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Buschmann H.-J.,German Textile Research Center North - West
Israel Journal of Chemistry | Year: 2011

Cucurbit[6]uril forms stable complexes with amine compounds in aqueous solutions. Some of the preformed complexes can be used for the synthesis of rotaxanes or polyrotaxanes. Polymers with threaded cucurbit[6]uril are also obtained from these complexes. Even by mixing a solid amino acid with solid cucurbit[6]uril a threading process takes place in the melt during the polycondensation. Structural flexible amino compounds are completely rigid after complex formation with cucurbit[6]uril. As a result, they are used as one component for the formation of polyelectrolyte layers on substrates. Furthermore some of the complexes, together with cations, are able to act as components in the formation of metal-organic networks. Spectroscopic measurements indicate a well-ordered formation of these networks. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA. Source


Opwis K.,German Textile Research Center North - West
Chemical Engineering Transactions | Year: 2010

Low-cost textile fabrics made of polyester (PET) or polyamides (PA) are alternative carrier materials for the immobilization of enzymes. With a low preparative and economic expense fabrics with a high enzyme load, a high relative activity and good permanence against enzyme desorption can be produced by photo-induced cross-linking and grafting processes using monochromatic excimer-UV-lamps. The flexible and open construction of fabrics allows a high substrate conversion. Moreover, conventional immobilization products are mostly produced as granulates or pellets, which must be filtered after the enzymatic reactions. Fabrics can be removed very quickly from the reactor without any filtration step and the solution contains no proteinous residues after the enzymatic reaction. Here, the enzyme catalase was immobilized on PET and PA fabrics by different photochemical processes. Depending on the support and the used reactive agents 20 - 70 mg enzyme per gram carrier could be fixed durably, which can be quantitatively analyzed by atomic absorption spectroscopy due to the iron content of catalase. The efficiency of the immobilization products were investigated by measuring the enzymatic decomposition of hydrogen peroxide in comparison to the free enzyme. The relative activity of the catalase after the immobilization was 5 - 20 % of the free, not fixed catalase. The immobilized enzyme showed even after 20 reuses a distinct activity and the integral activity over all reuses was nearly 3.5 times higher than the activity of the free catalase. Therefore, these promising new photo-induced immobilization techniques open widespread applications in bio-catalysis in the future. Copyright © 2010 AIDIC Servizi S.r.l. Source


Bahners T.,German Textile Research Center North - West
Journal of Adhesion Science and Technology | Year: 2011

Surface treatments introduce chemical modifications to the fiber surface that affect the surface free energy (SFE). This is done either with the obvious aim to change the wetting behavior, or to affect related properties, such as, e.g., adhesion phenomenon, surface conductivity, adsorption of proteins, etc. On planar substrates, the measurement of contact angles of specific liquids and making use of formalisms such as Neumann or Owens-Wendt equations is a commonly used approach to determine the surface free energy. It is to be observed that this direct approach is often and lightheartedly applied to porous and textured samples, such as textiles, too. The geometry of a textile is extremely complex and defined by the topography of the fiber, the construction of the yarn, and the construction of the fabric. In addition, polymer fibers may be porous and take up water from the environment. Accordingly, wetting is the result of simultaneous spreading on a rough surface, penetration, and capillary motion in the multi-porous system. Therefore, the critical consideration of any analytical method for wettability measurements cannot be overemphasized, and the present paper is meant to critically discuss the pros and cons of various methods common to the textile researcher. It can be summarized that contact angles can be useful for comparative measurements on hydrophobic samples, while the established drop penetration tests characterize the effects of fabric finishing, fiber surface modifications, etc. with limited quantification. By no means can these test be used to derive the SFE, and in all cases it is essential to avoid accidental distortions of the fabric. The single fiber micro-Wilhelmy method can be regarded as the only reliable method to obtain advancing and receding contact angles. © Koninklijke Brill NV, Leiden, 2011. Source


Messik F.,University of Marburg | Oberthur M.,University of Marburg | Oberthur M.,German Textile Research Center North - West
Angewandte Chemie - International Edition | Year: 2013

Reliably stable: A dipeptide building block with fully elaborated N-acyl hemiaminal proved to be a versatile precursor for echinocandinC, a prototypical member of the echinocandin group of antimycotic drugs. This first total synthesis of an N-acyl hemiaminal-containing echinocandin is concise and highly convergent, thereby making additional derivatives easily accessible. PG=protecting group. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Netravali A.N.,Cornell University | Bahners T.,German Textile Research Center North - West
Journal of Adhesion Science and Technology | Year: 2010

Obtaining good bonding between two dissimilar materials is critical for several aspects in textile finishing, processing and application, including the durability of common textile finishes and fabric coatings, and the performance of fiber reinforced composites. Both functional properties and long term performance are dependent on the effective adhesion between the fiber on one hand and finishing agent, coating polymer or resin on the other. It is generally accepted that good adhesion is achieved through covalent chemical bonding, acid-base interactions or hydrogen bonding, surface energies that favor complete wetting of the fibers, large specific surface area of fibers, and surface roughness that allows lock and key type mechanical bonding. In practice, various surface treatments have been applied to fibers to alter their surface characteristics and to improve their adhesion properties. For example, chemical modifications such as acid oxidation, corona or plasma pre-treatments have been commonly employed. This paper aims to provide some insight into photon-based processes which, depending on the spectral range of radiation and the characteristics of the radiation sources, can be used to bring about chemical as well as morphological changes to fiber surfaces. We have considered two major applications of surface modification; (1) textiles for improving adhesion to finishes and (2) fiber/resin adhesion enhancement in fiber reinforced composites to improve their mechanical properties. The technical approaches cover photo-chemical surface modification and micro-roughening of fiber surfaces using monochromatic UV lamps and pulsed UV excimer lasers. © 2010 Koninklijke Brill NV, Leiden. Source

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