**4. Cyclodextrins in textile waste water treatments**

The world production of dyes is estimated to be over 10 000 tonnes per year. Treatment of wastewater containing dyes is one of the most important ecological problems because the effluents containing the dyes are not only highly coloured, but also toxic to aquatic life. Textile effluents are highly variable in composition. They are generally characterized by high concentrations of colour, COD, BOD, TOC and dissolved solids. Wool and polyamide are dyed with the acid chrome dyes using the mordant dyeing technique causing the additional contamination of the effluents by high contents of chromium. Acid chrome dyes are the class of dyes that are at the same time most widely used in Eastern Europe and most difficult to eliminate. Due to the low biodegradability of dyes, conventional biological wastewater treatment is not very efficient.

reaction which was carried out using the pad-dry-cure process. Dyeability of cyclodextrin modified polypropylene fibres was enhanced when using three dyes belonging to different classes (disperse, acid and reactive dyes), using the exhaustion dyeing method. Formation of inclusion complexes between the dyes and -cyclodextrin bonded onto polypropilene fibres increase the exhausting rate of the dyes from the dyeing baths. The observed enhancement of dye uptake was due to the encapsulation of dyes in the cyclodextrin cavities on one hand and due to other interactions (ionic and hydrogen bonding) or even covalent bonding with the poly-citric acid/-cyclodextrin network in the case of reactive dye on the other hand. Various possible interactions between the reactive dye and fibres functionalized with -cyclodextrin are illustrated in Fig. 12. It was observed that the dyeing level depends on the modification rate of polypropylene fibres

**K/S values of PET/cotton blends**

ABC **Sample**

Fig. 11. K/S values of pre-treated PET/cotton blends dyed with Disperse Brown 1 (sample A), K/S values of samples dyed with the same dye (sample B) and K/S values of samples

A novel technique for preparation of -cyclodextrin-grafted chitosan was carried out by

The world production of dyes is estimated to be over 10 000 tonnes per year. Treatment of wastewater containing dyes is one of the most important ecological problems because the effluents containing the dyes are not only highly coloured, but also toxic to aquatic life. Textile effluents are highly variable in composition. They are generally characterized by high concentrations of colour, COD, BOD, TOC and dissolved solids. Wool and polyamide are dyed with the acid chrome dyes using the mordant dyeing technique causing the additional contamination of the effluents by high contents of chromium. Acid chrome dyes are the class of dyes that are at the same time most widely used in Eastern Europe and most difficult to eliminate. Due to the low biodegradability of dyes, conventional biological

dyed with the addition of -cyclodextrin into exhausting dye bath (sample C)

reacting -cyclodextrin citrate with chitosan (El-Tahlawy et al., 2006).

**4. Cyclodextrins in textile waste water treatments** 

wastewater treatment is not very efficient.

0,0 20,0 40,0 60,0 80,0 100,0

**K/S** 

with cyclodextrin.

Coagulation and adsorption onto various supports are the most frequently used physical methods. Due to interactions of ionic dyes with oppositely charged ionic surfactants, the extraction of ion pairs can also be used to remove dyes from aqueous streams. However, solvent extraction is not very useful as the concentrations of dyes present are usually low and the aqueous stream can be contaminated with diluents. Chemical methods such as oxidation and chlorination are more effective.

As a result of continuous water recycling, several groups of substances such as salts, organic micro pollutants, microorganisms, etc., are concentrated in the water loop and may cause water quality problems as well as health risks. The research is now focused also on the reduction/elimination of toxic organic pollutants like degradation products of dyestuffs and auxiliaries (phenols, aromatic amines, formaldehyde, persistent organic pollutants (POPs) etc), which can be formed also during the waste water treatment inside the factory or present in low concentrations in used chemicals or basic materials.

Basically, cytotoxicity of typical azo dyes may be relatively low, but the toxicity of related aromatic amine intermediates is very likely still significantly high due to their carcinogenicity or mutagenicity. Azo compounds like textile dyes can be reduced to amines through co-metabolism and the aid of azoreductases during decolourization treatments (Haug et al., 1991). As aromatic amines are difficult to be removed via traditional wastewater treatment and inevitably tend to be persistent, the toxicity evaluation of these amines will be apparently crucial to operation success or failure in dye decolourization and biodegradation afterwards. Aniline, the simplest and one of the most important aromatic amines, being used as a precursor to more complex chemicals, is toxic by inhalation,

Application of Cyclodextrins in Textile Dyeing 389

<sup>O</sup> <sup>O</sup>

COOH

O

O

O

HOOC <sup>O</sup>

O

O O

O

COOH

O

O

O

HOOC

O

O

O

COOH

COOH

O

O

O

O

O

O

COOH

COOH

O

<sup>O</sup> <sup>O</sup> HOOC

COOH

O

COOH

<sup>O</sup> HOOC

COOH

HOOC

O

COOH

O

O

Cyclodextrins have the ability to form inclusion complexes with a large number of organic molecules; this property enables them to be used in a variety of different textile applications. As cyclodextrins can incorporate into their cavities different dyes, they could be used as auxiliaries in dyeing process. Regardless the mechanisms of cyclodextrins actions, if there is a competition for sites on the fibre between dyes and cyclodextrins; or cyclodextrins slow down the dyes migration by forming complexes with the dyes molecules which are released slowly to the fibre, cyclodextrins can act as levelling or retardant reagents in various textile

In general, quality dyeing can be obtained and bath exhaustion can be improved when cyclodextrins are used as an additive (levelling reagent or retarding reagent) compared to commercially available auxiliaries; further improvement of colour levelness and some improvements in colour depth have been found when textile fibres were dyed in the presents of cyclodextrins. One of the main criteria for the complex inclusion is the size of cyclodextrins cavity and the size of the dyestuff molecules. The use of cyclodextrins in textile dyeing can not only improve the quality of the dyeing, but it can reduce the environmental impact of the exhausted baths. Further, covalently bonded cyclodextrins on textile support form inclusion complexes with organic pollutants. The adsorbed pollutants

Allabashi, R.; Arkas, M.; Hörmann, G. & Tsiourvas, D. (2007). Removal of some organic

pollutants in water employing ceramic membranes impregnated with cross-linked silylated dendritic and cyclodextrin polymers, *Water Research*, Vol.41, No.2, 476-486,

COOH

HOOC

COOH

O

COOH

O

O

O O HOOC

O

O

O O

HOOC

O

HOOC <sup>O</sup>

O

COOH

O

O

COOH

<sup>O</sup> <sup>O</sup> HOOC

HOOC

COOH

O

O

COOH

O

O

**5. Conclusion** 

**6. References** 

ISSN: 0043-1354

<sup>O</sup> <sup>O</sup> HOOC

Fig. 13. Assembly of molecular capsules

O

O

O

O

fibre (cotton, polyester, polyamide, polypropylene, polyacrylonitrile) dyeing.

will be converted into water and carbon dioxide by the incineration.

COOH

COOH

absorption through the skin or swallowing. To remove dyes and toxic micro pollutants several separation techniques, based on filtration, adsorption, and extraction could be applied.

The source of POPs in textile materials and textile effluents could be pesticides for cotton and other materials based on pentachlorophenol, known to be contaminated with dioxins; chloranyl based dyestuffs; textile processes using chlorinated chemicals contaminated with POPs; highly alkaline finishing media; brominated flame retardants and also the waste water after treatment with AOPs (e.g. irradiation with powerful UV lamp in the presence of accelerating agents like H2O2, NaOCl, Fenton's regent, etc). Concentrations of POPs in waste water and even on textile material after different finishing processes can be between 100 g/L to 20g/L. Apart from above mentioned POPs, phenol, and formaldehyde forming compounds and various aromatic amines (as the by-products and decomposition products of textile dyestuffs) present the most problematic pollutants in textile waste water.

Nowadays the membrane methods of separation are widespread as a method of wastewater treatment. The choice of the most suitable membrane process from a technical–economic point of view is very important. Having high dye retention, reverse osmosis (RO) and nanofiltration (NF) can be used for the treatment of dye waters from the textile industry. But industries are somehow reluctant to adopt highly energy-consuming RO and NF processes. Furthermore, NF/RO membranes have a lot more serious issues related to membrane fouling caused by colloids deposition, inorganic precipitation, and biological growth. Biofouling or biological fouling is the undesirable accumulation of microorganisms, plants, algae, and or animals on wetted structures.

Novel nano-porous polymers or nanosponges can be prepared for removal of organic pollutants from waste water. The polymeric «nanosponge» materials are not durable (usually they are in gel form), so they must be impregnated onto the pore structure of either a ceramic or some other porous surfaces. (Salipira et al., 2007). This technology is very specific for the target pollutant, it is very expensive and the removal of the adsorbed pollutant from the nanosponge is not possible. Usually the nano-porous polymers do not have high mechanical strength (Allabashi et al., 2007).

Textile materials are very important as filter materials. The cost of textile materials is acceptable (polyester, viscose), they have a sufficient mechanical strength; the pore size, especially the macro-pore size can vary, it depends on the type of textile (the density of nonwoven material) and on the diameter of fibres. Textile materials can be further modified to prepare filtration materials with additional adsorption.

The amount of aromatic organic pollutants (phenols, aniline, formaldehyde and others) can be reduced from dyeing wastewater by using cyclodextrins which can be immobilized on a water insoluble organic support. The new concept for modification of textile substrates is based on permanent fixation of supramolecular compounds - cyclodextrins on the material surface and thus imparts new functionality to the fabric (Mamba et al., 2007; Mhlanga et al., 2007).

The guest molecules could be various organic molecules and some metal ions as well. The formed assembly of nanocapsules on textile materials (Fig. 13) acts as selective filtration/adsorption media for various pollutants. Cyclodextrin covalently bonded onto a textile support will form inclusion complexes with organic toxic pollutants by »host-guest« mechanism. After the filtration process, the organic support with cyclodextrin containing organic compounds can be incinerated.

absorption through the skin or swallowing. To remove dyes and toxic micro pollutants several separation techniques, based on filtration, adsorption, and extraction could be

The source of POPs in textile materials and textile effluents could be pesticides for cotton and other materials based on pentachlorophenol, known to be contaminated with dioxins; chloranyl based dyestuffs; textile processes using chlorinated chemicals contaminated with POPs; highly alkaline finishing media; brominated flame retardants and also the waste water after treatment with AOPs (e.g. irradiation with powerful UV lamp in the presence of accelerating agents like H2O2, NaOCl, Fenton's regent, etc). Concentrations of POPs in waste water and even on textile material after different finishing processes can be between 100 g/L to 20g/L. Apart from above mentioned POPs, phenol, and formaldehyde forming compounds and various aromatic amines (as the by-products and decomposition products of textile dyestuffs) present the most problematic pollutants in

Nowadays the membrane methods of separation are widespread as a method of wastewater treatment. The choice of the most suitable membrane process from a technical–economic point of view is very important. Having high dye retention, reverse osmosis (RO) and nanofiltration (NF) can be used for the treatment of dye waters from the textile industry. But industries are somehow reluctant to adopt highly energy-consuming RO and NF processes. Furthermore, NF/RO membranes have a lot more serious issues related to membrane fouling caused by colloids deposition, inorganic precipitation, and biological growth. Biofouling or biological fouling is the undesirable accumulation of microorganisms, plants,

Novel nano-porous polymers or nanosponges can be prepared for removal of organic pollutants from waste water. The polymeric «nanosponge» materials are not durable (usually they are in gel form), so they must be impregnated onto the pore structure of either a ceramic or some other porous surfaces. (Salipira et al., 2007). This technology is very specific for the target pollutant, it is very expensive and the removal of the adsorbed pollutant from the nanosponge is not possible. Usually the nano-porous polymers do not

Textile materials are very important as filter materials. The cost of textile materials is acceptable (polyester, viscose), they have a sufficient mechanical strength; the pore size, especially the macro-pore size can vary, it depends on the type of textile (the density of nonwoven material) and on the diameter of fibres. Textile materials can be further modified to

The amount of aromatic organic pollutants (phenols, aniline, formaldehyde and others) can be reduced from dyeing wastewater by using cyclodextrins which can be immobilized on a water insoluble organic support. The new concept for modification of textile substrates is based on permanent fixation of supramolecular compounds - cyclodextrins on the material surface and thus imparts new functionality to the fabric (Mamba et al., 2007; Mhlanga et al.,

The guest molecules could be various organic molecules and some metal ions as well. The formed assembly of nanocapsules on textile materials (Fig. 13) acts as selective filtration/adsorption media for various pollutants. Cyclodextrin covalently bonded onto a textile support will form inclusion complexes with organic toxic pollutants by »host-guest« mechanism. After the filtration process, the organic support with cyclodextrin containing

applied.

textile waste water.

2007).

algae, and or animals on wetted structures.

have high mechanical strength (Allabashi et al., 2007).

prepare filtration materials with additional adsorption.

organic compounds can be incinerated.

Fig. 13. Assembly of molecular capsules
