Ether, cellulose

Methyl cellulose (MC) is a yellowish or white solid, with no odour or flavour. It is obtained by reaction of alkali cellulose with methylene chloride. It is soluble in 

Thermoplasticity Do not melt. Thermal degradation above 200°C Show apparent melting point Shiraishi et ah, 1983 

Hydrophobicity Hydrophilic. Swell in water Water resistance. Dimensional stability Rowell and Keany, 1991 

Biological resistance Easily attacked by insects and fungi Resistance to termites and fungi Rowell, 1997 

Biodegradability Readily biodegradable Retarded biodegradation Glasser et a/., 1994 

Cellulose ethers, such hydroxyethyl cellulose or hydrox5rpropyl cellulose, are water soluble cellulose derivatives which may be produced by etherification of alkali cellulose with epoxides, e.g., ethylene oxide or propylene oxide (36). Cellulose is made alkaline in sodium hydroxide solution and subsequently reacted with the corresponding alkylene oxides. 

Hydroxypropyl cellulose (HPC) is a non-ionic water-soluble and pH insensitive cellulose ether. It can be used as thickening agent, tablet binder and modified release and film coating polymer. Buccal delivery formulations containing HPC and polyacrylic acid are used for many years and is used for mucoadhesive delivery systems for several drugs. 

Hydroxypropylmethyl cellulose (HPMC) is a water-soluble cellulose ether that is mainly used in the preparation of controlled release tablets. Viscosity is the main variable responsible for controlling the release. The hydration and gel forming abilities of HPMC can be used to prolong the drug release of the active ingredient. 

Other applications of HA are as follows wound healing by extracellular regeneration, epithelial regeneration, topical treatment of dry eye syndrome and Sjogren s syndrome. It is also used as a viscosity agent in pulmonary pathology for achieving alveolar patency and as a filler for wrinkles and cutaneous lines. 

One interesting use of HA is in the field of viscosurgery and viscosupplementation. In reproductive medicine, HA enhances the retention of the mobility of cryo-preserved and thawed spermatozoa. This property is used to select viable spermatozoa and Improve artificial insemination and other in vitro fertilization methods. 

scribed previously there are a wide range of polymers that are used as components of pharmaceutical formulations. Classification of these materials may be performed according to chemical structure however other classifications based on the pharmaceutical applications of the polymers are frequently used. In light of the special i.st nature of these materials, this section will provide a brief overview of the main properties of some of the most frequently u.sed pharmaceutical polymers. It should be noted that the polymers described represent those that are most commonly used in phaimacy although it is recognised that there will be other polymers not included in this list that have pharmaceutical applications. The use of these polymers and those described in the next section will be highlighted in the latter sections of the review. 

They may also be used as the matrix layers in the formulation of transdermal delivery systems (a. 1). The general chemical name and properties of some commercially available polymethacrylates are given in Table 1. 

Polyvinyl alcohol is a water soluble polymer that is prepared by the hydrolysis of polyvinyl acetate and is represented by the formula (C2H.,0) , where n varies between 500-5000. The degree of hydrolysis and the degree of polymerisation determine the physical 

Chemical Name Trade Name Properties Applications 

Poly (butyl methacrylate, (2-dimethyl aminoethyl) methylacrylate) 1 2 1 R, R3= CH., r2 = CH2CH 2N(CH., r4 = ch c4H9 Eudragit E Cationic polymer. Soluble in gastric juices and weakly acidic buffer solutions pH 5. Film coalings. 

One danger is that the build-up of pressure would distort sample pans giving irreproducible scans that were dependent on the contact between the pan and the temperature sensor. Although TGA could be used to quantify any weight loss, the results would still depend on the moisture content of the samples prior to treatment. On an as is product, this could be quite variable. At elevated temperatures the sample would start to decompose and this would inevitably be detected as a weight loss. 

DSC sample pan. After each drop had been added, the solvent was evaporated. Repetitive addition of 20-30 drops produced a film suitable for analysis. Other techniques, including torsional braid analysis (TBA) and DSC were used to evaluate HPMC [122]. Not surprisingly, the techniques gave a wide range of values (157° to 180°C) which represents problems in producing a dry sample and possibly problems with conductivity caused by entrapped air. 

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Mixed alginate salts Mixed catalysts Mixed cellulose ethers... 

Two important classes are cellulose esters (qv) and cellulose ethers (qv). Cellulose esters are not water soluble and are not discussed here cellulose ethers are an important segment of water-soluble polymers. 

The derivatives are hydroxyethyl and hydroxypropyl cellulose. AH four derivatives find numerous appHcations and there are other reactants that can be added to ceUulose, including the mixed addition of reactants lea ding to adducts of commercial significance. In the commercial production of mixed ethers there are economic factors to consider that include the efficiency of adduct additions (ca 40%), waste product disposal, and the method of product recovery and drying on a commercial scale. The products produced by equation 2 require heat and produce NaCl, a corrosive by-product, with each mole of adduct added. These products are produced by a paste process and require corrosion-resistant production units. The oxirane additions (eq. 3) are exothermic, and with the explosive nature of the oxiranes, require a dispersion diluent in their synthesis (see Cellulose ethers). 

Major industrial uses for chloroacetic acid are in the manufacture of cellulose ethers (mainly carboxymethylceUulose, CMC), herbicides, and thioglycolic acid. Other industrial uses include manufacture of glycine, amphoteric surfactants, and cyanoacetic acid. 

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

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