Leather, natural

Leather-like materials now important in the market are of three main classes (/) vinyl-coated fabrics, (2) urethane-coated (synthetic) fabrics, and (J) man-made leathers. To appreciate their leather-replacement capabiUties it is necessary to know the stmcture of natural leather. 

Leather. Natural leather is made from hides, which are salted and cured, then taimed. Through the preparing process, useless matter which caimot be taimed, such as outerskin (epidermis) and flesh, are removed, leaving the tme skin (corium). In the tanning process, the fluid matter which maintains the skin in a flexible and moist condition is removed, and there remains nothing but the fibrous portion to be acted on by the tanning chemicals (1-3). 

Fig. 2. Schematic model of coUagen fiber bundle in natural leather.

Post Treatment. Coated fabrics can be decorated and protected by applying inks and coatings to the surface. Often the finished product is an attempt to simulate the look of leather. This is most common ia upholstery, luggage, and athletic bag constmctions where natural leather is the main competitor, although any number of decorative effects can be created and are used ia produciag products such as waHcoveriag. 

DNA, RNA, or protein, which can then be probed with a labeled sequence or antibody (Western blot assays), microscopy embedding, electrotechniques, skin protectants, microfilters, and others. Nitrocellulose continues to be used in photography, the manufacture of lacquers, patent and natural leathers, artificial pearls, process engraving, and cements. 

Naturally, leather absorbs some liquid water but mainly is water resistant. The leather industries do not claim that it is waterproof. So-called waterproof leathers are finished with water repellent agents such as organo-silicon, fluorocarbon and so on. Water absorption of leather can be tested by a static absorption method (ASTM D1815, 2000a). Cut the conditioned specimen with a circular cutter. Measure the diameter and thickness of the specimen. Calculate its volume in cubic centimetres. Weigh the specimen to the nearest 0.01 g. Immerse the specimen in distilled water at 23 1 °C in ahorizontal position with the grain side up. Leave the specimen immersed for a period of 30 min. At the end of immersion, take out the specimen and blot the surface of the specimen with filter paper to remove excess water. Weigh the specimen immediately to the nearest 0.01 g. Calculate the amount of water absorbed by the specimen ... 

Mixing CD complexes of thymol, eugeneol, isobutyl-quinoline, etc., to inolten PVC. a natural leather odor-emitting (leather-like) material, was prepared, e.g., for automobile door internal coverings. 

Natural leather is produced from the hides of animals by cross-linking the collagen protein contained in the hide. On the other hand, synthetic leathers are synthetic polymer composites with leatherlike properties. 

Leather must resist tearing, be stretchable, porous to moisture and air, and be capable of taking a surface texture and forming according to the requirements of fashion. Raw material scarcities and the work-intensive nature of natural leather preparation has led to a search for a synthetic leather over the last few decades. The well-known synthetic leathers consisting of fabrics covered with polyamides, polyurethanes, or poly(vinyl chloride) have been available for a long time. But these synthetic leathers cannot replace natural leather in all its applications, since the permeability and the feel of these materials are inferior. 

The material is now actually a preferred option to natural leather for many of the leading car manufacturers and their customers. 

Natural leather is a protein substance that can be dyed with acid dyes, among others. Finished leather also can be dyed or pigmented, the choice of color type depending on the nature of the finish. 

Qiang et al. used hb polymer with a terminal carboxyl group as an additive in auxiliary tanning of natural leather to improve the moisture absorption and permeability to water vapor of microfiber synthetic leather [261]. Recently, Ren et al. [262] prepared amino-terminated hb polyamide and grafted the same onto the polyamide microfiber synthetic leather employed for clothing, and organic... 

Haematin and haematoxylin are the coloring matter of longwood and have lost importance as a natural leather dye ( leather auxiliaries). 

The subsequent step is dyeing. RR-based products are only used as wetting agents, dispersers, leveling agents and after-treatment. Anionic, cationic and nonionic - surfactants are usually used. Natural dyes (- dyes, natural) such as yellow-wood or logwood extracts, are not used any more but may be revitalized if more natural leather would come in fashion. 

---