Researchers have attempted to develop and promote colored cotton in the previous 15-20 years [01Pri]. Small-scale production of colored cellulose fibers in light tan, cinnamon, green, pink, black, and red has been done and attempts have been made

Table 62.1 Comparison of selected fiber properties of naturally colored cotton with standard upland cotton [01Pri] Light cinnamon Dark cinnamon Champagne Green Upland cotton Strength (g/tex) 26.5 20.6 28.5 23.4 28.5 Elongation (%) 5.2 5.7 4.7 5.5 — Modulus 7.2 4.8 8.6 5.5 — Mean length (in.) 0.8 0.73 0.92 0.85 0.9 Uniformity (%) 81.0 77.6 82.1 78.5 80.9 Short fiber (%) 10.3 18.6 9.5 12.5 — Micronaire index 3.9 3.9 4.5 3.5 4.6

Table 62.2 Composition of white and three types of colored cottons [10Tei] Fiber White Brown Green Ruby Hemicellulose (#) 0.5 ± 0.4 9.9 ± 0.4 8.7 ± 0.9 11 ± 3.0 Cellulose (%) 97.7 ± 2.2 78.7 ± 0.4 80.3 ± 0.8 74 ± 2.0 Total lignin (%) 0.4 ± 0.1 9.9 ± 0.1 16.0 ± 2.0 13.8 ± 0.1

to process the colored cottons on textile machinery and develop textiles. In one study, colored cotton fibers (light and dark cinnamon, champagne, and green) were studied for their properties and the potential of converting the processed fibers into textiles was investigated on full-scale ring and rotor spinning machinery [01Pri]. Tables 62.1 and 62.2 provide selected properties of the naturally colored cottons used in the study. As seen in the tables, colored cotton contains consider­ably higher amounts of hemicelluloses and lignin and also waxes on the surface that imparts hydrophobicity to the fibers. The presence of wax and natural pigments provides the colored fibers resistance to growth against Aspergillus niger. However, the naturally colored cottons were found to severely degrade when buried in the soil along with substantial loss in fiber strength, but the rate of degradation was much lower than that of white cotton [10Che]. The fineness of the ring spun yarns produced was considerably low and the yarns showed considerable variations in properties as seen in Table 62.3. Similar results were also observed for the rotor spun yarns as seen from Table 62.4.

Morphologically, the white cottons and colored cottons had similar features as seen in Fig. 62.1. Microfibrils with lengths between 85 and 225 nm and diameters between 13 and 22 ^m are seen on all four fibers.

In another study, two naturally colored cottons (camel brown and olive green) were blended with conventional J-34 white cotton and spun into 8 s count ring spun yarns. Properties of the blended yarns were studied and the yarns were used as weft in various ratios and the fabrics obtained were scoured and bleached using various chemicals [02Par]. Tables 62.5 and 62.6 provide a comparison of the changes in K/S values for the cotton fabrics containing various extents of colored cotton fibers after scouring and exposure to light [02Par]. Substantial changes in the K/S values

Table 62.3 Properties of ring spun yarns produced from the four different colored cottons [01Pri] Light cinnamon Dark cinnamon Champagne Green Skein test Yarn number (tex) 19.5-37.3 20.7-37.5 19.8-36.8 20-37.4 CSP [kN m/kg] 2,176-2,600 1,968-2,225 2,225-2,600 2,678­ 3,046 Single yarn test Tenacity (kN m/kg) 13.1-15.5 11.3-13.4 13.9-15.7 15.7-17.8 Elongation (%) 4.9-6.0 5.2-6.5 4.4-5.8 5.7-6.8 Work to break (kN m/kg) 0.298-0.444 0.292-0.437 0.287-0.422 0.433­ 0.605 Uster evenness test Nonuniformity (CV %) 15.5-19.6 16-20.4 16.1-21.1 14.2-18.1 Thin places/1,000 m 23-158 50-318 30-235 0-115 Thick places/ 1,000 m 290-1,163 315-1,270 343-1,523 143-675 Neps/1,000 m 13-50 3-55 20-215 10-28

Table 62.4 Properties of rotor spun yarns produced from the four different colored cottons [01Pri] Light cinnamon Dark cinnamon Champagne Green Skein test Yarn number (tex) 19.5-37 19.7-36.6 20.1-36.6 19.9­ 36.5 CSP (kN m/kg) 1,947-2,274 1,689-1,959 2,006-2,266 2,123­ 2,477 Single yarn test Tenacity (kN m/ kg) 12.2-13.3 10.8-11.8 12.6-13.4 13.4­ 14.3 Elongation (%) 4.6-5.0 4.6-5.1 4.6-4.8 5.3-5.8 Work to break (kN m/kg) 0.276-0.356 0.257-0.336 0.278-0.329 0.364­ 0.447 Uster evenness test Nonuniformity (CV %) 11.2-12.8 11.5-12.8 11.2-12.8 11.5­ 12.8 Thin places/ 1,000 m 0-3 0-10 0-8 0-8 Thick places/ 1,000 m 3-23 13-15 3-30 3-13 Neps/1,000 m 0-25 5-25 5-20 5-13

are observed especially for blends containing higher amounts of colored cottons. Light fastness rating also showed that the blends containing higher amounts of colored cotton had lower color fastness, but the fastness improves after treatment with the various chemicals as seen in Table 62.7 [02Par].

Structural behavior and influence of different chemicals on the properties of two types (brown and green) of cotton were studied by Ishtiaque et al. [00Ish]. Increase in the hardness of water increased color intensity with K/S values increasing from 0 to 50 for the green cotton and from 50 to 80 for the brown cotton when the water

Fig. 62.1 Digital pictures of colored cottons (inset) and SEM image show similar morphologies between white and colored cottons [10Tei]. Reproduced with permission from Springer

Table 62.5 Changes in the K/S value of fabrics containing various amounts of green and brown cotton K/S value 100 % white K/S value Green cotton blend Brown cotton blend Type of cotton cotton 55.7 39.1 27.8 16.7 55.7 39.1 27.8 16.7 Un treated 0.26 2.04 1.19 1.01 0.78 3.60 1.96 1.45 1.01 Scoured 0.20 1.40 1.11 0.69 0.58 1.64 1.38 1.16 0.86 Total color difference 1.11 6.93 3.43 5.73 4.84 2.63 1.67 0.61 4.39

Table 62.6 Change in light-fastness values show that fabric blends containing higher amounts of colored cottons have faded to a larger extent than those containing lower amounts of colored cottons Type of cotton 100 % white cotton Green cotton blend Brown cotton blend 55.7 39.1 27.8 16.7 55.7 39.1 27.8 16.7 Un treated 0.26 2.04 1.19 1.01 0.78 3.60 1.96 1.45 1.01 Scoured 0.20 1.40 1.11 0.69 0.58 1.64 1.38 1.16 0.86 Total color difference 1.11 6.93 3.43 5.73 4.84 2.63 1.67 0.61 4.39

Table 62.7 Rating of light fastness of 100 % white cotton and blends containing various amounts of naturally colored cotton Type of cotton 100 % white cotton Green cotton blend Brown cotton blend 55.7 39.1 27.8 16.7 55.7 39.1 27.8 16.7 Un treated 3/4 3/4 2/3 2/3 2/3 3/4 2/3 2/3 2/3 Tannic acid treated 3/4 3/4 3 3 4/5 4/5 3/4 3/4 3/4 Aluminum potassium sulfate 3/4 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 Copper sulfate 3/4 4/5 4/5 5 5 4/5 5 5 5 Ferrous sulfate 3/4 4/5 4/5 5/6 5 4/5 5/6 5/6 5

hardness was increased from 0 to 400 ppm. The increase in shade depth with increasing water hardness was considered to be due to the interaction of the cotton with metallic salts like calcium and magnesium present in the water. Similar effect was also seen when the pH of water (90 °C) was increased from 7 to 11. However, the effect of increase in shade depth was more pronounced for the brown cotton compared to the green cotton. Bleaching of the fibers with hydrogen peroxide resulted in near complete removal of color for both the cottons. To obtain cotton with other colors, the green and brown cotton fibers were treated with various mordants and the changes in K/S values were observed. Table 62.8 provides the K/S values for the brown and green cottons after treating with various mordants. It was

Table 62.8 Changes in the K/S values after treating with various mordants [00Ish] Cupric sulfate [%] 0.0 0.5 1.0 1.5 2.0 3.0 K/S value Brown 47.44 19.57 21.86 22.40 21.93 21.06 Green 0.86 60.15 61.83 64.37 73.21 82.21 Tannic acid [%] 0.0 0.5 1.0 1.5 2.0 3.0 K/S value Brown 47.44 19.35 14.58 20.16 19.86 19.69 Green 0.86 75.91 62.95 61.20 54.89 66.80 Iron sulfate [%] 0.0 0.5 1.0 1.5 2.0 3.0 K/S value Brown 47.44 71.9 71.89 75.48 109.58 94.98 Green 0.86 52.20 54.16 70.32 68.44 — Aluminum potassium sulfate [%] 0.0 0.5 1.0 1.5 2.0 3.0 Brown 47.44 65.43 67.62 69.40 — 67.26 Green 0.86 54.24 54.24 59.24 59.20 56.14

also found that the colored cottons had higher flame resistance and better thermal degradation [00Ish]. Other researchers have also reported that colored cottons have better thermal resistance than white cottons. Degradation of colored cottons was observed at about 390 °C compared to 370 °C for the white cottons [01Par] which was attributed to the higher amounts of metals. Similarly, the colored cottons had higher flame resistance as seen from the higher limiting oxygen index (LOI) values in Table 62.9.

In addition to the limited colors available, the low moisture absorption of colored cottons is a major limitation. Colored cottons have moisture regain of about 3.9 % compared to 8.6 % for regular white cotton. The presence of fat and pectin on the surface was considered to be the major reason for the low moisture absorption of colored cottons. Gu has reported that colored cottons have a fat, lignin, and pectin content of 4.3, 9.3, and 0.5 %, respectively, compared to 0.6, 0, and 1.2 % for regular cotton [05Gu]. To increase the moisture absorption of colored cotton, the fibers were treated with hot water and various concentrations of sodium hydroxide. Table 62.10 shows that the moisture regain of the fibers increases substantially after treating with sodium hydroxide but without affecting the tensile properties. In a similar study, the effect of scouring and enzyme treatment on the moisture regain of buffalo brown and coyote brown cottons was investigated [09Kan]. A general trend of higher moisture regain was observed after the treatment [09Kan]. Figure 62.2a, b shows the extent of increase in moisture regain after various treatments. As seen in the charts, lipase provided the lowest increase in moisture regain. Figure 62.2c summarizes the changes in moisture regain after the various treatments [09Kan]. Other studies have shown that the color of the fibers becomes darker and deeper after scouring [08Kan]. It was also observed that the fiber pigment moved toward the outer portion of the fiber from the center during alkali treatment. Some pigments were also released from the fibers into the scouring bath. SEM images showed that the fibers became round and circular and, longitudinally, the fibers become flat as opposed to their natural twisted conformation [09Kan].

Table 62.9 Comparison of the flammability of white and colored cottons before and after treating with ferrous sulfate, aluminum sulfate, and copper sulfate [01 Par, 06Par] Cotton Fabric weight (g/nr) Thickness (mm) LOI (%) Untreated Fe treated A1 treated Cu treated Warp Weft Warp Weft Warp Weft Warp Weft White 270.65 0.87 18.9 19.0 19.2 20.1 19.9 20.2 20.1 22.9 Brown 268.21 0.83 22.4 22.6 23.1 26.5 22.8 25.9 23.2 26.0 Green 280.10 0.86 22.5 25.4 21.2 23.6 20.8 23.2 21.1 23.3

Table 62.10 Increase in the moisture regain (average ± CV %) of colored cotton fibers after treating under various concentrations of alkali [05Gu] 0 % Alkali 3 % Alkali 5 % Alkali Property 40 °С, 30 min 60 °С, 45 min 60 °С, 80 min 60 °С, 30 min 80 °С, 45 min 40 °С, 60 min 80 °С, 30 min 40 °С, 45 min 60 °С, 60 min Moisture regain (%) 8.15 ±15 8.4 ±11 7.5 ± 16 8.6 ± 13 8.5 ± 12 8.7 ±14 8.6 ±11 8.8 ±11 8.7 ±10 Tensile strength (cN) 1.8 ±17 1.6 ± 12 1.9 ±15 1.8 ± 14 1.7 ±13 1.6± 11 1.8 ±16 1.8 ± 14 2.0 ±14

WTMM

A

enzyme treated

Scoured

Scoured

Scoured

(СаСОЗ) and single

Ire dted

ТгмДталІ oonson

Fig. 62.2 Changes in the moisture regain of the colored cottons after various treatments

Recent studies have also reported that colored cottons contain up to 2.5 times higher wax content than white cottons [10Pan]. In the case of brown cotton, it was reported that the greater the color of the fibers, the higher was the wax content. Consequently, the colored fibers had lower cellulose content, particularly, the green cellulose fibers. Fibers containing higher levels of cellulose were found to have better fiber length, fiber strength, fineness, lint index, boll weight, and other fiber properties. An acidophic layer was reported on the secondary cellular wall of the green fibers but not seen on the other fibers [10Pan]. Further investigations by staining with osmium tetroxide have revealed the presence of a series of concentric rings in the secondary cell wall that formed a lamella pattern characteristic of a substance called suberin [99Ric]. Suberin was suggested to form a network of polymer molecules with the assistance of glycerol and therefore the colored fibers had higher hydrophobicity. Colored cottons were found to have cellulose I structure and similar unit cell dimensions compared to white cotton. However, crystallite dimensions for the colored cottons were different and varied with the treatment for

Table 62.11 Unit cell dimensions of white and colored cottons before and after extraction [99Ric] Sample a (nm) b (nm) c (nm) Y (°) V (nm3) P (g/cm) White cotton, ethanol extracted 0.79 0.83 1.04 96.8 0.682 1.570 Brown cotton, ethanol extracted 0.79 0.84 1.04 97.1 0.682 1.568 Green cotton, ethanol extracted 0.79 0.84 1.04 97.0 0.687 1.558 Green cotton, raw 0.79 0.83 1.04 96.9 0.677 1.581

Table 62.12 Crystallite dimensions of white and colored cottons with and without extraction [99Ric] Sample a (nm) b (nm) c (nm) Y (°) V (nm3) White cotton, ethanol extracted 6.29 5.91 6.50 93.0 312.0 Brown cotton, ethanol extracted 6.01 4.31 4.59 86.8 144.5 Green cotton, ethanol extracted 6.23 3.89 3.79 89.8 150.8 Green cotton, raw 5.59 3.12 3.25 63.2 74.8 lab|e 62.i3 battice Sample a (A) b (A) c (A) в parameters for the white Cellulose I 8.35 10.30 7.90 84.0 [00Che] White cotton 8.34 10.40 7.89 83.2 Green cotton 8.35 10.40 7.91 83.2 Brown cotton 8.32 10.40 7.88 83.5 Brown dyed 8.22 10.39 7.91 83.5

Sample	Winfit	Full prof
101	101	0020	Average	Average
White cotton	42	54	61	52	51
Green cotton	45	45	64	51	52
Brown cotton	42	45	63	50	52
Brown dyed	39	57	67	54	53

Table 62.14 Size of cellulose crystallites in white and colored cottons based on the FWHM and Full Prof methods [00Che]

cottons. As seen in Tables 62.11 and 62.12, the crystallites in green cotton become larger after extraction with ethanol. The degree of crystallinity also showed an increase. In another study on the microcrystalline size of naturally colored cottons, it was reported that the crystallite sizes based on 101 and 002 reflections of white and colored cotton were similar whereas the 10I crystallite was smaller [00Che]. The lattice parameters and crystallite sizes for the cottons studied are given in Tables 62.13 and 62.14 for comparison.

a, b, c are the dimensions of the unit cell in three dimensions. у is the interfacial angle, V is the volume of the unit cell, and p is the calculated density of the cellulose in the crystalline regions of the fiber.

Instead of using alkali, Demir et al. have used atmospheric plasma treatment to remove the wax on the surface and increase the hydrophylicity of the fibers [11Dem] and corresponding changes in the properties of the fibers were investigated. Unlike the alkali treatments where considerable changes in K/S values were observed, plasma treatment did not cause any change in the K/S values probably because the plasma could not penetrate inside the fiber and reach the pigment located in the middle and around the lumen of the fibers [11Dem]. It was suggested that plasma treatment would be an environmentally friendly approach to treat colored cottons and make them processable for textile applications.

An in-depth investigation was conducted to determine the possibility of devel­oping specialty textile products from colored cottons. Brown, green, and white cottons were characterized for their structure and properties and then made into needle punched fabrics [02Kim]. Table 62.15 provides a comparison of the properties of the cottons used in this study. The brown and white cotton were better thermal insulators than the green cotton and therefore the green cotton burned quicker than the other two colored cottons. The fibers could be processed on small-scale spinning equipment and made into yarns. Similarly, the fibers were also made into non-woven webs. It was suggested that blending the colored cottons with synthetic fibers such as lyocell was necessary to obtain products with good properties.

Naturally colored cottons were hydrolyzed using acid and the nanofibers obtained were studied as potential sources for developing various products. The naturally colored cottons were able to retain their color in a nanofiber suspension as shown in Fig. 62.3. It was suggested that the solutions from the colored cottons could be used to develop colored plastics without the need for additional dyes [10Tei].

62.3 Genetic Transformations of Colored Cotton

Studies have been done to genetically transform colored cotton and introduce the colored cotton into other plants. An Agrobacterium-mediated transformation of green-colored cotton was done to induce callus formation from hypocotyl explants on Murashige and Skoog medium containing 2,4-dichlorophenoxyacetic acid and kinetin. Among four different genotypes studied, embryogenic calli and plant regeneration was only observed in G9803 with 32 individual regenerants resistant to kanamycin being generated within 7 months. The transformation frequency was about 17.8 % and was confirmed using southern blot analysis and RT-PCR. Figure 62.4 shows the digital pictures of the generation of the transgenic plants [06Wei].

62.4 Limitations of Colored Cottons

In addition to the limited colors possible, there are several other restrictions of naturally colored cottons that have limited their commercial applications. Colored cottons have considerably lower yields than white cottons. In a study by Hua et al.,

Table 62.15 Properties of white and three-colored cotton used to develop non-woven fabrics determined using high volume instruments (HVI), advanced fiber information system (AFIS), and image analysis (IA) Mean length (in.) Fineness (mtex) Micronaire Maturity Fiber HVI AFIS AFIS FMT IA HVI FMT IA AFIS FMT IA White 0.94 0.98 164.7 183.6 166.8 4.1 4.08 3.78 0.46 0.47 0.36 Brown 14 0.83 0.91 166.6 179.2 149.9 4.2 4.20 3.52 0.47 0.49 0.40 Brown 15 0.60 0.75 163.7 152.1 170.9 3.0 3.17 2.76 0.43 0.42 0.27 Green 14 0.71 0.85 154.6 189.9 150.5 2.9 3.17 2.37 0.43 0.33 0.25

Fig. 62.3 Suspension of the various colored cottons and TEM images revealing the fibrillar nature of the colored cottons [10Tei]. Reproduced with permission from Springer

Fig. 62.4 Images of formation of embryo (a); mature somatic embryos (b); transformed plant (c); grafted transgenic plant (d); and picture of a transgenic colored cellulose plant growing in a greenhouse (e) [06Wei]. Reproduced with permission from Springer

Table 62.16 Yield properties of white and brown cotton [09Hua] Type of cotton Dry matter (g/m2) Boll number (bolls/m2) Boll mass (g/boll) Lint (%) White 365 60 4.8 39.7 Brown 323 51 3.9 35.8 Green 457 45 3.7 32.8

Table 62.17 Properties of white and colored cottons Type of cotton Length (mm) Uniformity (%) Strength (cN/tex) Elongation (%) Micronaire White 29.8 85.7 28.5 6.5 4.52 Brown 26.5 81.7 23.5 8. 3.02 Green 24.6 79.6 20.6 8.8 2.68

it was reported that brown cotton fiber and green cotton fiber had about 33.6 and

41.9 % lower yields than white cottons [09Hua]. About 17.4 and 11 % reduction in fiber lengths was also observed (Table 62.16). Vigorous vegetative growth was considered to be one of the major reason for the low yield and quality of the colored cottons. Table 62.17 provides a comparison of the properties of the white and colored cottons. As seen in the table, the colored cottons have lower boll numbers, boll mass, and considerably lower lint yield. Tensile properties of the fibers showed that the colored fibers had lower strength but higher elongation. Colored fibers also had substantially lower micronaire compared to the white cottons [09Hua].

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