Preparation of Methylcellulose

While reactions of low-molecular-weight compounds can sometimes be carried out in the gas phase, this technique is not applicable to macromolecular substances since they are not volatile. However, it is indeed possible to let low-molecular reagents act upon solid or dissolved polymers in gaseous form. This is done, for example, in the commercial preparation of methylcellulose by conversion of alkali cellulose with gaseous methyl chloride. 

The preparation of methylcellulose from cellulose may be represented as follows ... 

At X-ray fluorescence analysis (XRF) of samples of the limited weight is perspective to prepare for specimens as polymeric films on a basis of methylcellulose [1]. By the example of definition of heavy metals in film specimens have studied dependence of intensity of X-ray radiation from their chemical compound, surface density (P ) and the size (D) particles of the powder introduced to polymer. Have theoretically established, that the basic source of an error of results XRF is dependence of intensity (F) analytical lines of determined elements from a specimen. Thus the best account of variations P provides a method of the internal standard at change P from 2 up to 6 mg/sm the coefficient of variation describing an error of definition Mo, Zn, Cu, Co, Fe and Mn in a method of the direct external standard, reaches 40 %, and at use of a method of the internal standard (an element of comparison Ga) value does not exceed 2,2 %. Experiment within the limits of a casual error (V changes from 2,9 up to 7,4 %) has confirmed theoretical conclusions. 

The physical form of a material destined for oral administration often presents unique challenges. Liquids can be administered as supplied or diluted with an appropriate vehicle, and powders or particulates can often be dissolved or suspended in an appropriate vehicle. However, selection of an appropriate vehicle is often difficult. Water and oil (such as the vegetable oils) are used most commonly. Materials that are not readily soluble in either water or oil can frequently be suspended in a 1% aqueous mixture of methylcellulose. Occasionally, a more concentrated methylcellulose suspension (up to 5%) may be necessary. Materials for which appropriate solutions or suspensions cannot be prepared using one of these three vehicles often present major difficulties. 

The natural polymers frequently used for the preparation of pharmaceutical gels include tragacanth, pectin, carrageenan, agar, and alginic acid, as well as semisynthetic polysaccharides such as methylcellulose, hydroxymethylcellulose, and carb-oxymethylcellulose. 

The methyl ether of cellulose has a methoxyl content which varies between 6 and 33 %. Methylcellulose can be prepared by the action of methyl chloride or methyl sulfate on cellulose that has been previously treated with alkali. Purification is accomplished by washing the reaction product with hot water. The degree of methylation can be controlled to yield products with varying viscosities. Seven viscosity types of methylcellulose are currently produced with centipoise values ranging from 10 to 4000. Methylated cellulose of low methoxy content is soluble... 

Preparation of Electron-micrographs. The polystyrene-rubber polyblend sample was etched by solvent according to the technique developed by Traylor. A double replica technique was used to prepare the sample. The first replica was methylcellulose, the second platinum and carbon, 800 A. thick. 

Determination of the Viscosity of Methylcellulose Prepare a 2% solution of methylcellulose or other cellulose derivative, by weight, as directed in the monograph. Place the solution in the proper viscometer and determine the time, f, required for the solution to flow from the upper mark to the lower mark in orifice tube B. Separately determine the specific gravity, d, at 20720°. Viscosity, V = Kdt. 

Suspensions of polypyrrole were prepared by the FeCls oxidation of pyrrole in an aqueous solution of methylcellulose (49). The product was dried and yielded films with conductivities of 0.2 S/cm. Scanning electron microscopy revealed globular polypyrrole embedded in the methylcellulose matrix. After several months, these suspensions remained stable with no detectable precipitation. Similarly, the electropolymerization of 3-methyl-thiophene in solutions of poly(methyl methacrylate) and poly(vinyl chloride) was reported (50, 51). 

In tablet formulations, low- or medium-viscosity grades of methylcellulose are used as binding agents, the methylcellulose being added either as a dry powder or in solution.High-viscosity grades of methylcellulose may also be incorporated in tablet formulations as a disintegrant. " Methylcellulose may be added to a tablet formulation to produce sustained-release preparations. ... 

In ophthalmic preparations, a 0.5-1.0% w/v solution of a highly substituted, high-viscosity grade of methylcellulose has been used as a vehicle for eye drops. However, hypromellose-based formulations are now preferred for ophthalmic preparations. 

Esophageal obstruction may occur if methylcellulose is swallowed with an insufficient quantity of liquid. Consumption of large quantities of methylcellulose may additionally interfere with the normal absorption of some minerals. However, this and the other adverse effects discussed above relate mainly to the use of methylcellulose as a bulk laxative and are not significant factors when methylcellulose is used as an excipient in oral preparations. 

Sheskey PJ, Cabelka TD, Robb RT, Boyce BM. Use of roller compaction in the preparation of controlled-release hydrophilic matrix tablets containing Methylcellulose and Hydroxypropyl Methylcellulose polymers. Pharm Technol 1994 18 132-50. 

Other workers have used additives to enable the preparation of effectively water-soluble conductive polymer colloids. As early as 1986, Bjorklund and Liedberg102 observed that when pyrrole was oxidized by FeCl3 in the presence of aqueous methylcellulose (MWt 100,000), a PPy/methylcellulose sol was formed that could be characterized by scanning electron microscopy. Thin films could be obtained from the sol, exhibiting a conductivity of ca. 0.2 S cm-1. Subsequently, a range of neutral, water-soluble steric stabilizers such as poly(vinylalcohol), poly(ethyleneoxide) (PEO), or poly(vinylpyridine) have been successfully... 

Methods of Preparation of Hydrophobically Modified WSPs (HMWSPs). Incorporation of Hydrophobes into WSPs. Water-soluble cellulose derivatives ((hydroxyethyl)cellulose, (hydroxypropyl)cellulose, methylcellulose, etc.) or synthetic polymers containing hydroxyl groups (e.g., poly(vinyl alcohol)) can be reacted with a long-chain alkyl halide (2), acyl halide (2), acid anhydride (6), isocyanate (2), or epoxide (2, 3) under appropriate conditions to form an HMWSP. These reactions are shown in Scheme I. These postmodifications can be done in solution or in hetero-... 

Hydrox ropyl methylcellulose phthalate binder, in preparation of granules... 

Embriano PJ. Postoperative pressure after phacoemulsification sodium hyaluronate vs. sodium chon-droitin sulfate - sodium hyaluronate. Ann Ophthalmol 1989 21 85-90 Fechner PU. Methylcellulose in lens implantation. J Am Intraocul Soc 1977 3 180-181 Fechner PU, Fechner MU. Methylcellulose and lens implantation. Br J Ophthalmol 1983 67 259-263 Fechner PU. Preparation of 2% hydroxypropyl methylcellulose for viscous surgery. J Am Intraocul Implant Soc 1985 11 606-607... 

Ophthalmic delivery For administration of water-insoluble drugs into the eye, colloidal systems are used. Surface active polymers, such as polyvinyl alcohol, poloxamer, and methylcellulose are often added as particle stabilizers and viscosity enhancers. Particle size in such colloidal systems should not exceed 5-10 pm in diameter. Emulsions, liposomes, and micro- and nanoparticles, all stabilized by surfactants, are used in topical ophthalmic drug delivery [56]. For instance, an ophthalmic preparation of cyclosporin A, Restasis , is an emulsion stabilized by polysorbate 80 and polymer carbomer 1342. 

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