Anfangweiter 1. Cyclodextrins in Textile Fresheners

Textile fresheners contain cyclodextrins which remove the smell of cigarette smoke, cooking, pets and perspiration when the fresheners are sprayed onto textiles.
Fig. 1.31: Most textile fresheners contain cyclodextrins
 Fig. 1.32: To prevent the formation of odors as they develop, cyclodextrins must bond to the textile fibers

Fresheners can also be used to mask food smells in curtains, unpleasant odors in clothing, sofas and armchairs, and the smell of perspiration in sports textiles.
Subsequent washing removes the cyclodextrin complexes along with the trapped odors from the textile surface, so the textile fresheners must be constantly reapplied. For a permanent effect to be achieved, the cyclodextrins have to bond to the textile surface. In this way, a sports jersey could actually absorb the odors as they arise during a volleyball game. This can be achieved with a reactive derivative of β-cyclodextrin that employs an active group to facilitate covalent bonding to the fiber.
Anfangweiter 2. Cyclodextrins in Textile Finishes
To make the odor-absorbing property of cyclodextrins permanent in textiles, the cyclodextrin molecules must be anchored to the textile fibers to prevent them from being washed out.
Fig. 1.33: WACKER markets innovative products for functional textile finishing with cyclodextrins under the name CAVATEX®

Since natural cyclodextrins cannot bond directly to the textile surface, the cyclodextrins are first functionalized. Cyanuric chloride, which initially reacts to form a dichlorotriazinyl sodium salt in alkaline conditions, serves as the anchor molecule for the covalent bond to the cellulose fiber (see Fig. 1.).
Fig. 1.34: Cyanuric chloride is converted to the dichlorotriazinyl sodium salt before the reaction with β-cyclodextrin
AnfangweiterIn the second step, the anchor molecule dichlorotriazinyl reacts with a hydroxyl group in the β-cyclodextrin molecule in a nucleophilic substitution during which water is split off.
Fig. 1.35: A high yield of monochlorotriazinyl-β-cyclodextrin, the reactive derivative of β-cyclodextrin, is obtained in a one-pot reaction.
The C-Cl bond in the monochlorotriazinyl-β-cyclodextrin is so strongly polarized that the carbon atom from a cellulose molecule can be attacked by an oxygen atom from a hydroxyl group.
Fig. 1.36: Section of a cellulose molecule
In this way, the anchor molecule helps to bond the β-cyclodextrin to the cellulose fiber (see Fig. 1.37).
Fig. 1.37: The covalent bond to the cellulose fiber is effected in a condensation reaction during which hydrogen chloride is split off
Anfangweiter In industry, textile finishing with β-cyclodextrin is performed in a continuous process. The fabric is drawn through a bath containing the reactive monochlorotriazinyl β cyclodextrin, which bonds covalently to the fiber as it passes through heating blocks.
Fig. 1.38: In industry, cotton finishing with monochlorotriazinyl-β-cyclodextrin is performed in a continuous process

The German Center for Textile Research for the Northwest (Deutschen Textilforschungszentrum Nord-West) is researching and testing textile finishing methods based on cyclodextrin. To quantify the functionalization of a textile surface with cyclodextrins, the researchers have developed an analytical method which exploits the ability of cyclodextrins to form complexes.
Abb. 1.39: The German Centre for Textile Research for the Northwest (deutsches Textilforschungszentrum Nord-West) is developing and testing methods for textile finishing based on cyclodextrin

AnfangweiterAnalytical methods to determine the cyclodextrin loading in the fabric make use of the fact that cyclodextrins form a colorless complex with phenolphthalein. A fabric sample is treated with an alkaline, magenta-colored phenolphthalein solution of a specific concentration. The color intensity of the solution decreases due to the complexation of the phenolphthalein-dianion in the cyclodextrin molecule. The absorption of the supernatant solution is measured in a UV-VIS spectrometer. A calibrated ruler is used to determine the concentration of phenolphthalein-dianion in the solution. The concentration difference compared to the phenolphthalein solution at the start of the experiment indicates the cyclodextrin loading of the textile.
Fig. 1.40: When an alkaline phenolphthalein solution is pipetted onto a treated (left) and untreated (right) cotton strip, the ensuing color loss is proof of textile finishing with cyclodextrins

Textiles finished in this way can absorb unpleasant odors, such as those from cigarette smoke or pets, by forming host-guest complexes between the cyclodextrin molecules and the odor molecules.
Fig. 1.41: Men's suits finished with cyclodextrins were on the market as early as 2001

Complexation of essential sweat components can suppress microbiological processes and prevent the smell of sweat from occurring at all . Washing removes the encapsulated compounds from the cyclodextrin molecules, leaving the anchored cyclodextrin molecules free to absorb more odors.

Fig. 1.42: Schematic diagram showing the mode of action during the masking of unwanted odors and the release of an encapsulated active ingredient

The cyclodextrins anchored to the textile fibers can also be loaded with specific fragrant or skin-conditioning substances. As moisture triggers the dissociation of these host-guest complexes, the guest molecules are only released through perspiration or when drying oneself with a treated hand towel. This enables the controlled release of the guest components.
Fig. 1.43: Fragrances are released from the cyclodextrin molecules only when the bear is touched

References:

  • Wacker Chemie AG; Beta W7 MCT – New ways in surface modification
    (www.wacker.com/internet/webcache/de_DE/PTM/BioTec/Cyclodextrins/Derivatives/
    mct-new_ways.pdf)
  • Tausch, M.; von Wachtendonk, M.; Chemie 2000+ Band 3; C.C. Buchner Bamberg, 2005, S. 128
  • Buschmann, H.-J.; Fresh Air from the Bar; WACKER WORLD WIDE CORPORATE MAGAZINE 3-01, 2001, 14-17
  • Wacker Chemie AG; CAVATEX® Textilausrüstung mit Cyclodextrinen
    (www.wacker.com/internet/webcache/de_DE/_Downloads/ CAVATEX_TextFinish_Cyclo_DE.pdf))
  • Knittel, D.; Thoms, G.; Buschmann, H.-J., Schollmeyer, E.; Melliand Textilberichte; 6, 2005, 463-464
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