Shellac properties

The resin is too brittle to give a tme meaning to mechanical properties. The thermal properties are interesting in that there appears to be a transition point at 46°C. Above this temperature, specific heat and temperature coefficient of expansion are much greater than below it. The specific heat of hardened shellac at 50°C is lower than that of unhardened material, this no doubt reflecting the disappearance, or at least the elevation, of the transition temperature. 

From the point of view of the plastics technologist the most important properties of shellac are the electrical ones. The material is an excellent room temperature, low-frequency insulator and particular mention should be made of the resistance to tracking. 

Some typical physical properties of shellac are given in Table 30.4. 

Chemical nature Isolation of casein from milk Production of casein plastics Properties of casein Applications Miscellaneous Protein Plastics Derivatives of Natural Rubber Gutta Percha and Related Materials Shellac... 

In 1940 most of the shellac imported into the United States came in through the docks of Brooklyn. It was, therefore, appropriate that W. H. Gardner had selected the Polytechnic as the site to establish a national testing laboratory a few years before. Research at the laboratory, called the Shellac Bureau, centered on evaluating the properties of this important natural resin. On assuming his position in Brooklyn, Mark was assigned to the Shellac Bureau. 

Carmine belongs to the anthraquinone class of compounds and several other chemically closely related compounds are also used as colorants.25 Kermes is a well known colorant in Europe. It is obtained from the insects, Kermes ilicis or Kermococcus vermilis, which grow on oak trees. It contains kermisic acid, the aglycone of carminic acid, and its isomer ceroalbolinic acid. Its properties are very similar to carmine. Lac is a red colorant obtained from the insect Laccifera lacca which is found on several families of trees in India and Malaysia. The lac insects are better known for their production of shellac. They contain a complex mixture of anthraquinones. Alkanet is a red pigment from the roots of Alkanna tinctoria Taush and Alchusa tinctoria Lom. All three have been cleared for food use in Europe but not in the US. 

Although there are many other kinds of insect waxes, only two are of economic importance namely, shellac wax and Chinese insect wax. Shellac wax is derived from the lac insect, a parasite that feeds on the sap of the lac tree indigenous to India. The commercial wax is not ordinarily the native Indian lac wax, but is a by-product recovered from the dewaxing of shellac spar varnishes. Lac wax melts at 72-80°C, whereas commercial shellac wax melts at 80-84.5°C. Its high melting point and dielectric properties favor its use in the electrical industry for insulation. Chinese insect wax is the product of the scale insect. 

Cockeram HS, Levine SA. The physical and chemical properties of shellac. ] Soc Cosmet Chem 1961 12 316-323. 

Limmatrapirat S, Limmatrapirat C, Luangtana-Anan M, et al. Modification of physicochemical and mechanical properties of shellac by partial hydrolysis. Int J Pharm 2004 278(1) 41-49. 

It can be used together with shellac, which is a natural product and therefore subject to variations in quality, to obtain films with more consistent properties. 

Stability of shellac to UV radiation is the most important optical property. The principal application of shellac was in gramophraie records. The resin acts as a binder for about three times its weight of mineral filler. Today, the most important application of shellac is in surface coatings. It is also used in some French polish as adhesives and cements including valve capping and optical cements. Shellac is also used in the manufacture of sealing wax. 

The development of Bakelite by Leo H. Baekeland was actually an outgrowth of his search for a synthetic substitute for shellac. Such a material, he believed, might offer properties superior to those of natural shellac. 

The term plastics first included only natural polymers—usually animal proteins (horn and tortoise shell), tree resins, or insect secretions called shellac—that were subsequendy mixed with fillers such as wood flour to yield substances having better molding properties. (A polymer, from the Greek word poly, meaning many, and mer meaning unit, is a molecule with an extremely high molecular weight.)... 

Solvent-Soluble Natural Polymers. The exudate of the lac insect is dissolved in alcohol to yield shellac. This solution has adhesive properties and should be reversible by treatment with the appropriate alcohol or similar solvent, although it may present problems in other performance areas (8). Solvent-soluble plant gums, especially coniferous resins (e.g., from firs or pines) can be dissolved in organic solvents and used as adhesives. Solvent solutions of some plant waxes may also have limited utility in gluing. All such glues should be reversible by treatment with solvents similar to those they were dissolved in when applied. 

The author has found the carbohydrate binders (e g. starch, dextrin) superior to phenol formaldehyde resins, maleic and phthalate type resins, polyester, glyptal resins, shellac, vegetable rosins, urea formaldehyde resin and melamine resin in all experiments to date. Dextrins and starches combine good binding properties and low cost with simple handling requirements. 

Cyclohexyl acetate [622-45-7] is very slightly miscible with water, but completely miscible with common organic solvents. Its solvency properties are comparable to those of amyl acetate. Cyclohexyl acetate dissolves oils, fats, resins, waxes, cellulose nitrate, cellulose tripropionate and acetobutyrate, alkyd resins, unsaturated and saturated polyester resins, phenolic resins and aminoplasts, poIy(vinyI chloride), vinyl chloride copolymers, poly(vinyl acetate), poly(vinyl ethers), epoxy resins, and acrylic resins, basic dyes, blown oils, crude rubber, metallic soaps, shellac, and bitumen. 

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