What is Reduction cleaning and its application?
Reduction cleaning, polyester textile dyeing or printing post-treatment process. The fabric is treated with sodium hydroxide and sodium hydroxide solution to remove the disperse dye on the surface of the fiber. Surfactants are often used in the treatment.
Disperse dyes are non-ionic dyes with simple molecular structure and extremely small molecules. The dye is soluble in water. With the help of a dispersant, the dye is uniformly dispersed in the dye solution in the state of fine particles. Under high temperature and high pressure, although the disperse dye molecules are small, it is not completely guaranteed that all the dye molecules can enter the polyester fiber during dyeing. Some disperse dyes will adhere to the surface of the fiber. If these floating colors are not removed, the fastness will be poor. At this time, the strong reducing agent used for reduction and cleaning will destroy the dye molecules that have not entered the interior of the polyester fiber to improve the fastness and improve the shade. The recovery and cleaning classification of polyester.
Reductive cleaning under alkaline conditions
Soaping agent + reducing agent (sodium sulfide or thiourea dioxide) + alkali (caustic soda or soda ash).
Soaping agent: non-ionic surface active agent, which is conducive to dissolving, dispersing and preventing re-staining of floating color. Commonly used flat addition of O and nonylphenol polyoxyethylene ether Np10 have good effects.
Cationic surfactant: It is especially suitable for completely removing disperse dyes adsorbed in spandex, and significantly improving the color fastness of polyester/spandex dyeing (especially dark colors) (black nylon staining can reach 4-5 levels)
Reducing agent: Compared with sodium hydroxide, thiourea dioxide has the advantages of small odor, low dosage and high durability (high unit price).
When the fusogenic powder is used in an overflow dyeing machine, most of the reducing cleaning liquid will be wasted by the oxygen in the air when it is sprayed, and the open-width washing can be used less.
After removing the air in the overflow dyeing machine with nitrogen in advance, it was found that the amount of insurance powder can be greatly reduced.
Reductive cleaning under acidic conditions
Soaping agent (same as above) + reducing agent (sulfinic acid) + acid (acetic acid).
The advantages of reductive cleaning under acidic conditions: it can be reduced to 80-90℃ after dyeing, without draining liquid, and directly reductive cleaning; compared with sodium hydroxide, the reducing agent used under acidic conditions is less consumed by air oxidation.
Reduction cleaning under acidic conditions is not a panacea. In fact, compared with alkaline reduction cleaning process, reduction cleaning under acidic conditions is more effective for azo disperse dyes, and sometimes it is not as good as traditional alkaline reduction cleaning for anthraquinone disperse dyes. This is the reason why many dyeing factories use acidic reducing agents to find that the effect is not as good as that of alkaline reduction cleaning.