Cellulose ethers methylcellulose

Materials and composition. An ordinary Portland cement (CEM I 52.5 N) and CEN-Standard sand DIN EN 196-1 are used. Different types of polymers are added to the fresh mixtures a pol)rvinyl alcohol-acetate (PVAA, Celvol 805 of Celanese Chemicals), which is a 87-89% hydrolyzed pol5rvinyl acetate, and two cellulose ethers, methylcellulose (MC, Methocel A15-LV of... 

As with all cellulose ethers, methylcellulose increases the residence time of the preparation. In addition, methylcellulose possesses wound healing properties. Therefore the polymer is suitable as a tear substitute for dry eye especially for those with punctate lesions. A disadvantage are irritating insoluble cellulose particles present in methylcellulose. The amount of insoluble particles depends on the quality of the product... 

Cellulose is also commercially modified by acetylation to produce a material suitable for X-ray and cine film. Commercially cellulose ethers are also prepared, such as methylcellulose. This material is water-soluble and gives a highly viscous solution at very low concentrations. Hence it is widely used as a thickener in latex paints and adhesives, in cosmetics and for coating pharmaceutical tablets. 

Fluidized aqueous suspensions of 15% by weight or more of hydroxyethyl-cellulose, hydrophobically modified cellulose ether, hydrophobically modified hydroxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, and polyethylene oxide are prepared by adding the polymer to a concentrated sodium formate solution containing xanthan gum as a stabilizer [278]. The xanthan gum is dissolved in water before sodium formate is added. Then the polymer is added to the solution to form a fluid suspension of the polymers. The polymer suspension can serve as an aqueous concentrate for further use. 

Other thickeners used include derivatives of cellulose such as methylcellulose, hydroxypropylmethylcellulose, and cellulose gum natural gums such as tragacanth and xanthan (see Cellulose ethers Gums) the carboxyvinyl polymers and the poly(vinyl alcohol)s. The magnesium aluminum silicates, glycol stearates, and fatty alcohols in shampoos also can affect viscosity. 

The simplest representatives of cellulose ethers are the corresponding alkyl derivatives. The most common representatives manufactured industrially are methyl- and ethylcellulose. Methylcellulose is soluble in cold water when the DS is 1.4 to 2.0, whereas nearly completely substituted products (DS 2.4-2.8) are insoluble in water but soluble in organic solvents. 

Methylcellulose solutions generally form gels at higher temperatures. The gelation temperature is increased when hydroxyethyl or hydroxypropyl groups are introduced into the methylcellulose (cf. Section 9.6.2). Hy-droxyethylmethylcellulose and hydroxypropylmethylcellulose are prepared industrially by the reaction of alkali cellulose first with ethylene oxide or propylene oxide and then with methyl chloride. Similarly, hydroxyethyl-ethylcellulose is prepared by consecutive ethylene oxide and ethyl chloride treatments. Cellulose ethers with both methyl and ethyl groups have also been manufactured. 

In general, these groups of cellulose ethers have been used for their innate adhesive properties and to provide thickening to adhesive formulations. They are used for plywood adhesives, industrial adhesives, wallpaper paste, library paste, and latex adhesives. For example, methylcellulose is used in some adhesives as an additive to control viscosity, especially in the heat-cure phenol-formaldehyde glues and other hot-pressing adhesives. Hydroxyethylcellulose is used as an ingredient in polyvinyl acetate emulsions, where it acts as a thickener and protective colloid. 

Substituted Cellulose Ethers. Since their introduction for ophthalmic use, MC and other substituted cellulose ethers such as hydroxyethylcellulose, hydroxypropylcel-lulose, hydroxypropyl methylcellulose (HPMC), and carboxymethylcellulose (CMC) have been used in artificial tear formulations.These colloids dissolve in water to produce colorless solutions of varying viscosity. They have the proper optical clarity, a refractive index similar to the cornea, and are nearly inert chemically. Their relative lack of toxicity, their viscous properties, and their beneficial effects on tear film stability have made cellulose ethers useful components of artificial tear preparations. Historically, the most frequently used representative of this group was MC. 

Methylcellulose is a cellulose ether in which methyl groups have been substituted for hydroxyl groups on the 2-glucopyranose residues. It is soluble in cold water at low methoxy contents increased substitution increases the solubility in hydroalcoholic and alcoholic solutions.f ... 

Wirick MG. Study of the enzymic degradation of CMC and other cellulose ethers. / Polym Sci 1968 6(Part A-1) 1965-1974. Anonymous. Final report on the safety assessment of hydroxy-ethylcellulose, hydroxypropylcellulose, methylcellulose, hydroxypropyl methylcellulose and cellulose gum. / Am Coll Toxicol 1986 5(3) 1-60. 

Note that some cellulose ether products possess hydroxy-propyl substitutions in addition to methyl substitutions but are designated with the same trade name in a product line, differing only by a unique identifier code. These products should not be confused with the products that contain only methyl substitutions. A specification for methylcellulose is contained in the Food Chemicals Codex (FCC). 

Keywords Hydrophilic matrix Monohthic Drug delivery Extended release Formulation Cellulose ethers Hypromellose (hydroxypropyl methylcellulose,... 

Hydrophilic matrices are the most commonly used oral extended-release systems because of their abihty to provide desired release profiles for a wide range of drugs, robust formulation, cost-effective manufacture, and broad regulatory acceptance of the polymers. Table 11.2 shows a fist of hydrophific polymers commonly used for fabrication of matrices [17, 18]. Hydrophobic materials are also used either alone (hydrophobic matrix systems) or in conjugation with hydrophilic matrix systems (hydrophilic-hydrophobic matrix systems) and are also fisted in Table 11.2. Cellulose ethers, in particular hypromeUose (hydroxypropyl methylcellulose, HPMC), have been the polymers of choice for the formulation of hydrophilic matrix systems. 

Cellulosics. Cellulosic adhesives are obtained by modification of cellulose [9004-54-6] (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 [628-65-7], 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 [9004-55-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylcellulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylcellulose [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). 

Y. Tezuka, K. hnai, M. Oshima, and T. Chiba, Determination of substituent distribution in cellulose ethers by means of a carbon-13 NMR study on their acetylated derivatives. 1. Methylcellulose, Macromolecules, 20 (1987) 2413-2418. 

Hydroxypropyl methylcellulose acetate succinate (HPMCAS), a cellulose ether ester derived from HPMC esterifled with acetate and succinate groups, is an enteric polymer soluble only in water of high pH or in polar organic solvents like acetone or tetrahydrofuran (THE). The enteric performance is due to the presence of carboxylic groups. At low pH, HPMCAS exists in its protonated... 

Methyl cellulose ether. See Methylcellulose Methylchloroform. See 1,1,1 -Trichloroethane... 

Methods for the SEC analysis of ethyl cellulose (21,57) hydroxyethyl cellulose (57,79) cellulose acetate butyrates (80) allylated methylcellulose, triallyl cellulose, and glycidyl cellulose (48) tetrahydropyranyl cellulose, tetrahydropyranyl hydroxyethyl cellulose, and tetrahydropyranyl methylcellulose (14) carboxymethylcellulose (11,91) and cellulose ethers (97) have been described in... 

Water-soluble substituted celluloses are another class of stabilizers used in the suspension polymerization, mainly in the manufacture of PVC. These stabilizers are soluble in both the vinyl chloride and the aqueous phase [20]. Ckjnsequently, the stabilizer can also affect the stabihty of the primary particles inside the polymerizing monomer droplets and, thus, the final porosity of the PVC particles. Hydroxypropyl methylcellulose (HPMC) is a cellulose ether, produced byreacting cellulose with propylene oxide and methyl chlorine in an alkaline medium. As a result, a fraction of the hydroxyl groups (hydrophilic groups) of the cellulose... 

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