Shellac

• BPShellac
• JPPurified Shellac
• JPWhite Shellac
• Ph. Eur.Shellac
• USP–NFShellac

Lac; gum lac; lacca; orange shellac; bleached shellac; white shellac; dewaxed shellac; confectioner's glaze; E904

Purified resinous secretion of the lac insect, made up mainly of polyesters of hydroxy fatty acids (chiefly aleuritic acid) and sesquiterpenic acids (such as shellolic acid) · [9000-59-3]

Polymer, mixture or material of variable composition — no single molecular formula applies.

Coating agent, film former

Typical concentrations: — · Dosage forms: Solid

Shellac is used as a film-forming coating material for tablets and capsules, mainly as a moisture-protective sealing coat applied before sugar coating, and as a glaze for tablets and confectionery. It was formerly widely used for enteric coating, but because it dissolves only at a relatively high intestinal pH and its solubility falls on ageing, it has largely been replaced by synthetic enteric polymers. It is applied as a solution in ethanol or as an aqueous ammoniacal solution; it is also used in food glazes, cosmetics (for example hair sprays and mascara) and industrial lacquers.

A natural resin obtained from the secretion of the lac insect. It occurs as hard, brittle, translucent flakes or as a powder, ranging in colour from pale yellow (bleached shellac) to orange-brown (orange shellac), with a faint characteristic odour. Grades differ in colour, wax content (regular or dewaxed) and degree of bleaching.

Solubility

soluble in ethanol and in aqueous alkaline solutions such as ammonia and borax solutions; practically insoluble in water and acidic aqueous media

pH of dissolution

dissolves only at relatively high pH (about 7 and above), which limits its reliability as an enteric coat

Acid value

high, owing to free carboxylic acid groups; limits are set in the pharmacopoeias for each grade

Wax content

regular grades contain a few per cent of lac wax; dewaxed grades contain much less

Physical form

brittle flakes or powder; softens on warming

Shellac slowly polymerises on storage, particularly when warm, so that films become harder, less soluble and slower to dissolve or disintegrate; bleached shellac is less stable than orange shellac. Store in a well-closed container in a cool place.

Incompatible with strong oxidising agents. Because it is acidic, it may interact with basic drugs and alkaline excipients in a coating.

The lac insect (Kerria lacca) secretes the resin onto the twigs of host trees, mainly in India and Thailand. The encrusted twigs (stick lac) are scraped, crushed and washed to give seed lac, which is refined by melting and filtration or by solvent extraction; bleached shellac is produced by treating an alkaline solution with hypochlorite, and dewaxed grades are filtered to remove wax.

Shellac is used in oral pharmaceuticals and foods and is generally regarded as non-toxic and non-irritant at the levels used. Occasional allergic contact dermatitis has been reported, mainly from cosmetic use.

Observe normal precautions for the quantity handled. Ethanolic coating solutions are flammable and should be prepared and sprayed with adequate ventilation and away from sources of ignition.

Accepted as a food additive in Europe (E904). Included in the FDA Inactive Ingredient Database (oral capsules and tablets) and in non-parenteral medicines licensed in Europe.

Cellulose acetate phthalate; hypromellose phthalate; methacrylic acid copolymers; zein.

Because shellac films age and become less soluble, the disintegration and dissolution of shellac-coated products should be checked during stability studies. Aqueous ammoniacal shellac solutions avoid organic solvents and give films that are less affected by ageing.