Unit 1- Introduction of Tanning
- 1. NOTES PREPARED BY Mrs D.PREETHA
- 2. Unit 1 INTRODUCTION Sturcture and composition of animal skin-terminology involved in leather tanneries-chemistry of beam house processes-soaking, liming, unhairing, deliming, bating and pickling-preservation of animal skin-salt curing and brine curing UNIT II MATERIALS AND METHODS OF TANNING Vegetable tans –catechol tans-pyrogallol tans-vegetable tanning process and applications of vegetable tanned leather-Chrome tanning-chemicals used-method-type of leather obtained and its uses-aldehyde tanning-Artificial leather-Corfam-synthetic tans UNIT III POLLUTION AND TREATMENT OF TANNERY EFFLUNT Various finishing process in tanneries – drying – bleaching – fat liquoring – dyeing – calendaring Pollution caused by leather tanneries –Treatment of tannery effluents – primary , secondary and tertiary treatment. UNIT IV TEXTILE FIBRES Classification fo textile fibres – difference between celllulosic and synthetic fibres –identification of fibres by burning and solubility tests – chemical structure-physical and– chemical properties of cotton-silk. UNIT V BLEACHING ,DYEING & FINISHING Bleaching of cotton fabrics –peroxide bleaching –hypochlorite bleaching –dyeing of cotton with vat dyes-dyeing of wool acid dyes-dyeing of polyester with disperse dyes-textile finishing – mercerization – water repellent and water proof finish.
- 3. UNIT 1 Sturcture and composition of animal skin It is nothing but the skin of the animals were usually chosen for clothing since they wer bigger ,stronger and warmer. the tanned skin does not become hard or britting material. And is know as leather. skin-terminology involved in leather tanneries There are two types of leathers tannage first one is Before tannage another one is After tannge . The before tannage process is normal sequence .The After tannage is a order is a varies considerly for different types of leathers one is Heavy leathers another one is Light leather. chemistry of beam house processes-soaking, liming Soaking is the process of putting the skin in water to bring the dried skin back to flaccid. Liming may be carried out at the same time by immersing the hides and skins completely in lime and water. Unharing Leathe processing involves a series of unit operating of unharing is the first major step in the leather making. Deliming The deliming operation in leather processing is a drum paddle or pit based operation where two main objective are met.removal of alkali from the pelt and the consequent dewelling of the fibres. bating and pickling It is the further step in the purification of the hide prior to tanning making it cleaner, smoother and fine.Pickling is a process to treat the hide with salt and acid to bring the skin to the desired pH for either preservation or tanning. Preservation of animal skin Curing and brine curing The method is used to prevent putrefaction or damage of the skin before tanning is called curing. Brine curing is a one of the most efficient method of curing.it can be done in less time.
- 4. Sturcture and composition of animal skin It is nothing but the skin of the animals were usually chosen for clothing since they wer bigger stronger and warmer. the tanned skin does not become hard or britting material. And is know as leather. Other animal coverings such as the arthropod exoskeleton have different developmental origin structure and chemical composition T he adjective cutaneous means "of the skin" (from Latin cutis, skin). In mammals the skin is an organ of the integumentary systemmade up of multiple layers of ectodermal tissue and guards the underlying muscles bones ligaments and internal organs. Skin of a different nature exists in amphibians reptiles and birds All mammals have some hair on their skin, even marine mammals like whales dolphins and porpoise which appear to be hairless. The skin interfaces with the environment and is the first line of defense from external factors. For example, the skin plays a key role in protecting the body against pathogens and excessive water loss. Its other functions are insulation, temperature ,egulation, sensation, and the production of vitamin D folates. Severely damaged skin may heal by forming scar tissue This is sometimes discoloured and depigmented. The thickness of skin also varies from location to location on an organism. In humans for example, the skin located under the eyes and around the eyelids is the thinnest skin in the body at 0.5 mm thick, and is one of the first areas to show signs of aging such as "crows feet" and wrinkles. The skin on the palms and the soles of the feet is 4 mm thick and is the thickest skin on the body. The speed and quality of wound healing in skin is promoted by the reception of estrogen
- 5. TANNING Tanning is the process of treating skins and hides of animals to produce leather A tannery is the place where the skins are processed. Tanning hide into leather involves a process which permanently alters the protein structure of skin, making it more durable and less susceptible to decomposition and also possibly coloring it. Before tanning, the skins are unhaired, degreased, desalted and soaked in water over a period of 6 hours to 2 days. Historically this process was considered a noxious or "odoriferous trade" and relegated to the outskirts of town. Traditionally, tanning used tannin an acidic chemical compoundfrom which the tanning process draws its name (tannin is in turn named after an old German word for oak or fir trees, from which the compound was derived). The use of a chromium (III) solution was adopted by tanners in the Industrial Revolution
- 6. Soaking In soaking, the hides are soaked in clean water to remove the salt left over from curing and increase the moisture so that the hide or skin can be further treated. To prevent damage of the skin by bacterial growth during the soaking period, biocides, typically dithiocarbamates, may be used. Fungicides such as 2-thiocyanomethylthiobenzothiazole may also be added later in the process, to protect wet leathers from mold growth. After 1980, the use of pentachlorophenol and mercury-based biocides and their derivatives was forbidden
- 7. Liming Main article: Liming (leather processing) After soaking, the hides and skins are taken for liming: treatment with milk of lime (a basic agent) that may involve the addition of "sharpening agents" (disulfide reducing agents) such as sodium sulfide, cyanides, aminesetc. The objectives of this operation are mainly to: Remove the hair and other keratinous matter Remove some of the interfibrillary soluble proteins such as mucins Swell up and split up the fibres to the desired extent Remove the natural grease and fats to some extent Bring the collagen in the hide to a proper condition for satisfactory tannage The weakening of hair is dependent on the breakdown of the disulfide link of the amino acid cystine, which is the characteristic of the keratin class of proteins that gives strength to hair and wools(keratin typically makes up 90% of the dry weight of hair). The hydrogen atoms supplied by the sharpening agent weaken the cystine molecular link whereby the covalent disulfide bond links are ultimately ruptured, weakening the keratin. To some extent, sharpening also contributes to unhairing, as it tends to break down the hair proteins. The isoelectric point of the collagen in the hide (this is a tissue-strengthening protein unrelated to keratin) is also shifted to around pH 4.7 due to liming.
- 8. Unhairing and scudding Peeling hemlock bark for the tannery in Prattsville, New York during the 1840s, when it was the largest in the world Unhairing agents used at this time include sodium sulfide sodium hydroxide sodium hydrosulfite calcium hydrosulfide, dimethyl amine and sodium sulfhydrate The majority of hair is then removed mechanically, initially with a machine and then by hand using a dull knife, a process known as scudding.
- 9. Deliming and bating Main article: Deliming The pH of the collagen is brought down to a lower level so the enzymes may act on it, in a process known as deliming. Depending on the end use of the leather, hides may be treated with enzymes to soften them, a process called bating. In modern tanning, these enzymes are purified agents, and the process no longer requires bacterial fermentation (as from dung-water soaking) to produce them. Pickling Once bating is complete, the hides and skins are treated first with salt and then with sulfuric acid in case a mineral tanning is to be done. This is done to bring down the pH of collagen to a very low level so as to facilitate the penetration of mineral tanning agent into the substance. This process is known as pickling. The common salt (sodium chloride) penetrates the hide twice as fast as the acid and checks the ill effect of sudden drop of pH.
- 10. The standard values of moisture content and salt saturation of salted hides and skins were noted as 40-48% and ≥ 85%, respectively. 34,36 According to these standart values, moisture contents of our skin samples were determined low (<40%) for 4 sheep and 6 goat skin samples; normal (40-48%) for 7 sheep and 8 goat skin samples; high (>48%) for 14 sheep and 11 goat skin samples. However, the growth of both moderately halophilic bacteria, proteolytic and lipolytic moderately halophilic bacteria was not affected by low moisture content. ... .Minimum and maximum ash content of salted hides and skins were respectively stated as 14% and 48%. 34 While ash contents of the salted sheep skins ranged from 12 to 30%, ash contents of goat skins were between 11-32% (Tables I- II). Our experimental results showed that ash contents of the all skins, which are mostly related to NaCl, were sufficient for the growth of moderately halophilic bacterial populations. ...
- 11. BRINE CURING 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.