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|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
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Methyl cellulose (or methylcellulose) 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 an allergen.
Methyl cellulose 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. In the substitution reaction that follows, the hydroxyl residues (-OH functional groups) are replaced by methoxide (-OCH3 groups).
Different kinds of methyl cellulose can be prepared depending on the number of hydroxyl groups 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 methyl cellulose 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 methyl cellulose preparations can also differ in the average length of their polymer backbones.
Methyl cellulose has a lower critical solution temperature (LCST) between 40 °C and 50 °C. At temperatures below the LCST, it is readily soluble in water; above the LCST, it is not soluble, which has a paradoxical effect that heating a saturated solution of methyl cellulose will turn it solid, because methyl cellulose will precipitate out. The temperature at which this occurs depends on DS-value, with higher DS-values giving lower solubility and lower precipitation temperatures because the polar hydroxyl groups are masked.
Preparing a solution of methyl cellulose with cold water is difficult however: as the powder comes into contact with water, a gel layer forms around it, dramatically slowing the diffusion of water into the powder, hence the inside remains dry. A better way is to first mix the powder with hot water, so that the methyl cellulose particles are well dispersed (and so have a much higher effective surface area) in the water, and cool down this dispersion while stirring, leading to the much more rapid dissolution of those particles.
Methyl cellulose has an extremely wide range of uses, of which several are described below.
Methyl cellulose is very occasionally 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 croquette. Methyl cellulose is also an important emulsifier, preventing the separation of two mixed liquids.
The E number of methyl cellulose as food additive is E464 it is also known as hypromellose when used in food.
Methyl cellulose (AKA Methocel produced by Dow Chemical or Mecellose produced by Samsung Fine Chemicals) is also used as paint rheological modifier to prevent paint sagging problem.
When eaten, methyl cellulose 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.
The lubricating property of methyl cellulose is of particular benefit in the treatment of dry eyes (Keratoconjunctivitis Sicca). Dry eyes are common in the elderly and is often associated with rheumatoid arthritis. The lacrimal gland and the accessory conjunctival glands produce fewer tears. Methyl cellulose may be used as a tear substitute.
Methyl cellulose is used in the manufacture of capsules in nutritional supplements, its edible and nontoxic properties provide a vegetarian alternative to the use of gelatin.
Methyl cellulose finds a major application as a performance additive in construction materials. It is added to mortar dry mixes to improve the mortar's properties such as workability, open and adjustment time, water retention, viscosity, adhesion to surfaces etc. Construction grade methyl cellulose is not to be identified with food and pharmaceutical grade methyl cellulose and hydroxypropyl methyl cellulose, since it may be cross-linked with glyoxal for easy dispersion in water.
The construction materials can be cement-based or gypsum-based. Notable examples of dry mixture mortars which utilize methyl cellulose include: tile adhesives, EIFS, insulating plasters, hand-trowed and machine sprayed plaster, stucco, self-leveling flooring, extruded cement panels, skim coats, joint & crack fillers, and tile grouts. Typical usage is about 0.2% – 0.5% of total dry powder weight for dry mixture.
Derivatives of methyl cellulose, which improve upon the performance characteristics, include hydroxypropyl methyl cellulose (HPMC) and hydroxyethyl methyl cellulose (HEMC). These derivatives typically improve the characteristics such as water retention, vertical surface slip-resistance, open time, etc.
Methyl cellulose can be employed as a mild glue which can be washed away with water. This may be used in the fixation of delicate pieces of art as well as in book conservation to loosen and clean off old glue from spines and bookboards.
Methyl cellulose is used as sizing in the production of papers and textiles as it protects the fibers from absorbing water or oil.
Methyl cellulose is also used in cell culture to study viral replication. It is dissolved in the same nutrient containing medium in which cells are normally grown. A single layer of cells are grown on a flat surface, then infected with a virus for a short time. The strength of the viral sample used will determine how many cells get infected during this time. The thick methyl cellulose medium is then added on top of the cells in place of normal liquid medium. As the viruses replicate in the infected cells, they are able to spread between cells whose membrances touch each other, but are trapped when they enter the methyl cellulose. Only cells closely neighboring an infected cell will become infected and die. This leaves small regions of dead cells called plaques in a larger background of living uninfected cells. The number of plaques formed is determined by the strength of the original sample.
Aqueous methyl cellulose solutions have been used to slow bacterial cell motility for closer inspection. Changing the amount of methyl cellulose in solution allows one to adjust the solution's viscosity.
Methyl cellulose is used in the most common approaches to quantify multiple or single lineage-committed hematopoietic progenitors, called colony-forming cells (CFCs) or colony-forming units (CFUs), in combination with culture supplements that promote their proliferation and differentiation, and allow the clonal progeny of a single progenitor cell to stay together and thus form a colony of more mature cells.
The slimy, gooey appearance of an appropriate preparation of methyl cellulose with water, in addition to its nontoxic, nonallergenic, and edible properties, makes it popular for use in special effects for motion pictures and television wherever vile slimes must be simulated. In the film Ghostbusters, for example, the gooey substance the supernatural entities used to “slime” the Ghostbusters was mostly a thick water solution of methyl cellulose. The Aliens ooze and drip a great deal of methyl cellulose—especially the queen.
Methyl cellulose has been used to safely simulate molten materials, as well. In several of the Terminator films, it was back-lit with colored gels and films to reproduce the heated glow of iron in the large pouring ladles used to transport the metal from the smelting ovens to the various molds and forms. Methyl cellulose was also a stand-in for the lava flows on the volcanic surface of Mustafar, in Star Wars Episode III :Revenge of the Sith.
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