Importance

Tanning was the first manufacturing process in which man engaged. It has been indispensable item throughout history and is necessary to modern civilization in form of shoes, clothing, harness, belts and endless other useful articles.

General characteristics of leather

1. Strength- indication of fiber quality
2. Tensile strength
3. Strength tearing stretch
4. Tongue tearing strength

Steps in leather manufacture

1. Curing animal skin is covered with countless bacteria, the amount and kind varying with the environment of the animal and with the quantity and nature of the filth on the skin. As soon as the animal is slaughtered and life processes cease, the proteolytic bacteria may and do quickly attack the skin. To arrest these degenerative processes, the producer of the skin “cures” it. The skin is dehydrated by treatment salt such as NaCl or by drying in the air or by combination of the methods. Skin which is salted prior to drying are termed dry – salted, while those not salt – cured but merely air dried are called flint or flint dried. Poorly cured skin will not produce the highest quality leather. Lack of uniformity in curing makes it doubly difficult to maintain uniformity of tannery process and of the finished leather.
2. Soaking – the first tannery process given the cured hide or skin is termed “soaking”, i.e. it is soaked in water or an aqueous solution of a chemical. The extent and kind of soaking process required vary with the nature and condition of the skin itself, with the subsequent processes and the kind of leather to be made. The objects of soaking are to rehydrate the skin, proteins, to partially solubilize and remove the denatured dissolved proteins, to open up the contracted fibrous structure of the skin, to remove the curing salt in the case of salted skin and to clean the surface of filth.
3. Liming and depilation – the commonest method in the use today for effecting the separation of the epidermal system from the true skin is also one of the ancient origin and is known as liming, from the fact that saturated lime water.

The four main objectives of the liming process are:

1. To act chemically upon the epidermal system, so that the skin maybe properly unhaired
2. Partially to saponify the skin lipids
3. To swell and hydrate the shin proteins satisfactorily
4. To condition the skin physically and chemically for subsequent operations

Bating – refers to the action of proteolytic enzymes upon the skin or hide following the unhairing process. When hen or pigeon manure the process used was so called “bating”, when dog manure the process was so called “puring”. Fowl manure was usually employed for heavy hides since it rapidly penetrated the hide, possibly because its content of urinary products. Regardless of the type of manure employed, the process was filthy, disgusting, and healthy. It was established that the essential principle of the manure bate was the proteolytic enzyme.

The effects of proteolytic enzymes on the skin

1. Effect upon the skin collagen – the bate enzymes digest and remove the degraded collagen formed during the liming process
2. Effect upon the skin elastin fiber – digestion of elastin fibers occurred only when drastic bating methods were used
3. Effect upon the skin keratinous and other degradation products – the main function of enzymatic bates is their hydrolyzing action upon the keratinous material remaining in the limed skin
4. Effect upon coagulation proteins present in the skin – the interfibrillary proteins are removed by the bate enzymes
5. Pickling – is the process of treating the bated hides and skin with mixed solutions of acid and salt. The process is important because the conditioning of hides and skins are necessary for their long storage.

Types of microorganisms found on leather

Microscopic examination of the hides revealed that a wide variety of microorganisms were present in fresh hides including cocci, staphylococci, both (+) and (-) bacilli, large and small motile and non-motile, both gram (+) and (-) spirilla, together with yeast, molds and protozoa.

The bacteria are the most important microorganisms in tanning. There are two most important general groups of bacteria in tanning:

1. Proteolytic – digest protein
2. Non- proteolytic – do not digest protein or if ever only on a small extent

Among the yeast, Saccharomyces mycoderma was observed to be a felt covering on old tan liquor.

Of the molds, the Penicilla and Asperilla abound in tanneries. Both belong to the family Mucidinaceae. The predominant mold from fermenting vat is Aspergillus niger with minor admixtures of a species of Penicillium (Citromyces) and yeast. Five species of Aspergillus were found to thrive: niger, flavus, fumigatus, terreus which belong to the family Dimatiaceae.

Deterioration of leather caused by microorganisms

Conditions favoring the growth and action of microorganisms

1. available moisture – mold fungi will not grow and germinate below about 70-75% relative humidity
2. temperature
3. kind of food available
4. reaction of environment

Types of destruction caused by microorganisms

Hides and skin must be protected against the damaging action of bacteria from time of slaughter of the animal until after the hides are tanned. Hides of the skin consist essentially of protein material and the common action of bacteria on protein is known as “putrefaction”. In this action, the proteins are decomposed, with formation of foul -smelling reaction products. The fundamental action of tanning is to render hides and skin imputrecible. Tanneries abound in microorganisms which had been called the “tanner’s invisible friend or foe”. Although these microorganisms can do but little damage to the stock after it has been tanned, they can still live and reproduce in wet leather. Molds and mild dews can render leather unsightly and must therefore be guarded against even after tanning.

In putrefaction, the real damage is done by the enzymes which the bacteria produce and secrete in the course of their own reproduction. In order to prevent any appreciable bacterial damage in soaking, it is thus necessary to do one of these three things:

1. destroy the bacteria
2. create a condition unfavorable to their reproduction and secretion of enzymes, or
3. create a condition unfavorable to the activity of the enzymes

Prevention of growth of microorganisms on leather

Mold inhibiting agents for leather

1. phenol derivatives – prevents mold growth on leather during submerging.
2. B-naphtol
3. Chromium salts are said to possess a slight antiseptic action which may play a role

Leather in the Philippines

The leather in the Philippines is comparable to of other countries in terms of production capacity and technology management and marketing expertise. The local textile industry is more advance and sophisticated than those of Malaysia, Thailand and Indonesia.