Mechanical entrapment

Fibrillated Fibers. Instead of extmding cellulose acetate into a continuous fiber, discrete, pulp-like agglomerates of fine, individual fibrils, called fibrets or fibrids, can be produced by rapid precipitation with an attenuating coagulation fluid. The individual fibers have diameters of 0.5 to 5.0 ]lni and lengths of 20 to 200 )Jm (Fig. 10). The surface area of the fibrillated fibers are about 20 m /g, about 60—80 times that of standard textile fibers. These materials are very hydrophilic an 85% moisture content has the appearance of a dry soHd (72). One appHcation is in a paper stmcture where their fine fiber size and branched stmcture allows mechanical entrapment of small particles. The fibers can also be loaded with particles to enhance some desired performance such as enhanced opacity for papers. When filled with metal particles it was suggested they be used as a radar screen in aerial warfare (73). 

Immobilized enzymes are attached to a solid support by adsorption or chemical binding or mechanical entrapment in the pores of a gel structure but retain their catalytic power. Their merit is ease of separation from the finished reaction product. 

Another complex biochemical reaction is the polymerase chain reaction (PCR). It has also be implemented in liposomes (Oberholzer et al, 1995a). This reachon was interesting from the point of view of vesicle chemistry because the liposomal system had to endure the extreme PCR condihons, with several temperature cycles up to 90 °C (liposomes were practically unchanged at the end of the reaction) and furthermore, nine different chemicals had to be encapsulated in an individual liposome for the reaction to occur. This was carried out by mechanical entrapment from a solution that contained all components only a minimal number of the in situ formed vesicles could entrap all nine components. These odds notwithstanding, there was a significant synthesis. ... 

The occurrence of voids has been thoroughly documented in thick laminates [2], In almost all cases, they are apparently associated with the prepreg surface. The exact mechanism of void formation depends on the system, but in the most general case it can include mechanical entrapment as well as nucleation of stable voids in the resin phase. 

Voids can be formed by either entrapment of air mechanically or by one of two nucleation processes. Mechanical entrapment could include (1) entrained gas bubbles from the resinmixing operation, (2) bridging voids from large particles or particle clusters (quenched DDS curing agent, airborne particles, or paper release agent), (3) voids from wandering tows, fuzz... 

The mechanically entrapped acids may be sulfuric, nitric, acetic, or any other acid used in the manufg process. These acids will also initiate the decompn of org nitrates as described above... 

Antiacid Compounds or Antacids (Antazide or Sauerbindende Stoffe in Ger). Some explosives and propellants, especially those contg org nitrates (such as NG, NGc, NC, etc) may contain traces of mechanically entrapped acids, especially sulfuric acid. In other cases, acids (nitric and nitrous) might form on decompn of the above organic nitrates during storage, especially at high temps and in the presence of moisture. If these traces of acids are not immediately neutralized, they... 

Cotton, Chemical, The basic raw material from which NC and cellulose acetate are made. Chemical cotton is chemically purified cotton linters (See under). The raw linters contain impurities such as proteins, fats, waxes, pectins, sugars, inorganic salts and mechanically entrapped vegetation, dirt, wood etc, all of which must be removed... 

Sometimes much greater amounts of solvent can be immobilised by mechanical entrapment within particle aggregates. This occurs when voluminous flocculent hydroxide precipitates are formed. In solutions of long thread-like molecules the polymer chains may cross-link, chemically or physically, and/or become mechanically entangled to such an extent that a continuous three-dimensional network is formed. If all of the solvent becomes mechanically trapped and immobilised within this network, the system as a whole takes on a solid appearance and is called a gel. 

The sol-gel process is the name given to a number of processes in which a solution, or sol, undergoes a sol-gel transition. In this broadest sense, the term sol-gel refers to the preparation of inorganic oxides by wet chemical methods, irrespective of final form product—monolith, crystalline, or amorphous (1). Using sol-gel materials for mechanical entrapment of enzymes permitted stabilization of the proteins, tertiary structure owing to the tight gel network (2). Moreover, the easy insertion of substituent groups into... 

Coprecipitation — The -> precipitation of a normally soluble substance that is carried down during the precipitate formation of the desired substance. The coprecipitation of a substance arises from processes such as - adsorption, -r mixed-crystal formation, - occlusion and/or mechanical entrapment [i]. 

A low content of F-68 in the final product was not surprising. Uncharged chains of F-68 are merely mechanically entrapped during the nanoparticle assembly process, which involves charged molecules of the reactants. The inclusion of F-68, however, is crucial for particle steric stabilization. 

Sorption is a surface phenomenon determined by the surface charges and those of the ions surrounding it. One or more of the following mechanisms can be involved in the removal of species by sorption (i) mechanical entrapment, (ii) absorption, (iii) physical sorption, or (iv) chemical sorption on the surface of the solid particle. Physical adsorption (which is weaker than its chemical counterpart) occurs through Van der Waals forces and it is generally reversible and instantaneous. On the other hand, chemical adsorption or chemisorption occurs through the formation of chemical bonds at specific sites. This is closely related to ion exchange processes and complexation. 

Enzymes, immobiiized, are attached to a solid support by adsorption or chemical binding or mechanical entrapment in the pores of a gel structure, yet retain most of their catalytic powers -ase is a suffix identifying that the substance is an enzyme. The main part of the name describes the nature of the chemical reaction that can be catalyzed, as in cellulase, an enzyme that catalyzes the decomposition of cellulose... 

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