Degreasing is an essential process in tanning or fur processing. Only by removing the natural oils contained in the bare skin to a certain extent, can the collagen fibers be loose, creating favorable conditions for the smooth progress of various processes such as back tanning and other processes, so that the finished leather can reach a better state. Otherwise, due to the water resistance of the natural oils contained in the leather plate, it will be difficult for the back tanning, fatting, dyeing, coating and other processes to proceed smoothly, resulting in stiff leather feel. The surface is greasy, and the coating is easy to fall off.
According to the different degreasing methods, degreasing materials mainly include alkali, solvent, surfactant and enzyme. Solvent degreasing has high degreasing efficiency, but the cost is high, the pollution is large, the solvent recovery is difficult, so it has rarely been used alone, only as a component of degreasing agent.
Now generally mentioned degreasing agent mainly refers to the surfactant as the main component of degreasing material, the advantages of enzymatic degreasing more and more attention, so the following mainly introduces these two types of materials.
Emulsifying degreaser as a degreasing surfactant requires its own strong emulsifying ability, cationic surfactant emulsifying ability is low, so degreaser is mainly based on anionic and non-ionic emulsifiers, such as: Anionic surfactants such as sodium dodecyl benzene sulfonate, sodium n-butylnaphthalene sulfonate, sodium dodecyl sulfate and non-ionic surfactants such as OP 10, AEO-9, Perega-15 are the main components of degreasing agents or common degreasing materials in domestic tannery. Another reason why cationic surfactants are rarely used as leather degreasing is that leather degreasing, especially in the preparation section, is generally carried out under alkaline conditions, and the leather glue is negatively charged at a higher pH value, and it is easy to combine cationic materials, which will cause the cationic surfactants to lose the role of emulsifying grease. In the same way, the degreasing effect of anionic emulsifiers on pickled skin and blue skin is also reduced. Non-ionic emulsifiers have a wide range of action, but the degreasing effect at high pH is better than that at low pH.
Now the use of degreasing agents is wide, but it is also a surfactant complex at a high pH value, and some products have organic solvents, alkali and other ingredients to increase the degreasing effect. The composite of various materials not only makes the product have the function of emulsification and degreasing, but also has the function of wetting, permeation and dispersion, which can be used in multiple processes. Compared with other pre-treatment additives, domestic degreaser products have been developed relatively more, but basically are based on alkyl benzene sulfonate, flat plus, JFC, AEO and OP components and solvents, due to the restrictions of emulsifier varieties, domestic degreaser compared with imported products, most of them are inexpensive products, there is a certain gap in degreasing effect. Now the requirements for degreasing agents are getting higher and higher, not only the degreasing effect is good, but also have a wide range of use conditions, that is, the degreasing agent is required to have high acid resistance, alkali resistance, electrolyte resistance and temperature resistance to meet the use in different processes, in addition, it also requires degreasing agents with high efficiency, low cost, small dosage, low foam, easy to clean and other properties. It will not have a big negative impact on the water resistance and atomization value of waterproof leather, car cushion leather, etc. From the environmental perspective, it is necessary to develop and develop highly active surfactants, reduce their dosage, reduce the load of wastewater treatment, and more importantly, develop and develop biodegradable surfactants with high degreasing power, such as alkyl alcohol ether carboxylate (AEC) and amide ether carboxylate (AMEC).
Although the emulsification method and saponification method of defatase replace solvent defatting, the cost is low and the solvent pollution to the environment is solved, but the emulsification degreasing method itself has some problems. The degreasing temperature of raw skin is generally below 40℃, the degreasing effect is good at high temperature, but the temperature is too high, the skin will be greatly damaged, degreasing below 40℃, especially degreasing below the melting point of fat, at this time the fat is still solidified, the fluidity is poor, and the emulsification effect is poor; Emulsifying degreasing, grease into the wastewater, increase the biochemical load of wastewater, and most of the surfactants in degreasing agents, especially non-ionic emulsifiers, are very stable, difficult to degrade at non-extreme pH and high temperature, will bring new pollution. Due to the above problems, more and more attention has been paid to enzyme degreasing methods in recent years. A lot of work has been done on enzymatic degreasing. Enzymatic degreasing mainly uses lipase to catalyze the hydrolysis of oil molecules. Early lipase is mainly extracted from the pancreas of animals or produced by mold fermentation, its ideal pH value is 5 ~ 8, it is not suitable for use in the immersion or liming process, and at low PH value, the enzyme hydrolysis of oil molecules is easy to produce fatty acids, and even the formation of metal soap and not easy to remove. Most of the fat in the skin exists in the fat cells, lipase has no effect on the cell membrane, so it can not effectively remove the fat, and the fat is expensive, so the lipase degreasing method has not been widely used in the process of leather production.
Enzymatic degreasing in the application of leather production mainly depends on the performance of lipase, conditions of use and price and other factors, from the application point of view, the first to develop appropriate lipase products, that is, lipase in the pH8 ~ 11 range has high activity and stability, high heat stability (35℃), it is best to be compatible with surfactants. Such lipases can be used in processes such as soaking, liming and softening. Fatty acids and other substances produced by the hydrolysis of fats catalyzed by lipase can be dissolved in water or easily emulsified and removed at high pH value. Since lipase has almost no effect on the cell membrane, in order to further enhance its degreasing effect, the appropriate protease is added to the lipase degreasing to destroy the fat cell membrane, which is also the reason why the degreasing material (emulsifier or lipase) that does not destroy and inhibit the enzyme during the enzyme softening process will get a better degreasing effect.
Foreign studies believe that the main components of the cell membrane are phospholipids and proteins, which can be treated with phosphoesterase and protease respectively to achieve the effect of destroying the cell membrane, and then treated with lipase or surfactant to achieve the ideal degreasing effect. Therefore, it is required that the lipase be compatible with the protease, because the protease may have a hydrolytic destructive effect on the lipase (a protein). The application of defatase in tanning production must also have an appropriate price, that is, a suitable price. Performance ratio. At present, the lipase products used in leather are basically blank in China, and in recent years, many foreign leather companies have launched some degrease products, and have been applied in tanneries to a certain extent
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