Dyeing Auxiliaries

Acid

A chemical that will produce a pH of less than 7 in water solution. Many acids are used in dyeing. They include acetic acid, citric acid, formic acid , hydrochloric acid and sulfuric acid. Several other compounds, such as sodium bi sulfate and ammonium sulfate form acids in solution through hydrolysis. When making solutions of acids or when diluting concentrated acids, always add the acid to water, never the other way around. This is because some acids produce a great deal of heat when they mix with water so much that a small amount of water added to a large amount of acid may actually boil and cause extremely dangerous spattering.

Alkali

A subclass of base, though often used to refer to any base. Partly because the term “basic” is often rather confusing, “alkaline” is often used to refer to solutions that are basic - having pH greater than 7. Some common alkali used in textiles are sodium hydroxide, potassium hydroxide.

Carriers

There are some dyeing assistants which are used in altering the dispersing propertied of the dyes and also change the physical and chemical properties of the fibre. These are called carriers. Carriers are certain hydrocarbon, Substituted hydrocarbon, Phenols, amino acids, amides, alcohol, asters, ketone etc. They accelerate the rate of dyeing of polyester fibre with disperse dyes from aqueous dyeing medium of up to 100⁰ C. In these way carriers helps the transfer of dye molecule from dye bath on to the fiber for dyeing polyester fabric.

Dispersing agent

The dispersing agent is used to assist the disperse dye to solubilize in water so that the dye molecule can be transferred from the dye bath to the textile substrate. Dispersing agent is used for dyeing the polyester fiber.Dispersing agent should be such that it is effective under dyeing or printing conditions and should be suitable to dye with hard water, high temperature and dyeing assistant.

Dye Fixing Agent

Properties of a good fixing agent includes good capability with cross linking agents without promoting yellowing effect; good leveling and migration properties, does not affect the shade, has good affinity for the fiber, stable to steaming and dry heat, and improved all round fastness properties of the fabric or yarn. Fixative is generally used after completing the dyeing or in printing paste.

Leveling agent/Retarder

A chemical added to a dye bath to reduce the rate at which dye attaches to the fiber; also called leveling Agents.A retarder may be required to prevent a dye from attaching to fibers so quickly that it would be very difficult to achieve level dyeing. Retarders are often used with acid dyes. They may work by quickly attaching to the fiber thereby temporarily keeping the dye from attaching, or by quickly attaching to the dye, temporarily keeping the fiber from attaching to the dye. Simple chemicals such as sodium sulfate may act as retarders for some dyes in some conditions. There are many retarders on the market that are proprietary mixtures of chemicals, often formulated to be companions for specific dye families. Reserving agents can be thought of as a special class of retarder. The availability to art dyers of retarders is limited. So leveling agents agents are used to level dyeing.

Reducing agent

A chemist’s term for any chemical that causes gain of electrons by another chemical with which it reacts the reducing agent is itself oxidized in the process.Many reducing agents are used in dyeing processes. They include thiourea dioxide , sodium bisulfite, sodium formaldehyde sulfoxylate, sodium hydrosulfite and others. They are often used in discharge and stripping processes,and are used for converting insoluble vat or sulfur dyes to the soluble form. Solid-chemical reducing agents are often flammable.

Salt

An ionic compound that is formed by a neutralization reaction (reaction of an  acid  with a  base ). The best known salt, common salt, or sodium chloride (NaCl) is extensively used as an electrolyte in dyeing.

Sequestering agent

The most undesirable impurities in Fibre, Common salt, Glauber salt, Caustic Soda and Soda ash are the di- and tri-valent cations e.g. Ca⁺⁺ ,Mg⁺⁺ ,Cu⁺⁺, Fe⁺⁺⁺ etc. These ions increase hardness of the process bath and generate iron oxides in the bath. Calcium and Magnesium reacts with alkali and precipitates as a sticky substance onthe textile material, which creates patchy dyeing and discoloration of the fibre. The ferric oxide with cellulose and creates small pinhole on the fibres also damages the machinery by scale formation in the nozzles and base. To overcome these deleterious effects in the scouring and bleaching bath adequate amount of sequestering agent must be used. Sequestering agents prevent di-and tri-valentmetal ions from interfering with the chemical processing of the textile material. It prevents catalytic damage of cellulosic fibres in bleaching bath during hydrogen peroxide bleaching.

Softener (fabric softener) 

A chemical or chemical mixture intended to give fabric a soft hand.Softeners act primarily as lubricants for fibers, allowing them to slide over each other more easily, giving a softer feel. Some also help reduce static electric charge build up, and some are antimicrobial. Many softeners are surfactants , and they may be  cationic,  anionic or  non-ionic . Household laundry softeners are often based on cationic surfactants. Softeners can interfere with dyeing, so they should be removed by  scouring . Some, such as silicones, can be quite difficult to remove.

Softener (water softener)

Chemical(s) added to water to prevent hardness ions from interfering with other solutes. Sodium hexametaphosphate (SHMP) is commonly used as a softener in dyeing. It will hold moderate amounts of hardness ions in solution. Soda ash will soften water, but it does it by formation of insoluble precipitates that can deposit on fabric or equipment, so SHMP is often added before soda ash to prevent this. Water softening systems which use common salt exchange hardness cations for sodium

 

Wetting agent 

A chemical that helps water penetrate a material or form a film over its surface; usually a surfactant.

Wetting agents are often used in dyeing to help the dye solution penetrate to the individual fibres (they don’t usually help the dye penetrate from the surface of the fibre to the interior of the fibre). They can help in some fibre arts dyeing processes, but too much in a dye solution used for direct application may make the dye spread more than is wanted.