Considering the risks imposed by conventional cotton scouring and following the trend of scouring with enzymes, this study was undertaken to evaluate the bioscouring of cotton knit fabric involving saponin-enriched soapnut as a natural surfactant, applied from a bath requiring a few chemicals and gentle processing conditions, contributing to the eco-friendliness. The proposed application was compared to synthetic detergent engaged enzymatic scouring as well as the classic scouring with Sodium hydroxide. A cellulolytic pectate lyase enzyme (0.5%–0.8% o.w.f) was applied at 55 °C for 60 min at pH 5–5.5 with varying surfactant concentrations. A low concentration of soapnut extract (1 g/L to 2 g/L) was found sufficient to assist in the removal of non-cellulosic impurities from the cotton fabric after bioscouring with 0.5% o.w.f. enzyme, leading to good hydrophilicity indicated by an average wetting time of 4.86 s at the expense of 3.1%–3.8% weight loss. The scoured fabrics were further dyed with 1% o.w.f. reactive dye to observe the dyeing performance. The treated samples were characterized in terms of weight loss, wettability, bursting strength, whiteness index, and color value. The proposed application confronted level dyeing and the ratings for color fastness to washing and rubbing were 4–5 for all of the samples scoured enzymatically with soapnut. The study was also statistically analyzed and concluded.
Keywords: Scouring, Cotton, Enzyme, Soapnut, Surfactant
1. Introduction
The presence of non-cellulosic matters like pectins, waxes, lipids, proteins, etc. in the outermost layer of cotton fiber works as a shield against a rough environment and at the same time hinders the wettability and absorbency of it during subsequent processing due to those hydrophobic substances [1]. Because of its high performance and low cost, the elimination of lipophilic substances from the cotton cell wall is dominantly done by sodium hydroxide (NaOH). Extraction of the impurities is supported by emulsification and saponification [2]. But the consequences of driving caustic pretreatment result in cellulose degradation, higher alkalinity, Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and human toxicity due to the presence of NaOH and detergent and auxiliaries involved in the process [3]. Though solvent extraction using organic, non-polar mediums is a feasible alternative, it is only capable of removing natural fats and waxes, letting the pectins left [4]. To encounter the negative impacts of alkaline scouring using NaOH, the industry enjoys benefits also from quite sustainable processing like cutinase, pectinase, and lipase based enzymes [[5], [6], [7], [8]]. Being highly specific biological catalysts, enzymatic scouring is advantageous to conventional chemical scouring in terms of reduced usage of water, chemicals, and power as well as milder temperature and pH conditions [9]. The inclusion of non-ionic synthetic surfactant in the enzymatic scouring bath was resulted in significant improvement in the removal of waxes and fats [10]. However, the risk posed by synthetic surfactants, especially detergents can’t be ignored as they’re proven to cause health hazards such as respiratory, skin, eye irritation, etc. Also, their detrimental effects suffer the aquatic environment through their high value of BOD and COD [11]. Though a few attempts were made to perform scouring from baths containing reduced chemicals, eventually were not so sustainable. Single Lacoste cotton knit fabrics experienced scouring induced by only detergent and wetting agent but the experiment couldn’t avoid the high temperature required for obtaining comparable results which ultimately affected the energy consumption [12]. Researchers have proven practical demonstration of scouring as well as bleaching of fabrics using only water and without the help of any chemicals and auxiliaries. But the energy required to carry out that operation beyond the boiling temperature of water is undoubtedly a severe matter to put a question mark in terms of achieving sustainability [13].
Structurally, the undesired and non-cellulosic pectins are complex polysaccharides comprised of α-(1, 4) linked d-galacturonic acid backbone which acts as cementing material [14]. Therefore, the degradation of pectin by pectinases was reported to enhance the removal of other impurities [15]. Based on active sites, pectinases were classified into hydrolases, esterases, and lyases. Pectate lyase (Pel, EC 4.2.2.2 and EC 4.2.2.9) and pectin lyase (EC 4.2.2.10) had been found with catalytic action in degrading the pectic substrate through cleavage reaction with β elimination mechanism to generate 4,5-unsaturated oligo-galacturonate products [16,17]. Additionally, the introduction of cellulase enzyme in scouring was resulted not only in enhanced removal and degradation of seed-coat fragments but also in a significant improvement in the whiteness of fabrics [18].
Surface-active biomolecules or biosurfactants are found to play an imperative role in the textile industry in the processes of solubilization, softening, penetration, dispersion, emulsification, wetting, and detergency [19]. Soapnut (also known locally as ‘Ritha’ or ‘Reetha’) is the common name of the fruits obtained from the trees belonging to the genus Sapindus which is comprised of several species, distributed over the world [20]. The fruit of Sapindus mukorossi is mainly constituted of saponins (10%–11.5%), sugars (10%), and mucilage [21]. Being enriched in non-ionic saponin, soapnut has been used for centuries in shampoos, detergents, etc. as a potential bio-surfactant [22,23]. The analysis of Sapindus mukorossi with GC-MS instrument reported the detection of multiple saponins namely Cedrane having a molecular formula of C15H26, Squalene with a molecular formula of C30H50, and a pentacyclic triterpenoid saponin having a molecular formula of C30H48O2. Oleic acid and steric acid were also present which are among the main chemical constituents of saponins [23]. Structurally, saponins molecules are quite complex and formed by linking sugars to aglycone (a triterpenoid or a steroid or a steroidal alkaloid) which yields a combined hydrophilic-lipophilic character [24]. The chemical structure of saponin is represented in Fig. 1. Owing to its amphiphilic nature, it can sufficiently solubilize water-insoluble substances/hydrocarbons in comparison with synthetic surfactants. This nature-based surfactant is biodegradable, safer to use, less expensive, and effective in high temperatures [26].
Fig. 1.
Chemical structure of saponin [25].
Soapnut was used as an auxiliary in scouring but the process could not be declared as 100% eco-friendly as the bath contained caustic soda [27]. Sustainable scouring of cotton calico fabric using the separated application of alpha-amylase enzyme and Sapindus mukorossi extract had been experimented with to evaluate the cleaning efficiency as well as the healing functionality [28]. However, no bio-scouring was reported that utilized a bio-surfactant and an appropriate enzyme combinedly on cotton fabric. Hence, to explore the feasibility of completely eco-friendly scouring, the performance of soapnut extract (natural surfactant) comparative to Dynol TL-D H/C (water-based non-ionic surfactant comprising of C12–C14 polyoxyethylene ether, di-octyl sodium sulfosuccinate, and polydimethyl siloxane) in scouring with a cellulolytic pectate lyase enzyme named Biolase APC has been investigated over conventional alkaline scouring in terms of wettability, weight loss, bursting strength, surface appearance properties using reflectance spectrophotometer, wash fastness, and rubbing fastness.
2. Experimental
2.1. Materials
2.1.1. Fabric
Single jersey knitted grey fabric made of 100% cotton of 28 Ne and 150 g/m2 was used in the experiment.
2.1.2. Chemicals
The Biolase APC enzyme was supplied by Malaysian company Raas Biotech Sdn. Bhd. The enzyme was of pectate lyase type and was capable to eliminate protruding fibers from the surface of cellulosic substrates making them polished additionally, hence identified as cellulolytic pectate lyase by the manufacturer. Matured soapnut and acetic acid were collected from the local market. Dynol TL-D H/C detergent was sourced from Dysin-Chem Ltd. (Bangladesh). Sodium hydroxide flakes of brand Emplura® were purchased from Merck Specialities Private Limited, India. Besides, the auxiliaries named Invatex® CS (sequestering agent), Ultravon® RW (wetting agent), and Albafluid® C (anti-creasing agent) were collected from Swiss Colours Bangladesh Ltd.
A cold brand reactive dye named Novacron® Blue EC-GC (SwissColours Bangladesh Ltd.) was used in dyeing the scoured fabrics obtained from both enzymatic and conventional pretreatment. The salt Sodium chloride and the alkali Sodium carbonate belonged to the brand Emplura® (Merck Specialities Private Limited, India). To assist in uniform dyeing, Albatex® DBC (leveling agent) obtained from SwissColours Bangladesh Ltd. was also brought into action besides those auxiliaries used in caustic scouring.
2.2. Methods
2.2.1. Preparation of soapnut extract
After separating the soapnut pericarp from the seed, 25 gm of pericarp was soaked overnight in 250 ml soft water at room temperature [29,30]. This mixture was additionally vortexed at room temperature for 2 h and 45 min using a magnetic stirrer of the Auto Dispensing Machine of the Italian brand ‘Lawer’. The prepared extract was filtered and became 0.1 gm/cc or 10 wt% concentrated.
2.2.2. Enzymatic scouring
A bath of 150 ml volume was prepared for each sample of 10 g of raw cotton fabric at M:L of 1:15 having a distinguished concentration of enzyme as well as detergent as illustrated in Table 1 and Table 2. The experiments were carried out in 200 mL stainless steel dyepots, in an electrically heated laboratory dyeing machine (Goodbrand-Jeffreys, England) with a rotating speed of 40 ± 2 rpm. When the temperature of the bath containing water, detergent (Soapnut or Dynol TL-D H/C), and fabric inside the rotating dyer reaches 55 °C from room condition at a 1.5 °C temperature gradient then the pH of the bath was checked to maintain 5.0–5.5 by adding required amount of acetic acid. After pH confirmation, the Biolase APC enzyme was poured into the bath and was run for 60 min at 55 °C temperature. Then, the temperature was raised to 90 °C and kept for 15 min and finally, the bath was dropped to 70 °C, and rinsing with fresh water was carried at 55 °C temperature. The process and parameters for applying Biolase APC and Dynol TL-D H/C were known from the technical data sheets provided by their manufacturers.
Table 1.
Recipe of soapnut (natural detergent) embraced enzymatic scouring.
| Sample ID | Biolase APC (o.w.f.) | Soapnut Extract (g/L) |
|---|---|---|
| S-1 | 0.5% | 1 |
| S-2 | 1.5 | |
| S-3 | 2 | |
| S-4 | 0.6% | 1.2 |
| S-5 | 1.8 | |
| S-6 | 2.4 | |
| S-7 | 0.7% | 1.4 |
| S-8 | 2.1 | |
| S-9 | 2.8 | |
| S-10 | 0.8% | 1.6 |
| S-11 | 2.4 | |
| S-12 | 3.2 |
Table 2.
Recipe of Dynol TL-D H/C (synthetic detergent) embraced enzymatic scouring.
| Sample ID | Biolase APC (o.w.f.) | Dynol TL-D H/C (g/L) |
|---|---|---|
| D-1 | 0.5% | 1 |
| D-2 | 1.5 | |
| D-3 | 2 | |
| D-4 | 0.6% | 1.2 |
| D-5 | 1.8 | |
| D-6 | 2.4 | |
| D-7 | 0.7% | 1.4 |
| D-8 | 2.1 | |
| D-9 | 2.8 | |
| D-10 | 0.8% | 1.6 |
| D-11 | 2.4 | |
| D-12 | 3.2 |
2.2.3. Conventional scouring with caustic soda
The bath was set at room temperature maintaining a 1:15 ratio of 10 g of grey cotton fabric to liquor containing wetting agent (1 g/L), sequestering agent (1 g/L), anti-creasing agent (0.05 g/L), and sodium hydroxide (1.5 g/L). The same rotating dyer used for enzymatic scouring, was also employed for conventional scouring. The temperature of the bath was raised to 100 °C with a 1.5 °C gradient. After running at 100 °C for 45 min at pH 11, the bath is cooled down to 60 °C and drained. 55 °C temperature supported cold rinsing and neutralization with acetic acid (0.5 g/L) for 5 min separately. Soap wash was performed at 90 °C for 10 min with 1 g/L detergent. The sample thus prepared has been addressed as ‘Std’ in this paper.
2.2.4. Reactive dyeing of scoured fabrics
The dyebath was set with dye (1% o.w.f.), wetting agent (1 g/L), sequestering agent (1 g/L), leveling agent (1 g/L), anti-creasing agent (0.05 g/L) at room temperature maintaining 150 ml volume, equivalent to the proportion of scoured fabrics to liquor at 1:15. After running for 10 min, the temperature inside the rotating laboratory dyeing machine was increased to 60 °C. Sodium chloride (40 g/L) was added then and run for 15 min. Then the sodium carbonate was added to the bath at the amount of 10 g/L. The pH was around 11 and the bath was maintained so for 45 min before draining. For the after-treatment, the freshly dyed fabric was rinsed at 55 °C for 10 min and then separately neutralized with acetic acid (0.5 g/L) at the same condition. Soap washing was done with detergent (1 g/L) and sodium carbonate (0.5 g/L) at 95 °C for 10 min maintaining pH 8–9.
2.3. Characterization
The following tests were carried out after scouring and dyeing cotton knit fabrics to observe the effects of soapnut in the scouring bath. Before testing, the fabric samples were conditioned in a standard atmosphere (20 °C ± 2 °C and 65% relative humidity) for 4 h.
2.3.1. Weight loss (%)
Changes in the weight of fabrics were calculated in terms of weight loss (%) considering the difference in fabric weight before and after scouring [31].
2.3.2. Wettability
The wettability of scoured fabrics was evaluated by the water drop test method according to the AATCC standard (Test Method 39-1980). The calculation was done by recording the time (in seconds) required for the disappearance of a drop of distilled water which was allowed to fall from a height of 1 cm on a fabric sample stretched with the help of a wooden frame. Average values of 10 different observation points of the fabric sample were used as wetting time.
2.3.3. Bursting strength
Bursting strength is an important indicator of the mechanical properties of fabrics. The test was carried out according to ISO 13938-2:2019 method where the test area was maintained as 7.3 cm2 (30.5 mm diameter). A pneumatic bursting strength tester (P1000 M229 B) of SDL International was used for the test. Strength at burst was calculated in unit KPa after subtracting the diaphragm pressure from the mean bursting pressure. The mean values of two different points were considered as the bursting strength.
2.3.4. CIE whiteness (L* values)
The values of whiteness (CIE L*) of the raw and scoured samples were determined using Datacolor 850 reflectance spectrophotometer and measured according to the Commission Internationale de l’Elclairage (CIE) standard using illuminant D65 [10].
2.3.5. Color strength (K/S value)
The color strength of the dyed fabric is simply expressed via the K/S value where ‘K’ and ‘S’ denotes the absorption and scattering coefficients of the dyed fiber. The K/S value is calculated from the ‘R’ value which is the ‘maximum absorption wavelength of the dyed fabric (λmax)’ through the Kubelka-Munk Equation as follows [32]:
| K/S = (1−R)2/2R |
The K/S values were measured by the Datacolor 850 reflectance spectrophotometer.
2.3.6. Colorfastness to washing
The change in the color of the dyed samples and the staining of the multifiber adjacent fabric against washing was performed according to ISO 105-C03:1989 standard. ‘Eco Dyer’ which is an electric heat-conducting type and rotary drum structured laboratory dyeing machine from the brand Rapid was employed to do washing and the ‘Spectra-X’ color matching cabinet of Presto Stantest Private Ltd., India was used for color fastness grading assessment.
2.3.7. Colorfastness to rubbing
The resistance of color of the fabrics to rub off and stain other materials was determined through both wet and dry rubbing tests as prescribed in ISO 105-X12:2016 with the help of a manual crockmeter of SDL International, England. Grading was done with the help of the ‘Spectra-X’ color matching cabinet.
2.3.8. Statistical analysis
Statistical analysis of the experimental results was done through co-efficient of variation (CV%) and two-tailed t-Test. CV% was calculated to determine the differences in results for weight loss, wettability, bursting strength, and K/S value. The t-Test was done to look for the degree of significance of the factors. P-values less than 0.05 were considered significant.
3. Results and discussion
3.1. Assessment of weight loss
Based on the variety of cotton, non-cellulosic materials comprised of pectic substances, hemicelluloses, waxes, proteins, amino acids, and various organic and inorganic salts are responsible for acquiring roughly 5% of the total weight [33]. Since the non-cellulosic impurities are eliminated through scouring, little amount of weight is released from the fabric. In industrial applications, a weight loss of 3–6% is considered acceptable; since an excessive loss in weight results in reduced fabric strength and durability [34]. To evaluate the loss of weight, all of the samples assigned for scouring including caustic scouring, enzymatic scouring with natural detergent (soapnut), and synthetic detergent (Dynol TL-D H/C) were examined.
The results in Table 3 show that, among all the soapnut-engaged samples, increasing the soapnut concentration from 1 g/L to 2 g/L against the constant concentration of 0.5% enzyme resulted in increased weight loss of fabric. It can be assumed that the available pectin impurities were well-digested at the lowest enzyme concentration of 0.5% when paired up with soapnut extract. The 3.8% weight loss achieved by using 2 g/L soapnut (S-3) was identical to the reduction of weight obtained by classic alkaline scouring with caustic soda.
Table 3.
Weight loss percent of different treated scoured fabrics along with the co-efficient of Variation (CV)% and the p-value.
| Sample ID | Weight Loss (%) | Sample ID | Weight Loss (%) | Co-efficient of Variation (CV%) | Sample ID | Weight Loss (%) | Co-efficient of Variation (CV%) | p-value of two-tail t-Test |
|---|---|---|---|---|---|---|---|---|
| Std | 3.8 | S-1 | 3.4 | 10.23 | D-1 | 2.8 | 7.69 | 0.0233 |
| S-2 | 3.1 | D-2 | 2.4 | |||||
| S-3 | 3.8 | D-3 | 2.6 | |||||
| S-4 | 2.6 | 13.34 | D-4 | 2.5 | 8.35 | 0.6199 | ||
| S-5 | 3.0 | D-5 | 2.9 | |||||
| S-6 | 2.3 | D-6 | 2.9 | |||||
| S-7 | 2.2 | 6.55 | D-7 | 2.9 | 27.78 | 0.1538 | ||
| S-8 | 2.5 | D-8 | 4.3 | |||||
| S-9 | 2.3 | D-9 | 2.6 | |||||
| S-10 | 2.1 | 2.66 | D-10 | 2.8 | 9.73 | 0.0093 | ||
| S-11 | 2.2 | D-11 | 2.8 | |||||
| S-12 | 2.2 | D-12 | 3.3 |
In contrast, the fabric D-8, which was processed with 0.7% enzyme and 2.1 g/L synthetic detergent was characterized by the highest weight loss equivalent to 4.3%, which may result from the almost complete elimination of the non-cellulosic constituents of the cuticle and primary wall [35]. All the weight loss values other than that of the sample D-8 were between 2.1% and 3.8%, indicating the extent of the removal of the amount of non-cellulosic impurities in cotton that can be accomplished herein.
The application of soapnut extract at 0.8% o.w.f. concentration of enzyme resulted in the minimum variation in weight loss results as measured as 2.66%. In contrast, the most precise estimation expressed as 7.69% variation, was found for 0.5% o.w.f. concentration of enzyme applied simultaneously with the synthetic surfactant.
Between the two distinct cases of enzymatic treatment, the difference in the results reached statistical significance as the p-values were found 0.0233 and 0.0093 when the concentrations of the enzyme were 0.5% o.w.f. and 0.8% o.w.f. respectively.
3.2. Evaluation of wettability
The wettability of the scoured fabrics was examined to observe both the degree of hydrophobic impurities removed and the evenness of the water drop as it got spread on the fabric.
From Table 4, the results reveal that samples treated with soapnut showed lower hydrophilicity in general, compared to those of Dynol TL-D H/C treated and the conventionally scoured one, with water drop absorption time exceeding 2.20 s. Though good wetting property indicated by the wetting time of fewer than 5 s was exhibited by four out of the twelve samples, the assistance of Biolase APC enzyme in degrading the pectin and the subsequent emulsification rendered by the biosurfactant soapnut, made the other cotton fabrics satisfactorily absorbent to water [36].
Table 4.
Wetting time of different treated scoured fabrics along with the co-efficient of Variation (CV)% and the p-value.
| Sample ID | Wettability (seconds) | Sample ID | Wettability (seconds) | Co-efficient of Variation (CV%) | Sample ID | Wettability (seconds) | Co-efficient of Variation (CV%) | p-value of two-tail t-Test |
|---|---|---|---|---|---|---|---|---|
| Std | 1.90 | S-1 | 5.77 | 25.45 | D-1 | 3.80 | 35.38 | 0.1221 |
| S-2 | 3.45 | D-2 | 3.44 | |||||
| S-3 | 5.35 | D-3 | 1.80 | |||||
| S-4 | 10 | 63.37 | D-4 | 1.99 | 61.42 | 0.2832 | ||
| S-5 | 6.27 | D-5 | 5.23 | |||||
| S-6 | 2.20 | D-6 | 1.96 | |||||
| S-7 | 2.98 | 31.67 | D-7 | 2.73 | 51.70 | 0.0903 | ||
| S-8 | 5.60 | D-8 | 2.50 | |||||
| S-9 | 3.96 | D-9 | 0.82 | |||||
| S-10 | 7.75 | 14.32 | D-10 | 1.04 | 16.06 | 0.0005 | ||
| S-11 | 5.90 | D-11 | 0.99 | |||||
| S-12 | 6.40 | D-12 | 0.76 |
An increase in both the concentration of enzyme and soapnut did not result in consistently higher hydrophilicity. This might be associated with the interaction of the lipophilic part of the soapnut-extracted non-ionic surfactant with the hydrophobic regions located inside the enzyme that was supposed to bring conformational changes that eventually decreased the ability of pectate lyase to access the cotton fabric even at comparatively higher concentrations [37]. So, it is an indicator that the dosing of the lowest range of concentration (1 g/L to 2 g/L) of soapnut to just 0.5% enzyme-containing bath is enough to cause the required pectic hydrolysis.
Similar to the weight loss result, the lowest time range of water absorption denoting the maximum water absorbency was recorded for the use of 1.6 g/L to 3.2 g/L Dynol TL-D H/C surfactant at 0.8% concentration of the enzyme. This impressive effect obtained from increased concentration of enzyme and synthetic surfactant can be explained by the fact of reduced surface tension of the fabric and facilitating the enzymes to easily penetrate fibers' micropores and cracks [7,38].
At 0.8% o.w.f. concentration of enzyme, the separate applications of both the soapnut-extract and synthetic surfactant yielded to the lowest CV% of 14.32% and 16.06% respectively. Also, at that same concentration of enzyme, a significant difference between the wettability of soapnut-involved bioscoured fabrics and Dynol TL-D H/C-involved bioscoured fabrics was observed via t-Test since the corresponding p-value resulted in 0.0005.
3.3. Determination of bursting strength
Bursting strength is an indicator of changes in fabric strength when that has undergone certain processing. Loss of fibers in pretreatment influences the strength of the fabric. At the same time, the elimination of a considerable quantity of glycerides along with the formation of oxy-cellulose is responsible for strength loss [12].
As illustrated in Table 5, the average bursting strength (in Kilo Pascal, KPa) of soapnut extract treated samples against 0.5%, 0.6%, 0.7%, and 0.8% enzyme concentrations were 355.17, 368.50, 346.8,4 and 374.17 respectively. In contrast, following the same set of concentrations of enzyme, Dynol TL-D H/C involved bioscoured samples yielded bursting strength (in the same KPa unit) of 378.60, 360.67, 330.33, and 347.17 respectively. Considering the consistency of results achieved for all the samples and relating the values of bursting strength to the grades obtained from the weight loss test, it was observed for samples S-2, S-3, S-7, S-8, D-4, D-5, D-7, D-8, D-11 and D-12 that, the bursting strength decreased with the increase in surfactant concentration.
Table 5.
Bursting strength of different treated scoured fabrics along with the co-efficient of Variation (CV)% and the p-value.
| Sample ID | Bursting Strength (KPa) | Sample ID | Bursting Strength (KPa) | Co-efficient of Variation (CV%) | Sample ID | Bursting Strength (KPa) | Co-efficient of Variation (CV%) | p-value of two-tail t-Test |
|---|---|---|---|---|---|---|---|---|
| Grey | 408 | S-1 | 375 | 7.69 | D-1 | 378 | 1.07 | 0.2146 |
| S-2 | 366.50 | D-2 | 375 | |||||
| S-3 | 324 | D-3 | 383 | |||||
| S-4 | 360 | 2.24 | D-4 | 371.50 | 2.62 | 0.3409 | ||
| S-5 | 376.50 | D-5 | 356.50 | |||||
| S-6 | 369 | D-6 | 354 | |||||
| Std | 369 | S-7 | 354.50 | 8.44 | D-7 | 344.50 | 4.94 | 0.4417 |
| S-8 | 314.50 | D-8 | 334 | |||||
| S-9 | 371.50 | D-9 | 312.50 | |||||
| S-10 | 365 | 2.29 | D-10 | 376 | 8.43 | 0.1999 | ||
| S-11 | 375.50 | D-11 | 348 | |||||
| S-12 | 382 | D-12 | 317.50 |
The application of soapnut extract at 0.6% o.w.f. concentration of enzyme contributed to the minimum variation as expressed as 2.24% in the bursting strength results. In the case of synthetic surfactant involved treatment, the most precise estimation was found for 0.5% o.w.f. concentration of enzyme as the CV% was as low as 1.07%. Besides, statistically non-significance differences were found in the t-Test since none of the p-values were either equal or less than 0.05.
3.4. Evaluation of CIE L* values
Due to the adsorption of natural pigments of cotton fiber to the pectic and proteinic substances present in the fiber, the whiteness values of the scoured fabrics are crucial to measure [39].
From Table 6, it can be observed that the enzymatic removal of impurities provided on average 2.67% and 3.52% improvement in the whiteness of the cotton fabric measured as CIE L* when treated with soapnut and synthetic surfactant respectively. Whereas, the conventional alkaline scouring resulted in a 6.44% gain in CIE L* over the raw fabric. Despite using comparatively higher concentrations of enzyme and surfactants, no significant difference was observed for the whiteness values.
Table 6.
CIE L* values of different treated scoured fabrics.
| Sample ID | CIE L* | Sample ID | CIE L* | Sample ID | CIE L* |
|---|---|---|---|---|---|
| Grey | 82.45 | S-1 | 84.51 | D-1 | 85.33 |
| S-2 | 84.80 | D-2 | 85 | ||
| S-3 | 84.58 | D-3 | 85.46 | ||
| S-4 | 84.76 | D-4 | 85.25 | ||
| S-5 | 83.84 | D-5 | 85.30 | ||
| S-6 | 84.69 | D-6 | 85.35 | ||
| Std | 87.76 | S-7 | 85.69 | D-7 | 84.90 |
| S-8 | 84.87 | D-8 | 85.49 | ||
| S-9 | 84.94 | D-9 | 85.56 | ||
| S-10 | 85.03 | D-10 | 85.82 | ||
| S-11 | 83.71 | D-11 | 85.75 | ||
| S-12 | 84.41 | D-12 | 85.02 |
Since the Biolase APC enzyme degraded only the pectin, so the whiteness of bioscoured cotton fabrics was less enhanced than the whiteness of the alkali-scoured one [40]. However, the enhancement in the whiteness value of a bioscoured hydrophilic fabric is not a major criterion of relevance unless the substrate is to embrace dark color further [41].
3.5. Evaluation of color strength
The K/S values provide a direct measure of the color yield or color strength information of the specimen dyed.
Table 7 presents the K/S values of the dyed fabrics at a maximum absorption wavelength of 630 nm. Due to the increased value of lightness of the alkali-treated fabric, all of the enzyme-treated fabrics were darker than the conventionally scoured standard sample.
Table 7.
K/S values of different treated dyed fabrics along with the co-efficient of Variation (CV%).
| Sample ID | K/S | Sample ID | K/S | Co-efficient of Variation (CV%) | Sample ID | K/S | Co-efficient of Variation (CV%) |
|---|---|---|---|---|---|---|---|
| Std | 5.126 | S-1 | 5.3535 | 3.26 | D-1 | 6.1425 | 0.38 |
| S-2 | 5.5337 | D-2 | 6.0966 | ||||
| S-3 | 5.7148 | D-3 | 6.1125 | ||||
| S-4 | 5.5111 | 5.19 | D-4 | 6.3837 | 2.77 | ||
| S-5 | 5.8386 | D-5 | 6.0561 | ||||
| S-6 | 5.2660 | D-6 | 6.1335 | ||||
| S-7 | 5.5186 | 3.60 | D-7 | 6.3356 | 1.36 | ||
| S-8 | 5.8156 | D-8 | 6.5095 | ||||
| S-9 | 5.9168 | D-9 | 6.4074 | ||||
| S-10 | 5.6883 | 6.28 | D-10 | 6.1214 | 4.28 | ||
| S-11 | 5.9929 | D-11 | 5.6377 | ||||
| S-12 | 5.2846 | D-12 | 5.7684 |
The variations in the K/S values of the surfactant-assisted bioscoured fabrics were insignificantly marginal. The average color value (5.620) obtained from the soapnut extract-treated samples was lower than the average value of 6.142 of Dynol TL-D H/C treated fabrics. The lowest coefficient of variation percentage (CV%) of K/S values as a measure of dye uniformity was found with the application of surfactants at 0.5% o.w.f. concentration of enzyme and it was 3.26% in the case of soapnut extract-treated samples whereas the CV% was 0.38% in the case of samples treated with the synthetic surfactant.
3.6. Assessment of colorfastness to washing and rubbing
To achieve the expected performance of the dyed samples when subjected to external forces, colorfastness to washing and colorfastness to rubbing were carried out for each sample.
Table 8 reveals that the colorfastness grades for washing were found mostly to be 4/5 and 5 in almost all cases including conventionally treated samples. Rubbing fastness ratings were also much acceptable for each sample as the dry rubbing ratings appeared to be almost constant as 4/5 whereas the wet rubbing grades were 4 in major cases.
Table 8.
Colorfastness to Wash and Rubbing of different treated scoured fabrics.
| Sample ID | Color Fastness to Washing |
Color Fastness to Rubbing |
|||||||
|---|---|---|---|---|---|---|---|---|---|
| Color change |
Color staining |
||||||||
| Cotton | Acetate | Cotton | Nylon | Polyester | Acrylic | Wool | Dry | Wet | |
| Std | All of the samples confronted a rating of 4/5 | 4/5 | 4/5 | 5 | 5 | 4/5 | 4/5 | 4/5 | 4 |
| S-1 | 4/5 | 4 | 5 | 5 | 5 | 4/5 | |||
| D-1 | 4/5 | 4 | 4/5 | 4/5 | 5 | 4/5 | |||
| S-2 | 4/5 | 4/5 | 5 | 5 | 5 | 4 | |||
| D-2 | 4/5 | 4 | 4/5 | 4/5 | 4/5 | 4/5 | |||
| S-3 | 4/5 | 4 | 5 | 5 | 4/5 | 4 | |||
| D-3 | 4 | 4/5 | 4/5 | 4/5 | 4/5 | 4/5 | |||
| S-4 | 4/5 | 4 | 4/5 | 4/5 | 4 | 4/5 | |||
| D-4 | 4/5 | 4/5 | 5 | 5 | 5 | 4/5 | |||
| S-5 | 4/5 | 4 | 4/5 | 4/5 | 4/5 | 4/5 | |||
| D-5 | 4/5 | 4 | 4/5 | 4/5 | 5 | 4 | |||
| S-6 | 4 | 4/5 | 4/5 | 4/5 | 5 | 4/5 | 4/5 | ||
| D-6 | 4/5 | 4/5 | 4/5 | 4/5 | 4/5 | 4/5 | 4 | ||
| S-7 | 4/5 | 4/5 | 5 | 5 | 4/5 | 4/5 | |||
| D-7 | 4/5 | 4 | 4/5 | 4/5 | 5 | 4 | |||
| S-8 | 4 | 4/5 | 4/5 | 4/5 | 4/5 | 4/5 | |||
| D-8 | 4/5 | 4 | 4/5 | 4/5 | 4 | 4/5 | |||
| S-9 | 4/5 | 4/5 | 4/5 | 4/5 | 5 | 4/5 | |||
| D-9 | 4/5 | 4/5 | 4/5 | 4/5 | 4/5 | 4/5 | |||
| S-10 | 4/5 | 4 | 5 | 5 | 5 | 4 | |||
| D-10 | 4/5 | 4/5 | 5 | 5 | 5 | 4/5 | |||
| S-11 | 4/5 | 4 | 5 | 5 | 4 | 4 | |||
| D-11 | 4/5 | 4/5 | 5 | 5 | 4/5 | 4/5 | |||
| S-12 | 4/5 | 4 | 4/5 | 4/5 | 4/5 | 4/5 | |||
| D-12 | 4/5 | 4/5 | 4/5 | 4/5 | 4/5 | 4/5 | |||
3.7. Overview of results
A separate table combining all the results obtained from weight loss, wettability, bursting strength, CIE L*, and K/S tests is presented as Table 9, which might be helpful to the reader for personal understanding.
Table 9.
Overview of results from weight loss, wettability, bursting strength, CIE L*, and K/S tests.
| Sample ID | Experimental Results |
|||||
|---|---|---|---|---|---|---|
| Weight Loss (%) | Wettability (seconds) | Bursting Strength (KPa) | CIE L* | K/S | ||
| Grey | – | – | 408 | 82.45 | – | |
| Std | 3.8 | 1.90 | 369 | 87.76 | 5.126 | |
| Bioscouring with natural surfactant | S-1 | 3.4 | 5.77 | 375 | 84.51 | 5.3535 |
| S-2 | 3.1 | 3.45 | 366.50 | 84.80 | 5.5337 | |
| S-3 | 3.8 | 5.35 | 324 | 84.58 | 5.7148 | |
| S-4 | 2.6 | 10.00 | 360 | 84.76 | 5.5111 | |
| S-5 | 3.0 | 6.27 | 376.50 | 83.84 | 5.8386 | |
| S-6 | 2.3 | 2.20 | 369 | 84.69 | 5.2660 | |
| S-7 | 2.2 | 2.98 | 354.50 | 85.69 | 5.5186 | |
| S-8 | 2.5 | 5.60 | 314.50 | 84.87 | 5.8156 | |
| S-9 | 2.3 | 3.96 | 371.50 | 84.94 | 5.9168 | |
| S-10 | 2.1 | 7.75 | 365 | 85.03 | 5.6883 | |
| S-11 | 2.2 | 5.90 | 375.50 | 83.71 | 5.9929 | |
| S-12 | 2.2 | 6.40 | 382 | 84.41 | 5.2846 | |
| Bioscouring with synthetic surfactant | D-1 | 2.8 | 3.80 | 378 | 85.33 | 6.1425 |
| D-2 | 2.4 | 3.44 | 375 | 85 | 6.0966 | |
| D-3 | 2.6 | 1.80 | 383 | 85.46 | 6.1125 | |
| D-4 | 2.5 | 1.99 | 371.50 | 85.25 | 6.3837 | |
| D-5 | 2.9 | 5.23 | 356.50 | 85.30 | 6.0561 | |
| D-6 | 2.9 | 1.96 | 354 | 85.35 | 6.1335 | |
| D-7 | 2.9 | 2.73 | 344.50 | 84.90 | 6.3356 | |
| D-8 | 4.3 | 2.50 | 334 | 85.49 | 6.5095 | |
| D-9 | 2.6 | 0.82 | 312.50 | 85.56 | 6.4074 | |
| D-10 | 2.8 | 1.04 | 376 | 85.82 | 6.1214 | |
| D-11 | 2.8 | 0.99 | 348 | 85.75 | 5.6377 | |
| D-12 | 3.3 | 0.76 | 317.50 | 85.02 | 5.7684 | |
4. Conclusion
The biosurfactant saponins from soapnut extract were utilized for the bioscouring of cotton fabric over a broad range of enzyme and surfactant concentrations. The synergetic combination of the soapnut extract and the enzyme reveals a great potential for textile applications, characterized by comparatively lower weight loss, instant absorbency, and comparable dyeability towards reactive dyes. No significant difference was observed in the dyeing properties of the samples involving both conventional alkaline scouring and bioscouring. However, the main challenge concerning biosurfactants is their large-scale production, process control, and cost-effectiveness. In future works, the competitive performance of a wide selection of biosurfactants could be explored. Another research field recognized is the evaluation of the effluent characteristics of conventional scouring and bioscouring.
Author contribution statement
Sk. Mohammad Raafi: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.
Sharfun Nahar Arju: Analyzed and interpreted the data.
Md. Asaduzzaman, Hasibul Haque Khan, Md. Rokonuzzaman: Performed the experiments; Contributed reagents, materials, analysis tools or data.
Data availability statement
Data included in article/supp. material/referenced in article.
Declaration of interest’s statement
The authors declare no competing interests.
Acknowledgement
This research is a part of an undergraduate dissertation that is being carried out in the Wet Process Engineering Department, Bangladesh University of Textiles (BUTEX). The authors are indebted to the Bangladesh University of Textiles, and Orient Chem-Tex Limited for providing their laboratory facilities. The authors would like to express thanks to Md. Kawsarul Islam, Assistant Professor (Department of Mathematics and Statistics, BUTEX) for the suggestion to analyze the results with proper statistical techniques.
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Data Availability Statement
Data included in article/supp. material/referenced in article.