Improvement in dyeing and physical properties of wool fabrics through pretreatment based on the bacterial culture of Stenotrophomonas maltophilia DHHJ

Abstract

Wool fiber is a valuable natural material in the textile industry, but keratin cuticles on its surface can deteriorate product quality. Wool fabric finishing has a long-standing problem in meeting the goal of environmental sustainability. In this study, we developed an eco-friendly simple method of wool fabric treatment based on direct incubation with the whole culture of Stenotrophomonas maltophilia DHHJ, a keratinase-producing bacterial strain. This processing method effectively reduced roughness for the surface of wool fiber and wool fabric samples by removing the cuticle scales. The keratinolytic treatment altered many physical properties of the wool fabrics, such as felting shrink, bursting strength, elongation at break, and diameter. The dyeability of wool fabric was substantially improved due to the pretreatment. The surface modification accelerated the rate of dyeing-bath exhaustion for wool fabric samples under a mild processing condition and the dyeing equilibrium was achieved within 10 min at a relatively low dyebath temperature (below 70°C). The pretreatment with the keratinase-secreting bacterial culture was beneficial for dyeing uniformity and rubbing color fastness. Besides, the fuzzing and pilling properties of wool fabrics were ameliorated in the fabric samples incubated with the bacterial culture.

Keywords

Wool fabric keratinase cuticle low-temperature dyeing

Wool is a type of natural fiber derived from sheep and some other animals. As the oldest textile material known, wool fiber has been widely applied in the textile and apparel industry. Its inherent attributes, such as beauty, durability, thermal insulation, and tailorability, make wool fiber a versatile material ideal for making high-grade garments. The woolen industry, due to its economic importance, plays a vital role in the global manufacturing sector.

α-Keratin is a fundamental component of wool, accounting for up to 95% by weight of wool fiber. Wool fibers have a well-organized molecular structure, which includes two predominant parts: the cortex and the cuticle. As the interior structure of wool fibers, the cortex makes up 90% of the fiber, and is primarily responsible for mechanical attributes such as strength, resilience, rigidity, and durability. The cuticles, a protective structure surrounding the cortex on the surface of wool fibers, are covered by a layer of wax, which confers wool fiber with a water-repellent feature. The hydrophobic wool cuticles make wool dyeing inefficient through hindering the diffusion/penetration of dye molecules into the fiber, and are also responsible for undesired processing features, such as pilling, felting, and shrinking.¹

In the conventional process, wool dyeing needs to be performed in an acidic environment with a long reaction time at a temperature near boiling point to obtain desirable dye penetration and leveling. These harsh conditions can, however, erode the wool inner fiber through the hydrolysis of peptide bonds and consequently cause massive changes in the chemical and mechanical properties of fabrics.² Such damage can be minimized by reducing the operation time and/or the dyebath temperature. However, these measures reduce the dyeing efficiency for wool fabrics. In addition, the great amount of chemicals required in dyeing processes has become an increasing threat to the environment. Attempts based on chemical and physical methods have been made to improve wool dyeability with low temperature and/or less harmful chemicals, including pretreatments with nonionic surfactants or liposomes,³ chitosan,^4,5 a combination of plasma activation and chitosan attachment,⁶ and ultrasound irradiation.⁷

The wool cuticle is also considered as a major culprit for fuzzing and pilling tendency, a long-standing problem for knitted wool fabrics, which refers to the formation of small fuzzy balls on the fabric surface. Pilling is the consequence arising from abrasion on the surface of fabric, which results in an unsightly or worn-out appearance and a short service life for wool clothing. Different smoothing treatments for the fiber surface have shown improvement in the anti-pilling property.^8,9 Nonetheless, these processes may increase the environmental burden due to wastewater pollution or high-level power consumption. The chemical methods are not readily controlled to produce uniform effects on the wool surface and may also compromise some fiber properties. Moreover, these fabric pretreatment strategies in dyeing or anti-pilling processes would be incompatible with a cost-conscious industrial application.

Therefore, there is an unmet need for new eco-friendly alternatives to deal with those problems, among which employment of proteolytic enzymes has emerged as a promising strategy to reduce the dependency on harmful chemicals as well as water and energy resources. Various keratinase-secreting bacteria and fungi have been identified with the potential for breaking down keratinaceous waste materials, while research efforts aimed at effectively treating wool scales have been done with keratinolytic proteases originating from various microorganisms.^10–14 A novel bacterial strain, Stenotrophomonas maltophilia DHHJ, has been discovered.¹⁵ It showed robust feather-degrading activity in a previous study and valuable potential for feather waste management. Here, we sought to repurpose such application in wool refinement by harnessing the keratinase-containing bacterial culture to develop an environmentally friendly and cost-effective wool pretreatment method.

Materials and methods

Treatment of wool fibers and fabrics with keratin-degrading bacterial culture

Worsted knitted wool blend fabrics that contained 85% unbleached wool yarn (64S and 21–23 microns in diameter) and 15% polyester yarn were obtained from Shanghai Greenmei Textile Corp. (Shanghai, China) and used throughout the study. Wool fibers (56S and 27.1–29 microns in diameter) were obtained from Yancheng Xueer Textile Co., Ltd (Jiangsu, China).

The Stenotrophomonas maltophilia DHHJ bacterial treatment for wool fabrics was performed in a Rushton turbine-agitated 5 L Biostat B laboratory-scale fermenter (Shanghai Baoxing Corp., China). Briefly, bacterial culture was started by inoculating a single clone of DHHJ in 5 mL BB media (0.5% beef extract, 1% peptone, 0.5% NaCl, pH 7.4–7.6) and it was shaken for 16 h at 35°C. Then 1.0 mL culture was mixed with 100 mL BB media in a 500 mL shaking flask to continue the growth. When OD₆₀₀ reached to 0.6–0.8, the whole volume of culture was transferred into a 5 L fermenter containing 3 L medium (30 g wool-blended fabrics, 30 g glucose, 1.2 g KCl, 0.9 g NaCl, 12 g Tween 80, Na₂HPO₄:KH₂PO₄ = 12 g:0.9 g, pH 7.4–7.6.). The other parameters in the treatment included air pressure (0.08 MPa), airflow (2.5 L/min), culture temperature (35°C), and stirring speed (250 rpm). The procedure of the treatment is detailed in Supplementary Figure 1, and is hereinafter referred to as DHHJ treatment.

Wool–polyester blend dyeing process

The samples of wool blend fabrics were conditioned in 50°C water and then immersed in a pre-warmed dyebath (40°C and bath ratio of 1:50), which was prepared with 2% (owf) acid black ATT dye (C.I. Acid Black, Shanghai Shanyuan Chemical Dyestuff Co., Ltd) and 2% (owf) concentrated sulfuric acid with a final pH of 2.5–3.0. The dyeing bath was gradually heated to a certain temperature at a rate of 2°C/min. When the dyeing process was completed, the samples were sequentially rinsed with tap water and warm water (30°C), and then dried at 80°C for 12 h.

Dye fixing process

The fixing agent, CWF (1.5% owf, Jiaxing Kerui Silicone Co., Ltd, Zhejiang, China), was dissolved in distilled water with an appropriate amount of glacial acetic acid to prepare the fixing solution (pH 4.0). Fabric specimens were immersed into the 80°C dyeing solution for 25 min with frequent stirring. After completing the dyeing process, the samples were subject to sequential wash steps with cold water, soap (2 g/L soap, 1 g/L soda ash, 95°C for 10 min, bath ratio 1:30) and clean water, and then dried at 80°C for 12 h.

Weight loss, strength, and shrinkage testing

In weight loss, strength, and shrinkage tests, the treated wool samples were conditioned for 24 h at 20°C with 65% relative humidity. The weight loss of the wool fabrics after DHHJ treatment was expressed as a percentage and calculated using the following equation, where W1 and W2 are the weight of the conditioned wool fabric before and after enzymatic treatment, respectively
$Weight loss % = \frac{W 1 - W 2}{W 1} \times 100 %$

The final dyebath exhaustion was calculated according to the following formula, where C(t₀) and C(t_f) are the initial and final dyebath concentrations (g/L), respectively
$E % = \frac{C (t_{0}) - C (t_{f})}{C (t_{0})} \times 100 %$

In the shrinkage test (FZ/T 70009-2021), 0.8 kg of wool fabric samples were washed three times at 40°C using laundry powder (4 g/L) and neutral soap flakes (0.5 g/L) with a bath ratio of 1:20, following further washing with water twice. Dewatering and drying were then conducted to reach the balance of moisture absorption and release. A felting shrinkage assay was performed using fabric specimens of 200 mm × 200 mm and the data was calculated using the formula
$Felting shrinkage (%)$

$= (1 - \frac{fabric area after washing}{fabric area before washing}) \times 100 %$

The treated or untreated wool fabrics were dried to constant weight at 105°C, and then the decrement rate was determined using the formula
$Percentage of weight loss (%) = (1 - \frac{wool fabric weight after treatment}{wool fabric weight before enzyme treatment}) \times 100 %$

Keratinase activity

The keratinase activity was determined with the method described previously.¹⁵ The reaction mixture contained 10 mg keratin powder in 2 mL 0.05 mol/L Tris–HCl (pH 7.8) buffer and 1 mL enzyme liquid, which was obtained from a bacterial culture harvested at 72 h. The mixture was incubated at 35°C for 1 h, and the reaction was stopped by adding trichloroacetic acid to the final concentration of 200 g/L. After centrifugation at 10,000 rpm at 4°C for 10 min, the absorbance of supernatant was determined at 280 nm. One unit of enzyme activity corresponds to the amount of enzyme that cause a change of absorbance of 0.1 at 280 nm at 35°C for 1 h.

Protein concentration

The total protein of the fractions was measured with Lowry Protein Assay Kit (Sangon Biotech Co., Ltd., Shanghai, China).

Morphological study of wool fabrics using scanning electron microscopy

The morphology of the treated and untreated wool fabrics was observed using scanning electron microscopy (SEM; JSM-5600LV, Jeol, Japan). The samples were coated with a thin layer of gold for SEM analysis.

Dyeing rate test

The dyeing reaction was performed for the samples of wool blend fabrics in clean beakers with pre-warmed (40°C) dye liquid. Different dyeing temperatures from 40°C to 90°C were maintained with digital water baths. Two microliters of dyeing liquid were taken out at each time point and diluted to 50 mL with distilled water for absorbance measurement (λ_max = 621 nm). Absorbance E_i was calculated according to the following formula
$Percentage of dyeing (%) = (1 - \frac{E_{i}}{E_{0}}) \times 100 %$
where E_i is the absorbance of dye residue and E₀ is the absorbance of standard dye.

Color measurements were carried out on dyed fabric samples to evaluate the color difference. A Datacolor 650 (USA) spectrophotometer was used to measure color variations (DE) and reflectance percentage (R_e, %).

The color strength (K/S) was evaluated using the Kubelka–Munk equation
$\frac{K}{S} = \frac{{(1 - R_{e})}^{2}}{2 R_{e}}$
where K is the adsorption coefficient, S is the scattering coefficient, and R_e is the reflectance at the maximum wavelength (value between 0 and 1).¹⁶

Dyeing uniformity S(λ) was calculated according the formula below, which was based on K/S values from eight random parts on each fabric sample
$S (λ) = \sqrt{\frac{\sum_{i = 1}^{n} {[\frac{x_{i}}{\bar{x_{i}}} - 1]}^{2}}{n - 1}}, {\bar{x}}_{i} = \frac{1}{n} \sum_{i = 1}^{n} x_{i}$

Fastness to rubbing test

The test was evaluated using the GB/T3920-2008 standard. The wool fabric samples were allowed to equilibrate with a constant temperature (21 ± 1°C) and 64–66% humidity for 16–24 h. Each testing fabric was fixed on the rubbing head with a support of backing fabric, which was moistened with distilled water when measuring the wet rubbing fastness. The dry or wet rubbing test was performed respectively at a rate of one reciprocating cycle per second 10 times. After the treatment, the staining degree of the backing fabrics was assessed in accordance with the standard gray sample card.

Pilling characterization

The pilling performance of wool fabrics was evaluated using GB/T4802.3-2008, a standard testing method for pilling with a rolling type pilling tester (YG 512, Darong Textile Instrument Co., Ltd, China). Three observers independently assessed each sample by comparing it with a set of photographic standards (subjective rating) based on the following scale: 5 (no pilling), 4 (slight pilling), 3 (moderate pilling), 2 (severe pilling), and 1 (very severe pilling). The pilling performance procedures were as described previously.¹⁷

Fabric burst strength and fabric elongation

The strength and fabric elongation of wool fabrics were measured according to the method of the GB/T19976-2005 standard with an electronic fabric strength tester (HD026-200, Nantong Hongda Experiment Instrument Co., Ltd, China). Circular samples (125 mm²) were tested on a 1000 N load cell at an extension rate of 300 ± 10 mm/min. The representative specimens were chosen by avoiding edges or creased parts of the fabric materials.

Results and discussion

Effectiveness of treatment with DHHJ bacterial culture on wool fiber

Keratinases isolated from different microorganisms have been known to be effective for wool fiber refinement. We previously isolated a feather-degrading bacterial strain, which possesses potent activity for breaking down keratin.¹⁸ However, whether the culture medium from keratinase-producing bacteria can be directly applied to wool fiber processing remains undetermined. To this end, we incubated wool fabric samples in the DHHJ bacterial culture and detected high keratinase activity after a 48-h reaction, which showed a steady and modest increase thereafter (Figure 1). Meanwhile, as a consequence, there was an elevated level of soluble proteins (from 0.59 to 0.61 mg/mL) during the incubation. These data indicated the potent wool-degradation function of the DHHJ bacterial culture (Figure 1). To evaluate the efficacy of DHHJ bacterial growth culture on the treatment of cuticle layers of wool fiber, the wool samples were inoculated with DHHJ bacterial culture for 48 h. As shown in Figures 2(a) and (b), the surfaces of treated wool fibers were revealed to be much smoother than the mock-treated control, indicating that the wool fiber cuticle layers were efficiently removed by the bacterial culture incubation. Consistent with this finding, the diameters of wool fibers were significantly decreased after DHHJ treatment (Figure 2(c)), which dropped from 29.09 μm for control fibers to 27.05 μm for 48-h treated samples.

Figure 1.
The keratinase activity of whole S. maltophilia DHHJ bacterial culture on wool fabric degradation. (Each column or data point represents the mean of three independent replicates.)

Figure 2.
Scanning electron microscopy (SEM) of morphological change of wool surface treated with S. maltophilia DHHJ bacterial culture and wool fiber diameter measurement: SEM images for control (a); wool fiber with the DHHJ treatment for 48 h (b) and diameter measurement of wool fibers (c). (Each column represents the mean of 50 independent replicates; **p < 0.01.)

Treatment effect of DHHJ bacterial culture on wool fabric

We further assessed the effect of DHHJ treatment on worsted knitted wool blend fabrics. Figure 3(a) illustrates the experimental setting in a 5-L bioreactor, in which the testing fabric samples were directly incubated with DHHJ bacterial culture, and the surfaces of wool fabrics were then examined at multiple time points using SEM. Obviously, the wool fiber cuticles were extensively diminished in treated fabrics compared with the untreated control (Figures 3(b)–(e)), revealing less roughness on the wool surface. The continuing loss of fiber cuticles was seen following a prolonged incubation, as shown in Figure 3(c) (72 h) and Figure 3(d) (96 h). Therefore, SEM analysis clearly demonstrated the capability of the DHHJ cells for the removal of fiber cuticle layers. However, the excess treatment with keratinase-secreting DHHJ culture caused progressive damage to the interior fiber texture, and thus the pretreatment should be properly controlled in practical application.

Figure 3.
Scanning electron microscopy (SEM) of wool fabrics treated with S. maltophilia DHHJ culture: (a) wool fabric samples incubated with bacterial culture in a 5 L Biostat B bioreactor; (b)–(e) representative SEM images for control (b), 48 h (c), 72 h (d), and 96 h (e).

As a protective layer of scales on the outside of wool fibers, the cuticle makes the fiber surface extremely water-repellent. This property can impede dye molecules from attaching, spreading, and penetrating into the deep layer of the fibers, causing a dyeing difficulty problem. Here, our study demonstrated the action of culture from the keratinolytic bacteria on removal of the cuticle from wool fiber. Mechanistically, this method is based on the proteolytic process, which can be performed in a controllable and mild condition. It is worth noting that the utilization of the whole bacterial culture can result in an effective treatment for the wool surface, while other researchers have reported that purified keratinase alone is unable to fully hydrolyze the keratin substrate.^19,20 It is still unclear why the activity of keratinase in a purified form will be attenuated. Whether other co-factors or proteases are needed for the full function of keratinase remains to be experimentally proven. In wool processing, compared to the use of purified enzymes, the direct application of the culture from this keratinase-producing bacterium would be more practical and cost-effective.

Wool fabric properties after DHHJ treatment

The susceptibility to shrinkage after laundering is a problematical issue for wool fabrics. Therefore, to make machine-washable wool fabrics, shrink-resistance treatments are generally applied in wool fiber processing.²¹ We evaluated how DHHJ treatment affects the felting shrinkage property of wool fibers. As shown in Table 1, felting shrinkage showed a time-dependent reduction following treatment with a concurrent increase in weight loss of wool fibers, likely due to DHHJ treatment-mediated removal of the cuticles. According to the standard of the Woolmark company, wool fabrics will be considered to be machine-washable if the felting shrink is less than 3%. In this study, the felting shrink was 2.50% at 72 h and 1.91% at 96 h during the treatment period, which meets an acceptable quality standard.

Table 1.
Felting shrinkage and weight loss of wool fabrics after Stenotrophomonas maltophilia DHHJ treatment

Time (h) Felting shrinkage (%)
Weight loss (%)

Control Treatment Control Treatment

48 10.13 ± 1.34 4.18 ± 0.50 1.10 ± 0.33 5.57 ± 2.50

72 11.57 ± 2.30 2.50 ± 0.68 2.03 ± 0.23 7.09 ± 1.16

96 12.99 ± 1.82 1.91 ± 0.35 1.05 ± 0.20 7.10 ± 0.51

T-test (P-value) 0.03 (<0.05) 0.007 (<0.01)

Degrees of freedom 2 2

Note: each data was from three independent experiments, and standard deviations are shown.

The wool structural changes due to DHHJ treatment led us to explore other processing-related physical properties of fabrics. Indeed, the DHHJ showed the capability to cause a profound impact on wool fabric features. As can be seen in Figure 4(a), along with the bacterial culture treatment, the wool fiber bursting strength was significantly decreased at 48 h in comparison with the untreated control samples. In addition, there was a downward trend in the property of elongation at break (Figure 4(b)). In contrast, no obvious change was found in the areal density of wool fabrics during DHHJ treatment (Figure 4(c)).

Figure 4.
Mechanical properties of wool fabrics treated with S. maltophilia DHHJ culture: (a) fabric bursting strength; (b) fabric elongation and (c) areal density of wool fabrics. Each column represents the mean of three independent replicates. **, p < 0.01.

The precise mechanism underlying alternation in bursting strength and elongation after DHHJ treatment at break remains elusive. The fiber cortex is generally considered to be the main determinant for these physical properties. According to the structural feature of wool fabrics, we know that the cuticle cells on the surface of wool fibers can point to ‘with-scale’ as well as ‘against-scale’ directions. This feature likely facilitates the interlocking interaction among cuticle scales, which may contribute to the resistance against the action from external stretching forces applied on the wool fabrics. When wool fabric samples were treated with DHHJ bacterial culture, the wool fiber surfaces were transformed from rough to smooth, as revealed by SEM, due to the removal of cuticle layers. Indeed, as expected, the bursting strength and elongation at break concurrently decreased in the treated samples. A long treatment time further weakened these physical properties, suggesting a gradual loss of cortex components.

The previous studies^22–24 and aforementioned alternations in physical features of treated wool fibers suggest that normally there is a tradeoff between maintaining the integrity of the interior fiber structure and removing surface scales. The excess digestion can not only peel off the cuticles, but also progressively attack the cortex parts, possibly rendering the wool quality downgraded, if not unusable. A well-controlled process is therefore crucial for keratinolytic treatment. In a practical application, it will be necessary to ensure a bacterial culture with minimal batch variation in keratinase activity as well as optimize parameters in the wool treatment, such as inoculation time, temperature, and so forth. To avoid these potential issues, it is important to standardize the bacterial culture condition as well as establish a sensitive and reliable method for monitoring keratinolytic activity.

Effect on dyeing properties of wool fabric

A series of dyeing tests was conducted with wool fabrics to determine the influence on dyeability of the DHHJ culture treatment (Figure 5). Figures 5(a)–(f) show the results of dyeing exhaustion for DHHJ-treated fibers and untreated controls under conditions with different dyeing temperatures/time settings. When dyeing with high temperatures (70°C or above), the maximum dyebath exhaustion was found within 10 min of dyeing for pretreated samples or more than 20 min for untreated controls, and dyebath exhaustion was only marginally enhanced for the pretreated groups following dyeing temperature increase. In contrast, there was a striking discrepancy in dye absorption between treated or untreated fabrics under conditions below 70°C. Over 90% of dye exhaustion in the dyebath was found at 60°C within 10 min, while the control needed 40 min to reach the same level. Furthermore, the degrees of dyebath exhaustion were more than 90% at 40°C as well as at 50°C in treated samples after 20-min staining, but only 43.35% at 40°C or 68.95% at 50°C for control samples, whose dyeing exhaustion never exceeded 80% during the whole process. Taken together, efficient dyeing can be achieved with lower dyebath temperature and shorter processing time for the wool fabrics treated with the DHHJ bacterial culture. Consistently, we found that the pretreated wool fibers showed strong coloration under the low-temperature dyeing conditions (Figure 6). More interestingly, the bacterial treatment improved the performance of wool fibers in dyeing uniformity (Table 2) as well as rubbing color fastness (Table 3) at the different dyeing temperatures.

Figure 5.
Dyeing properties of wool fabrics treated with or without Stenotrophomonas maltophilia DHHJ at different temperatures. (a-f). Dotted line represents the treatment with DHHJ for 72 h and solid line is the untreated samples.

Figure 6.
Effect of Stenotrophomonas maltophilia DHHJ treatment on the dyeability of wool fibers.

Table 2.
Effect of Stenotrophomonas maltophilia DHHJ treatment on dyeing uniformity of wool fabrics

Temperature (°C) 40 50 60 70 80 90

Control 0.14 0.14 0.14 0.08 0.07 0.05

Treatment 0.04 0.04 0.04 0.04 0.06 0.04

Table 3.
Rubbing color fastness assessment of wool fabrics with Stenotrophomonas maltophilia DHHJ treatment

Temperature (°C) Dry rubbing fastness
Wet rubbing fastness

Untreated samples Treated samples Untreated samples Treated samples

40 4 4–5 3–4 4

50 4 4–5 3–4 4

60 4 4–5 3–4 4

70 4 4–5 3–4 4

80 4 4–5 3–4 4

90 4 4–5 3–4 4

The wool fiber samples were inoculated with or without the DHHJ culture medium for 72 h. The dyeing processing was performed at different temperatures for 40 min.

A high dyebath temperature can increase the dyebath exhaustion; however, the processing quality of fabrics will be negatively affected by high-temperature treatment. The tenacity, breaking elongation, and breaking load of the treated wool fibers are negatively affected by high-temperature dyeing.^25,26 Moreover, high-temperature processing can make the wool surface rough.²⁷ Conversely, dyeing at low bath temperature can give wool fabrics a more natural feel and durability.²⁸ Meanwhile, dyeing under low-temperature and short-time conditions will be cost-effective and energy-efficient. Therefore, several dyeing improvements based on chemical or physical solutions were proposed,²⁹ which obtained some interesting results. However, these processes required special dyeing conditions and equipment, and thus a challenge might exist in the implementation of these fabric pretreatments. In addition, the extensive application of chemicals in these treatments leads to an increase in environmental concerns.³⁰ In this regard, our study showed a promising green technology for wool processing, which can achieve a desirable dyeing effect under a mild condition in a time-saving manner.

Pilling performance of wool fabric

The fuzzing and pilling property is an essential aspect for the surface appearance of fabrics, which is a serious consideration in making high-quality textile materials. The fuzzing and pilling performance was assessed for the front and back sides of fabrics dyed at different temperatures, and the data are shown in Table 4 and Figure 7. The scores of the pilling property were noticeably improved across all DHHJ-treated samples under various dyebath temperature settings. The front and back sides of treated samples revealed comparable fuzzing and pilling characters, while slightly inferior performance was found on the back sides of fabrics versus the front counterparts in the control group.

Table 4.
Effect of Stenotrophomonas maltophilia DHHJ treatment on the pilling performance of wool fabrics in the dyebath at different temperatures

Temperature (°C) 40 50 60 70 80 90

Front side

Control 3 3 3 3 1–2 1

Treatment 5 5 4–5 4–5 4–5 4–5

Back side

Control 2–3 2–3 2–3 2–3 2 1

Treatment 5 5 5 4–5 4–5 4–5

Figure 7.
Pilling performance of the wool fabrics: (a) control and (b) 72-h treatment.

Scales between 3 and 5 in the fuzzing and pilling performance are generally recognized as acceptable or good quality grades for knitted wool fabrics. According to this standard, the results in Table 4 demonstrate the correlation between DHHJ treatment and improvement in fuzzing and pilling performance of wool fabrics. The high dyebath temperature that is prone to provoke the fuzzing and pilling tendency on fabric surfaces showed a greater influence on untreated fabric samples than treated ones.

Conclusion

In an effort to develop an easily operated and environmentally friendly approach for wool processing, we conducted a small-scale assay in a 5 L bioreactor to investigate the direct application of DHHJ culture in wool treatment and found the following: (1) the treatment can effectively degrade the cuticle of wool fiber; (2) the keratinolytic pretreatment with the bacterial culture has an influence on many physical properties of wool fibers, such as felting shrink, bursting strength, elongation at break, and diameter; (3) the treatment facilitates the dyeing process of wool fabrics and the dyeing equilibrium can quickly be reached within 10 min under a dyebath temperature of 70°C; (4) the treated fabric samples exhibit better performances in dyeing uniformity and rubbing color fastness; and (5) the treatment considerably improves the anti-fuzzing and anti-pilling capability of wool fabrics.

Supplemental Material

sj-pdf-1-trj-10.1177_00405175221106231 - Supplemental material for Improvement in dyeing and physical properties of wool fabrics through pretreatment based on the bacterial culture of Stenotrophomonas maltophilia DHHJ

Supplemental material, sj-pdf-1-trj-10.1177_00405175221106231 for Improvement in dyeing and physical properties of wool fabrics through pretreatment based on the bacterial culture of Stenotrophomonas maltophilia DHHJ by Zhang-Jun Cao, Ao Tang, Juan Wang, Yun-Long Zhang, Guang Yang and Xing-Qun Zhang in Textile Research Journal

Time (h)	Felting shrinkage (%)	Weight loss (%)
48	10.13 ± 1.34	4.18 ± 0.50	1.10 ± 0.33	5.57 ± 2.50
72	11.57 ± 2.30	2.50 ± 0.68	2.03 ± 0.23	7.09 ± 1.16
96	12.99 ± 1.82	1.91 ± 0.35	1.05 ± 0.20	7.10 ± 0.51
T-test (P-value)	0.03 (<0.05)	0.007 (<0.01)
Degrees of freedom	2	2

Temperature (°C)	40	50	60	70	80	90
Control	0.14	0.14	0.14	0.08	0.07	0.05
Treatment	0.04	0.04	0.04	0.04	0.06	0.04

Temperature (°C)	Dry rubbing fastness	Wet rubbing fastness
40	4	4–5	3–4	4
50	4	4–5	3–4	4
60	4	4–5	3–4	4
70	4	4–5	3–4	4
80	4	4–5	3–4	4
90	4	4–5	3–4	4

Temperature (°C)	40	50	60	70	80	90
Front side
Control	3	3	3	3	1–2	1
Treatment	5	5	4–5	4–5	4–5	4–5
Back side
Control	2–3	2–3	2–3	2–3	2	1
Treatment	5	5	5	4–5	4–5	4–5

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Natural Science Foundation of China (no. 31570106 and 31000989), the Fundamental Research Funds for the Central Universities (no. 2232021G-03), and the Science and Technology Commission of Shanghai Municipality (no. 20DZ2254900).

ORCID iD

Zhang-Jun Cao

Supplemental material

Supplemental material for this article is available online.

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Temperature (°C)	Dry rubbing fastness		Wet rubbing fastness
Temperature (°C)	Untreated samples	Treated samples	Untreated samples	Treated samples
40	4	4–5	3–4	4
50	4	4–5	3–4	4
60	4	4–5	3–4	4
70	4	4–5	3–4	4
80	4	4–5	3–4	4
90	4	4–5	3–4	4