How chromium-free tanning agents and pH regulators are reshaping modern tanning processes

The leather processing industry covers natural leather (tanning) and artificial leather , combined finished leather Production is an important part of light industry. Although the raw materials and process paths of these two products differ, both heavily rely on various basic chemicals, additives, and functional materials during processing.

Natural Leather Processing

Natural tanning is usually divided into preparation stages, tanning stages, and wet dyeing and finishing stages.

Preparation section Raw hides need to be treated with soaking, depilation, soaking in ash, and degreasing. Sodium sulfide Commonly used as an auxiliary hair removal, Sodium hydroxide, calcium hydroxide (Lime) is used for soaking to expand fibers and saponify oils. Sodium chloride Used as a preservative to prevent the hides from spoiling during storage or transportation. This stage is also used Ammonia water And Hydrogen peroxide Assists in degreasing and cleaning the leather surface.

Tanning and re-tanning section Tanning is a key step in transforming raw hides into leather. Besides chrome tanning, the use of chrome-free tanning agents is gradually increasing, such as: glutaraldehyde, disaldehyde starch, disaldehyde cellulose and Furanformaldehyde (Furfural), which can be used as the main tanning agent or a secondary tanning agent. Phenol Used for the preparation of synthetic tanning agent monomers. Melamine, melamine and other applications can be used to produce resin-based retanning fillers to improve the fullness and firmness of leather.

Wet dyeing, finishing, and finishing section During the dyeing, greasing, and finishing stages, Formic acid, acetic acid It is commonly used to adjust the pH of dye baths and promote dye absorption. p-phenylenediamine It is an intermediate for some dyes and additives. Triethanolamine During the fat-adding process, it plays an emulsifying and pH regulation role. Urea, dicyande It can be used as a fiber softener or filler component. Coating formula Sodium acetate Used as a buffer, Sodium silicate Used as an adjuvant in certain filling or finishing formulations. Formaldehyde It is still used as a crosslinking agent under specific process conditions (must comply with safety standards), Glutaraldehyde It can also serve as a cross-linking function in coating.
General basic raw materials pH adjustment is widely used in various processes Anhydrous sodium carbonate, sodium bicarbonate, sodium hydroxide, formic acid, acetic acid 。 Aluminum sulfate, aluminum chloride, potassium aluminum sulfate dedecahydrate (Alum) serves as an aluminum salt and plays an auxiliary or hazardous role in re-tanning and filling.

artificial leather and joined forces finished leather Processing

Resin synthesis and modification

PU (polyurethane) or PVC (polyvinyl chloride) resins are artificial leather , combined finished leather The main material. Triethanolamine Can be used as a chain extender or crosslinking catalyst additive; Urea, dicyandiamide, melamine and other applications can be used to synthesize modified resins or as additives to improve coating performance.

Coagulation and processing auxiliaries

In wet PU mixing finished leather During production, Formic acid, acetic acid Used for pH adjustment and solidification speed control in coagulation baths. Anhydrous sodium carbonate, sodium bicarbonate, sodium hydroxide Used for acid-base neutralization and regulation in reaction systems or washing processes. Sodium chloride It is often added to coagulation baths to regulate the coagulation rate.

Filling and finishing are related

Sodium silicate Used as fillers or heat-resistant modifiers in certain specific formulations. glutaraldehyde, formaldehyde (Under strict control conditions) can be used for crosslinking specific functional coatings. Hydrogen peroxide Used as an oxidizer in some surface treatment processes. Aluminum sulfate, aluminum chloride, potassium aluminum sulfate dedecahydrate It is used in certain special finishes or surface modification processes.

Dyes and coloring additives

p-phenylenediamine As an intermediate, it can be used for synthesis and is suitable for use artificial leather surface dyes or pigment additives.