Shellacs

JP Purified shellac, White shellac PhEur Lacca USPNF Shellac 

Bleached shellac CertiSeal dewaxed orange shellac E904 lac Mantrolac R-49-, orange shellac refined bleached shellac regular bleached shellac Swanlac. 

Shellac is a naturally occurring material consisting of a complex mixture of constituents that may be obtained in various refined or modified forms see Section 13. 

The PhEur 2005 defines four types of shellac depending on the nature of the treatment of the crude shellac (seed lac) wax-containing shellac bleached shellac dewaxed shellac and bleached dewaxed shellac. The USPNF 23 similarly defines four types of shellac orange shellac dewaxed orange shellac regular bleached (white) shellac and refined bleached shellac. The JP 2001 defines two types purified shellac and white shellac (bleached). 

Shellac also contains about 5-6% wax along with gluten, other impurities, and a small amount of pigment. The exact composition of shellac may vary depending upon the country of origin and method of manufacture.  

The constituency of traditional adhesives is limited to the single binders listed above contemporary adhesives are likely to combine one or more binders with some combination of the following additives  

In the context of adhesives, cement is a natural rubber- or silicone-based elastomeric. Rubber cements contain a suitable solvent such as naphtha or aromatic hydrocarbons. Pyroxylin cements are adhesives based on solutions of nitrocellulose in alcohol, ether, or another solvent. Hydraulic cements used in construction, such as portland or pozzolana cement, are nonhazardous mixtures composed of some combination of lime, alumina, and silica which sets into a hard product (concrete) when water is added (the term portland 

Certain binders are flammable and other additives may be hazardous, but it is the common use of flammable solvents as thinners or diluents that presents the primary hazard in transportation. 

Flammable Flammable liquid, see Flammable Liquids and Class 3, p.96 

Liquid, see Terminology, Liquid, p.241 Pyroxylin, see Nitrocellulose Products, p.l61 

Peak Notation Assignment of Main Peaks Molecular Weight Retention Index Relative Intensity 

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V—Vitrified S—Silicate R—Rubber RF—Rubber reinforced B—Resinoid BF—Resinoid reinforced E—Shellac O—Oxychloride... 

Bond Type. Most bonded abrasive products are produced with either a vitreous (glass or ceramic) or a resinoid (usually phenoHc resin) bond. Bonding agents such as mbber, shellac, sodium siHcate, magnesium oxychloride, or metal are used for special appHcations. 

Shellac. Shellac wheels are limited to a few appHcations where extreme coolness of cut is required and wheel life is immaterial. They are produced by mixing shellac [9000-59-3] and abrasive grain in a heated mixer, then rolling or shaping to the desired configuration. 

Articles of circular cross section may be made in iron paste molds. To keep the inner surface of the paste mold moist, it is coated with shellac or varnish and a mixture of charcoal and linseed oil is baked on. Hot iron molds ate used for ware of any shape, particularly for screw threading, multiple decoration, or raised lettering. 

Many older finishes can be removed with single solvents or blends of petroleum solvents and oxygenates. Varnish can be removed with mineral spirits, shellac can be stripped with alcohols, and lacquers can be removed with blends of acetates and alcohols (lacquer thinners). The removal mechanism is one of dissolving the coating, then washing the surface or wiping away the finish. This method is often used to reamalgamate or liquefy old finishes on antique items of furniture. 

As solvents, the amyl alcohols are intermediate between hydrocarbon and the more water-miscible lower alcohol and ketone solvents. Eor example, they are good solvents and diluents for lacquers, hydrolytic fluids, dispersing agents in textile printing inks, industrial cleaning compounds, natural oils such as linseed and castor, synthetic resins such as alkyds, phenoHcs, urea —formaldehyde maleics, and adipates, and naturally occurring gums, such as shellac, paraffin waxes, rosin, and manila. In solvent mixtures they dissolve cellulose acetate, nitrocellulose, and ceUulosic ethers. 

Natural resins are generally described as solid or semisolid amorphous, fusible, organic substances that are formed in plant secretions. They are usually transparent or translucent yeUow-to-brown colored, and are soluble in organic solvents but not in water. The principal uses for natural resins are in varnishes, printing inks, adhesives, paper size, and polymer compositions. The term natural resins includes tree and plant exudates, fossil resins, mined resins, and shellac. They often have been altered from their original state during isolation and processing. For some appHcations, the resins have been chemically modified to increase their industrial utiUty. 

Unlike other natural resins, shellac [9000-59-3] is derived from the hardened secretion of the lac insect (species l ccifer (Tachardia) lacca Kerr (family Coccidae), also known as Kerns lacca (Kerr)). Shellac is a refined grade of the cmde lac secretion and is the most widely known lac product. Therefore, shellac has been accepted as the common generic term. Over 50% of the world s supply is produced in the Indian provinces of Bihar and Orissa, with the remainder originating in adjacent areas of southeast Asia such as Sri Lanka, China, Thailand, and Myanmar. 

Lac became an important component of decorative and protective finishes by the nineteenth century. It is ironic that the success of shellac led to the synthetic resin industry. Baekeland developed phenoHc resins while trying to find a substitute for shellac. 

Raw lac is first treated to remove water-soluble carbohydrates and the dye that gives lac its red color. Also removed are woody materials, insect bodies, and trash. It is further refined by either hot filtration or a solvent process. In the heat process, the dried, refined lac is filtered molten through cloth or wine screens to produce the standard grades of orange shellac. In the solvent process, lac is dissolved and refluxed in alcohol solvents, filtered to remove dirt and impurities, and concentrated by evaporation. The lac can be further decolori2ed in this process to produce very pale grades. Bleached shellac is prepared by treatment with dilute sodium hypochlorite and coalesced into slabs. 

Composition. Shellac is primarily a mixture of aUphatic polyhydroxy acids in the form of lactones and esters. It has an acid number of ca 70, a saponification number of ca 230, a hydroxyl number of ca 260, and an iodine number of ca 15. Its average molecular weight is ca 1000. Shellac is a complex mixture, but some of its constituents have been identified. Aleuritic acid, an optically inactive 9,10,16-trihydroxypalmitic acid, has been isolated by saponification. Related carboxyflc acids such as 16-hydroxy- and 9,10-dihydroxypalmitic acids, also have been identified after saponification. These acids may not be primary products of hydrolysis, but may have been produced by the treatment. Studies show that shellac contains carboxyflc acids with long methylene chains, unsaturated esters, probably an aliphatic aldehyde, a saturated aliphatic ester, a primary alcohol, and isolated or unconjugated double bonds. 

Uses. Synthetic resins have taken over a large share of the market for shellac. Unpigmented shellac is used on floors, woodwork, and paneling. 

White pigmented shellac is used as a primer—sealer for iaterior appHcations. Shellac is used as a protective coating for pharmaceuticals to maintain the potency of medication. Several coats of shellac gla2e protect medication from the effects of stomach acids so that the medication is not released before the tablet reaches the intestines. 

Candy is coated with shellac to seal in moisture and keep the product fresh. The coating provides a high gloss to the confection, which improves its appearance. Citms fmits and some apples are often coated with shellac. This improves the appearance, while allowing the fmit to breathe without spoilage. Shellac is used as a stiffener for felt hat bodies, primarily for recreational hats. It is also used to stiffen playing cards, providing "snap."... 

The poly(vinyl acetal) prepared from acetaldehyde was developed in the early 1940s by Shawinigan Chemicals, Ltd., of Canada and sold under the trade name Alvar. Early uses included injection-molded articles, coatings for paper and textiles, and replacement for shellac. Production peaked in the early 1950s and then decreased as a result of competition from less expensive resins such as poly(vinyl chloride) (see Vinyl polymers, poly(vinyl chloride)). 

Oxidized castor oils are excellent nonmigrating, nonvolatile plasticizers (qv) for ceUulosic resins, poly(vinyl butyral), polyamides, shellac, and natural and synthetic mbber (see Rubber, natural). The high viscosity products are also used as tackifiers in gasket compounds and adhesives (qv) because of good oil and solvent resistance. They also serve as excellent pigment grinding media and as a base for inks (qv), lubricating oils, and hydrauHc oils (62). 

Cyclohexanoae is miscible with methanol, ethanol, acetone, benzene, / -hexane, nitrobenzene, diethyl ether, naphtha, xylene, ethylene glycol, isoamyl acetate, diethylamine, and most organic solvents. This ketone dissolves cellulose nitrate, acetate, and ethers, vinyl resias, raw mbber, waxes, fats, shellac, basic dyes, oils, latex, bitumea, kaure, elemi, and many other organic compounds. 

One principal use of cyclohexanol has been in the manufacture of esters for use as plasticizers (qv), ie, cyclohexyl and dicyclohexyl phthalates. In the finishes industry, cyclohexanol is used as a solvent for lacquers, shellacs, and varnishes. Its low volatiUty helps to improve secondary flow and to prevent blushing. It also improves the miscibility of cellulose nitrate and resin solutions and helps maintain homogeneity during drying of lacquers. Reaction of cyclohexanol with ammonia produces cyclohexylamine [108-91-8], a corrosion inhibitor. Cyclohexanol is used as a stabilizer and homogenizer for soaps and synthetic detergent emulsions. It is used also by the textile industry as a dye solvent and kier-boiling assistant (see Dye carriers). 

Black shiny shellac on tinned iron sheet 70 0.821 Hard, glossy plate 74 0.945 ... 

Black matte shellac 170-295 0.91 Soft, gray, rough (reclaimed) 76 0.859 ... 

Coke, petroleum, calcined. 35-45 D28X Shellac, powdered or granulated 31 B26K5... 

It is advisable to saturate all corks with sodium silicate solution after fitting and boring them (p. 3, Note i). They are then covered with lead foil, wired in, and coated with shellac. 

This includes inorganic materials such as mica, glass fibre and asbestos etc., impregnated or glued together with varnishes or compositions comprising ordinary organic substances for heat resistance such as oil-modified synthetic resins, bitumen, shellac and Bakelite. 

In the manufacture of varnish, heat is necessary for formulation and purificahon. The same may be true of operations preparing paints, shellac, inks, and other protective or decorative coahngs. The compounds emitted to the atmosphere are gases, some with extremely low odor thresholds. Acrolein, with an odor threshold of about 4000 /xg/m, and reduced sulfur compounds, with odor thresholds of 2 are bofh possible emissions... 

Further east another natural resin, lac, had already been used for at least a thousand years before Pliny was bom. Lac is mentioned in early Vedic writings and also in the Kama Sutra of Vatsyayona. In 1596 John Huyglen von Linschoeten undertook a scientific mission to India at the instance of the King of Portugal. In his report he describes the process of covering objects with shellac, now known as Indian turnery and still practised ... 

Early records also indicate that cast mouldings were prepared from shellac by the ancient Indians. In Europe the use of sealing wax based on shellac can be traced back to the Middle Ages. The first patents for shellac mouldings were taken out in 1868. 

By 1900 the only plastics materials available were shellac, gutta percha, ebonite and celluloid (and the bitumens and amber if they are considered as plastics). Early experiments leading to other materials had, however, been carried out. The... 

There is rather less scope for the re-emergence of the animal-based plastics such as casein, shellac and the blood albumin products. 

When this is done it is seen that in all cases plastics materials, before compounding with additives, consist of a mass of very large molecules. In the case of a few naturally occurring materials, such as bitumen, shellac and amber, the compositions are heterogeneous and complex but in all other cases the plastics materials belong to a chemical family referred to as high polymers. 

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