Fatliquoring is an important process in leather processing. It can give the finished leather a soft, plump, elastic and other excellent feel and greatly improve its physical properties. Leather fatliquors are generally made up of emulsifiers, neutral oils and fatliquors. Leather fatliquoring is mostly emulsified fatliquoring. Neutral oils in fatliquoring materials are emulsified by emulsifiers and brought into the finished leather. The proportion of neutral oils (or modified oils) to emulsifiers and the types of active groups have considerable influence on Fatliquoring efficiency.

There are many classification methods of leather fatliquoring agents, but they can be divided into two broad categories, one is synthetic fatliquoring agents, the other is compound and functional fatliquoring agents. But from the product composition and function, fatliquoring agents in recent years are more complex and functional development.

1. Synthetic fatliquoring agent

The main sources of synthetic fatliquors are petroleum and petrochemicals. The former is paraffin and mineral oil, the latter is fatty acid, fatty acid ester, fatty amide and fatty alcohol. Synthetic methods include sulfonation, sulfation, chlorination, sulfuric chlorination, etc. Sulfonyl chloride and aliphatic amide can be obtained. The products have good bonding to leather, excellent light resistance and mercerizing properties.

2. Compound and functional fatliquoring agent

2.1 combined fatliquoring agent

After the 1980s, the development of bonded fatliquoring agents has been booming in China. The so-called bonded fatliquoring agents have a variety of active groups that can permanently combine with leather collagen or chromium ions on leather, thereby reducing the loss of oil in leather. Binding fatliquoring agent is usually made by introducing enough active groups which can bind to leather into oil molecules, reacting oil with alkyl alkanolamine, and then introducing carboxyl and sulfonic groups. The dry cleaning fatliquoring agent is mainly based on the high activity of alkyl alcohol amide. In China, Liu Yisheng et al. firstly used rapeseed oil amidation, esterification method to produce hydroxyethyl fatty amide succinate sulfonate binding fatliquoring agent. After fatliquoring, the leather has good plumpness, clean leather surface, wax, mercerization and strong adhesion. According to this synthetic method, RCF-bonded Fatliquor and CM-1-bonded fatliquor were synthesized from castor oil and cottonseed oil to meet the domestic demand for bonded fatliquor. However, as far as the most common fatliquoring agent SCF is concerned, the poor emulsifying ability, low electrolyte resistance and poor penetration also affect its performance. In view of the above problems, Li Ming used fatty acid methyl ester amide lactone to introduce carboxyl group, sulfonation to introduce sulfonic group method to prepare TCF-bound compound fatliquoring agent, its fatliquoring effect is prominent, product emulsification is good, permeability is strong, leather absorption and combination is fast, full and oily.

3 phospholipid fatliquoring agent

Phospholipid fatliquoring agent is generally divided into two kinds: one is made of natural phospholipids directly compound fatliquoring agent, such as Lu Xuyong and other sulfated castor oil, Pingjia and soybean phospholipids compound fatliquoring agent, which is characterized by good filling to make the skin plate thickening. Shen Yiding and others have prepared multifunctional phosphoric acid fatliquoring agents by using soybean phospholipids and mineral oils, modified mineral oils, high-carbon alcohols and soybean alcohol amide. The leather has waxy feeling, soft body and waterproof effect. In addition, many other domestic units also used a variety of phospholipid fatliquoring agents.

The other is that the lipids (mainly castor oil) are treated with phospholipids, and then combined with phospholipids and other auxiliaries to make phosphate fatliquoring agent. For example, Zheng Tao used castor oil and methanol for ester exchange, and phosphoric acid as phosphorylation agent to synthesize phosphate ester based products and other products for leather fatliquoring, its oil wettability, fullness is ideal. Some people use phosphorus pentoxide to modify oil by phosphorylation, but there are some problems in controlling the reaction. Alkylphosphate, which is mainly composed of synthetic monoesters, is the most suitable product for leather fatliquoring, and its softness, elasticity and waterproofness are guaranteed.

4 containing silicone fatliquoring agent

The silicone monomer in the fatliquoring agent is mainly due to its good lubricity and water repellency. It was introduced that the static water absorption of silicone waterproof leather was reduced from 105% untreated to 10-30% after treatment, and the dynamic flexion could reach more than 10,000 times. The leather showed good properties. Wangbaohe et al. treated the oil with organic silicon. They grafted the vegetable oil with hydroxyl-terminated polysiloxane and then sulfated it. The leather had a strong "silicon feeling" after fatliquoring. Zhang Zhongzhong grafted dimethyldichlorosilane with modified soybean oil so that silicone could not migrate in leather fatliquoring because of its polarity. The product is applied to suede leather and soft leather with obvious effect. The leather is soft, smooth, mercerized and waterproof.

5 electrolyte resistant fatliquoring agent

The electrolyte resistance of fatliquoring emulsion is based on the requirement of leather step by step fatliquoring. In the actual pickling, chrome tanning and fatliquoring, the fatliquoring emulsion needs sufficient acid resistance and electrolyte stability. Cationic fatliquoring agent or cationic/nonionic fatliquoring agent made of hexadecyl trimethyl ammonium chloride, engine oil, petroleum and nonylphenol polyoxyethylene ether was the earliest fatliquoring agent used in pickling and chrome tanning in China. This fatliquoring agent has the characteristics of acid and chrome tanning liquid in use. However, due to the single function, there are also some problems, such as poor absorption, and the use of other fatliquoring and retanning materials in the same bath. In view of the above problems in recent years, various units in the development of fatliquor have been given priority to consider, the products also have their own characteristics.

For example, Li Ming used in the development of acid-resistant multifunctional fatliquor.