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The lac insect belongs to the family of a scale insect and mealy bugs of the super family 'coccoidea'.

Large number of tiny red larvae of about 0.5 mm. long come out of each mother cell and settle on the tender portions of fresh twigs of certain trees called lac hosts. The larva is sufficiently mobile to crawl along the branches of trees to find fresh succulent twigs. When it has fixed its position and inserted its probocis into the trees it secretes a protective coating consisting of a dark red chitinous scale and a yellow to reddish resin called the lac resin. The insects mature under the protective covering of the resin which becomes hard. Wax glands near the vital pores - the oval region, the breathing pores and the anal pore keep them open by secreting wax filaments.

The larvae mould thrice inside the cell and becomes sexually mature male and female insects in about eight weeks. The female cell is roundish and the insect remains fixed to the twig. The male cell is somewhat longer with a round trap door through which the insect, sometimes winged, comes out, walks over the females, fertilising several of them and dies. Their direct contribution to resin production is insignificant.

The female insect increases in size to accommodate her large number of growing eggs. The secretion of the resin and wax now proceed at a faster rate and a continuous layer is formed by coalescence and coatings. in another 14 weeks, when the female insect is about to lay eggs, she begins to contract, allowing light into the cell which shows up as yellow spots. When hatched, the larve emerge to begin a new life cycle of about six months. Thus, the insect completes two life cycles in a year yielding two lac crops. On an average three hundred thousand insects produce one kg. of lac resin.

The insects thrive in certain species of trees under suitable climatic conditions. in India two strains of lac insect occur, namely, the Rangini and the Kusmi.'

CULTIVATION OF LAC India and Thailand are the main countries where lac is cultivated. Over 90% of Indian lac comes from the States of Bihar, Madhya Pradesh, West Bengal, Maharashtra and Orissa.

The principal lac hosts in India are Palas and Ber of the Rangini strains and the Kusum for Kusmi strains. In Thailand the rain-tree is the principal lac host. The cultivation of lac is fairly simple. The host trees are pruned in proper season and when the new shoots come out, two or three sticks of broodlac containing living insects are tied on to branches near them. The larvae swarm out, settle on the shoots and go on producing the resin. After the infection of the trees with brood lac, the crop needs little or no attention till the time of harvesting. The crop is cut, and after keeping a portion apart to serve as broodlac for the next crop, the rest is scraped off from the twigs and sold in the market as Sticklac. Freshly scraped sticklac contain plenty of moisture and is usually left in the shade to dry.

Sticklac is then sold by the cultivators in small quantities in village markets to the manufacturers or their agents and thus supplementing the income of some 2-3 million rural folk, mostly Adivasis.

Rangini strain products the main crop, Baisacky which comes to the market in April-May. The corresponding Katki crop which comes in October-November is mostly used as broodlac for the next Baisacky. The Kusmi strain also yields two crops - Aghani and Jethwi - the latter serving as broodlac for the fromer which is the major Kusmi crop.

The quality and consequently the value of sticklac depend upon a variety of factors, namely, the broodlac and the host tree, the climatic conditions and the season of harvesting - whether the crop is harvested before larval emergence or after and also how it has been dried and stored. Among the Rangini crops, Baisacky is better than Katki and is case of Kusmi, -Aghani is superior to Jethwi. Again Baisacky lac from Ber fetches a higher price than that grown on Palas. In India, the yield of sticklac averages 3/4 times the weight of broodlac used.

STICKLAC & SEEDLAC REFINING OF STICKLAC Sticklac is converted to commercial grades of Seedlac and Shellac. The yield of refined lac from sticklac varies between 40-60% depending of the host tree, area of cultivation and other factors. apart from lac resin, sticklac contains 6-7% of lac wax, 3-5% water moisture, colouring matter (lac dye), and impurities like insect debris, wood pieces, sand etc.

The refinement of sticklac into seedlac, the semiprocessed material, is mostly carried out in cottage scale or semi-mechanised factories in the lac-growing areas. Seedlac is then converted to shellac of various grades, either by hand-made process in the cottage industries or machine-made process in mechanised industries. CONVERSION INTO SEEDLAC Sticklac is first crushed and sieved to remove sand and dust and at the same time rubbing the lac against the sides of the Vat to break open the insect bodies and dissolving the colouring matter in water. The lighter impurities float on the surface and form a scum which can be easily removed. The coloured water containing lac dye is drained out. The washing is repeated until the dye and most of the impurities are removed.

The lac thus cleaned is spread on large, clean, open air floor to dry. After drying, it is winnowed and sieved to get the commercial variety to seedlac. The dusty lac which is eliminated by sieving is known as Molamma lac and falls under the category of Refuse lac. Molamma contains approximate 55-80% lac. PROPERTIES OF SHELLAC Shellac, the only known commercial resin of animal origin, is a hard, tough, amorphous and easily brittle resinous solid. It is practically odourless in the cold, but evolves a characteristic smell on heating or melting . Superior grades are light yellow in colour, while the inferior grades range from deep orange brown to almost dark red. The resin is associated with colouring matter, odoriferous principles and varying quantity of wax. Lac resin entirely free from these associates is unknown although commercially available dewaxed and decolourised lac is the closest approximation.

The lac resin is not a single compound, but consists of intimate mixture of several components. The manner in which these components are linked togetjer to build up the shellac components. The manner in which these components are linked together to build up the shellac complex has baffled intensive chemical research during the last few decades.

When slowly heated, it softens at 65-70oC and melts between 1.14 to 1.21. It has a molecular weight 1006, acid value 65-75 and saponification value 220-230. shellac is insoluable in water, glycerol, hydrocarbon solvents and esters, but dissolves readily in alcohol and organic acids. The most popular solvent of shellac is spirit.

Aqueous solution of inorganic alkalis readily dissolve shellac. Usually the milder alkalis - ammonia borax and sodium carbonate are employed to prepare aqueous solution.

Shellac can be split into two fraction by ether. The ether soluable portion which is about 30% called the soft resin is stickly and viscous. The ether insoluable portion called the hard resin or the pure resin has higher softening and melting points (84oC and 94oC) than Shellac.

When lac is heated between 120-150oC and maintained over a prolonged period, the resin gradually becomes more viscous and rubbery due to polymerisation, and becomes insoluble in the standard solvent.

STORAGE The shellac produced is normally allowed to cool off after stretching for a few hours and then transferred to a cool-shedded godown. It is best stored in air-conditioned ware-houses which maintains a temperature between 14-18oC.

Storage under such conditions maintains the quality of lac although its main function is to prevent shellac from blocking in the hot weather which is encountered for most of the year in India. The blockiness of shellac is quite a problem in many industries and as a result the use of air-conditioned storage in ships has increased very largely in order to ensure arrival of shellac at its destination in free and good condition

INDUSTRIAL USES OF SHELLAC Due to the versatility of the lac resin, it finds innumerable uses in different industries. From the standpoint of industrial uses of shellac, one or more of the following properties are of great importance:

(1) Shellac dissolves in a wide variety of alkaline or rapidly drying alcoholic solvents, but is resistant to a number of other solvents, particularly hydrocarbons.

(2) Its films show excellent adhesion to a wide variety of surfaces, posessing high gloss, hardness and strength.

(3) shellac is a powerful bonding material with low thermal conductivity and a small coefficient and expansion. Its thermal plasticity and capacity of absorbing large amounts of filters are noteworthy.

(4) Its electrical properties include high dielectric strength, low dielectric constant and characteristic freedom from tracking.

(5) It is resistant to the action of ultraviolet rays.

(6) Shellac is non-poisonous.

Scientific and technical developments in the field of synthetic resins have been responsible for lac being replaced in many of its traditional fields, but at the same time science has helped to elucidate the complex nature of lac resin and open up new potentialities.

The investigations of different groups of scientists have shown that it is a polyester type of resin formed from hydroxyl fatty sesquiterpene acids. the main fatty acid - aleuritic acid - and a mixture of sesquiterpene acids are present in approximately equal amounts constituting 70-75% of the total resin. An average lac resin molecule has five free hydroxyl and one carboxyl group accounting for its special properties.

Lac resin or its component acids can be modified with phenol and some accelerators mainly organic imides to give a new type of elastomerand plastomer which has shown immense possibility in leather finishes as pigment binder. It has also shown promising properties to be used as aqueous medium for decorative and protective coating for wood, plastic, metal etc. Its satisfactory adhesive and electrical properties make it suitable for its use in assembling mica for electrical insulation. As the material can be masticated and extruded directly on to wires, it may be used for cable insulation. On thermal polymerisation, the material is unaffected by common solvents.

The future of shellac however depends on its recognition as additive to synthetics. The compatibility of lac with epoxy and the resultant improvement in properties have been subjected to several patents. One such example is the fluidised bed method of coating with lac/epoxy mixtures containing as much as 75% lac. Lac has been successfully compounded with acrylates polyesters and isocynates. Grafting and copolymerisation of lac with ethylene oxylated lac with various synthetic monomers are being extensively investigated in different research laboratories. Some of the present important and popular use of shellac are: Wood Finishing Shellac is unrivalled for wood finishing and furniture polishing. The art of polishing with shellac consists of producing on a carefully prepared surface a very thin film of the resin from its solution in alcohol. Two or three coats, applied with a pad, result in a rich glossy and durable finish. Shellac may also be brushed or sprayed. Bleached shellac is used to produce a transparent finish to bring out the natural beauty of the light coloured wood. Large quantities of bleached shellac are used for floor polishes in the United States, specially for making so-called No-Rub polishes that can be applied by brushing, spraying or even by wiping with a short cloth. Shellac is also used as sealer and undercoat.

Printing Ink During the recent years use of shellac in printing ink industry has considerably increased. Various types of inks particularly flexographic ink and water-proof ink contain shellac. The former is fast drying aniline ink, transparent or opaque, much used for rotary printing of numerous types of packing materials ranging from foils to plastics. The chief characteristics of shellac are strong adhesion and excellent binding power for dyes and pigments, superior flow, gloss, slip and abrasion resistance and good definition in printing. It is also quick-drying, free from any objectionable odour and possessing long shelf life. In addition, where colour permits, shellac enhances colour intensity and strength of print.

Transparent dye inks based on shellac being true solution for low viscosities need some modification. The addition of pigments to shellac solution to obtain opaque light fast inks greatly increases the viscosity which is sometimes necessary for the ink maker to modify the basic resin solution in order to bring viscosity within workable range. Electrical Industry The excellent electrical properties of shellac, its freedom from tracking, its good adhesion and thermoplastic properties have established for this resin a very important place in electrical industry. In all its uses it is either applied dissolved in alcohol as an insulating varnish or in the molten state as a binder in large moulded articles. It is mainly used in the manufacture of insulating varnishes and cements, moulded insulators, laminated and moulded mica products (micanite and micafolium), laminators, paper boards, tubes and coated or ompregnated paper, cloth and silk.

For the manufacture of micanite, mica splittings are bonded with shellac varnish to the required thickness and then pressed at 150-160oC for two hours under high pressure. In another process, mica sheets and shellac powder are dropped down a tower until necessary thickness is obtained and then consolidated. Micanite is one of the most valuable materials for electrical insulation. Micafolium is a wrapping material consisting of one or two thin layers of mica splittings bonded to strong kraft paper with shellac. This is a general purpose insulator for large electrical appliances and is applied by a hgot ironing process. Hot moulding micanite needs to be flexible when hot and to achieve this, large flakes of mica are used and shellac bond increases to more than 10%. This type of micanite is used for commutator cones, V-rings, transformer rings, tubes etc. A very fluid shellac is required.

Leather and Footwear industry Tanners use shellac, suitably pigmented, to produce a flexible, waterproof and glossy finish on leather. Shellac is also applied for s final durable non-tacky and glossy finish to leather articles. Shoe polishes can be made with shellac wax.

Shellac for Pharmaceutical, Confectionary Glazes and Fruit Coating Superior grades of shellac dissolved in special denatured alcohol are the glazes employed for coating pharmaceutical tablets and confectionaries by the Pan method. In confectionaries, these glazes are sometimes applied by brush or spray.

In pharmaceutical tablet coating, the functions of shellac are: To serve as a moisture barrier protecting the co-ingredients As a enteric coating To control disintegration As a granulating agent As a finishing coat over wax prior to the printing of trade mark.

The main use of shellac in the confectionary industry are for coating chocolate goods such as extruded chocolates, chocolate covered nuts and raisins and similar products. Shellac has become an important ingredient for fruit coating composition. Substantial quantity of Shellac is consumed in fruit coating industry. The coating for confectionary of fruit performs one or more of the following functions: Enhances and protects the gloss Serves as a barrier to moisture either entering or leaving the confection. Prevents blocking together Extends shelf life.

Cosmetic Industry Shellac has a worldwide use in hair spray and hair lacquer industry. It contains all the chemical and physical properties required by the cosmetic chemist in formulating hair-grooming products. The ability of shellac to hold the hair is an obvious basic requirement and its non-hygroscopic nature ensures that the hair keeps well groomed in high humidity or when exposed to rain. Its solubility in alcohol, the usual cosmetic colvent makes for easy formulation and its solubility in mild alkalis makes for easy removal by shampoos. Shellac has a wide range of compatibility with other resins, plasticisers and softeners used in hair lacquers. Normally decolourised or bleached shellac is used in this industry.

Paper Varnish Enormous quantities of paper varnishes are used for glazing paper, wrappers, labels, display cards etc. where adhesion on high gloss are imperative and consequently light coloured shellac is an essential ingredient. Glossy silky finish on superior quality playing cards is obtained by giving the blanks a coat of shellac varnish before the final cutting. There is nothing quite like shellac for this application.

Hat Industry Although hat is no longer an essential article of dress, but still hat trade even nowadays is a big consumer of shellac. Both fur and wool felts are made by similar processes. The hood is treated with an aqueous solution of shellac - a process known as proofing. ' Photographic Industry Shellac varnish is used to protect negative and sound tracks on talky film. Shellac is also used for preparing dry mounting paper and in the cold top enamel process of photo engraving and etching. Rubber Industry When shellac is compounded with rubber, it toughens the latter and makes it more resistant to wear as in rubber soles and heels, flow tiles and moulded rubber articles. Varnishes for finishing rubber articles are also made from shellac.

Paint Industry A number of formulations have been developed on the use of shellac in the paint industry. Primers for undercoat having excellent protective capacity have been formulated with shellac. Enamel and emulsion paints based on shellac are also being produced. A very important application of shellac is in the road marking paint. Grinding Wheels In grinding wheels, shellac as a bond for abrasive grains such as aluminium oxide, silicon, carbide and emery. Shellac bonded grinding wheels have considerably elasticity and are specially useful for precision work such as final grinding of camshafts, hardened steel, chilled rolls and for polishing of lenses and razor blades. During grinding the heat of friction slightly softens the shellac and the dulled abrasive grains break off to expose a fresh, sharp cutting surface. Automobile Industry Most important use of shellac in the automobile industry is the gasket cement. Shellac is insoluble to petroleum and this property is utilised in shellac-based gasket cement.

Shellac Moulding Shellac is a typical thermo-plastic material. In moulding operation, thermo-plastic compounds have the disadvantage that the mould requires to be cooled before opening. but on the other hand thay have the disadvantage that scraped and spoiled articles can be reworked. ordinary shellac even with its limitations to heat resistance is excellent moulding resin capable of very high degree of acuracy. The fludity of the base persists during moulding operation and therefore takes perfect impression of the mould.

The moulding properties of shellac are utilised in the manufacture of various products: Gramophone Records: The manufacture of gramophone records was formerly the largest single outlet for shellac. But in recent years shellac has been displaced almost completely by synthetic resins. However, records of 78 r.p.m are still based on shellac. Dental compositions: Dental plate blanks are plastic compositions comprising of shellac fatty acids and waxes with filters and colouring matter. Sufficiently softened in warm water, they take an impression from which the hand mould is made.

Sealing Wax: The widely known sealing wax contains shellac turpentine, rosin and fillers including colouring matter. Shellac is essential for good adhesion, toughness, tenacity and preventing discolouration on melting.

Other moulded articles: Inspite of extensive use of bakelite and other synthetic resins for a wide variety of plastic mouldings, shellac is still used for making some items.

By-Products

The important by-products obtained during manufacture of Shellac are Molamma, Kiri, Passewa, Shellac Wax and Lac Dye.

Molamma: This product is obtained during winnowing or sieving of washed seedlac. It is usually in the form of fine dust comprising of lac associated with wood particles and such other ingredients as are normally common in sticklac. This lac content varies from 45 to 80%.

Kiri: This is the residue retained in the bag after refining seedlac into shellac by hot filtration process. It contains apart from lac, materials like sand, insect debris and such other materials as are normally associated with seedlac. kiri is usually available in the form of round slabs. Lac content varies from 40-70%.

Passewa: The product is obtained by boiling the cloth bag used for refining seedlac into shellac by the indigenous process. It is usually found as thick, slabs having a lac content to the extent of 90%.

Shellac Wax: Lac contains about 5% of wax. During the manufacture of dewaxed shellac, the wax is recovered. the wax has properties similar to the carnauba wax and has a number of industrial applications.

Lac Dye (Laccaic Acid): Lac dye is obtained during washing of seedlac. Previously it was an important export commodity, but with the invention of synthetic dyes, the lac dye lost its field. At present it is practically a waste product. Research has been carried out both in India & China to find its application as a colouring matter of food and beverages. the toxicological test has proved that lac dye is harmless to the living system.

ANALYSIS OF SHELLAC

There are different tests for shellac, some of which are mandatory and some are optional.

Among the mandatory requirements as specified by Indian Standards Institution (ISI) are:

(i) Matter insoluble in hot alcohol

(ii) Colour Index

(iii) Tests for detection of rosin, orpiment and other arsenical impurities.

Among the optional tests are:

(i) Volatile matter

(ii) Wax percent

(iii) Ash

(iv) Matter soluble in water

(v) Flow

(vi) Life or heat polymerisation test

(vii) Acid value

(viii) Iodine value etc.

The matter insoluble in hot alcohol varies from 0.2% in very high grade of dewaxed decolourised shellac to 2.5% for inferior grades of shellac. .