Polymers from cellulose

The crystal structure and three-dimensional network prevent cellulose from behaving as a polyol for PU syntheses. To overcome this problem a liquefaction process in the presence of organic solvents was developed and resulted in products suitable for PU synthesis. Yan and co-workers (2008) liquefied corn stalk, an agricultural by-product, and tested it for the synthesis of PU foams blown by water. The report revealed that such polyurethane foams had excellent mechanical and thermal properties and could be used as heat insulating materials. 

In addition to its renewability and satisfactory mechanical properties, cellulose presents biocompatibility, which makes it possible to use in some pharmaceutical applications. Different chemical modifications allow different applications of cellulose, such as oxycellulose for controlled drug delivery matrices, sodium carboxymethyl cellulose as emulsifying agents, and cellulose acetate phthalate for tablet coatings (Kamel et al, 2008). 

Just like starch, cellulose has also been shown to exhibit some important electro-active properties. For instance, cellophane was found to be a piezoelectric material that transforms electrical energy into mechanical energy. Nevertheless, some cellulosic blends, for example the blend of cellulose xanthate and propylene oxide-grafted hydroxyethyl cellulose with PEG, showed conductivities around 10 and lO S/cm (Finkenstadt, 2005). 

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The LAL reaction is specific for endotoxin with the exception of a glucose polymer from cellulose, yeast, and certain other microbial sources, known as (1 —> 3)-p-D-glucanJ This glucan activates LAL the same as endotoxin and produces a synergistic enhancement of the PPC in kinetic LAL studies. The BET allows glucan-containing products to be tested by LAL reagents that are treated to make them specific for endotoxin and avoid a false-positive result. 

Odberg, L, Tanaka, H., Glad-Nordmark, G. and Swerin, A. (1994) Transfer of polymers from cellulosic fibers to filler particles. Colloids and Surfaces A Physicochemical and Engineering Aspects, 86, 201-205. 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Polymers. Hydrocarbons from petroleum and natural gas serve as the raw material for virtually all polymeric materials commonly found in commerce, with the notable exception of rayon which is derived from cellulose extracted from wood pulp. Even with rayon, however, the cellulose is treated with acetic acid (qv), much of which is manufactured from ethylene (see Fibers, regenerated cellulosics). 

Figure 13 Schematic diagram of the dependence of <7 on pressure. (F) Denotes folded-chain nucleus, (B) denotes bundle-like nucleus and (B ) denotes addition of ethyl cellulose liquid crystal polymer. (From Refs. 104, 110, 111, and 117.)...

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