Bio-Fuel

                                                                  BIO FUEL

Biofuels are fuels largely derived from living organisms that use the sun as their main energy input. Energy may be put into planting, fertilizing, harvesting, and processing the crops, but most of the energy, in the final plant product, comes from the sun. Through the process of photosynthesis plants convert solar energy into chemical forms of energy (carbohydrates, fats, etc.). Plant convert solar energy into a chemical form more usable as a fuel. Biofuels are considered carbon neutral. That is, they release no net amount of carbon dioxide into the atmosphere.This because the carbon dioxide that is released during combustion was originally absorbed from the atmosphere during the process of photosynthesis.Hence, no extra CO2 is pumped into the atmosphere The process of photosynthesis can be summarised by the equation below.

6H2O + 6CO2 => C6H12O6 + 6O2

Palm oil is used to produce biofuel.  . A process known as transesterification is commonly used to produce biodiesel. Chemically, transesterification is the process of exchanging the alkyl group of an ester with another alkyl group, from a different alcohol. Vegetable oil contains fatty acids bonded to glycerol to form triglycerides. In the case of biodiesel, a vegetable oil ester is combined with a simple alcohol, methanol, and a catalyst, resulting in the breakup of the triglyceride ester to form glycerol and three methyl esters (biodiesel) A typical molecule of biodiesel looks like the structure below.  Mostly it is a long chain of carbon atoms, with hydrogen atoms attached, and at one end is what wecall an ester functional group .

Making good biodiesel requires several other steps besides the transesterification reaction(as shown in the right).  The first is to remove any traces of water in the vegetable oil.  If this is not done, the water will later react with the vegetable oil in the reaction and make soap.

If soap gets made, then later it complicates the steps after the transesterication reaction that are needed to separate the biodiesel from leftover methanol, the NaOH or KOH catalyst, and the glycerol byproduct.Diesel engines can burn biodiesel fuel with no modifications (except for replacing some rubber tubing that may soften with biodiesel).  This is possible because biodiesel is chemically very similar to regular diesel, shown below.  Notice that regular diesel also has the long chain of carbon and hydrogen atoms, but doesn’t have the ester group.Actually, the first diesel engines didn’t run on “diesel” fuel, but on vegetable oil, a sample molecule of which is shown below.  Notice that it also has the long rows of carbon and hydrogen atoms, but is about three times larger than normal diesel molecules.  It also has ester functional groups , like biodiesel.That larger size of vegetable oil means that in cold weather it gels, making it hard to use in an engine.  Converting it into biodiesel makes it a smaller molecule, closer to the size of regular diesel, so that it has to get colder than vegetable oil before it starts to gel.

Miracle Of Tooth Paste with chemistry

Miracle Behind The Shiny Teeth !

Toothpaste is probably the first product that everyone use in the morning as well as the last before going to bed. A smile with white and healthy teeth and gums is what everyone wants to have. Every toothpaste contains binders, abrasives, flavors, sweeteners, fluorides, tooth whiteners, a preservative, and water.
     Toothpaste, which contains sodium fluoride, belongs to the group of weak bases. The high pH of the toothpaste helps to kill the bacteria that reside in our mouth at the time of brushing. Those bacteria prefer a neutral to slightly acidic environment, exactly the conditions of our unbrushed mouth. Tooth enamel naturally loses its minerals and decays. Fluoride works with calcium and phosphate to slow this process and improve remineralization, or the production of new tooth enamel. Fluorides reduce decay by increasing the strength of teeth. Sodium fluoride is the most commonly used fluoride. Sodium perborate is used as a tooth whitening ingredient. Most toothpastes contain the preservative p-hydrozybenzoate. Water is also used for dilution purposes. Fluoride has also been added to other dental products like mouthwash and the fluoride varnish used by dentists.      So, brushing your teeth twice in a day is very important as it keeps your teeth clean and shiny like this,

Secret of Scent(Perfumes)

Secret Behind The Wonderful Scent World!!!

   Nowadays, perfumes are commonly and widely being used in daily life by everyone. Perfume has been used for century to cover the body odor.

   Perfumes encompass a wide variety of chemicals (called notes), which are tailored for specific occasions and seasons. In fact, most of the perfumes are engineered to have three-part of structure.

1)Top notes: light scent that fade quickly

2)heart notes: scent last for several hours

3)Base notes: Scent stick stubbornly to the skin

  A perfume basically consists of 78-95% of ethyl alcohol, and the rest are essential oils. Staying power of the perfume is highly depend by the rate of evaporation.

  Many methods are used to synthesis the perfume.

A) Maceration

1) Raw ingredients are soaked in the solvent.

2) The fragrances are drawn out and collected.

B) Expression

1) Raw ingredients are being compressed.

2) The aromatic oils are being squeezed out.

   By using perfume, our will smell amazingly unique, provides ultimate expression of individuality and causing others to take notice of ours unique style and grace. 

Cosmetics Secret

Secret of beauty J

  Cosmetics (colloquially known as makeup or make-up) are care substances used to enhance the appearance or odor of the human body. They are generally mixtures of chemical compounds, some being derived from natural sources, many being synthetic.

   In the U.S., the Food and Drug Administration (FDA) which regulates cosmetics, defines cosmetics as "intended to be applied to the human body for cleansing, beautifying, promoting attractiveness, or altering the appearance without affecting the body's structure or functions." This broad definition includes, as well, any material intended for use as a component of a cosmetic product. The FDA specifically excludes soap from this category.

 

   During the 20th century, the popularity of cosmetics increased rapidly. Cosmetics are increasingly used by girls at a young age, especially in the United States. Due to the fast-decreasing age of make-up users, many companies, from high-street brands like Rimmel to higher-end products like Estee Lauder, have catered to this expanding market by introducing more flavoured lipsticks and glosses, cosmetics packaged in glittery, sparkly packaging and marketing and advertising using young models. The social consequences of younger and younger beautification  had much attention in the media over the last few years.

    Criticism of cosmetics has come from a variety of sources including some feminists, religious groups, animal rights activists, authors and public interest groups. Growing awareness and preference for cosmetics exists for cosmetics lacking toxic ingredients, especially those derived from petroleum,sodium lauryl sulfate (SLS), and parabens.

Beauty can make happy J

Cosmetics are regarded as a means of enhancing one's complexion and beautifying the skin. For examples,

·        Skin creams and lotions can be used to deep-cleanse the skin.

·        If pores in the skin are blocked, it may lead to infection and acne formation. Various cosmetic cleansing products thoroughly cleanse the skin and remove the dirt and microorganisms from the skin.
·        After cleansing, moisturizers are applied to prevent drying of the skin and to keep it smooth and radiant. Moisturizers also offer excellent protection against cold winds and act as a lubricating agent.

·       There are special sun-protection creams/lotions that can protect you from the harmful UV rays of the sun. These creams minimize the risk of skin cancer, which is the result of exposure to sun rays.

·        Many cosmetics contain vitamins such as A, D, E and K. These vitamins are essential for healthy skin and hair.

·       To cope with body odor, one can use deodorants and perfumes. These help in making one feel fresh all through the day.

·       Apart from skin care, there are also varieties of shampoos and conditioners available, which keep the hair clean, soft and healthy.

Besides that, cosmetics are used not only for skin care, but also to treat certain skin problems. Dark spots or pimples on the face can be hidden using cosmetic products like concealers. You can enhance your most attractive facial features using makeup. Moreover, you can also cover dark circles and wrinkles using various anti-aging creams and eye makeup. Apart from that, not only your face, you can also decorate your nails using attractive nail colours. The wide range of hair colours available today also helps you to modify and highlight your hair in the colour and shade of your choice.

Sometimes too much beauty is not good for health L

  Increasingly, people react to the pollution in their environment with skin diseases and allergies. Just five to ten percent of the approximately 30 million allergy sufferers in Germany react excessively to certain additives and preservatives, both in their food and in their cosmetic products.

    Over the years, numerous methods were developed that were aimed at making products more durable and less perishable. As part of this, countless synthetic additives, which were then admixed to the care products to preserve these longer. Meanwhile, many of these substances are suspected trigger allergies or even cancer can. These findings are based on long-term studies, only in the wake of the global disease spread and thus many people could be made. In spite of previous laboratory and animal experiments, it was not possible to study these long-term effects before the introduction of these substances. The result we see now: Excessive sensitivity of many people on certain products.

  In a nutshell, cosmetics can bring about a huge change in your personality. However, you need to be cautious while using the same. Before buying any cosmetic products, make sure that they are meant for your skin type lest you want to break out into an allergy. Buy products of reputed brands and you will be assured of excellent quality.

Why Can’t Soap Cleanse Our Clothes?

Why Can’t Soap Cleanse Our Clothes?

Soap is the result of the mixture of potassium salts of fatty acids which is obtained from vegetable oils or animal fats and which is reacted with an alkali such as potassium hydroxide. This process of reacting the potassium salts of fatty acids with an alkali is known as saponification.

The saponification process is mostly practiced and performed for the making of soap industrially. This process involves the process of heating animal fats or vegetable oil and reacting with an alkali in order to give the result of soap and water mixed with glycerine. The another part of the process is neutralization of fatty acids with an alkali. The fats and oils are hydrolyzed with a high-pressure steam to produce fatty acids and glycerine. After that, the fatty acids is purified by distillation and neutralization with an alkali to yield soap and water.

If the alkali is sodium hydroxide, then, the sodium soap will be formed. Sodium soaps are made in solid form. Thus, they are also known as ‘hard’soaps. In contrast, if the alkali is potassium hydroxide, then, the soap formed will be smoother and is found in liquid form. This type of soaps is usually found in liquid-hand soaps and shaving cream. The carboxyl group present at the end of the soap molecule is attracted towards the water which is hydrophilic while the other end of the soap molecule which is a hydrocarbon chain is attracted to oil and grease which are non-polar substances rejected by water molecules. This end is known as the hydrophobic end.

Although,soap is a cleaning agent, the cleaning action of soap is affected by water hardness. Soap is proved to be less efficient in cleaning when dissolved in hard water. The water is labeled as hard water due to the presence of mineral salts such as Calcium ions and Magnesium ions which contributes to the formation of the insoluble precipitate also known as scum when soap reacts with these mineral salts. The scum formed on clothes makes the fabric stiff and thus causes a visible stain to deposit on clothes. Moreover, scum attaches to the internal parts of washing machines.

The reaction of soaps with hard water decreases the amount of soap present to be used for the cleaning action. However, if soap is let to react with soft water, the soil on stains and dirts on the clothes shows the presence of mineral salts which eventually reduces the effectiveness of soap in the cleaning action. Therefore, soap is inflexible to be used for laundry purposes, especially in a variety of fibres, washing temperatures and water conditions nowadays.

 

 

Organic chemistry Introduction

Introduction to organic chemistry:-

Organic chemistry is the study of carbon and the study of the chemistry of daily life. Life is based on carbon's ability to form diverse structures and an endless number of different carbon based on molecules. We are living in a world which is largely shaped by organic compounds. There is hardly any walk of life where we do not need the organic compounds. The food that we eat is essentially a mixture of organic compounds. The changes which the food undergoes in our bodies are organic chemical reactions. The clothes that we wear (wool, cotton, leather, synthetics) are all organic in character. The soap, cosmetics, perfume, oils, plastics, explosives, rubber, dyestuffs, paper, insecticides, and many more are all organic compounds. The sources of primary energy we still use every day (petroleum, natural gas, coal) are organic in nature. In the medical field, organic compounds are indispensable. Antibiotics, sulpha drugs, alkaloids, aspirin, iodoform, and many are organic compounds. There is hardly any industry which is not dependent on organic compounds.

            Organic chemistry is that branch of chemistry that deals with the structure, properties, and reactions of compounds that contain carbon. It is a highly creative science. In addition to being plentiful, organic compounds are also unique. This is because carbon atoms have the ability to form strong bonds with many different elements. Carbon atoms are also able to bond covalently to other carbon atoms, while simultaneously forming strong bonds with other nonmetal atoms. When carbon atoms bond together, they can form chains consisting of thousands of atoms. They can also form rings, spheres, and tubes.

 Chemists in general and organic chemists in particular can create new molecules never before proposed which, if carefully designed, may have important properties for the betterment of the human experience. In terms of Ph.D. population, organic chemistry is the largest chemistry discipline, in both total numbers, annual Ph.D. graduates, and in annual production. Organic chemistry is the study of carbon and the study of the chemistry of life. Since not all carbon reactions are organic, another way to look at organic chemistry would be to consider it the study of molecules containing the carbon-hydrogen (C-H) bond and their reactionsOrganic chemistry is a branch of chemistry that involves the study of organic carbon compounds. It encompasses the structures, composition, and synthesis of carbon-containing compounds. In understanding organic chemistry, it is important to note that all organic molecules consist not only of carbon, but also contain hydrogen. While it is true that organic compounds can contain other elements, the bond between carbon and hydrogen is what makes a compound organic.

Originally, organic chemistry was defined as the study of compounds created by living organisms. However, its definition has been enlarged to include artificially synthesized substances as well. Before 1828, all organic compounds were obtained from living organisms. Scientists didn’t believe it was possible to synthesize organic compounds from inorganic compounds. Many attempted to do so and failed. However, in 1828, urea was synthesized from inorganic substances, paving the way for a new definition of organic chemistry.

Organic chemistry deals not only with the chemistry of life and the natural carbon compounds but also with the huge, increasing number of synthetic carbon compounds. We are living in a world which is largely shaped by organic compounds. There is hardly any walk of life where we do not need the organic compounds. There is hardly any industry which is not dependent on organic compounds. It is the most beautiful branch of science which has great applications in our everyday life. All our requirements would not have been fulfilled without the knowledge of organic chemistry. The understanding of organic chemistry dates back to the nineteenth century. Scientists claimed that things obtained from plants are too complex to study and recreate in the laboratory. Inorganic chemistry, another main branch of chemistry, was believed to be much simpler and easier to do research. The scientists believed that all the organic matter were held by a vital force. They then named these compounds as organic.

Leather preparation process

The leather production process

The tanning industry enables a by-product of the food industry to be recovered and made into something special and noble.

Leather tanning is without a doubt one of the oldest human activities.  In the beginning, skins obtained from hunting and livestock breeding could be used for clothing as a protection from the atmospheric elements.

The tanning process has undergone many changes from prehistory to today, especially in the twentieth century,  when industrialization and new machines have allowed development in the research for specific  and less polluting chemicals and  new methods of tanning and finishing.

Leather is produced traditionally even today. The skin, discard  of the food industry, is "recycled" from the tanneries and processed  with advanced machinery and vast research, in such a way  to make it a  “noble” and fashionable material. There is a large number of tanneries, but the uniqueness of the result is given by the ability and the skill of experienced  craftsmen.

Immediately after killing the animal, in order to avoid degradation processes in the tissues, the skin is salted, dried or refrigerated before the production process of tanning starts.  Skins are salted with common marine salt, which penetrates very quickly into the fibers, helping to  a partial removal of water. This is a very efficient and economical process , easy to apply and widespread. The drying system is to eliminate  as much water as possible from the skin,  so to avoid the development of micro-organisms and bacteria. The  drying system is more suitable  for sheep and goat skins,  while less to preserve cowhides.

Defrost is another method , but  it is not common in Italian slaughterhouses:  this system cools the skin at very low temperatures

The leather manufacturing process can be basically divided into three major phases: tanning, re-tanning and finishing.

All  chemical tanning operations are used to stabilize the skin making it unputrescible and are carried out with the use of water in the drums.
The drum is the typical machine for tannery : it consists in a cylinder rotating around its own axis , filled  with water, chemical reagents and skins.

The drum used to be a simple wooden cylinder  and  has now transformed into a complex computer-controlled machine that regulates the input of water, the temperature, the speed of rotation, and the release of chemical reagents, thus avoiding manual errors.

THE LEATHER PREPARATION PROCESS

The preparation for tanning, starting from preserved raw materials,  may be divided as follows:

Leather soaking: Once cured, the skins are then soaked in water for several hours to several days. The water and  surfactants help in the removal of salt, dirt, debris, blood and excess animal fats. Rehydration is  also reintroduced.

Leather  fleshing: subcutaneous material is removed. 

Leather unharing: the majority of hair is removed. 

Liming  is used to loosen the fibers allowing the skin to  absorb chemicals that will be used later in the tanning processes. Limed hides appear swollen and with an increased thickness,  therefore can be easily  split into two or more layers. The  splitting is necessary for the heavy  cow hides, which are too  thick to be used in the production of manufactured items. The process is carried out with the splitting machine in which the limed skin is pushed by two cylinders against a band blade which cuts the skin in two layers parallel to its surface.
The top layer  is  the grain (typical design of the skin of the animal, the external part) this is the full grain part , while the lower layers  are the flesh split. In general, the thinner skins (sheep, goats and calves) are skived but  not split.

Deliming:  this process  brings to removal of alkali from the  pelt with the consequent deswelling of the fibers and helps lowering of the  pH to the values used in the bating process. it Is carried out with slightly acidic chemicals.

Bating :  is an operation to complete the deliming  process, by eliminating residues of other substances and  loosen the fibers of the skin,  in order to smooth the grain  and achieve  a soft and flexible leather.

Degreasing: is carried out to remove and to reduce the natural fatty acids from the skin, which   could lead to difficulties in the absorption of chemicals. The degreasing process  removes excess fat and distribute it evenly .

Tanning is the process which converts the protein of the raw hide or skin into a stable material which will not putrefy and it is suitable for a wide variety of end applications,  the leather.

There are several types of tanning: chrome tanning is the most widespread. The duration of the  Chromium tanning is around 2 or 3 hours for small and thin skins,  up to a maximum of 24 hours for thicker  ones. At the end of the tanning  the skins appear blue-green. This is called wet-blue and at this stage it can be sold.

The vegetable tanning is the oldest, made with the use of tannins which give the vegetable tanned leather shades of brown, more or less intense.

There are two types of vegetable tanning:

- slow  tanning  in which the skins are immersed in tanks containing solutions of increasing concentrations of tannins. This method takes about 30 days and is meant to produce leather for soles,  very thick and stiff leathers.
- rapid tanning , made ??in the drums which , due to the rotation, creates a more flexible leather suitable for any kind of  productions. This process  lasts about 36 to 48 hours.

Re tanning:

The tanned leather is not yet usable to produce articles.

It is still wet and  even if  dry , it would be too rigid and  colored with the typical color of tanning used.

To turn it into a marketable product  the leather must be further treated with  chemical and mechanical  processes in the drums.

Drying process:  is a mechanical operation  which  eliminates most of the water soaked by the tanned leather,  by pressing  the skins between two cylinders , where  the top one  is covered with pewter.

Shaving  : this operation smoothens the thickness of the whole surface of the skin and eliminates the residues of fleshing. This operation is carried out  with  a cylinder machine where the top one is provided with helical blades.  

Splitting - the leather is split into one or more horizontal layers. This can be done after liming or after chrome tanning. The choice depends on the product we want to achieve.

Re tanning - additional tanning agents are added to impart properties and change the features of the main tanning : to achieve a thick and stiff leather, skins need to be re tanned with vegetable tannins- For a soft and flexible leather , re tanning needs to be with chrome .

Dyeing is the process which gives the leather  the requested color.  It Is made in the drums with dyes.

Stuffing - fats/oils and waxes are added between the fibers,  thus giving the leather the flexibility and the softness needed for the various products. 

Drying :  all above mentioned processes are carried out with water so leather needs to be dried.  This can be done to various moisture levels,  by simple exposure to air ,  by temperature controlling or  by vacuum. All  drying systems aim to achieve a uniform drying and constant timing. The choice of the drying system depends not only on  economic factors but also on the end-use material.

FINISHING:

It 's the final stage and  the most complex process, which  includes all operations to be carried out on dried skins,   to change the surface effect,  both for aesthetic and functional aims. Finishing can be mechanical or chemical.

Mechanical finishing operations may include:

POLISHING : to create a shiny surface by rubbing it with a velvety wheel

IRONING and PLATING: to obtain a flat and smooth surface

EMBOSSING :to obtain a three-dimensional print

TUMBLING by rotating the drum quickly to create a more evident grain and a smooth   surface

Chemical Finishing involves the application of a film, natural or synthetic by using curtain coaters, roller coatings and spraying.

Leather Tanning(Processing)

Tanning and Leather Finishing

Tanning is the chemical process that converts animal hides and skins into leather. The term hide is used for the skin of large animals (e.g., cows or horses), while skin is used for that of small animals (e.g., sheep). Hides and skins are mostly by-products of slaughterhouses, although they may also come from animals that have died naturally or been hunted or trapped. Tanning industries are usually located near stock-raising regions; however, hides and skins may be preserved and transported prior to tanning, so the industry is widespread.
The tanning process consists in strengthening the hide’s protein structure by creating a bond between the peptide chains. The hide is composed of three layers: epidermis, dermis and subcutaneous layer. The dermis consists of about 30 to 35% protein, which is mostly collagen, with the remainder being water and fat. The dermis is used to make leather after the other layers have been removed using chemical and mechanical means. The tanning process uses acids, alkalis, salts, enzymes and tanning agents to dissolve fats and non-fibrous proteins and chemically bond the collagen fibres together.
Tanning has been practised since prehistoric times. The oldest system of tanning relies on the chemical action of vegetable material containing tannin (tannic acid). Extracts are taken from the parts of plants that are rich in tannin and processed into tanning liquors. The hides are soaked in pits or vats of increasingly strong liquors until they are tanned, which may take weeks or months. This process is used in countries with low levels of technology. This process is also used in developed countries to produce firmer, thicker leather for shoe soles, bags, cases and straps, although process changes have been introduced to shorten the time needed for tanning. Chemical tanning using mineral salts such as chromium sulphate was introduced during the late 19th century and has become the primary process to produce softer, thinner leather for goods such as handbags, gloves, garments, upholstery and shoe uppers. Tanning may also be accomplished using fish oils or synthetic tannins.
There is great variation in the scale and types of tanning facilities. Some tanneries are highly mechanized and use closed automatic systems and many chemicals, whereas others still use largely manual work and natural tanning substances with techniques essentially unchanged over the centuries (see figure 1). The type of product required (e.g., heavy-duty leather or fine flexible leathers) influences the choice of tanning agents and the finishing required.
Figure 1. Manual working methods in an Afghanistan tannery

Process Description
Leather production can be divided into three stages: preparation of the hide for tanning, which includes processes such as the removal of hair and adherent flesh; the tanning process; and the finishing process. Finishing includes mechanical processes to shape and smooth the leather and chemical treatments to colour, lubricate, soften and apply a surface finish to the leather (see figure 2). All of these processes may take place in one facility, although it is common for leather finishing to be conducted at locations different from tanning in order to take advantage of transportation costs and local markets. The implication is that it affects the likelihood of cross-contamination among the processes.
Figure 2. Typical processes for leather tanning & finishing

Curing and shipment. Because raw hides and skins decay rapidly, they are preserved and disinfected prior to shipment to the tannery. The hide or skin is flayed from the carcass and then preserved by curing. Curing can be accomplished by a variety of means. Curing by drying is suitable in regions where hot and dry climatic conditions prevail. Drying consists of stretching the hides on frames or spreading them on the ground in the sun. Dry-salting, another method of curing hides, consists of rubbing the fleshy side of the hide with salt. Brine curing, or brining, consists of submerging the hides in a solution of sodium chloride to which naphthalene may have been added. Brining is the most common form of preservation in developed countries.
Prior to shipment, hides are generally treated with DDT, zinc chloride, mercury chloride, chlorophenols or other agents for disinfection. These substances may represent hazards both at the site of curing and on receipt at the tannery.
Preparation. The cured hides and skins are prepared for tanning by several operations, collectively referred to as beamhouse operations. First the hides are sorted, trimmed and then washed in vats or drums. Disinfectants such as bleaching powder, chlorine and sodium acid fluoride in the water prevent putrefaction of hides. Chemicals such as caustic soda, sodium sulphide and surfactants are added to the water to accelerate soaking of dry-salted or dried hides.
The soaked hides and skins are then limed by immersing in milk of lime to loosen the epidermis and hair roots and to remove other unwanted soluble proteins and fats. In another method, a depilatory paste of lime, sulphide and salt is applied to the flesh side of the skins in order to save hair and wool. The limed hides are unhaired to remove the loosened hairs and defleshed. Epidermal debris and fine hair roots are mechanically removed by the scudding operation.
These operations are followed by deliming and bating with buffering salts, such as ammonium sulphate or ammonium chloride, and the action of proteolytic enzymes neutralizes the high alkalinity of limed hides. In pickling, hides are placed in an acid environment consisting of sodium chloride and sulphuric acid. The acid is necessary because chrome-tanning agents are not soluble under alkaline conditions. Vegetable-tanned hides do not need to be pickled.
Many of the beamhouse operations are carried out by processing the hides in solutions using large pits, vats or drums. Solutions are piped or poured into the containers and later emptied through pipes or into open drainage channels in the work area. The chemicals may be added to the containers by pipes or manually by workers. Good ventilation and personal protective equipment are needed to prevent respiratory and dermal exposure.
Tanyard. Various substances may be used for tanning, but the main distinction is between vegetable and chrome tanning. Vegetable tanning may be carried out either in pits or in rotating drums. Rapid tanning, in which high concentrations of tannins are used, is carried out in rotating drums. The chrome-tanning process most often used is the one-bath method, in which the hides are milled in a colloidal solution of chromium (III) sulphate until tanning is complete. A two-bath chrome-tanning process was used in the past, but this process involved potential exposure to hexavalent chromium salts and required more manual handling of the hides. The two-bath process is now considered obsolete and is rarely used.
Once tanned, the hide is further processed to shape and condition the leather. The hide is removed from the solution and excess water is removed by wringing. Chrome leather must be neutralized after being tanned. Splitting is the longitudinal division of wet or dry leather that is too thick, for articles such as shoe uppers and leather goods. Roll machines with cutting blades are used to further reduce the leather to the thickness required. A large amount of dust may be released when the leather is split or shaved while dry.
Re-tanning, colouring and fat-liquoring. After tanning, most leathers except sole leathers undergo colouring (dyeing). Generally, colouring is performed in a batch mode; and re-tanning, colouring and fat liquoring operations are all performed in sequence in the same drum with intermediate steps of washing and drying. Three major types of dyes are used: acid, basic and direct. Blends of dyes are used in order to obtain the exact shade desired, so the composition is not always known except by the supplier. The purpose of fat-liquoring is to lubricate leather to give it strength and flexibility. Oils, natural fats, their transformation products, mineral oils and several synthetic fats are used.
Finishing. After drying, vegetable tanned leather is subjected to mechanical operations (setting and rolling) and given a final polish. The finishing process for chrome leather includes a series of mechanical operations and, normally, the application of a covering layer to the leather surface. Staking is a mechanical beating operation used to make the leather soft. To improve the final appearance, the grain side of the leather is buffed using a sanding drum. This process generates a tremendous amount of dust.
A final surface finish is applied, which may contain solvents, plasticizers, binders and pigments. These solutions are applied by pads, flow coating or spraying. Some tanneries employ hand labour to apply the finish using pads, but this is usually carried out by machines. In flow coating, the solution is pumped into a reservoir above the conveyor carrying the leather and flows down onto it. In most cases, painted or sprayed leathers are not dried in ovens, but on trays on shelves. This practice provides a wide evaporating surface and contributes to air pollution.
Hazards and Their Prevention
Infectious hazards. In the early stages of the beamhouse operations, there may be some risk of infection due to zoonoses from the raw hides. Anthrax was a recognized hazard among workers engaged in handling hides and skins, particularly dry and dry-salted hides. This hazard has been virtually eliminated in tanneries due to disinfection of hides prior to shipment to the facilities. Colonies of fungi may develop on leathers and on the surface of the liquors.
Injuries. Slippery, wet and greasy floors form a serious hazard in all parts of a tannery. All floors should be of impervious material, have an even surface and be well drained. Good maintenance and housekeeping are essential. Mechanized transfer of hides and skins from one operation to another and proper drainage of liquors from vats and drums will help to reduce spillage and manual-handling ergonomic problems. Open pits and vats should be fenced to prevent injuries due to drowning and scalds.
There are many hazards connected with the operating parts of the machines—for example, injuries caused by revolving drums, in-running rollers and knives. Efficient guarding should be provided. All transmission machinery, belts, pulleys and gear wheels should be guarded.
Several operations involve manual lifting of the hides and leather, which represents an ergonomic hazard. Noise associated with the machinery is another potential hazard.
Dust. Dust is produced in a variety of tanning operations. Chemical dust can be produced during the loading of hide-processing drums. Leather dust is produced during mechanical operations. Buffing is the major source of dust. The dust in tanneries may be impregnated with chemicals, as well as fragments of hair, mould and excrement. Effective ventilation is needed for dust removal.
Chemical hazards. The large variety of acids, alkalis, tannins, solvents, disinfectants and other chemicals can be respiratory and skin irritants. Dusts of vegetable tanning materials, lime and leather and chemical mists and vapours arising in the various processes may be responsible for causing chronic bronchitis. Several chemicals may cause contact dermatitis. Chrome ulceration may occur in chrome tanning, especially on the hands. Exposures in the beamhouse operations are mainly to sulphur compounds such as sulphides and sulphates. Since these are alkaline substances, there is a potential to generate hydrogen sulphide gas if these substances contact acids.
Potential cancer-causing agents used in leather tanning and finishing include hexavalent chromium salts (in the past), aniline and azo dyes, vegetable tannins, organic solvents, formaldehyde and chlorophenols. The International Agency for Research on Cancer (IARC) evaluated the leather tanning industry in the early 1980s and concluded that there was no evidence to suggest an association between leather tanning and nasal cancer (IARC 1981). Case reports and epidemiological studies since the IARC evaluation have indicated increased risk for cancers among leather tanning and finishing workers—including lung cancer, sinonasal cancer and pancreatic cancer associated with leather dust and tanning (Mikoczy et al. 1996) and bladder cancer and testicular cancer associated with dyes or solvents in the finishing process (Stern et al. 1987). None of these associations is clearly established at this time.