Abstract
The effect of chitosan on printing performance of cotton/wool blend fabric was explored in this study. A cots-wool blend was printed with direct, acid and reactive dyes after treating the fabric with varying concentrations of chitosan. Improvement in colour depth was found without adverse effect on colour fastness.
Key words: chitosan, print quality, cots wool fabric, k/s value
Introduction
Blended textile of wool and cotton has many pleasing features, like warmth, good moisture absorption, strength and soft handle. In combination with cotton, wool provides outstanding wrinkle resistance and crease retention, so that the shape retention is improved according to the proportion used. In addition, the wool contributes good draping quality and elasticity, and reduces the hazard of melted holes due to burning tobacco. The presence of cotton reduces cost and improves strength.
The aesthetic demand of consumers is satisfied by application of colouring agents on textiles by dyeing and printing. Lots of work has been reported on dyeing of cotton/ wool blend, especially to solve problems in blend dyeing. Single-stage and two-stage dyeing processes have been developed. However, very little work has been done in the area of printing of cotton/wool blend.
Wool is very hygroscopic and can absorb 20% of its weight of moisture. This is because of the presence of polar groups and large amorphous regions in its polymer system. Due to the wide variety of functional groups present in its molecular structure, it can be dyed with direct, acid, basic and reactive dyes.
Cotton has good affinity for dye penetration due to the presence of polar groups (hydroxyl groups). It can be dyed with direct and reactive dye. The difference in the physical, chemical and molecular structure of cotton/ wool makes printing of cotton/ wool blend difficult in order to obtain a uniform shade.
Various chemicals and auxiliaries are used to bring about a modification in the physical structure or to help in swelling of fibres or dissolution of dyes; or to increase affinity for dyes.
Chitosan is a cationic natural biopolymer. It is obtained by alkaline N-deacetylation of chitin6, the most abundant natural polymer after cellulose. It comprises copolymers of glucosamine and N-acetyl glucosamine4.It ideally consists of 2-amino-2-deoxy-(1-4)-_-D-glucopyranose residues (D-glucosamine units) and may include a small number of N-acetyl-D-glucosamine units.
Most of the natural occurring polysaccharides, eg. cellulose, dextrin, pectin, alginic acid, agar, agarose and carrageens, are natural and acidic in nature, whereas chitin and chitosan are examples of highly basic polysaccharides. Whereas chitin has few solvents, chitosan is readily soluble in dilute acids and hence it has been extensively examined for potential commercial applications. It is linear polyamine, and contains reactive amino groups and reactive hydroxyl groups. It can chelate many transitional metal ions.
Chitosan is a remarkable biomaterial because of its numerous biological and immunological activities. In particular, its non-toxic and biodegradable properties4,9 have attracted considerable attention for biomedical, textile and chemical industrial applications.
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| Chemical structure of chitosan |
The antimicrobial activity of chitosan against different groups of microorganisms, such as bacteria and fungi, has received considerable attention in recent years. The ability of chitosan to immobilise microorganisms derives from its polycationic character. Its protonated amino groups block the protein sequences of microorganisms, thus inhibiting further proliferation.
In addition, chitosan may be used in textile dyeing and finishing as a substitute for various other chemicals traditionally used in textile processing8. Chitosan can be used in combination with a thickener and binder as well as used in the dye bath. As in printing, printing paste made from chitosan, acetic acid and pigments at appropriate viscosity give stable paste and can also be used in the dye bath. Owing to its unimolecular structure it has an extremely high affinity for many classes, including disperse, acid, direct, reactive, vat, sulphur, etc. Textile fibres having poor affinity for dyes can be blended or surface coated with chitosan, which makes them more receptive to dyeing with many dyes1.
Perusal of literature showed that the effect of chitosan on resist printing of cotton with reactive dyes has been studied10. A study on digital inkjet printing of chitosan-treated cotton fabric has also been conducted2. In addition, studies on the role of chitosan in wool finishing, and on the dyeing and antimicrobial characteristics of wool fabrics, have already been carried out3,7. A study on the application of chitosan in pigment printing was conducted, in which use of chitosan as a combined thickener and binder in pigment printing was examined in comparison with a commercial printing system (Alco print). Printing pastes made up from mixtures of chitosan, pigment and acetic acid at the appropriate viscosity gave satisfactory prints on polyester and 67:33 polyester/cotton woven fabrics1.
The study reported herein deals with the use of chitosan for modification in printability of cots-wool fabric.
Methodology
Material
a. Fabric
Commercially available cotton/wool blend of 50:50 ratios was used.
b. Chemicals
Dyes – Three types of dyes belonging to different class were used:
- Direct Dye (Direct Yellow 44)
- Reactive Dye (Reactive Yellow 39)
- Acid dye (Acid Yellow 114)
Others Chemicals – Acetic acid, Tartaric acid, Glycerol, Urea, Sodium bi carbonate
Method
Preparation of Chitosan Solution
A stock solution of chitosan of medium viscosity was prepared by dissolving 0.25g chitosan in 50ml of distilled water. 5ml of citric acid of 20% concentration was used to assist in dissolution. It was left for 24 hours. Fabric was treated with 0.5%, 1.0%, 1.5 % concentration of chitosan before printing.
Preparation of Printing Paste
Printing paste for each individual dye was prepared according to following recipes:
Aftertreatment of Printed Fabric
Fabric was printed with each dye. Printed fabric was dried at room temperature and steamed at 100⁰C for 30 minutes to fix the prints. After that fabric was washed.
Analysis of Print Quality
Quality of print was analysed on the basis of depth of shade, evenness and sharpness of outline of print, and texture. K/S value was calculated to determine depth of shade on A C S spectrophotometer. Evenness, sharpness of print and texture were assessed by a panel of 10 judges from the field of clothing and textiles, on a five-point rating scale. The weighted mean score was calculated for each criterion.
Determination of Colourfastness of Printed Samples
Printed samples were subjected to testing as per standard procedures for their ability to withstand light (light fastness), washing (wash fastness), ironing (ironing fastness) and rubbing (rubbing fastness).
Results and Discussion
Print Quality and Texture of Cots-Wool Fabric
The present study was conducted to find out the effect on printability of pretreatment of the cots-wool fabric with different concentrations of chitosan. Table 1 shows the results, ie. the effect of chitosan on print quality in terms of depth of shade, evenness of print, and sharpness of outline, as well as the texture of cots-wool fabric.
Light shades were obtained when cotton/ wool fabric (control samples) was printed with different dyes. Comparative analysis shows that depth of shade was higher in fabric printed with acid dye, followed by direct and reactive dyes. It was found that depth of shade increased when fabric was pretreated with chitosan. It kept on increasing with an increase in the amount of chitosan from 0.5% to 1.5%. However, little further increase in depth of shade was found on increasing the concentration. Some difference in depth of shade of different dyes was found. The deepest colour was obtained in fabric printed with acid dye after treating with 1.5% concentration of chitosan.
Chitosan is cationic biopolymer. It contains amino groups (-NH2-). These amino groups acted as dye sites for anionic direct, acid and reactive dye, thus enhancing dye uptake. At lower pH chitosan free amines are protonated, attracting anionic dyes. This may be the reason for the increase in acid dye uptake of printed fabric. Another reason may be that sorption of chitosan is exothermic: hence an increase in temperature leads to increase in dye sorption.
Analysis of evenness of print revealed that evenness of prints improved after treating fabric with chitosan. Very level print was obtained with direct dye in comparison to reactive and acid dyes. In general, best results were obtained when cots-wool fabric was treated with 1.5% concentration of chitosan.
Improvement in sharpness of prints was also found. Again, sharpness of print was found to be highest after treatment with 1.5% concentration of chitosan with direct dye, with the exception of acid dye, where 0.5% chitosan gave the sharpest outline of prints.
Textural analysis revealed loss in texture of cotton/ wool fabric after printing. Fabric became stiff.
It can be said that prints of good colour yield, and superior sharpness and evenness, were obtained when fabric was pre-treated with 1.5% concentration of chitosan and then printed with the printing paste of direct dye, but the texture deteriorated.
Colourfastness of Printed Fabric
It is clear from Table 2 that fastness to washing of fabric printed with direct, acid and reactive dyes, improved when fabric was treated with 1.5% concentration before printing. Similarly wet and dry rubbing fastness of printed fabrics also improved. Improvement in light fastness was also observed. Thus treatment of fabric with chitosan did not adversely affect colourfastness of printed fabrics.
Conclusion
Thus it can be said that the printability of cotton/wool blend was enhanced when chitosan was used to treat the fabric before printing. But some loss in texture quality of printed fabric occurred.
References
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2. Choi R. S. P, Yuen M.W. C., Ku A. K. S. and Kan W. C. (2005) Digital inkjet printing for chitosan treated cotton fabric, Journal of Fiber and Polymers, vol. 6, No. 3
3. Giridev et al Dyeing and antimicrobial characteristics of chitosan treated wool fabrics with henna dye
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