Sodium hydrosulfide is primarily used for hair removal and tanning in the leather industry, and its specific applications and functions are as follows.
1. Hair Removal
– Principle: Sodium hydrosulfide, a strong reducing agent, breaks the disulfide bonds in hair, disrupting its structure and facilitating easy removal.
– Operation: During hair removal, prepare a solution of sodium hydrosulfide at a certain concentration. Soak the rawhide in it. Under specific temperature and time conditions, allow the sodium hydrosulfide to react fully with the hair to achieve hair removal.
2. Leather Tanning
– Principle: In tanning, sodium hydrosulfide serves as an auxiliary tanning agent. It chemically reacts with leather proteins, filling the gaps between leather fibers. This enhances the leather’s strength, toughness, and water resistance, and improves its appearance and feel.
– Operation: In the middle to late stages of tanning, add an appropriate amount of sodium hydrosulfide to the tanning solution. Let it work with other tanning agents. After a period of stirring and soaking, the sodium hydrosulfide can participate fully in the tanning reaction.
The ratio of sodium hydrosulfide to other tanning agents depends on the tanning process, leather type, and tanning objective. Here are some common scenarios:
2.1 Ratio of vegetable tannin to sodium hydrosulfide
– Vegetable tannin: Generally 10% – 30% of the leather weight. It provides tanning properties, giving leather durability and flexibility.
– Sodium hydrosulfide: Usually 0.1% – 0.3% of the leather weight. As an auxiliary tanning agent, it enhances leather’s softness and grain fineness. For example, in some high – grade leather retanning processes, using 0.2% sodium hydrosulfide with 15% vegetable tannin can make the leather grain tighter and softer.
2.2 Ratio of synthetic tannin to sodium hydrosulfide
– Synthetic tannin: Generally 3% – 10% of the leather weight. It has good filling and water – resistance properties, boosting leather’s strength and wear resistance.
– Sodium hydrosulfide: About 0.1% – 0.2% of the leather weight. When used with synthetic tannin, it promotes tanning agent penetration for a more uniform tanning process.
2.3 Ratio of chromium tanning agent to sodium hydrosulfide
– Chromium tanning agent: Usually 3% – 5% of the leather weight. It’s a common tanning agent that gives leather high tensile strength and water resistance.
– Sodium hydrosulfide: Generally no more than 0.2% of the leather weight. In chromium tanning, it adjusts the pH of the tanning solution to better suit tanning agent penetration and binding.
2.4 Other tanning agents and sodium hydrosulfide ratio
– Zeolite tanning agent: About 5% of the leather weight. It has good filling and stability properties in the tanning process.
– Sodium hydrosulfide: About 0.2% of the leather weight. When used with zeolite tanning agent, it improves tanning efficiency and quality.
3. Other Roles
– Softening: Sodium hydrosulfide, used to make polysulfides, accelerates the softening of dry hides during water immersion. This makes leather easier to process and softer, better preparing it for subsequent steps.
– Desulfurization: Acting as a leather desulfurizing agent, it effectively removes sulfur compounds from leather. This prevents quality issues and processing problems, ensuring leather’s stability.
– Environmental: In leather processing wastewater treatment, sodium hydrosulfide reacts with heavy metal ions. It forms insoluble sulfide precipitates, effectively removing heavy metals, reducing wastewater toxicity, and lessening environmental pollution.
