Shellac

Chemical properties

solid

Chemical properties

Shellac is a natural resin that may be obtained in a variety of colors ranging from light yellow to dark red in the form of hard, brittle flakes with or without wax, depending on the refining process; see Sections 4 and 13. The different types of shellac include bleached shellac, bleached dewaxed shellac, dewaxed and decolorized shellac, dewaxed flake shellac, dewaxed orange shellac, dewaxed shellac, orange shellac, purified shellac, refined bleached shellac, regular bleached shellac, regular waxy shellac, wax-containing shellac, and white shellac. The flakes may be crushed or milled to a coarse or fine powder. Bleached shellac is supplied as a coarse offwhite powder. Shellac is tasteless and may have a faint odor. The typical odor of shellac is the result of a complex fragrance system.

The Uses of Shellac

Shellac is used in the preparation of cosmetic products such as mascara and acrylic nail products. It is also used in the formulation of aqueous-core capsules for riboflavin release.

The Uses of Shellac

Chiefly in lacquers and varnishes; also in manufacture of buttons, grinding wheels, sealing wax, cements, inks, phonograph records, paper; for stiffening hats; in electrical machines; coating confections and medicinal tablets; finishing leather.

Production Methods

Shellac or lac is cultivated and refined from lacca, a resinous secretion produced by the tiny insect Kerria lacca (Kerr) Lindinger (Coccideae), formerly Laccifer lacca (Kerr). The insects are parasitic on certain trees, mainly in India. In Thailand and South China, the resin is secreted by another species, Laccifer chinensis (Madihassan) on different trees. The insects pierce through the bark of the tree and transform the sap into a natural polyester resin, called stick lac,which is secreted through the surface of their body. The resin forms thick encrustations on the smaller branches and twigs, which are then scraped off the twigs and further processed to produce seed lac, as it is known at this stage. Seed lac is then refined to become shellac.
The chemical composition, properties and the color of shellac depend on the insect or insect strain, and thus the host tree, as well as the process used for refining. Three very different processes are used for refining the seed lac to shellac (bleaching, melting, and solvent extraction), resulting in products with different characteristics and properties.
Bleaching process Refined bleached or white shellac is obtained by dissolving seed lac in an aqueous alkaline solution, which is then filtered, dewaxed, and bleached with sodium hypochlorite to completely remove the color. However, changes in the molecular structure and the addition of chlorine substituents may lead to self-crosslinking and polymerization. Melting process After melting the seed lac, the highly viscous molten lac is pressed through a filter and drawn to a thin film. Once cooled, the film breaks into thin flakes. The shellac wax is not removed by this process and the color depends on the type of seed lac used.
Solvent extraction process Solvent extraction is a very gentle process for refining shellac. The seed lac is dissolved in ethanol, and wax and impurities are removed by filtration. Activated carbon is used to produce light-colored grades. After a further filtration step and the removal of ethanol, the resin is drawn to a thin film, which breaks into flakes after cooling. The properties of the final product depend on the type of seed lac used and are influenced by the processing parameters and the grade of activated carbon.
PhEur 6.2 and USP32–NF27 define four types of shellac depending on the refining method, and the JP XV mentions two types.
The use of the term ‘pharmaceutical grade’ as well as the quality of the shellac depends on the manufacturer. Seed lac is mainly produced in India, Thailand and China. Orange shellac, refined by the melting process, is manufactured by several companies in India, Thailand and South-East Asia. Bleached shellac is produced in the USA, Canada, Japan, India, Thailand and South China. Dewaxed orange shellac is refined by the solvent extraction process in Germany, Japan and India.

Definition

shellac: A hard resin produced as asecretion by a plant parasite, thesouth-east Asian lac insect Laciferlacca. It is used in sealing wax, varnish(French polish), and electrical insulators.

Hazard

(Alcohol solution) Flammable, dangerous fire risk.

Pharmaceutical Applications

Shellac is widely used as a moisture barrier coating for tablets and pellets due to its low water vapor and oxygen permeability. It has usually been applied in the form of alcoholic or aqueous solutions (pharmaceutical glazes). However, due to stability problems with alcoholic shellac solutions, it has had limited use in the pharmaceutical industry for modified-release or enteric coatings.
Shellac, particularly novel aqueous shellac solutions, is mainly used in food products and nutritional supplements. Recent research results indicate good application properties and chemical stability of shellac films from aqueous shellac solutions. Aqueous ammonium shellac solutions, based on dewaxed orange shellac, do not show the problems exhibited by alcoholic shellac solutions and are used as an enteric coating for pellets, tablets, soft and hard gelatine capsules, primarily in nutritional supplements.
Shellac is a primary ingredient of pharmaceutical printing inks for capsules and tablets, and can be applied as a 40% w/v alcoholic solution. It has also been used to apply one or two sealing coats to tablet cores to protect them from moisture before being film- or sugar-coated.
Other applications of shellac are the coating or encapsulation of powders or granules, e.g. in probiotics. Prior to the introduction of film coating, a combination of shellac, cetostearyl alcohol and stearic acid was used as an enteric coating. In cosmetics, shellac is used in hairsprays, mascara and lipstick formulations. Aqueous shellac solutions are also used for colonic drug delivery.

Safety

Shellac is used in oral pharmaceutical formulations, food products, and cosmetics. It is generally regarded as an essentially nonirritant and nontoxic material at the levels employed as an excipient.

storage

After long periods of storage, shellac becomes less readily soluble in alcohol, less fluid on heating, and darker in color.
Shellac should be stored in a well-closed container at temperatures below 15°C. Wax-containing grades should be mixed before use to ensure uniform distribution of the wax. Orange and dewaxed orange shellac have a shelf-life of 1 to 2 years. The shelf-life of bleached shellac is approximately 6 months.

Incompatibilities

Shellac is chemically reactive with aqueous alkalis, organic bases, alcohols, and agents that esterify carboxyl groups. Therefore, shellac should be used with caution in the presence of such compounds.

Regulatory Status

Accepted as a food additive in the USA, Europe, and Japan. Included in the FDA Inactive Ingredients Database (oral capsules and tablets). Included in nonparenteral medicines (oral tablets and capsules, often in printing ink formulations) licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.