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Dope dyeing: In dope dyeing, pigments are added to the polymer solution itself before extruding the fibers. The process provides the dyed fibers with excellent fastness properties. The dope dyeing applies to synthetic fiber only.
Dyeing is normally done in a special solution containing dyes and particular chemical material. Dye molecules are fixed to the fiber by absorption, diffusion, or bonding with temperature and time being key controlling factors. The bond between dye molecule and fiber may be strong or weak, depending on the dye used.
An unfavorable side reaction in the dyeing process is the conversion of the vinylsulfone group to the 2-(hydroxy)ethylsulfonyl group: [4] Reaction of vinylsulfone compounds with water/OH − during dyeing. The hydroxylated, unreactive dye has to be washed out during the post-treatment.
Although almost all dyeing can be done in a vat, the term vat dye is used to describe a chemical class of dyes that are applied to cellulosic fibre (i.e., cotton) using a redox reaction as described below. Because of the use of caustic soda, and the very high pH of the dye bath in the dyeing process, wool cannot be dyed using vat dyestuffs.
A very rare heterogeneous process is the fiber acetate process, which is only used for the production of cellulose triacetate as an end product. In this process, the cellulose is suspended in a non-solvent (such as benzene) and esterified with acetic anhydride in the presence of perchloric acid as catalyst.
Dow Chemical developed a synthetic process for indigo in 1915, and American industry and universities worked together to reverse engineer German chemical production secrets. After the war some American munitions factories converted to dye-works, intuiting that if the reverse was possible for the German chemical industry during the war, then it ...
Dietitians explain what red dye number three is, if you should be worried about it, and what to do with the food that has it now that it has been banned. The Fascinating Backstory Behind Red Dye No. 3
The like charges repel each other, and the addition of salt aids in dyeing by generating a positive charge on the cotton surface. [7] [8] The industry has predominantly used reactive dyes to color knitted cotton goods. The treatment of salt-laden, colored effluent generated by the dyeing process is one of the industry's primary concerns. Cotton ...