Preparation and properties of commonly used dyes

by

Preparation and properties of commonly used dyes

Dye, substance used to impart colour to textiles, paper, leather, and other materials such that the colouring is not readily altered by washing, heat, light, or other factors to which the material is likely to be exposed. Dyes differ from pigments, which are finely ground solids dispersed in a liquid, such as paint or ink, or blended with other materials. Most dyes are organic compounds (i.e., they contain carbon), whereas pigments may be inorganic compounds (i.e., they do not contain carbon) or organic compounds. Pigments generally give brighter colours and may be dyes that are insoluble in the medium employed.

Preparation of dyes

In 1856 the first commercially successful synthetic dye, mauve, was serendipitously discovered by British chemist William H. Perkin, who recognized and quickly exploited its commercial significance. The introduction of mauve in 1857 triggered the decline in the dominance of natural dyes in world markets. Mauve had a short commercial lifetime (lasting about seven years), but its success catalyzed activities that quickly led to the discovery of better dyes. Today only one natural dye, logwood, is used commercially, to a small degree, to dye silk, leather, and nylon black.

Recognition of the tetravalency of carbon and the nature of the benzene ring were key factors required to deduce the molecular structures of the well-known natural dyes (e.g., indigo and alizarin) and the new synthetics (e.g., mauve, magenta, and the azo dyes). These structural questions were resolved, and industrial processes based on chemical principles were developed by the beginning of the 20th century. For example, Badische Anilin- & Soda-Fabrik (BASF) of Germany placed synthetic indigo on the market in 1897; development of the synthetic process of this compound was financed by profits from synthetic alizarin, first marketed in 1869.

There was also interest in the effects of dyes on living tissue. In 1884 the Danish microbiologist Hans Christian Gram discovered that crystal violet irreversibly stains certain bacteria but can be washed from others. The dye has been widely used ever since for the Gram stain technique, which identifies bacteria as gram-positive (the stain is retained) or gram-negative (the stain is washed away). The German medical scientist Paul Ehrlich found that methylene blue stains living nerve cells but not adjacent tissue. He proposed that compounds may exist that kill specific disease organisms by bonding to them without damaging the host cells and suggested the name chemotherapy.

Properties of commonly used dyes

  • The outstanding characteristics of the basic are brilliance and intensity of their colors.
  • The bright colors achieved from basic dyes do not usually occur with other dye classes.
  • Many of the basic dyes are sparingly soluble in water.
  • The addition of glacial acetic acid helps to dissolve the basic dye quickly in water.
  • Basic dyes are readily soluble in alcohol or mentholated spirit.
  • The basic dyes are poor fastness to light and vary with regard to washing fastness from poor to moderate.
  • An important property of basic dyes is that they will combine with tannic acid to form an insoluble compound provided mineral acid is absent.
  • The wet fastness of the basic dyes on protein fibres can also be improved by back tanning. This consists of after treating the dyed material with tannic acid in order to form the insoluble complex thereby reducing the tendency to migrate.
  • The basic dyestuff will combine with direct or sulphur or some acid dyestuffs. So they cannot be used together in the same bath. But basic dyestuffs are used in after treating cotton or other materials dyed with direct colors. Here the direct dyestuff acts as mordant.

Preparation of detergents

Although there are three ways of manufacturing dry laundry detergent, only two are commonly used today. In the blender process favored by smaller companies, the ingredients are mixed in large vats before being packaged. The machines used are very large: a common blender holds 4,000 pounds (1,816 kilograms) of mixed material, but the blenders can accommodate loads ranging from 500 to 10,000 pounds (227 to 4,540 kilograms). By industry standards, these are small batches for which the blender process is ideal. While some settling may occur, the resulting detergent is of high quality and can compete with detergents made by other processes. The second commonly used method of production is called the agglomeration process. Unlike the blender process, it is continuous, which makes it the choice of very large detergent manufacturers. The agglomeration process can produce between 15,000 and 50,000 pounds (6,800 and 22,700 kilograms) of detergent per hour. In the third method, dry ingredients are blended in water before being dried with hot air. Although the resulting product is of high quality, the fuel costs and engineering problems associated with venting, reheating, and reusing the air have led to this method being largely replaced by agglomeration.

The blender process

  • First, ingredients are loaded into one of two machines: a tumbling blender or a ribbon blender. The tumbling blender, shaped like a rectangular box, is turned and shaken from outside by a machine, while the ribbon blender is a cylinder fitted with blades to scrape and mix the ingredients. After the ingredients inside the blender have been mixed, a doorway at the bottom of the bowl is opened. With the blender still agitating the ingredients, the mix is allowed to run out onto a conveyor belt or other channeling device. The belt then moves the detergent to another area of the factory where it can be dropped into boxes or cartons for delivery to wholesalers or distributors.

The agglomeration process

  • In this method, dry ingredients for a detergent are first fed into a large machine known as a Shuggi agglomerator. Inside the agglomerator, sharp, whirling blades mix the material to a fine consistency; the process resembles food being textured inside a food processor.
  • After the dry ingredients have been blended, liquid ingredients are sprayed on the dry mix through nozzles fitted into the agglomerator’s walls. The blending continues, causing an exothermic (heat-producing) reaction to occur. The resulting mixture is a hot, viscous liquid similar to gelatin that hasn’t hardened.
  • Next, the liquid is allowed to flow out of the agglomerator. As it leaves the machine, it collects on a drying belt where its own heat, exposure to air, and hot air blowers render it friable, easy to crush or crumble. The newly made detergent is then pulverized and pushed through sizing screens that ensure that no large lumps of unmixed product go out to the market. The result of this process is a dry detergent made up of granules of the mixed detergent.

Liquid detergent 

If the detergent is to be liquid rather than powder, it is simply mixed back in—after all ingredients are blended—with a solution consisting of water and various chemicals known as solubilizers. The solubilizers help the water and detergent blend together more fully and evenly.

Preparation of explosives

A blasting agent is any material or mixture consisting of a fuel and oxidizer that is intended for blasting and that is not otherwise classified as an explosive. A blasting agent consists primarily of inorganic nitrates (ammonium and sodium nitrates) and carbonaceous fuels. The addition of an explosive ingredient, such as TNT, in sufficient quantity, changes the classification of the mixture from a blasting agent to an explosive.

Ammonium nitrate, for its weight, supplies more gas upon detonation than any other explosive. In pure form, ammonium nitrate is almost inert (powerless) and is composed of 60 percent oxygen by weight, 33 percent nitrogen, and seven percent hydrogen. Two characteristics make this compound both unpredictable and dangerous. Ammonium nitrate is water soluble and if uncoated, can attract water from the atmosphere and slowly dissolve itself. For this reason, most prills have a protective coating of wax or clay which acts as a moisture retardant. The second and most important characteristic is a phenomenon called “cycling.” This is the ability of a material to change its crystal form with temperature. Ammonium nitrate will have one of five crystal forms depending on the temperature. The cycling phenomenon can seriously affect both the storage and performance of any explosive which contains ammonium nitrate. Most dynamites, both regular nitroglycerin or permissibles, contain some percentages of ammonium nitrate, while blasting agents are almost totally comprised of this compound. The cycling effect in dynamite is not due to other ingredients mixed with the ammonium nitrate. For this reason, cycling does not greatly affect dynamite the way it does ANFO.

The two temperatures at which cycling will occur under normal conditions are 0 and 90°F. This is to say that products which are stored over the winter, or for a period of time during the summer, most likely will undergo some amount of cycling. During the summer, in poorly ventilated powder magazines, the cycling temperature may be reached daily.

Properties of explosives

In general, an explosive has four basic characteristics:

  • It is a chemical compound or mixture ignited by heat, shock, impact, friction, or a combination of these conditions;
  • Upon ignition, it decomposes rapidly in a detonation;
  • There is a rapid release of heat and large quantities of high-pressure gases that expand rapidly with sufficient force to overcome confining forces; and
  • The energy released by the detonation of explosives produces four basic effects; (a) rock fragmentation; (b) rock displacement; (c) ground vibration; and (d) air blast.

Preparation of paints

Paint is a term used to describe a number of substances that consist of a pigment suspended in a liquid or paste vehicle such as oil or water. With a brush, a roller, or a spray gun, paint is applied in a thin coat to various surfaces such as wood, metal, or stone. Although its primary purpose is to protect the surface to which it is applied, paint also provides decoration.

A paint is composed of pigments, solvents, resins, and various additives. The pigments give the paint color; solvents make it easier to apply; resins help it dry; and additives serve as everything from fillers to antifungicidal agents. Hundreds of different pigments, both natural and synthetic, exist. The basic white pigment is titanium dioxide, selected for its excellent concealing properties, and black pigment is commonly made from carbon black. Other pigments used to make paint include iron oxide and cadmium sulfide for reds, metallic salts for yellows and oranges, and iron blue and chrome yellows for blues and greens.

Making the paste

Pigment manufacturers send bags of fine grain pigments to paint plants. There, the pigment is premixed with resin (a wetting agent that assists in moistening the pigment), one or more solvents, and additives to form a paste.

Dispersing the pigment 

The paste mixture for most industrial and some consumer paints is now routed into a sand mill, a large cylinder that agitates tiny particles of sand or silica to grind the pigment particles, making them smaller and dispersing them throughout the mixture. The mixture is then filtered to remove the sand particles. Instead of being processed in sand mills, up to 90 percent of the water-based latex paints designed for use by individual homeowners are instead processed in a high-speed dispersion tank. There, the premixed paste is subjected to high-speed agitation by a circular, toothed blade attached to a rotating shaft. This process blends the pigment into the solvent.

Thinning the paste

Whether created by a sand mill or a dispersion tank, the paste must now be thinned to produce the final product. Transferred to large kettles, it is agitated with the proper amount of solvent for the type of paint desired.

Canning the paint

The finished paint product is then pumped into the canning room. For the standard 8 pint (3.78 liter) paint can available to consumers, empty cans are first rolled horizontally onto labels, then set upright so that the paint can be pumped into them. A machine places lids onto the filled cans, and a second machine presses on the lids to seal them. From wire that is fed into it from coils, a bailometer cuts and shapes the handles before hooking them into holes precut in the cans. A certain number of cans (usually four) are then boxed and stacked before being sent to the warehouse.

Properties of paints

  • Exterior paint is exposed to all types of varying weather conditions. Exterior paint is therefore required to provide protection against UV radiation of the sun as well as fungal growth.
  • It’s made to combat mildew as well as fading. In addition, they have to be fade resistant as they face very high temperatures.
  • The resins used for exterior paint can be softer so that they can withstand temperature changes and ill effects due to exposure to moisture. They are supposed to be flexible and not easily crack on expansion/contraction.
  • Exterior paint must be tougher and should be capable of resisting peeling and crumbling.
  • Interior paint is more to do with aesthetics and decoration purposes and at the same time, they need to add properties of easy maintenance, wash ability and dampness prevention. It’s designed to withstand abrasion.
  • Interior paint is also designed to be more delicate than exterior paint because they occupy the same space as you do.
  • Interior paint is so made that they can be scrubbed and can resist staining. Interior paint is formulated to be more resistant to physical damage.

 

Preparation and properties of varnishes

Wood is valuable for structural purpose and decorative purpose also. Wood has plant origin. The wood used for building construction is known as Timber. Forests produce a huge quantity of timber. Cellulose, Hemicellulose, Lignin and other substances are the constituents of wood. Aliphatic compounds, phenols, fats, waxes, terpenes, terpenoids etc. are found in woods. Stilbenes, Tannins, Flavonoids and Lignanas are phenolic compounds available in woods.

Preparation of varnishes

Drying oil

There are many different types of drying oils, including linseed oil, tung oil, and walnut oil. These contain high levels of polyunsaturated fatty acids.

Resin

Resins that are used in varnishes include amber, kauri gum, dammar, copal, rosin (pine resin), sandarac, balsam, elemi, mastic, and others. Shellac is also a resin. In the 1900s in Canada, resins from local trees were used to finish pianos. As a result, these now antique pianos are considered difficult to refinish. However, shellac can be used over the existing resins provided sufficient time is allowed for thin coats to cure. Thus the original finish can be returned to its original lustre while preserving the color and age-related crackle.

Solvent

Traditionally, natural (organic) turpentine was used as the thinner or solvent, but has been replaced by several mineral-based turpentine substitutes such as white spirit or “paint thinner”, also known as “mineral spirit”.

Spirit varnishes made with alcohol are conveniently prepared and on account of their rapid drying and leaving no disagreeable smell are in frequent use in the household for covering various articles of art. Resin is a class of non-volatile (non-evaporating), solid or semisolid organic substances obtained directly from certain plants as exudations or prepared by polymerization of simple molecules. Some hard and soft resins used in varnishes are amber, copal, shellac, sandarac, mastic, resin of turpentine, dammar etc. Rosins are classified as pale yellow, yellow, and reddish to yellow, brown or black rosin. If the injection water be not completely expelled the rosin is opaque.

If the essential oils have not been completely eliminated the rosin is viscous and tacky. Spirit varnishes are more or less thin, more or less viscous, colourless or more or less coloured, opaque or transparent solutions, of one or more natural resins, e.g. shellac and shandarac etc., in one more appropriate volatile solvents which leave on evaporation a thin, more or less resistant film which both adorns and protects the object on which it is applied.

Application of varnish on wood work is carried out in the following steps:

Preparation of surface

The wood surface is made smooth by thoroughly rubbing it by means of sand paper or pumice stone.

Knotting

The process of knotting is carried out exactly in the same way as adopted for painting wood work.

Stopping

Stopping is done by means of hot weak glue size so that pores on the surface are filled up. Alternately, boiled linseed oil can be applied in two coats. The dry surface then be rubbed down with sand paper.

Coat of varnish

On the cleaned surface, two or more coats of varnish are applied. Next coat is applied only when the previous coat has dried up thoroughly.

Properties of varnish

Properties of ideal varnish should be :

  • It should give glossy surface. Should be durable.
  • It should dry rapidly after application.
  • It should not develop cracks after drying.
  • It is commonly used on wooden surfaces.
  • Colour of varnish should not fade away with time.
  • It should not hide the natural grain of inner surface of timber.
GPSC Notes brings Prelims and Mains programs for GPSC Prelims and GPSC Mains Exam preparation. Various Programs initiated by GPSC Notes are as follows:- For any doubt, Just leave us a Chat or Fill us a querry––