Classifications

• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/04—Mineral tanning

Definitions

• the invention relates to a product and process of obtaining free-of-chrome tanned leathers with applications in the field of leather processing.
• wet-blue is bought and sold around the globe and provides the basis for more than 80% of total leather production [1].
• Wet -blue is obtained from raw hides / skins with basic chrome sulphate tanning, which is the standard tanning procedure.
• chromium (III) tanning agents uptake under typical technological conditions is of the order of 60 - 80 % of the offered quantities (typical offer: 80-90 kg Cr-tanning salts/t of pelt weight), with 3-7 kg Cr 3+ /t of raw hides /skins (2-7g Cr(III)/Lt of exhaust tanning liquor) discharged with the process effluent.
• Chromium (VI) and its salts are classified as known carcinogens not used for tanning and normally absent from chromium (III) tanning salts.
• leather and fur sector produce also leather wastes.
• the tannery can only transfer 1/3 of raw hides and skins into leather or other marketable products, while the rest has to be disposed/ incinerated.
• Leather wastes also contain chromium (III) due to tanning process. Chromium can occur in different oxidation states and its compounds behave differently. Most Cr(VI) compounds are highly toxic and classified as MAK III A 2 carcinogens. So, leather waste containing chromium is considered toxic for environment and man and is an important environmental issue for the footwear industry in recent decades. Also, it is a big problem with current costs in leather waste management in leather, fur and footwear sector.
• the tanning sector has been working to discover new tanning agents that give leather similar properties to those given by chromium (III) salts.
• Ti(IV) forms compounds with tanning properties, but they are difficult to obtain, as titanium salts can be completely hydrolysed with the separation of the metatitanic acid insoluble in water (TiO 3 H 2 ).
• titanium sulphate-based compounds are masked with formate, phtalate, glutamate, citrate, tartrate, acetate and are basified using agents such as sodium sulphite / magnesium oxide / ammonia, hexamethylene tetramine; at low pH they are fixed in leather due to H + - O 4 S(TiO) n SO 4 - + H complexes which react with functional groups of collagen, but also by physical deposition in the interfibrillary gaps of collagen as it is shown in the figure below (left).
• Zr(IV) forms complexes with tetrameric structures (see figure, right).
• Easy hydrolysis of zirconium complexes and their precipitation in the form of oxihydrates lead to the formation of white oxide sediments inside the fibrous structure of collagen, which stabilize collagen structure and provide the leathers with a white colour and very good fullness.
• Zr tanning compounds bind to polar amine groups of side chains of collagen, leaving the carboxyl groups unblocked, so that leather pretanned with zirconium salts does not hinder subsequent binding of chromium used for retanning to carboxyl groups.
• the technical problem solved by the invention consists in producing a mixed tanning product based on titanium and zirconium, which eliminates the disadvantages of tanning products based on Ti or Zr in that the product acts synergistically in leather, through the complexes of the two metals, and provides increased stability of collagen fixing bonds, as well as a bovine leather tanning process using the complex tanning product in order to obtain semi-processed chrome-free wet white leather.
• the tanning product according to the invention eliminates disadvantages of known tanning agents in that it contains 8-15% technical grade sulfuric acid of min. 95% concentration, 3-10% unrecyclable mixed metallurgic waste (selected so as to have a composition of min. 95% Ti, min. 95% Zr, max. 5% Al, max. 1% Fe and max. 0.5% V), 15-25% technical grade sodium citrate, and 1.0-4% technical grade magnesium oxide, having the appearance of a gray-white powder with a content of 8-18% Ti and Zr metal oxides, so that the ratio of TiO 2 :ZrO 2 ranges between 1:1 and 3:1 and the pH value of 10% solution is 1.8-2.2.
• Wet-white leathers obtained can be further processed in a conventional manner, using
• the composition of the tanning product obtained is the following: 4.45% Ti, 4.40% Zr, 9.85 Mg, 0.28%Al, 0.18% Fe, 0.09% V.
• the resulting wet-white leathers have a smooth grain, pleasant appearance, white colour, very good fullness and a shrinkage temperature of 72°C, which allows subsequent mechanical operations of wringing, splitting and shaving.
• Chemical characteristics of wet-white leathers are: 2.2% extractable substances, 3.83% metal oxides, 10% ash content, 4.43 pH of aqueous extract. Elemental analysis shows that wet white leathers contain: 1.38 mg/Kg Ti, 1.34mg/Kg Zr, 0.009mg/Kg Fe, 0.015mg/Kg Al, 0.005mg/Kg V.
• Leathers are further processed by retanning and finishing in a conventional manner.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Treatment And Processing Of Natural Fur Or Leather (AREA)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (2)

Cited By (1)

Citations (10)

• 2014
  • 2014-03-10 RO ROA201400191A patent/RO130248B1/ro unknown
  • 2014-03-14 EP EP14464004.2A patent/EP2918687A1/fr not_active Withdrawn

Patent Citations (10)

Non-Patent Citations (1)

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