Methylcellulose

Methylcellulose (or methyl cellulose) is a chemical compound derived from cellulose. It is a hydrophilic white powder in pure form and dissolves in cold (but not in hot) water, forming a clear viscous solution or gel. It is sold under a variety of trade names and is used as a thickener and emulsifier in various food and cosmetic products, and also as a treatment of constipation. Like cellulose, it is not digestible, not toxic, and not allergenic.

Chemistry

Chemically, methylcellulose is a methyl ether of cellulose, arising from substituting the hydrogen atoms of some of cellulose's hydroxyl groups -OH with methyl groups -CH₃, forming -OCH₃ groups.

Different kinds of methylcellulose can be prepared depending on the number of hydroxyl groups so substituted. Cellulose is a polymer consisting of numerous linked glucose molecules, each of which exposes three hydroxyl groups. The Degree of Substitution (DS) of a given form of methylcellulose is defined as the average number of substituted hydroxyl groups per glucose. The theoretical maximum is thus a DS of 3.0, however more typical values are 1.3 - 2.6.

Different methylcellulose preparations can also differ in the average length of their polymer backbones.

Methylcellulose does not occur naturally and is synthetically produced by heating cellulose with caustic solution (e.g. a solution of sodium hydroxide) and treating it with methyl chloride.

The CAS number of methylcellulose is 9004-67-5.

Solubility and temperature

Methylcellulose dissolves in cold water. Higher DS-values result in lower solubility, because the polar hydroxyl groups are masked. The chemical is not soluble in hot water, which has the paradoxical effect that heating a saturated solution of methylcellulose will turn it solid, because methylcellulose will precipitate out. The temperature at which this occurs depends on DS-value, with higher DS-values giving lower precipitation temperatures.

Preparing a solution of methylcellulose with cold water is difficult however: as the powder comes into contact with water, a gluey layer forms around it, and the inside remains dry. A better way is to first mix the powder with hot water, so that the methylcellulose particles are well dispersed in the water, and cool down this dispersion while stirring, leading to the dissolution of those particles.

Uses

Thickener and emulsifier

Methylcellulose is often added to hair shampoos, tooth pastes and liquid soaps, to generate their characteristic thick consistency. This is also done for foods, for example ice cream or whipped cream. Methylcellulose is also an important emulsifier, preventing the separation of two mixed liquids.

The E number of methylcellulose as food additive is E461.

Treatment of constipation

When eaten, methylcellulose is not absorbed by the intestines but passes through the digestive tract undisturbed. It attracts large amounts of water into the colon, producing a softer and bulkier stool. It is used to treat constipation, diverticulosis, hemorrhoids and irritable bowel syndrome. It should be taken with sufficient amounts of fluid to prevent dehydration.

Because it absorbs water and potentially toxic materials and increases viscosity, it can also be used to treat diarrhea.

A well-known trade name of methylcellulose when used as a drug is Citrucel by GlaxoSmithKline, but generic versions are also widely available.

Lubricant

Methylcellulose is used as a variable viscosity personal lubricant; it is the main ingredient in K-Y Jelly.

Artificial Semen

For its non-toxic and anti-allergenic properties, methylcellulose is often used in the pornographic industry to simulate semen in large quantity, in order to shoot movies related to bukkake fetish. It is preferable to food-based fake semen because this last solution can often cause problems, especially when the ingredient used contains sugar. Sugar is said to cause yeast infection when it is injected in the vagina.

Artificial tears and saliva

Solutions containing methylcellulose or similar cellulose derivatives (see below) are used as substitute for tears or saliva if the natural production of these fluids is disturbed.

Paper and textile sizing

Methylcellulose is used as sizing in the production of papers and textiles. It protects the fibers from absorbing water or oil.

Glue and binder

Methylcellulose can be employed as a mild glue which can be washed away with water. This is used for example in the fixation of delicate pieces of art.

Methylcellulose is the main ingredient in many wallpaper pastes.

It is also used as a binder in pastel crayons.

Construction materials

Methylcellulose finds a major application in construction materials. It is added to mortar dry mixes to improve the mortar's properties such as water retention, viscosity, adhesion to surfaces etc.

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