Integrated enzymatic and chemical treatment for single-stage preparation of cotton fabrics

Abstract

Starch sized 100% cotton woven fabrics need desizing, scouring and bleaching treatments prior to coloration and finishing. Traditionally, alpha-amylase-based enzymatic desizing and combined scouring and bleaching with an alkali, surfactant and H₂O₂ are used. Constant research is conducted on combining the desizing, scouring and bleaching processes into a single step by many researchers. This paper aims at combining enzymatic desizing and alkaline H₂O₂ scouring cum bleaching with a surfactant and stabilizer. The treatment resulted in efficient desizing, scouring and bleaching, leading to excellent size removal, absorbency, seed/mote removal and whiteness index levels, and comparable tensile and tear strength levels to that of the two-step process. The dyeability aspects were comparable in terms of surface color strength (K/S), color difference (ΔE) and fastness ratings. Around 50–75% savings in water, energy, power, time and effluent generation were reported. The chemical oxygen demand, biological oxygen demand, total dissolved solids, pH and turbidity values of the resulting effluent were found to be remarkably lower. The technology was also tested industrially and found to be successful.

Keywords

cotton starch size alpha-amylase enzyme combined desizing scouring and bleaching effluent

The textile wet processing sector is a major consumer of water and energy during production. Washing of processed goods is an essential step to render a clean substrate. The consequences of wet processing are water pollution, risks to aquatic life and consumers, water demands and scarcity, GHG (greenhouse gas) emission risks and effluent treatment costs, emission risks, etc. The current technology trends to meet sustainability are many, viz. lowest liquor ratio, continuous processing technology, combined processing, shorter process time, improved washing technology, clean technology adoption, improving energy efficiency, green chemical systems, adoption of zero liquid discharge (ZLD) compliance, etc.

Cotton fabrics are the most preferred wear on the grounds of comfort, moisture regain and cool absorbent properties. Cotton gray goods need to be prepared prior to dyeing, printing and finishing. The industrial pre-treatment is traditionally carried out as α-amylase enzyme-based desizing, alkaline scouring with a surfactant and H₂O₂-based bleaching with intermediate washings. Alkaline scouring and H₂O₂ bleaching are combined in a single step practically. Full white fabrics need enzymatic desizing, alkaline scouring and H₂O₂ bleaching with optical brightening agents. The above-mentioned processes are carried out as individual processes or combined/discrete step scouring and bleaching after desizing based on the machinery availability in the plants.

Enzymes are applied at a mild pH and moderate temperatures of around 60℃ in general, but can be tailor made through culture to impart stability even at harsh pH and higher temperature conditions. However, desizing requires the application of bacterial enzymes at or around 60–70℃ and mild acidic pH. This is the major constraint to combine alkaline H₂O₂ scouring and bleaching with enzymatic desizing. Many researchers are opting for combining the desizing, scouring and bleaching processes into a single step. Biochemists attempt a complete enzymatic pre-treatment option by using selective enzyme species. The advantages are that enzyme applications provide a gentle reaction, specific molecular hydrolysis, biodegradability and fiber safety. An extensive review on enzyme applications and mechanisms was presented by Araujo et al.¹ Amylases are useful for desizing, cellulases for biopolishing, pectinases and lipases for scouring and oxidoreductases (catalases) for removing residual peroxides. El-fallal et al.² presented an exclusive review on starch and amylase enzymes as regard to the source, structures, hydrolysis activity, mechanisms, enzyme production and quality aspects. Starch is a polymer of glucose, present as alpha-amylose and amylopectin. Amylose is soluble in water; butamylopectin and the starch granule itself are insoluble. Buschle-Diller and Yang³ reported an elaborate study on amyloglucosidase (AMG) desizing, combined with bio-scouring, applying acid/alkaline pectinase and glucose oxidase for H₂O₂ generation and bleaching. A comparable whiteness index, low energy, scope of reuse of the enzymatic desize bath and inferior absorbency were reported to be feasible. Opwis et al.⁴ conducted lab- and bulk-scale trials on combined desizing and scouring using α-amylase and a mixed hemicellulase and pectinase enzyme combination. They reported that acceptable levels of desizing efficiency, seed removal efficiency, wettability and whiteness index were obtainable. Idalina Goncalves et al.⁵ used combined nano-emulsions of laccase–H₂O₂ mixture along with medium frequency ultrasound (850 kHz_, 12 W) and obtained increased whiteness levels, 50% reduction in H₂O₂ and 40℃ reduction in temperature for a reaction time of 90 minutes. Efficient wetting and rewetting properties by the ultrasound-induced cavitation effect were reported to be feasible. A published work by MinL⁶ explored the possibility of one-bath–two-step desizing, scouring and bleaching of starch sized cotton fabric. Desizing was carried out using alpha amylase, second-stage scouring and bleaching using sodium bicarbonate at pH 7.3, bleach activator TBBC (triethylammoniomethyl benzoyl butyrolactam buffer chloride), stabilizer and H₂O₂ bleaching at 60℃. This process was reported to consume less water and use a milder pH and lower temperature in the 50–60℃ range. Spicka and Tavcer⁷ conducted a one-step desize, scour and bleach process with complete enzymatic components on starch sized cotton fabrics. They used a mixture of AMGs, pullulanase, pectinase and glucose-oxidase enzyme. H₂O₂ was generated and activated by TAED (tetra acetyl ethylene diamine). An increase in pH to 7.5 using soda ash resulted in the conversion of H₂O₂ to per acetic acid (PAA) and diacetyl ethylene diamine. An acceptable level of tensile strength of the treated fabric, close to neutral pH effluent and biodegradable TOC (total organic carbon)/chemical oxygen demand (COD) content, and lower energy, time and water were reported feasible and medium level (51) the whiteness index was obtained. Ali et al.⁸ reported on single bath desizing–bleaching–reactive dyeing of starch sized cotton terry towel (399 GSM) without draining the baths at intermediate stages.

The major disadvantages of pectinase scouring, as concluded by Mojsov⁹ (2014), were ineffective mote removal and their appearance in dyed goods. Whiteness attainment was also a major task, making it unsuitable for full white goods. Waxes were also reported to not have been efficiently removed. Shaikh¹⁰ reported comprehensively on the consumption of water in textile wet processing units. Within the preparation process, the water consumption patterns in liters/1000 kg of fabric were reported to be 500–8200, 2500–21,000, 20,000–45,000 and 2500–25,000 for sizing, desizing, scouring and bleaching, respectively.

In their strategic research on cleaner and sustainable production in textile wet processing, Alkaya et al.¹¹ presented the overall effluent characteristics for a textile mill, in terms of BOD (biological oxygen demand), COD, color, pH and volume of effluent on a comparative basis for woven, knit fabrics and yarn. Ren¹² proposed a comprehensive assessment of environmental performance indicators (EPIs) for textile processes and products. The process EPIs were focused on water usage, BOD, COD, TDS (total dissolved solids), VOCs (volatile organic compounds), energy, AOXs (absorbable organic halides), toxic substances and metals. For finishing, toxic substances, such as formaldehyde, urea, and aquatic toxicity levels were also included.

Surribas et al.¹³ reported two-step semi-continuous preparation of cotton fabric by alpha-amylase and pectinase enzyme-based combined desizing and scouring at 60℃, deactivation at boiling after processing and two-stage bleaching with H₂O₂ and Na₂Sio₃ stabilizer. (a) Combined desizing and scouring using dextrozyme and pectinase enzymes at pH 4.1, 62℃ for 60 min, followed by H₂O₂ bleaching with Na₂SiO₃ stabilizer. (b) A one-step continuous process using thermo stable amylase (Texazyme TA-10), wetting, chelating agents and H₂O₂ with a phosphate buffer at alkali pH facilitated by Na₂Sio₃ at 105℃. Residual peroxide inactivation was carried out with second-stage catalase enzyme and chitosan microspheres. At lower temperatures, two in one or three in one processes with feasible time reduction were reported to be obtainable. El Shafie et al.¹⁴ conducted two-step and one-step processes for combined bio-scouring and PAA bleaching of cotton fabric. (a) PAA-based desizing at 80℃, 30 min followed by PAA and cellulase enzyme-based scouring and bleaching process at 60℃. A whiteness index value of 74 and 85% tensile strength retention were reported to be obtainable. (b) Desizing using ammonium persulfate at 80℃, 60 min, followed by PAA and cellulase enzyme-based scouring and bleaching process at 60℃ for 60 min. This process reported a lower whiteness index value of 61 and 80% tensile strength retention. (c) One-step process using exclusive PAA at 60℃ for 60 min. A lower whiteness index value of 47.8 and 91% tensile strength retention were obtained. (d) One-step desizing, scouring and bleaching using PAA and cellulase enzyme at 60℃ for 90 min. A whiteness index value of 61and 81% tensile strength retention were obtained. Raja et al.¹⁵ reported the feasibility of combined enzymatic scouring and bleaching using Xymo Nat Scour, 1.5 g/l H₂O₂, 0.5% wetting agent and 1 g/l NaOH at boiling 1 h on natural cotton fiber. An acceptable level of absorbency and a whiteness index value of 72 were reported to be obtainable.

This work attempts to accomplish enzymatic desizing, alkaline scouring and H₂O₂ bleaching in a single-step pre-treatment process toward achieving energy efficiency, a reduction in process time, energy and wastewater load and ensuring the effective removal of size, impurities and coloring matters from gray cotton.

Experimental details

Plain woven gray cotton fabric, starch sized, possessing warp and weft (40^s× 40^s), ends and picks/inch (136 × 72, 144 GSM) was used for this study. Alpha-amylase (PT cell KRA), Demineralizer cum stabilizer (Supra RHD), five in one surfactant (penetration, wetting, emulsifying, extraction and rewetting properties), low foam, APEO (alkyl phenyl ethoxylate)-, NPEO (nonyl phenyl ethoxylate)-, OPEO (octyl phenyl ethoxylate)-free non-ionic-crypto anionic surfactant (Penfac NVFL), core neutralizer acid, all from Ankha Kaizen Technologies, 50% W/V hydrogen peroxide (H₂O₂) and 48% sodium hydroxide (NaOH) lye were used.

Enzymatic desizing, combined scouring and bleaching, one-bath desizing, scouring and bleaching (ODSB) treatments meant for ready for dyeing (RFD) status were carried out. The methodology adopted was bath-based pad-batch and pad-steam modes.

The details of the sequence of processes, washing and method of application (bath/pad-batch/pad-steam) are given in Table 1.

Table 1.

Ready for dyeing/half-white: process method, process sequence, washing and equipment details

Method code	Method	Process sequence	Equipment
M-1A	Bath method (two-step)	Enzymatic desizing, washing-combined scouring and H₂O₂ bleaching, washing-drying	Laboratory open bath water heater with automatic temperature control (make: Paramount Testing Instruments)
M-1B	Bath method (ODSB)	One-bath desizing, scouring and H₂O₂ bleaching, washing-drying	Laboratory open bath water heater with automatic temperature control (make: Paramount Testing Instruments)
M-2	Pad-batch method (ODSB)	One-step desizing, scouring and H₂O₂ bleaching, washing-drying	Laboratory 2 bowl rubber mangle padder with adjustable pneumatic pressure system, electrical drive with speed control (make: SPI Equipments India Pvt Ltd)
M-3 A	Pad-steam method (two-step)	Enzymatic desizing, washing- combined scouring and H₂O₂ bleaching, washing-drying	Laboratory 2 bowl rubber mangle padder with adjustable pneumatic pressure system, electrical drive with speed control (make: SPI Equipments India Pvt Ltd) & laboratory steamer with temperature control (make: SPI Equipments India Pvt Ltd)
M-3B	Pad-steam method (ODSB)	One-step desizing, scouring and H₂O₂ bleaching, washing-drying	Laboratory 2 bowl rubber mangle padder with adjustable pneumatic pressure system, electrical drive with speed control (make: SPI Equipments India Pvt Ltd) & laboratory steamer with temperature control (make: SPI Equipments India Pvt Ltd)

ODSB: one-bath desizing, scouring and bleaching.

Process trial details: woven fabric ready for dyeing

Based on the above pre-treatment process sequences, process condition details of specific methods regarding chemical the bath/pad recipe, bath conditions, such as liquor ratio, temperature, pH, duration of treatment, padding recipe, hot/cold pad, number of dips, nips (squeezing), process energization/reaction mode-like steaming/bath temperature, reaction duration, pick up % and washing details data are presented for the woven RFD status. The substrates were washed using dip washing baths with a standard liquor ratio of 1:30 with intermediate squeezing and finally drying. Table 2 shows the process details, conditions and washing details of the RFD process methods. Table 3 shows the details of tests meant for the determination of wastewater characteristics, such as COD, BOD, TDS, pH and turbidity of the RFD process effluent.

Table 2.

Ready for dyeing process, conditions and washing details

Details/parameters	Bath methodM-1 A (two-step)		Bath method M-1B	Pad-batch method M-2	Pad-steam method M-3 A (two-step)		Pad-steam method M-3B
Details/parameters	Desizing	Scouring and bleaching	ODSB	ODSB	Desizing	Scouring and bleaching	ODSB
Supra RHD	5 g/l	4 g/l	5 g/l	6 g/l	6.5 g/l	5 g/l	15 g/l
Penfac NVFL	8 g/l	8 g/l	9 g/l	18 g/l	12 g/l	10 g/l	35 g/l
PT cell KRA	50 g/l	–	50 g/l	80 g/l	80 g/l	–	550 g/l
50% H₂O₂	–	20 g/l	20 g/l	75 g/l	–	70 g/l	100 g/l
48% NaOH	0.4 g/l	20 g/l	20 g/l	32 g/l	1.5 g/l	27 g/l	80 g/l
Application mode	B.M.	B.M.	B.M.	Hot P.B.	Hot P.S.	P.S.	Hot P.S.
M:L ratio	1:30	1:30	1:30	–	–	–	–
Dip/nip	–	–	–	4 dip/4 nip	4 dip/4 nip	4 dip/4 nip	16 dip/16 nip
Pick up	–	–	–	100%	100%	100%	100%
Temperature	90℃	90℃	90℃	90℃ Hot	90℃ Hot	R.T. padding	90℃ Hot
Reaction time	90 min	80 min	100 min	18 h	15 min	30 min	30 min

WASHING AND COMBINE WATER

C.W. N

Total bath combined water

C.W. N

Total bath combined water

C.W. N

Total bath combined water

C.W. N

Total bath combined water

C.W. N

Total bath combined water

C.W. N

Total bath combined water

C.W. N

Total bath combined water

H.W.-2 90℃

H.W.-1 90℃

H.W.-2

BATH OUT

H.W.-1

ODSB: one-bath desizing, scouring and bleaching.

Table 3.

Ready for dyeing process water testing methods and instruments

S. no	Test parameter	Instrument used
1	pH of water samples	Digital TDS/conductivity meter, bench model 503 A (make Infra)
2	Total dissolved solids (TDS) in ppm	Digital pH meter model 111 (make Deep Vision)
3	Turbidity in NTU (nephelometric turbidity units)	Digital turbidity meter, bench model 331 E (make EI-Deep Vision) range up to 1000 NTU
4	Biological oxygen demand (BOD) in ppm	Standard IS: 3025 (part 4)/5210B procedure with 5 days incubation at 20℃
5	Chemical oxygen demand (COD) in ppm	Standard IS: 3025 (part B)/5220 C closed regular method

Fabric testing

The pretreated fabrics were tested for specific performance criteria, such as GSM, residual starch, desizing loss (%), scouring and bleaching loss (%), absorbency, whiteness index, tensile strength and tearing strength, using appropriate standard test procedures and equipment, which are listed in Table 4. Prior to testing, the test fabric samples were conditioned at standard 65 ± 2% relative humidity (RH), 20 ± 2℃ temperature atmosphere for 4 h prior to testing.

Table 4.

Test instruments and test details for ready for dyeing fabric parameters

S. no	Test parameter	Instrument used	Test method
1	GSM estimation was done using GSM cutter (make - Power Equipments)	Digital electronic balance of 5 mg accuracy (make: ESSAE, India)	ISO-3801
2	Residual starch estimation	Standard Iodine solution staining, viewing in DL-65 light source	Reference to Tegewa violet scale
3	Desizing loss estimation	Electric drier oven with temperature control (New Lab Equipments), digital electronic balance of 5 mg accuracy (make: ESSAE, India)	IS 1383-1977b method (Indian standard)
4	Scouring and bleaching loss %	Electric dryer oven with temperature control (New Lab Equipments), digital electronic balance of 5 mg accuracy (make: ESSAE, India)	IS 1383-1977b
5	Absorbency estimation	a) Drop test apparatus and b) Wicking height estimation apparatus	a) Drop test – AATCC, TS-018 b) Wicking height estimation - AATCC 197-2011
6	Whiteness index of bleached woven fabric	Data color 600™ computer color matching system, under light source DL-65 (Day Light) by 10° observor mode	ASTM-E313-00 (American Society of Testing Methods)
7	Tensile strength of processed woven fabrics (warp and weft directions)	Electronic tensile strength tester (make: State Engineering Company, Coimbatore)	Raveled strip method ASTM 5035-95
8	Tearing strength of processed woven fabrics sample (warp and weft methods)	Grab test using tearing strength tester (make: Kannan Metal Industries, Ahmedabad)	ASTM 1424-96

Dyeing

The comparative dyeability characteristics of RFD woven fabrics, processed by various process modes, were assessed by simultaneous dyeing of the samples under standard conditions. Bi-functional reactive dyes were used, as they are eco-friendly and have good fastness. Three basic primary bi-functional reactive dyes, namely Chemistar yellow ME₄GL (CI number (160 A)/CAS No. 129898-77-7) – (2%), Chemistar red ME₄BL (CI number 195/CAS No. 93050-79-4) – (0.2%) and Chemistar blue ME₂RL (CI number 248) – (1.8%), were used for three color combination shades of a total of 4%. The samples were dyed at the standard liquor ratio of 1:30 using a programmable infrared (IR) heated laboratory dyeing machine (SPI Infra color, SPI equipment India Pvt Ltd). A standard dyeing program at 60℃ using 60 g/l vacuum salt for exhaustion and mixed alkali (6.5 g/l of soda ash and 1 g/l of 48% NaOH lye) for fixation were used. After dyeing, the samples were washed as per the standard washing procedure comprising cold wash, cold wash neutral, hot soaping at 90℃ using 1.5 g/l non-ionic soap (Clear N RWS from Ankha Kaizen Technologies), hot washing at 90℃, followed by cold washing, squeezing and drying using a laboratory dryer.

The dyed samples were assessed for surface color strength (K/S) and color difference (ΔE) using the data color 600™ computer color matching system, under light source DL-65 (day light) at 10° observer mode. The bath process M-1 A method RFD sample dyed fabric was taken as the standard reference for comparison. The color fastness to wash was determined by the ISO-C03 procedure, using 5 g/l soap and 2 g/l soda ash at 60℃ for 30 min, rinsed with cold water and dried. A programmable laundrometer (Paramount) and heater system were used. The wash fastness to water, color change and color staining were determined by using standard gray scale references. The fastness to rubbing ISO-105 × 12 procedure (wet and dry) was assessed using a crock meter (Paramount Testing Instruments) using 900 g standard weight and the standard gray scale reference. The respective K/S values, ΔE, wash fastness ratings to change of color and staining and rubbing fastness (wet and dry) of various process modes were recorded and tabulated.

Industrial-level process trials

The single-stage desizing, scouring and bleaching using (1) stabilizer Supra RHD, (2) alpha-amylase enzyme PT cell KRA, (3) five in one wetting agent Penfac NVFL along with (4) 50% H₂O₂ and (5) 48% NaOH was tested at the laboratory level successfully on the 40^S Ne × 40^S Ne (136 × 72) plain woven cotton fabric. The other commercial cotton varieties, starting from 7^S Ne × 7^S Ne to 80^S Ne × 80^S Ne (low, medium and high GSM fabrics) count range, were also tested for the ODSB process and the process conditions were standardized. This ODSB process technology is implemented in two jigger process units and the new end users are likely to increase. Further initiatives are in progress toward ODSB process implementation by hot pad-batch and pad-steam process at continuous bleaching range (CBR) units via padder modification. Our methodology enables single-step combined enzymatic desizing, alkali scouring and H₂O₂ bleaching within a short time of 45–75 mins at a temperature 90℃ as per fabric GSM criteria.

Results and discussion

RFD fabric characteristics

The fabric performance factors, such as desizing loss, scouring and bleaching loss combined desizing, scouring and bleaching loss residual starch rating by Tegewa violet scale, absorbency values by drop test and wicking height estimation, whiteness index, tensile strength and loss % (warp and weft) and tearing strength and loss % (warp and weft) values are presented in Table 5.

Table 5.

Ready for dyeing fabric characteristics

Method	20 cm × 20 cm gray fabric weight in grams	Desize loss %	Combined scouring and bleaching loss %	Combined desizing, scouring and bleaching loss %	Tegewa scale rating	Absorbency		Whiteness index	Tensile strength and loss %				Tearing strength and loss %
Method	20 cm × 20 cm gray fabric weight in grams	Desize loss %	Combined scouring and bleaching loss %	Combined desizing, scouring and bleaching loss %	Tegewa scale rating	Drop test value in seconds	Wicking height value in cm	Whiteness index	Warp (N_f)	Loss %	Weft (N_f)	Loss %	Warp (N_f)	Loss %	Weft (N_f)	Loss %
Bath method M-1A	5.752	8.097%	4.42%	12.52%	8	1.36	7.6	84.41	346.95	Refer standard	320.27	Refer standard	8.2	Refer standard	6.6	Refer standard
Bath method M-1B	5.748	–	–	12.39%	8	1.34	7.8	78.92	317.3	8.55%	289.52	9.69%	7.5	8.92%	5.3	19.69%
Pad-batch method M-2	5.749	–	–	12.24%	8	1.39	7.4	79.42	313.12	9.75%	288.56	9.9%	10.97	10.12%	8.2	21.21%
Pad-steam method M-3A	5.754	7.82%	4.29%	12.11%	7	1.51	6.9	72.9	321.55	7.32%	293.69	8.3%	9.4	8.16%	7.5	18.18%
Pad-steam method M-3B	5.751	–	–	11.97%	8	1.38	7.5	83.2	308.89	10.97%	286.32	10.6%	6.9	11.18%	5.0	22.72%

Desizing efficiency

The residual starch estimation by Tegewa scale ratings for the two-stage bath, pad-batch and pad-steam ODSB processes were found to be higher (8) compared to the two-stage pad-steam process (7). The presence of higher residual starch in the pad-steam process samples could be attributed to the dilution effect by contact steam and poor gray fabric penetration.

The weight loss % after desizing/scouring and bleaching/ODSB was calculated based on the following formula

where W₁ is the weight of the sample before processing and W₂ is the weight of the sample after a specific process. In the case of ODSB trials, the individual desizing loss % could not be ascertained. Desizing loss % could be assessed for only the two-stage bath and pad-steam processes. The desizing loss percentages of 8.097% for process method M-1 A and 7.82% for process method M-3B were obtained.

Scouring and bleaching loss

Scouring and bleaching loss % values in the case of the M-1 A and M-3 A methods were 4.42% and 4.29%, respectively, showing acceptable limits for the two-step process.

Combined desizing, scouring and bleaching loss

In the case of the ODSB process, only combined desizing, scouring and bleaching loss % could be evolved. The loss % of all the methods ranged from 11.97% to 12.517%, which was found to be in a close range.

Scouring efficiency by absorbency value

Drop test

The absorbency estimation by drop test values in seconds were found to be closer (from 1.34 to 0.39 seconds) for all process methods. The two-stage pad-steam process method (M-1 A) samples showed higher timing of 1.52 seconds due to the presence of possible residual starch.

Wicking height

The absorbency estimation by wicking height test values in centimeters were found to be closer (from 7.4 to 7.8 cm) for all process methods. The two-stage pad-steam process method (M-3 A) samples showed a lower value of 6.9 cm. This trend was observed in the drop test values also.

Whiteness index

The whiteness index values for the bath, pad-batch and pad-steam (three in one) methods showed closer values from 84.41% to 78.92%. The two-step pad-steam process method (M-3 A) samples showed a lower whiteness index value of 72.9.

Tensile strength loss

The tensile strength values in Newton force (N_f) for various process methods were estimated in the warp and weft. The loss % of tensile strength compared to method M-1 A as standard was also calculated based on the following formula

where T₁ is tensile strength in the M-1 A method processed sample and T₂ is tensile strength of the specific method treated sample. The ODSB process method samples showed 8.55% in warp/9.6% in weft for M-1B; 9.75%/9.9% for M-2; and 10.97%/10.6% loss, which were slightly higher for M-3B. The warp-wise loss % ranged from 7.32% to 10.97% and in the weft was from 8.3% to 10.6%. Reference to mill level test data for the bulk process unmercerized RFD material of this 40^s Ne × 40^s Ne quality related to the tensile strength of the gray and processed samples in the warp and weft directions, and the obtained values were found to be comparable.

Tearing strength loss

The tearing strength values in Newton force (N_f) were estimated and reported process method wise, in the warp and weft directions. Keeping the method M-1 A processed sample value as standard, comparative loss % values in tearing strength were calculated and are presented. For the ODSB process method, the results were 8.92% in warp/19.69% in weft for M-1B; 10.12%/21.21% for M-2; and 11.18%/22.72% loss, which were found slightly higher for M-3B.The warp-wise loss % ranged from 8.16% to 11.18% and that in the weft was from 18.18% to 22.72%. Reference to mill level test data for the bulk process unmercerized RFD material of this 40^s Ne × 40^s Ne quality related to the tearing strength of the gray and processed samples in the warp and weft directions, and the obtained values were found to be comparable. Another major observation was that the bulk-scale jigger machine processed fabrics of the ODSB process method showed no drastic tensile/tearing strength loss in case of the RFD process, compared to the two-step process. The only difference is the dosage of chemicals based on OWF%. The lab trials were based on grams per liter, which were at higher concentration levels compared to the industrial process. The tensile and tearing strength loss % could be controlled by suitable modification of the component chemical dosage of H₂O₂, NaOH lye concentrations.

Dyeability

The comparative dyeability characteristics in terms of K/S values, ΔE values, ratings of wash fastness to change in color and staining and rubbing fastness, dry and wet, are presented in Table 6. As regard to dyeability, the RFD M-1 A method was kept as the standard reference sample (4.55), and the K/S values of dyed samples from various RFD process methods ranged from 4.35 to 4.55, within a variance level of ± 5%. The ΔE values were also found to be closer to 0.78 (from 0.73 to 0.83).

Table 6.

Dyeing test report for ready for dyeing fabric

Method	ΔE value	K/S value	Wash fastness rating		Rubbing fastness rating
Method	ΔE value	K/S value	Change in color	Staining	Dry rub	Wet rub
M-1A	Standard reference	4.55	4.0	4–5	5	4–5
M-1B	0.78	4.41	4.0	4–5	5	4.0
M-2	0.78	4.37	4.0	4–5	5	4–5
M-3A	0.83	4.35	4–5	4–5	5	4–5
M-3B	0.73	4.36	4.0	4–5	5	4–5

This indicated that the tone and depth of dyed samples were closely comparable without any marked deviations. The wash fastness rating values, in terms of change in color, were 4 (for four samples) and 4–5 (for one sample). The fastness to stain rating was found to be 4–5 for all samples. This indicated a comparably good level of wash fastness of all process RFD samples that were dyed for the trial. The dry rubbing fastness of all process samples was found to be 5, and the wet rubbing of all process samples to be 4–5. All the above data indicated that the ODSB process is comparable to the two-stage process method.

Characteristics of wastewater

The combined process and wash water effluent characteristics were estimated for experimental process methods in terms of COD, BOD, TDS, pH and turbidity values, which are presented in Table 7 with appropriate units. Figure 1 shows a bar chart of respective water characteristics of all process methods effluents and illustrates the comparative values of BOD, COD and TDS.

Figure 1.

Comparative water parameter data. COD: chemical oxygen demand; BOD: biological oxygen demand; TDS: total dissolved solids.

Table 7.

Water characteristics for ready for dyeing effluent

Water parameters (unit)	Bath method M-1A	Bath method M-1B	Pad-batch method M-2	Pad-steam method M-3A	Pad-steam method M-3B
COD (ppm)	3857	1878	932	615	1122
Reduction percentage	Standard	51.3%	75.8%	84.05%	71%
BOD (ppm)	682.74	323.79	160.68	87.22	205.61
Reduction percentage	Standard	52.6%	76.4%	87.22%	69.8%
TDS (ppm)	3670	6715	3422	626.5	1048
Reduction percentage	Standard	Excess 45.34%	6.75%	82.9%	83%
pH	9.42	12.31	11.94	9.35	11.04
Turbidity (NTU)	134	102	29.22	28	31.6
Reduction percentage	Standard	23.88%	78.2%	79%	76.4%

COD: chemical oxygen demand; BOD: biological oxygen demand; TDS: total dissolved solids.

COD values

The two-step process bath method and pad-steam method showed COD values of 3857 and 615 mg/l (or) ppm (parts per million) levels due to the presence of hydrolyzed starch. For the ODSB process, the bath, pad-batch and pad-steam methods showed values of 1878, 932 and 1122 mg/l (or) ppm levels, respectively. The reduction in COD values ranged from 51.3% to 75.8% compared to method M-1 A as the standard reference.

BOD values

The BOD values also reflected the same trend as the COD values. The two-stage bath method and pad-steam method showed BOD values of 682.74 and 87.22 in mg/l (or) ppm levels. For the ODSB process, the bath, pad-batch and pad-steam methods showed values of 323.9, 160.68 and 205.61 in mg/l (or) ppm levels, respectively. The reduction in BOD values ranged from 52.6% to 76.4% compared to method M-1 A as the standard reference.

TDS values

The TDS value in ppm for two-stage processes of the bath and pad-steam methods showed levels of 3670 and 626.5. For the ODSB process, the bath, pad-batch and pad-steam methods showed values of 6715, 3422 and 1048 in mg/l (or) ppm levels, respectively. The reduction in TDS values ranged from 6.75% to 83%. The pad-batch ODSB method showed a just feasible TDS reduction of 6.75%, compared to method M-1 A as the standard reference. The ODSB (M-1B) method showed a higher value of 6715 mg/l (or) ppm, which was 45.34% higher than that of the reference standard. The dosage for the ODSB bath method being measured in grams per liter is the main attributed reason for the higher TDS value.

The two-stage process M-1 A has a dilution effect. Practical conditions of chemical dosage in jiggers call for % based on weight of fabric and, hence, there is scope for TDS reduction in the bulk process. The following work out justifies the above statement: for example, 2% of 48% NaOH OWF basis in the jigger for 100 kg of fabric will result in 2 kg in total water of 400 l at 1:4 M:L ratio. Meanwhile, 20 g/l of 48% NaOH for 1:30 M:L ratio in the experimental process will result in 100 kg of material, 3000 l of water and 60 kg of 48% NaOH. This works out to be 60 / 3000 × 400 = 8 kg. This is reflected in the higher TDS value.

pH values

The lower pH value of 9.42 for the combined effluent of the two-stage bath method and 9.35 for the pad-steam method were obtained. The ODSB process effluent pH values ranged from 11.04 to 12.31 for the pad-steam process. The grams-per-liter-based dosage and reduced number of baths are the causes.

Turbidity

Turbidity values are represented in NTU units. The two-stage process of the bath and pad-steam methods showed turbidity values of 134 and 28, respectively. For the ODSB process, the bath, pad-batch and pad-steam methods showed values of 102, 29.22 and 31.6 levels, respectively. The reduction in turbidity values ranged from 23.88% to 78.2%, compared to method M-1 A as the standard reference. The higher turbidity value of M-1 A is due to the two-stage process of wetting agent addition. Lower values are attributed to padding-based processes in which the effective concentration of the wetting agent is lower.

Water, steam and time consumption and savings data for the realistic estimation of water, based on industrial working conditions, such as the jigger (bath), pad-steam, pad-batch and washing conditions (bath and continuous mode), were produced and are presented in Table 8 for comparative assessment for 1000 kg of cotton fabric measuring 5000 m in length. Figures 2 –4 show bar charts of comparative water, steam and time consumption data for various process methods.

Figure 2.

Comparative water consumption data.

Figure 3.

Comparative steam consumption data.

Figure 4.

Comparative process and washing time consumption data.

Table 8.

Water, steam and time consumption data for 1000 kg of fabric/5000 m

Method	No. of baths (process + washing)	Process machine	Washing machine	Total consumption of water in liters	Percentage savings of water	Total steam consumption for process and washing (kg)	Percentage savings of steam consumption	Total time consumption for process and washing	Percentage savings in total time (minutes)
M-1A	8	Jigger	Jigger	25,000	Standard	6240	Standard	1020	Standard
M-1B	4	Jigger	Jigger	13,000	48%	3120	50%	570	44%
M-2	3	2A) padder + batch roll	Jigger	10,000	60%	1720	72.4%	1225	Nil (excess 20%)
M-2	3	2B) padder + batch roll	Continuous washing	5000	80%	1010	83.8%	955	6.37%
M-3A	6	Padder + steamer	Continuous washing	10,000	60%	4505	27.8%	470	53.9%
M-3B	3	Padder + steamer	Continuous washing	5000	80%	2450	60.7%	235	76.9%

For the ODSB process reaction mechanism, physically the starch layer is swollen by hot water and gets washed off in the case of the bath method. In the case of the hot pad-batch and pad-steam methods, multiple dipping and nipping (mangling) squeezes out the swollen starch layer. This leads to successive penetration of ODSB chemical components into the core of the fiber. In the chemical reaction part, H₂O₂ being corrosive, enhances an effective penetration of desized enzyme being assisted by the surfactant. Alkali pH beyond 11 and H₂O₂ accelerate the oxidation process; the initial energy is utilized for decomposing starch (amylase and amylopectins) into sodium gluconate and sodium pectinate. These are potential stabilizers for H₂O₂ bleaching by which fabric safety is ensured at elevated pH.

Apart from anionic stabilization by demineralizer cum stabilizer, the released sodium gluconate, sodium pectinate and preservatives in the enzyme formulation and the nascent oxygen species (O*), the hydroxyl ion activity on enzyme molecules is blocked, due to which enzyme hydrolysis by alkali pH is prevented. Alkali scouring and oxidative bleaching are also simultaneously enhanced by the ODSB process reaction. The complimentary, accelerated and stabilized reaction leads to an efficient desizing, scouring and bleaching process, ensuring fiber safety also.

Conclusions

The three in one process of enzymatic desizing, alkali souring and H₂O₂ bleaching was successfully performed. The process was found successful on RFD/half-white status cotton goods. The existing jigger-based bath method, pad-steam process method and new class hot pad-batch methods were made viable for ODSB treatment for RFD status. Fabric performance factors, such as desizing efficiency in terms of residual starch by the Tegewa scale rating, absorbency in terms of the drop test and wicking height values, CIE (International Commission on Illumination) whiteness index values for RFD (70+) and tensile strength values (Nf), were found comparable with the normal two-step-treated reference samples. A higher percentage loss of tensile and tearing strength cases are controllable by modified chemical recipe/dosage conditions. The selvedge to body bleaching was found to be uniform in the case of ODSB treatment in bulk. The dyeability characteristics of all the methods were found to be comparable in terms of K/S values, ΔE values, wash fastness rating to staining and color change and rubbing fastness (dry and wet) ratings. In the case of the ODSB process, ecologically safer bleaching was achieved without sodium hypochlorite bleach, leading to ease of effluent treatment.

Industrial-level bulk trials on the jigger machine using the ODSB process treatment were successfully performed.

The advantages found were 50%+ water, steam energy and time savings when compared to the traditional two-step or multi-step methods for RFD state fabrics. The methodology was also found to be suitable for pad-steam method applications. The new class hot pad-batch ODSB treatment was also made viable with additional process energy savings by using steam heat only for the padding liquor.

In the case of the ODSB process, the effluent generation was found to be lower, apart from reduced pollution potentials, such as COD/BOD, TDS, pH and turbidity. Oxidative bleaching of size and scouring impurities led to reduced COD/BOD levels, which contribute to ease of effluent treatment. Single-step combined enzymatic, alkaline scouring and H₂O₂ bleaching was made technically and industrially feasible. This can lead to sustainable textile wet processing of cotton fabrics with additional improvements in fabric performance, whiteness index values and dyeability aspects.

Footnotes

Declaration of conflicting interests

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

Funding

The authors received no financial support for the research, authorship and/or publication of this article.

References

Araujo

Casal

Cavaco-Paulo

. Application of enzymes for textile fibers processing. Biocatal Biotransform 2008; 26: 332–349.

El-fallal A, Dobara MA, El-sayed A, et al. Starch and microbial α-amylases: from concept to biotechnology application. In: Chang C (ed) Carbohydrates-comprehensive studies on glycol biology and glycol technology. Intech Publication, 2012, pp.459–475.

Buschle-Diller

Yang

. Enzymatic bleaching of cotton fabrics with glucose oxidase. Text Res J 2001; 71: 388–394.

Opwis K, Knittel D, Schollmeyer E, et al. Combined use of enzymes in the pre- treatment of cotton. In: Deutsches Textilforschungszentrum Nord-West gGmbH, Frankfurt, Germany, June 2008, vol. 12, pp.566–573. Research Gate Publication.

Goncalves

Martins

Loureiro

, et al. Sonochemical and hydrodynamic cavitation reactors for laccase/hydrogen peroxide cotton bleaching. Ultrasonic Sonochem 2014; 21: 774–781.

Min

. An environmentally benign approach to cotton preparation: One bath enzymatic desizing, scouring and activated bleaching. NCSU Librar 2012; 12: 451–451.

Spicka

Tavcer

. Complete enzymatic pre-treatment of cotton fabric with incorporated bleach activator. Text Res J 2013; 83: 566–573.

Ali

Khatri

, et al. Integrated desizing-bleaching- reactive dyeing process for cotton towel using glucose oxidase enzyme. J Clean Prod 2014; 66: 562–567.

Mojsov

. Biotechnological applications of pectinases in textile processing and bioscouring of cotton fibers. In: Proceedings of II International Conference Industrial Engineering and Environmental Protection 2012 (IIZS 2012), Zrenjanin, Serbia, 31 October 2012, pp. 314–322.

10.

Shaikh

. Water conservation in textile industry. Pakistan Text J 2009; 58: 48–51.

11.

Alkaya E, Bogurcu M, Ulutas F, et al. Cleaner (sustainable) production in textile wet processing. In: Nemr A (ed) Non-conventional textile waste water treatment, New York: Nova Science Publishers Inc, 2012, pp. 1–26.

12.

Ren

. Development of environmental indicators for textile process and product. J Clean Prod 2000; 8: 473–481.

13.

Surribas

Martinez

Alaman

, et al. Bio-technological solutions for reducing environmental impact of cotton processing. AATCC Rev 2013; 13: 44–49.

14.

El Shafie

Fouda

MMG

Hashem

. One-step process for bio-scouring and per acetic acid bleaching of cotton fabric. Carbohydr Polym 2009; 78: 302–308.

15.

Raja

ASM

Arputharaj

Saxena

, et al. A one bath chemo-enzymatic process for preparation of absorbent cotton. Sci Dir 2016; 8: 254–256.