Cold-Pad-Batch Bio-Pretreatment of Cotton Woven Fabrics: A Case Report on Industrial Trials

The noncellulosic constituents of cotton fiber are known to be waxes, pectins, hemicellulose, proteins, and mineral matters ranging from 4 to 12% of the dry fiber weight and to be located mostly in the cuticle, in the primary cell wall, and in the lumen. Natural cotton wax of 0.4 to 1.0% serves as a protective barrier to water penetration comprising the cuticle on the outer surface of the fiber while pectins of 0.7-1.2% are present as a poly-Dgalacturonic acid in the form of insoluble salts of Ca, Mg, and Fein the primary cell wall underlying the waxy cuticle [1,2]. Abstract


Introduction
The noncellulosic constituents of cotton fiber are known to be waxes, pectins, hemicellulose, proteins, and mineral matters ranging from 4 to 12% of the dry fiber weight and to be located mostly in the cuticle, in the primary cell wall, and in the lumen.
Natural cotton wax of 0.4 to 1.0% serves as a protective barrier to water penetration comprising the cuticle on the outer surface of the fiber while pectins of 0.7-1.2% are present as a poly-Dgalacturonic acid in the form of insoluble salts of Ca, Mg, and Fein the primary cell wall underlying the waxy cuticle [1,2].
reproducible high quality results in dyeing of cotton fabrics, pretreatment process is required to reduce impurities sufficiently to improve cotton fabric wettability ( Figure 1). Besides natural impurities such as wax and pectins of which removal is essential [3], removal of secondary added impurities are also important. In the case of cotton knitted fabrics, the added chemicals are those lubricants, for example, paraffin waxes used in spinning the yarn and on the knitting machine that comprise about 0.5 -2 % of fabric weight [4,5] and are removed in scouring process together with natural cotton wax. For cotton woven fabrics, a separate enzymatic desizing process has been carried out traditionally to remove starch-based sizes added on warp yarns about 15% of the yarn weight in weaving [6] while synthetic sizes applied to man-made fibers are generally water soluble and can be removed in scouring process [2]. The conventional alkaline pretreatment process has been replaced with environment friendly approach using different enzymes. For examples, amylases for removing starch-based sizing and cellulases for denim-washing and biopolishing were introduced in the1960s and in the1980s, respectively while pectinase for cotton scouring was launched in the 2000s [3,[6][7][8][9][10]. Because pectin acts as glue in the primary cell wall of cotton fibers, the different components present in the primary cell wall layer can be removed easily in a subsequent washing procedure after enzymatic destabilization of the pectin structure [8]. According to (Figure 2(a)), neutralization can be omitted in bioscouring and effluent from alkaline scouring is darker than from bioscouring. In addition to lower loss in weight (Figure 2(b)) and lower pH of scoured fabrics (Figure 2(c)), other beneficial properties from bioscouring using pectinase have been reported to be softer handle, reduction of chemical load to environment and energy consumption as well as lower pilling tendency due to lower damage to fiber (Figure 2(d)) when compared to alkaline scoured fabrics [3,[10][11][12][13]. Combined bioscouring and biopolishing as well as combined desizing and bioscouring in one step have been also proposed [10].
Cold-pad-batch equipment for pretreatment and dyeing consists of a pad mangle, a means of winding fabric onto a roll and washing chambers with advantages of much reduced water consumption, relatively low cost of equipment, higher productivity over a single batch wise equipment such as a jet dyeing machine [14,15]. However, textile dyeing companies that are equipped with cold-pad-batch machines and run their conventional cold-pad-batch alkaline pretreatment are faced with the difficulty to introduce the new technology in spite of knowing that batch wise enzymatic scouring is successfully implemented. The aim of this case study is to try enzymatic coldpad-batch bio-pretreatment using the equipment of industrial sites and compared its performance with the company's conventional cold-pad-batch alkaline chemical pretreatment.

Materials
Two kinds of cotton woven fabrics were used and characteristics of each fabric were presented in Table 1. Chemicals such as NaOH (50%), sodium carbonate and hydrogen peroxide (35%) were all industrial grade. Company-specific wetting agent

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(DGA-W15, Actiron AT-2), scouring agent, oxidative desizing agent, and H2O2 stabilizer were used in the company's chemical pretreatment. Enzymes were Aquazyme 240L and Scourzyme L from Novozymes.  The first CPB bio-pretreatment was tried with 100% cotton woven fabric of 200 yards in one company where the company's CPB alkaline pretreatment was carried out according to ( Figure  3(a)). The second CPB bio-pretreatment was run with cottonblend woven fabric of 1000 yards in another company according to the process schematized in (Figure 3(b)). For comparisons, each company's conventional pretreatment was carried out with the same cotton fabric as used in bio-pretreatment. (Figure 3(c)) shows the overall view of the cold-pad-batch process done in two companies.

Industrial trials of Cold-Pad-Batch pretreatment
The CPB bio-pretreatment was carried by padding, batching and washing with hot water in a four-box washer. The details for CPB bio-pretreatment were as followings: The first box contained emulsifying agent to wash out enzymatically degraded pectins and other impurities that came out together. Sodium carbonate (Na 2 CO 3 ) was used for pH adjustment of enzyme padding solution. Because the temperature of padding and batching was about room temperature, amylase of low-temperature type was chosen because it was proved to be more effective than amylase of high-temperature type and importance of removal of sizing agent for enzymatic scouring performance was reported [16].

Measurements
Treated fabrics were conditioned and subjected to water drop test. A round fabric sample with a diameter of 10cm was cut and mounted on the test plate of Gravimetric Absorbency Testing System (GATS, M/K Systems, Inc. USA) where absorbed weight per gram of fabric sample was recorded every 0.4sec for 10sec. Additional water absorbency test was carried with all fabric samples according to the AATCC water drop test (test method TS-018) and time for absorbing a water drop was measured. Colored aqueous solution of 1% direct blue dye was additionally used for drop test on cotton-blend fabric. Color measurements of treated fabrics were taken with Macbeth Color Eye 3000 using D65 daylight as the illuminant. Whiteness, L-value and b-value were measured.

Results & Discussion
Performance of pretreatment is evaluated mainly by water absorbance of treated fabrics. When absorbance data were compared in (Figure 4(a)), 100% cotton woven fabrics obtained by two different CPB pretreatments resulted in the almost same absorbance between the simultaneous enzymatic desizing and scouring and the enzymatic desizing followed by alkaline scouring. Both new CPB bio-pretreatment and the company's conventional alkaline pretreatment were tried with cotton fabric in industrial scale of 200 yards. With the company's CPB equipment according to Industrial Trial No.1 presented in (Figure  4(b)) where both pretreatments contained CPB bleaching at the end. When the simultaneous enzymatic desizing and scouring by CPB was tried in the other company with cotton-blend fabrics, absorbance data by GATS revealed that cotton-blend fabric after CPB bio-pretreatment absorbed less water than after the second company's conventional pretreatment in which the simultaneous alkaline desizing, scouring and bleaching by CPB was carried out (Figure 4(b). However, the drop test on cotton blend fabric obtained by CPB bio-pretreatment was less than 3 seconds that is regarded to satisfy the absorbency standard for drop test that AATCC (American Association of Textile Chemists and Colorists) recommends to be in the range of 1 to 5sec. All other fabrics were wetted in less than 2 seconds by drop tests.
The cotton-blend fabric used in industrial trial No.2 consisted of the warp yarn of 100% cotton and the weft yarn of 60% nylon and 40% polyurethane. Therefore, CPB bio-pretreatment seemed to remove less impurities on the weft yarn than the company's CPB chemical pretreatment while CPB bio-pretreatment worked very well on 100% cotton warp yarn as evidenced by drop test results ( Figure 5(a)). In this industrial trial No.2 where the treated cotton blend fabric was 1000 yards in length, absorbance data measured in the spot of 100, 450, 680, 900 and 1000 yards proved the homogeneous treatment by CPB bio-pretreatment across the long length ( Figure 5(b)).   Table 2 shows the results of color measurements of cotton fabrics treated by enzymatic CPB pretreatment and each company's conventional chemical CPB pretreatment in industrial scale. Whiteness, lightness and b-values were focused among color measurement parameters. Bigger values in whiteness and L represent lighter and whiter while bigger b values mean yellowness of fabric. When values of final fabrics biopretreated were compared to those pretreated conventionally, subsequent dyeing of bio-pretreated fabrics is expected to give as reproducible results as those pretreated conventionally regardless of paleto deep shade dyeing both in industrial trial No. 1 and No. 2.

Conclusion
Industrial trials on bio-pretreatment of 100% cotton and cotton-blend woven fabrics by cold-pad-batch methods using the combination of amylase of low temperature type for desizing and alkaline pectinase for scouring gave the satisfactory results in water absorption and whiteness of pretreated cotton fabrics as well as the homogeneity of water absorption across the 1000 yards of fabric length. These results allow textile dyeing companies to use their existing CPB facilities for the introduction of new enzymatic pretreatment process substituting for a conventional strong alkaline process while maintaining their production capacity.