Application of Chitosan in textile Wet Processing

Chitin and chitosan have higher affinity for dyes and metals and certain surfactants, which
contribute to water pollution. Using the shellfish waste thus has two-fold
advantage: -

a) First to find a viable method to purify dye wastewaters.

b)To use natural resources, which could otherwise had been wasted.

After use for color removal the spent sorbent further finds use as a fibrous raw material for papermaking.

The use of chitosan as a combined thickener and binder in pigment printing has been studied in comparison with the commercial printing system. Printing pastes made from chitosan, acetic acid and pigments at appropriate viscosity give stable pastes and satisfactory results on polyester and polyester –cotton blends.

Chitosan can also be used in the dyebath, because due to the unimolecular structure it has an extremely high affinity for many classes of dyes, including disperse, direct, reactive, acid, vat, sulphur etc. Rate of diffusion of dyes in cellulose is similar to that in cellulose. Sorption of chitosan is exothermic: hence an increase in temperature leads to an increase in dye sorption. At lower pH chitosan free amines are protonated causing to attract anionic dyes.

Chitosan is used as a shrink-proofing agent and also is used to increase the dye uptake of wool. In its protonated form, it exhibits the behavior of a cationic polyelectrolyte, forming viscous solutions and interacting with the oppositely charged molecules. Thus it is suitable for processing of wool near its isoelectric point, offering minimum fiber damage and providing good quality. However the main limitation is the uneven distribution on the fabric surface.A new ecological method for shrink proofing of the wollen fabric is based on the enzymatic pretreatment and chitosan deposition on the wollen fabric. This
method shows the enzymatic pretreatment has an essential influence on the shrink proofing qualities and chitosan stabilizes the shrink proofing property. It also increases the kinetics of dyeing and causes a decrease in hydrophobicity.

Antimicrobial finishing is very important because cotton fabrics have poor resistance to microorganisms and thus the possibility of harming the human body. Due to the Antimicrobial action of the amino group at the C-2 position of the
glucosamine residue, chitosan is also known to be an antimicrobial polysaccharide. The ability of chitosan to immobilize microorganisms derives from its polycationic character. Its protonised amino groups block the protein sequences of microorganisms, thus inhibiting further proliferation. Chitosan binds to the negatively charged bacterial surface disrupting the cell membrane and altering its permeability. This allows materials to leak out of the bacterial cells resulting in cell death. Chitosan can also bind to DNA inside the cell inhibiting mRNA and hence protein synthesis. Recent studies have revealed that chitosan is more effective in inhibiting the growth of bacteria than chitosan oligomers. Also the antibacterial effect of chitosan oligomers are reported to be dependent on its molecular weight.
1,2,3,4-Butanetetracarboxylic acid (BTCA) and citric acid are representative of polycarboxylic acids that crosslink with cotton through an esterification reaction. BTCA is the most effective of these plycarboxylic acids, but its cost is very high; citric acid is a less effective crosslinking agent but is not as costly. However, cotton fabrics treated with citric acid alone exhibit appreciable yellowing, although there have been some investigations undertaken to reduce this yellowing.
Generally, cellulose is treated with chitoan by dissolving the chitosan in dilute acetic acid solution, but this method does not create any firm chemical bonds between chitosan and cellulose and thus is not durable to repeated laundering. The esterification reaction not only occurs between citric acid and cellulose but also between citric acid and the hydroxy groups of
chitosan, and free carboxylate groups can also react with the amino groups of chitosan resulting in a salt linkage. It is widely known that the Antimicrobial properties of cotton treated with chitosan is attributed to amino groups of chitosan, which convert to ammonium salts in dilute acid solution; the salt then binds to the negatively charged surface of the microorganism..

As a durable press and an Antimicrobial finishing agent for cotton fabric, citric acid and chitosan show satisfactory results. The WRA and DP rating of treated cotton fabrics increase, and there are slight improvements in tensile and tear strength using chitosan as abn extender of the crosslinking chain. A high Antimicrobial property level is obtained by treatment with CA as
well as chitosan, and despite repeated launderings, the Antimicrobial property remains at over 80%.
Chitosan is expected to be one of the safest and most effective Antimicrobial agents for hospital applications where many antibiotic substances are used. Chitosan is especially important in depressing the growth of methicilin resistant taphylococcus aureus, which is resistant to most antibiotic substances. Hygienic yarns can also be made through the addition of chitosan fibres. Chitosan fibers are blended with cotton fibers and a yarn is spun out of this blend; 10% chitosan component is sufficient to achieve a hygienic effect. This effect should endure 20 washes.(1)currently, there is also a hightened interest in protecting health care workers from diseases that might be carried by patients. Especially for surgical gowns, there is an increasing need to protect medical staff from infection by bloodborne pathogens such as HIV and HBV> gowns should be able to prevent “ strike through” or “wetting out” of the fabric, and so surgical gown materials should have not only
Antimicrobial properties but also blood barrier properties. Chitosan and fluoropolymers seem to be the most suitable finishing agents for providing surgical gown materials with barriers against microorganisms and blood. Because many medical products including surgical gowns are used in close proximity to human skin, the hand and air permeability of these materials are also very important. Recently, single-use gowns made from non-woven have gained in popularity because non-woven fabrics block fluids so well and single-use gowns are so reliable.

One of the most important characteristics of chitosan is its Antimicrobial activity at specific molecular weights. Protonated amine groups in chitosan inhibit the growth of microorganisms by holding negatively charged microorganism ions. Many studies have examined chitosan as an Antimicrobial finish for textile materials, either for production of low molecular weight
chitosan followed by its application on textile fibers or for co-spinning or co-casting of low molecular weight chitosan with cellulose molecules to make Antimicrobial fibers and films. However, these methods had to produce chitosan with specific molecular weights, which could considerably increase production costs. In addition, insolubility of chitosan in neutral or alkaline conditions further limited its application.

A quarternery ammonium derivative of chitosan, N-2-hydroxy propyl-3-trimethylammonium chitosan chloride (HTCC), is synthesized as an Antimicrobial finish for cotton using a reaction of glycidyltrimethylammonium chloride (GTMAC) and chitosan. The use of crosslinking agents or binders increase laundering durability of cotton treated with HTCC. A 5% nonionic binder applied along with 0.1% or higher concentration of HTCC on cotton is quite effective in increasing the laundering durability of the HTCC-treated cotton.

There are some reports about the utility of chitosan polymer to impart Antimicrobial activity in textile finishing. For example, chitosan salt produced by an organic acid was bound to the surface of textiles by a tremendous amount of resin, which formed cross-links. When fully deacetylated chitosan is depolymerised into chito-oligosaccharide with sodium nitrite, its DP can be
controlled by adjusting the amount of sodium nitrite added to the acetic acid solution containing the fully deacetylated chitosan.Chitosan when applied along with DMDHEU results in a substantial improvement in soil removal when oily soil is applied to cotton fabrics. The highest levels of soil removal are exhibited by fabric samples treated with DMDHEU with chitosan of average molecular weight below 21,000. the improvement in soil removal attributes to the prevention of deep soiling due to blocking of pore structure abd the increase in hydrophilicity by chitosan treatment.Chitosan treated samples of cotton with resin treatment show higher moisture regain values, this is because amine and hydroxyl groups provide reactive sites for
water.Various methods such as physical, chemical, and biological treatments are used for deodorizing. In the field of cosmetics, antibacterial agents, antiperspirants, and fragrances are used to effectively reduce or mask malodors. The antibacterial agents
control the bacteria that decompose human fats found in sweat to produce low molecular weight fatty acids. Using the same technology, the textile industry applies antibacterial agents for odor control. However, because antibacterial agents can attack human skin as well, there are only a limited number of such chemicals allowed for use in textile treatment.Over the past
few years, a considerable number of studies have been done on the performance of chemical deodorizers that swiftly couple with targeted odor substances. Their neutralizing ability makes such of low molecular weight substances less volatile. For example, these chemical deodorizers can target sweat, which generally shifts from human skin to fabric and then is concentrated to generate unfavorable odors after bacterial decomposition.

However, existing chemical deodorizes are highly surface active and can cause unpleasant results such as discoloration, aggregation, and skin irritation. Notably, most of the highly active substances are hydrophilic, and their activities become
weak under hydrophobic conditions. Chitosan was selected because while its primary amino group possibly deodorizes, its high molecular weight offers safety. The polymerization reactions of methacrylic acid with chitosan were done in water, and the emulsions were free of monomeric acid. The polymer particles showed high deodorizing performance, even in hydrophobic and hydrophilic circumstances, and fabric treated with the emulsion was also found useful for deodorizing.

In the manufacturing and coloration of cotton fabrics, the textile industry experiences dyeing problems with some lots of cotton. The cotton does not absorb dye uniformly and creates tiny white or light-colored spots. This results from small
clusters of immature cotton called neps. Immature cotton results from a variety of reasons e.g. plant disease, insect attack, premature harvesting after using harvest-aid chemicals, or adverse weather conditions.

Previous research has shown that pretreatment of cotton fabrics with chitosan significantly improves the dye coverage of neps. After dyeing with reactive dye using standard procedure dyed fabrics are treated with chitosan by exhaust or pad-batch method. The chitosan treatment alone did not cover the neps in the dyed fabrics. However, after redyeing with 0.1-0.2 dye, the neps were more or less completely covered. The coverage ratings increased from 1-2 to 4-5. The chitosan aftertreatment and redyeing with a small amount of dye caused very little change in total color difference value. There is a significant increase
in k/s value of dyed fabric. Nep coverage improved the quality of the dyed fabrics.

Among synthetic fibers, polyester (PET) exhibits excellent properties such as elastic recovery, dimensional stability. However, it does not absorbwater or moisture well. As a result, friction can cause static electricity to occur. Electric resistivity of natural fibers is 10⁹ to 10¹⁰ Ω.cm; polyester fiber is less than 10¹⁵ Ω.cm; water is 10³ Ω.cm. This static electricity causes electric shock, fiber contamination during textile finishing.Many endeavors to endow an antistatic property to polyester include research to change the characteristics of fiber surface. Chitosan shows high moisture regain even in low relative humidity and does not swell much in water; thus it can resist the decrease the durability that water causes. A permanent antistatic finish can be achieved by crosslinking hydrophilic materials that form an insoluble conductive sheath on the surface of the fiber. So chitosan seemingly has the potential to improve the water-absorbency and antistatic properties of polyester fiber.

Polyester fibers can be grafted with AA or NVF by preirradiation with γ rays. By acid hydrolysis, amide groups on the fiber surface can be converted into amino groups. Chitosan can then be grafted to modified polyester surfaces by either esterification or imine formation. The highest surface density of amino groups can be achieved by imine formation between chitosan and glutaraldehyde- treated PET-g-NH₂.

Chitosan grafted polyesters show antibacterial activity for MRSA, S. aureus-2, and E. coli. The antibacterial activity increases with the surface density of amino groups. Furthermore, the antibacterial activity for E. coli is higher than that for the other bacteria, whereas the antibacterial activity for MRSA is the lowest.