1. Chrome tanning agent: used for various inorganic salt tanning agents. The preferred component is trivalent basic chromium salt. Strong combination with protein fiber endows chrome tanned leather with the characteristics of softness, high strength, washability and difficulty in de-tanning. The finished leather has light color, beautiful appearance, good dyeing and finishing performance, good ductility, good moisture and heat resistance and stability, and the shrinkage temperature is about 100℃. When preparing chrome tanning agents in tanneries, dichromate is usually used to react with sulfuric acid, and then industrial glucose is added for reduction. The processing process is complicated and the pollution is serious. Now, ready-made solid hexachrome tanning agents can be purchased directly from the market. The chrome tanning liquor is concentrated and dried to make powder tanning agent for sale, and the finished product is dark green powder.
2. Zirconium tanning agent: Tanning with zirconium tanning agent began in the early 1930s. Compared with aluminum salt, iron salt and chromium salt, it is a new type of inorganic tanning agent. Its main feature is that the tanned leather is pure white with better filling performance, and the tanned leather feels full and firm. Common zirconium salts include zirconium sulfate and zirconium chloride. Because its tanning performance is better than that of zirconium chloride, zirconium sulfate is commonly used. Tanning is generally done by dry powder and pickling.
3. Aluminum tanning agent: Aluminum tanning agent is an early tanning agent. Before chrome tanning agent appeared, leather and fur were widely used to make leather, glove leather, saddle leather and fur. Its characteristic is that tanned leather is pure white, soft, fine and compact with good ductility. Its disadvantage is that it is not water-resistant, and water immersion or washing will lead to de-tanning. A new process of combining aluminum tanning with inorganic tanning agent or vegetable tanning agent can produce various kinds of leather for various purposes.
4. Plant tanning agent: Polyphenol tanning agent extracted from roots, stems, leaves, skins, trees, fruits and shells of plants, containing tannin organic polyphenols. Powdered materials become tanning agents directly or after sulfitation treatment, and vegetable tanning agents are the main tanning agents of shoe leather, industrial leather and luggage leather, which also make the retanning agents of light-colored leather light in color, strong in toughness, elastic, unbreakable and good in wear resistance.
5. Oil tanning agent: Oil tanning agent is a method for tanning valuable leather, which is formed by oxidation of unsaturated fatty acids, animal oils and vegetable oils and chemical reaction with bare skin collagen. At present, synthetic oil tanning agents have been widely used to replace precious fish oil, and synthetic oil tanning agents have been replaced by new formaldehyde tanning methods.
6. Formaldehyde tanning agent: Aldehydes and their derivatives are generally not used as the main tanning agents in leather making. Mainly used for composite tanning such as pre-tanning and retanning. It can be used in combination with inorganic tanning agents such as aluminum, chromium, zirconium and titanium, and can also be used as synthetic tanning agent. Formaldehyde has a strong adsorption capacity on protein, which can significantly increase the shrinkage temperature of finished leather.
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