Insoluble shellac

The seedlac may then be converted to shellac by either a heat process or by solvent processes. In the heat process the resin is heated to a melt which is then forced through a filter cloth which retains woody and insoluble matter. In the solvent process the lac is dissolved in a solvent, usually ethyl alcohol. The solution is filtered through a fine cloth and the solvent recovered by distillation. 

Variation in the details of the solvent processes will produce different grades of shellac. For example, when cold alcohol is used, lac wax which is associated with the resin remains insoluble and a shellac is obtained free from wax. Thermally processed shellacs were greatly favoured for gramophone records as they were free from residual solvent and also contained a small quantity of lac wax which proved a useful plasticiser. 

The lac resin is associated with two lac dyes, lac wax and an odiferous substance, and these materials may be present to a variable extent in shellac. The resin itself appears to be a polycondensate of aldehydic and hydroxy acids either as lactides or inter-esters. The resin constituents can be placed into two groups, an ether-soluble fraction (25% of the total) with an acid value of 100 and molecular weight of about 550, and an insoluble fraction with an acid value of 55 and a molecular weight of about 2000. 

Lac is derived from lac resin, the hardened secretion of the lac insect, the only known resin of animal origin. The lac insect, Kerria lacca, formerly known as Laccifer lacca, is a natural parasite of a variety of trees in large areas of southern Asia. Three different products are derived from lac resin lac dye, lac wax, and shellac. To obtain the lac resin, twigs encrusted with the secretion of the insects are cut down from the trees, then the incrustation is separated from the twigs, washed with water, and filtered. The wax and shellac, which are insoluble in water, remain as a solid residue of the filtration, while the soluble red dye (lac) is obtained as a powder when the water from the filtered solution is evaporated. The coloring matter in lac dye is an organic compound known as laccaic acid. 

Shellac is a complex mixture made of mono- and polyesters of hydroxy-aliphatic and sesquiterpene acids, which can be separated into two fractions the soft resin, soluble in ether, mainly consisting of monoesters [134], constituting about 30% of the total resin and the hard resin, ether insoluble, which has quite a complex polyester composition, and... 

Delayed release can also be applied for chronotherapeutic dosing, whereby the drug is administered in sync with the body s internal circadian rhythm. Verelan PM is an example of chromotherapeutic formulation that utilizes the combination of water-soluble polymers (povidone and gelatin) in conjunction with insoluble polymers (shellac). 

Constituents (See also tables IV and V) Besides shellac rosin, lac dye contains the water-soluble dyes laccaic acid A, B, C, D, and E and three water-insoluble dyes (62-68). 

Shellac, Bleached, occurs as an off white to tan, amorphous, granular resin. Shellac is obtained from lac, the resinous secretion of the insect Laccifer (Tachardia) lacca Kerr (Fam. Coc-cidae). Shellac, Bleached, is obtained by dissolving the lac in aqueous sodium carbonate, followed by bleaching with sodium hypochlorite, precipitation of the bleached lac with a dilute sulfuric acid solution, and drying. It is freely (though very slowly) soluble in alcohol, insoluble in water, and slightly soluble in acetone and in ether. Shellac, Bleached, is usually dissolved in a suitable solvent for application to food products. 

Shellac is insoluble in water, but soluble in alcohol, acetone and turpentine, it slowly absorbs paraffin and swells up. The solution in alcohol is popular as shellac varnish. It can be used in combination with chlorates. Shellac powder does not cake so much during storage over a long time but a loaded composition which contains shelTac and paraffin or oil degenerates or shrinks slowly, and it sometimes causes an unexpected rapid burning through the gap created between the composition and the container. 

Tablets may be formulated with coatings such as shellac, resin, or styrene-maleic acid copolymer. These coatings are insoluble in acid but dissolve readily at neutral or alkaline pH. Thus they are ideally suited to prevent drug release until the formulation has passed from the stomach into the small intestine. Preventing drug release in the stomach may protect drugs that are acid labile. It may also protect the patient from irritant substances like iron salts, diethylstilbo-estrol, and some anti-inflammatory agents. Release, and subsequent systemic availability of drugs from these formulations is likely to be highly sensitive to stomach emptying patterns.

Glaessner, Austria, 1931), ammoniacal bleached shellac (Wruble, 1933), stearic acid, carnauba wax, petrolatum, elm bark, and agar (Miller, 1935, and Worton, 1938), and abietic, oleic, and benzoic acids with methyl abietate (Eldred, 1937). Since 1940, research on enteric coatings has focused on the synthesis of resinous polymers, which are insoluble in acids, such as cellulose acetate phthalate (Hiatt, 1940) and a glycerol-stearic acid-phthalic anhydride ester (Volweiler and Moore, 1940). 

Shellac or lac is obtained by purification of the resinous secretion of the insect Laccifero (Tachardia) lacca Kerr (Homoptera, Coccidae). The insect lives on the sap of the stems of various trees secretions are found most abundantly on the smaller branches and twigs, which are broken off and constitute sticklac. After scraping of the twigs and soaking in water, the water-soluble components are removed by treatment with dilute alkali. The resulting water-insoluble material is called seed lac. 

Derivation A natural resin secreted by the insect Laccifer lacca (Coccus lacca) and deposited on the twigs of trees in India. After collection, washing, and purification by melting and filtering, it is formed into thin sheets, that are later fragmented into flakes of orange shellac. This may be dewaxed and bleached to a transparent product. Soluble in alcohol insoluble in water. 

The presence of free hydroxy and carboxyl groups in lac resin makes it very reactive, in particular to etherification involving either type of group. Of particular interest is the inter-etherification that occurs at elevated temperatures (>70°C) and leads to an insoluble polymerized product. Whereas ordinary shellac melts at about 75°C, prolonged heating at 125-150°C will cause the material to change from a viscous liquid, via a rubbery state, to a hard solid. One of the indications that the reaction involved is etherification is that water is evolved. The reaction is reversible and if heated in the presence of water the polymerized resin will revert to the soluble form. Thus shellac cannot be polymerized under pressure in a mold since it is not possible for the water to escape. Polymerization may be retarded by basic materials, some of which are useful when the shellac is subjected to repeated heating operations. 

Aromatic hydrocarbons are used as diluents in solutions of cellulose nitrate, cellulose esters, and ethers with true solvents such as esters and ketones. Rubber, polyisobutene, and molten polyethylene also dissolve in them. Poly(vinyl chloride), solid polyethylene, polyamides, and shellac are, however, insoluble or only swell. 

Cyclohexanone [108-94-1] (Hexanone) is insoluble in water, miscible with organic solvents. It is a high boiler with very good solvency for cellulose nitrate, cellulose ethers and esters, colophony, shellac, alkyd resins, natural and synthetic resins, chlorinated rubber, rubber, vinyl polymers and copolymers, polystyrene, ketone and ketone-formaldehyde resins, fats, oils, waxes, blown oils, and bitumen. [14.268],... 

Isobutyl acetate [110-19-0] is a colorless, neutral liquid with a pleasant, fruity odor. It is miscible with organic solvents, but immiscible with water. Isobutyl acetate has a high solvency for cellulose nitrate, colophony, damar resin, ketone and ketone-formaldehyde resins, maleate resins, urea and melamine resins, and phenolic and alkyd resins. Polymers such as polystyrene, poly(vinyl ethers), poly(vinyl acetate), polyacrylates, chlorinated rubber and vinyl chloride copolymers, as well as fats, greases, and oils are readily dissolved. Postchlorinated poly(vinyl chloride) is less soluble. Polyisobutene, cellulose ethers, polymethacrylates, poly(vinyl butyrals), natural rubber, and manila copal are swollen. Shellac, cellulose acetate, cellulose acetobutyrate, poly(vinyl chloride), and poly(vinyl formal) are insoluble. 

Nitropropane [ 79-46-9] is a colorless, nonhygroscopic liquid with a mild odor. It dissolves cellulose nitrate, cellulose ethers, alkyd resins, chlorinated rubber, poly(vinyl acetate), vinyl chloride copolymers. Poly(vinyl chloride), colophony, polyacrylonitrile, waxes, rubber, and shellac are insoluble. It is used as a cosolvent in paints to improve pigment wetting, flow properties, and electrostatic processing it also reduces the paint drying time. 2-Nitropropane is classified as carcinogenic. 

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