Drying of leather

D. Skansi, Z. Bajza an A. Arapovic, Experimental evaluation of the microwave drying of leather, J. of the society of Leather Thechnologies and chemists, 79, 171-177. 

You can analyze material balance problems involving water vapor in air in exactly the same feshion as you analyzed the material balance problems for the drying of leather (or paper, etc.), depending on the information provided and sought. (Humidity and saturation problems that include the use of energy balances and humidity charts are discussed in Chap. 4.)... 

Tanamer [Cytec]. TM for sodium polyacrylate adhesive for use during the drying of leather. 

All techniques mentioned here have found industrial-scale applications or have been field-tested. Most of the feedstocks considered are in the form of liquids, pastes, sludges, or granular solids, except for the fluid bed dryer with active solids (for drying of leather) and the Remaflam dryer for textiles. New technologies for drying paper are covered in the chapter on pulp and paper drying. This chapter effectively updates several chapters in this handbook. 

Particulates Solids to be dried - particulates Adsorbent particles Enhanced heat/mass transfer rates, e.g., drying of leather... 

In paste drying the leather is spread on glass or porcelain plates and held in place with a low strength water-soluble paste. The plates are on a conveyor and the drying is done in a drying tunnel. The dryer usually has several temperature- and humidity-controUed zones to control the rate of drying and to prevent overdrying. 

Surface evaporation can be a limiting factor in the manufacture of many types of products. In the drying of paper, chrome leather, certain types of synthetic rubbers and similar materials, the sheets possess a finely fibrous structure which distributes the moisture through them by capillary action, thus securing very rapid diffusion of moisture from one point of the sheet to another. This means that it is almost impossible to remove moisture from the surface of the sheet without having it immediately replaced by capillary diffusion from the interior. The drying of sheetlike materials is essentially a process of surface evaporation. Note that with porous materials, evaporation may occur within the solid. In a porous material that is characterized by pores of diverse sizes, the movement of water may be controlled by capillarity, and not by concentration gradients. 

Numerous other uses of microwaves have appeared in the recent years - essentially drying of different types of material (paper, rubber, tobacco, leather. ..), treatment of elastomers and vulcanization, extraction, polymerization, and many applications in the food-processing industry. 

Now determine the zero point of the balance. Then grasp the sodium hydroxide-asbestos tube, which must not be touched with the fingers after wiping, with the small dry chamois leather cloth, open the stop-cock (stopper) for a short time so as to permit equalisation of pres- fig. 39... 

The variety of applications emphasizes the versatility of naphtha. For example, naphtha is used in paint, printing ink, and polish manufacturing and in the rubber and adhesive industries, as well as in the preparation of edible oils, perfumes, glues, and fats. Further uses are found in the dry-cleaning, leather, and fur industries and in the pesticide field. The characteristics that determine the suitability of naphtha for a particular use are volatility, solvent properties (dissolving power), purity, and odor (generally the lack thereof). 

Bg Cold Sweating.—In America, especially in Now York, New Hampshire, and in many parts of the Northern division of Pennsylvania, a process is in general use, called tho cold sweating, by which the hair can he removed,. and a yield of leather estimated at seventy to eighty per cent, acquired whilst, by oHier means employed, such as by steam and lime depilation, not more than thirty to forty per cent, of the dry hides are retained... 

The other hydrocarbon acids arc not a industrially significant. In many potential markets the lower price of acetic acid keeps them blocked out. Formic acid is used in textile drying and leather treatment. Propionic acid is used in the production of propionates, plasticizers, and herbicides Butyric acid finds a variety of specialty uses in producing plasticizers and esters. 

An unspecified enzyme was also used to treat leather wastes [70]. The degradation of leather wastes yielded a water-soluble hydrolysate that could be concentrated and dried to produce fine flour, which was claimed to be used for a variety of commercial purposes. 

Intestines were often used as casings for sausage and other foods. They were also used as condoms and to hold and carry water or other substances. Intestines were sometime slit lengthwise and dried like leather. The stomachs of larger animals were sometimes used as containers for water and other liquids. The stomachs and bladders of animals were used as pouches or bags to store pigments, mixed paints, herbs, medicines, and other powdered materials. 

Dry pile Ritter was the first who constructed piles of galvanic cells with dry separators, e.g., of leather. The function of these piles is based on the small amounts of humidity in these separators. 

Leather lettering pieces on the spines of leather-bound books are usually very thin and were attached with little paste. For this reason and because of chemical decay, many labels have either disappeared or can be levered off without difficulty. Reattachment with wheat paste can be hazardous for the novice because of the immediate weakening effect of the adhesive on the extremely thin and weak leather, which may also be darkened in the process. PVA is to be preferred because it has low water content. However, this may militate against its sticking to powdering leather, so it may be a good plan to paste the foundation of the panel and let it dry before reattaching the label with PVA. 

R) Microwave and dielectric energy is not suitable for mass drying of books because of the invariable presence of metal in the form of clips, staples, foil, and even iron and copper in the paper itself and the higher reaction to this energy by leather, some adhesives, etc. (6). 

The long established use of chromium salts in the tanning of leather has been reflected in interest in the determination of chromium in leather extracts. Generally the leather is leached with acids or complexing agents such as oxine to remove the metal salts. Della Monica and McDowell [189] recommended leather strips be air dried at 80°C for 24 h and ground to pass a 10 mesh screen. The powder was vacuum dried at 70°C for 16 h and then 100 mg refluxed with 25 ml 2M hydrochloric acid. The filtered acid was aspirated into a flame. For chromium a fuel-rich air/acetylene flame or a nitrous oxide/acetylene flame is to be recommended. 

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