Some new reactive polymers for the immobilization of enzymes.
From poly(vinyl alcohol) precursors, various reactive carriers for the immobilization of enzymes were synthesized. As insoluble starting polymers, the following products were used: poly(vinyl alcohol), gels crosslinked with terephthalaldehyde, hydrolyzed beads of crosslinked poly(vinyl acetate), poly(vinyl acetate-co- ethylene) tubes coated with poly(vinyl alcohol), and poly(vinyl alcohol)-containing synthetic pulp. Reactive groups introduced into these carriers or methods for their activation included the diazonium- and isothiocyanato group, and the glutardialdehyde-, BrCN, 2, 4, 6-trichloro-s-triazien, and p-benzoquinone methods. Furthermore, SH-specific reactive groups such as N-substituted maleimide groups or activated mixed disulfides with 2-thiopyridyl groups could be introduced into PVA-polymers. Enzymes like hydrolases (e.g. papain, trypsin, chymotrypsin, urease), oxidoreductases (e.g. glucose oxydase, catalase, glucose-6-phosphate dehydrogenase) as well as the example of transferase hexokinase coimmobilized with glucose-6-phosphate dehydrogenase, were immobilized by reactive poly(vinyl alcohol) carriers. The properties of the immobilized enzymes were investigated.
Polyethylen‐Fibride: Herstellung und Eigenschaften
Unter Polyethylen-Fibriden versteht man in Langsrichtung hochorientierte Faserchen mit zellstoffahnlicher Gestalt von bis zu einigen Millimetern Lange. Sie sind aufgrund ihrer auseren und inneren Morphologie eine neue Erscheinugsform von Polyethylen. Die Herstellung von Polyethylen-Fibriden basiert auf dem physikalischen Vorgang der scherinduzierten Kristallisation, d. h. darauf, das Polyethylen aus einer Losung unter dem Einflus einer Dehnstromung in Form von sogenannten Shish-Kebabs kristallisiert. Als Herstellungsverfahren kommen vor allem die Polymerisation unter Scherbedingungen und die Flash-Verdampfung von Polyethylen-Fibride hydrophilieren. -- Wegen ihrer besonderen auseren Morphologie, die der von Cellulosefaserchen (Zellstoff) sehr ahnlich ist, haben (hydrophilierte) Polyethylen-Fibride interessante Eigenschaften, so z. B. ein hohes Adsorptionsvermogen und die Fahigkeit zur Bildung von Wasserstoff-Bruckenbindungen. Hervorgehoben sei auch die Moglichkeit zu chemischen Reaktionen an der Oberflache der Fibride.
Phase formation during mechanical alloying in the Ti–Si system
Abstract Mechanical alloying of Ti–Si powder mixture or TiH 1.924 –Si powder mixture was performed by high-energy ball milling, in which the Ti to Si mole ratio was 1:2. The phase formations in both mixtures during milling were investigated by X-ray diffraction. Mechanical alloying a mixture of elemental powders led to the formation of TiSi 2 equilibrium compound, while when starting from Si + TiH 1.924 , a metastable phase was formed. The metastable phase completely transforms to TiSi 2 when the mechanically alloyed powder is annealed at temperatures above 800 °C. Two different pathways of phase transitions during mechanical alloying are attributed to the existence of hydrogen atoms, i.e., when starting from Si + TiH 1.924 compared to Si + Ti, the kinetics for the formation of the TiSi 2 intermetallic compound slows down. The kinetics related to the different phase transitions depending on the starting powder mixture are discussed.