Synthetically modified cellulose

The flow behavior in miniaturized hemodialyzer modules with two types of biocompatible membrane materials, SMC and SPAN, was investigated by using doubly distilled water as the flowing fluid in both compartments, subsequently termed membrane side (M) and dialysate side (D), respectively (Figure 4.6.1 (c, d)) [12], SMC stands for Synthetically Modified Cellulose and SPAN for Special PolyAcryloNitrile-based copolymer (Akzo Nobel, Membrana GmbH), both types representing standard membrane material. The capillaries made from this hollow... 

SPAN module. It was mentioned at the beginning that the special polyacrylonitrile fibers of SPAN have a wall thickness of 30 gm, which is considerably thicker than the 8 gm wall thickness of the SMC modules [19]. As a consequence, the presence of stronger capillary effects from the special porous fiber material of the SPAN module would be a reasonable conclusion. Furthermore, the texture of the special polyacrylonitrile fibers is expected to have better surface properties, supporting the permeation of molecules as compared with synthetically modified cellulose. In conclusion, both convection and diffusion effectively contribute to the filtration efficiency in a SPAN module, whereas for the SMC membrane, diffusion is the driving force for molecular exchange, the efficiency of which is also considerable and benefits from the large surface-to-volume ratio. 

Bowry S, Rintelen T. Synthetically modified cellulose a cellulosic hemodialysis membrane with minimized complement activation. ASAIO J 1998 44 M579-83. 

A number of after-treatments with polyester copolymers carried out after sodium hydroxide processing are reported to produce a more hydrophilic polyester fabric (197). Likewise, the addition of a modified cellulose ether has improved water absorbency (198). Other treatments used on cotton and blends are also effective on 100% polyester fabrics (166—169). In this case, polymeri2ation is used between an agent such as DMDHEU and a polyol to produce a hydrophilic network in the synthetic matrix (166—169). 

A number of synthetic polymers that are widely used commercially are soluble in water. These tend to have very polar functional groups and include such polymers as poly(vinyl alcohol), poly(acrylic acid), and the modified celluloses. 

Regenerated proteins from casein (lanital), peanuts (ardil), soybeans (aralac), and zine (vicara) are used as specialty fibers. Regenerated and modified cellulose products, including acetate, are still widely used today and the production of fibers is similar to that described above for synthetic fiber production. Most regenerated cellulose (rayon) is produced by the viscose process where an aqueous solution of the sodium salt of cellulose xanthate is precipitated in an acid bath. The relatively weak fibers produced by this wet spinning process are stretched to produce strong rayon. 

Polymer modifications represent a valuable synthetic approach to unique polymer compositions, structure, and properties not readily available by the direct polymerization of monomers. Modified polymeric products already exist in the commercial world (modified celluloses, for example) so the approach is not new. However, it is an interesting and challenging opportunity to develop new materials for a variety of specialty applications using the "chemistry on polymers" approach. 

There are two types of membranes, cellulosic and synthetic or polymeric ones. Cellulosic membranes can be in regenerated cellulose (cuprophan, Bioflux from Membrana, Germany) or modified cellulose (cellulose acetate or diacetate, from Asahi, triacetate cellulose from Baxter and Nipro, which has a high hydraulic permeability or Hemophan from Membrana). Cuprophan was originally the most common one, because of its low cost, but is no longer produced because of its lower biocompatibility and hydraulic permeability. A wide variety of polymeric membranes are now available with both high and medium hydraulic permeabilities. Only the Eval... 

The possibility of grafting synthetic polymers to cellulose immediately attracted worldwide attention as a new and exciting way to modify cellulose and extend its uses against the rapidly growing competition from synthetic polymers themselves. The well known phrase attributed to Theodore Roosevelt, "if you can t beat them, join them", if somewhat trite, seems particularly appropriate at this point. Research in the field blossomed quickly and is still an extremely active subject of study. For example, in a very recent (and the first) book on the subject by Hebeish and Guthrie (4) more than one thousand references are quoted. 

Several graft copolymers were prepared based on the anionic polymerization method to overcome some of the major problems encountered in radical-initiated grafting. This method is used to prepare a living synthetic polymer with mono- or dicarbanions to react with modified cellulosic substrates under homogeneous conditions. For example, polyacrylonitrile carbanion was prepared to react with cellulose acetate to generate a cellulose acetate-polyacrylonitrile graft polymer [142]. 

The present book is a follow-up of a previous one with the title Analytical Pyrolysis of Natural Organic Polymers published by Elsevier as vol. 20 in the series Techniques and Instrumentation in Analytical Chemistry. In addition to the discussion on pyrolysis of various natural polymers, the previous book contains information on chemically modified celluloses, modified starches, etc. For this reason, the present book does not include synthetically modified natural polymers. Information on the pyrolysis process and pyrolytic techniques in general also can be found in the book on natural polymers. 

Chemically modified cellulose in the form of cellulose nitrate or nitrocellulose was made and tested for commercial applications in Britain in the 1855-1860 period without much success. The discovery by Hyatt, in 1863, that cellulose nitrate could be plasticized with camphor to give moldability to the blend, made this material much more useful. By 1870, celluloid (plasticized cellulose nitrate) was being produced into a variety of commercial products such as billiard balls, decorative boxes, and combs. Nitrocellulose was also soluble in organic solvents, unlike cellulose, and so could be applied to surfaces in solution to form a coating, as in airplane dopes and automobile lacquers. It could also be solution spun into fibers (synthetic silk) and formed into photographic film, or used as a laminating layer in early auto safety glass. It was also used as an explosive. The hazard introduced to many of these uses of nitrocellulose by its extremely flammable nature resulted in an interest to discover other cellulose derivatives that could still be easily formed, like nitrocellulose, but without its extreme fire hazard. 

This chapter will discuss the synthetic processes and reactions used to modify cellulose and produce cellulosic derivatives. Their properties and uses will also be presented. 

The chemical industry s interest in polymers dates back to the 19th century. In those days it was a case of synthetically modifying natural polymers with chemical reagents to either improve their properties or produce new materials with desirable characteristics. Notable examples were nitration of cellulose giving the explosive nitrocellulose, production of regenerated cellulose (rayon or artificial silk) via its xanthate derivative, and vulcanization of rubber by heating with sulphur. Manufacture of acetylated cellulose (cellulose acetate or acetate rayon) developed rapidly from 1914 onwards with its use both as a semi-synthetic fibre and as a thermoplastic material for extrusion as a film. 

Most early efforts focused on the development of thin layer matrix precoated membranes, including those made of nylon and other synthetic polymers, nitrocellulose, anion- and cation-modified cellulose and regenerated cellulose. Several manufacturers currently offer 96-well plates with proprietary coatings for LC-MALDI-MS applications. This approach was described in more detail above. As mentioned previously, all of these sample preparation methods were originally developed for pre-purified samples or fractions, not for analytes eluting from an HPLC or capillary electrophoresis column. 

Both rayon and acetate rayon are made from chemically modified cellulose and were the first commercially important synthetic textile fibers. In the production of rayon, cellulose fibers are treated with carbon disulfide, CSg, in aqueous sodium hydroxide. In this reaction, some of the —OH groups on a ceUulose fiber are converted to the sodium... 

Synthetically Modified Polysaccharides. Water solubility can be conferred on a number of naturally occurring polysaccharides by synthetic derivations producing charged or polar functionality. Two of nature s most abimdant polysaccharides, cellulose and chitin, have been synthetically modified in a multitude of ways to produce polymers with significant commercial utilization (86,87). 

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