Question

Which types of dye are not used to dye nylon and polyester fibres?
A.Vat dyes
B.Basic dyes
C.Disperse dyes
D.Insoluble azo dyes

Answer 1

Hint:Vat dyes can be used to dye cellulose fibre using a redox reaction. Basic dyes are mainly used in colouration of paper. Disperse dyes are water insoluble types of dyes. Azo dyes are used in the azoic dyeing process.

Complete answer:
Vat dyes are the dyes used in the process of vat dyeing (vat dyeing is simply dyeing which can take place in bucket or container or vat). Vat dyes are used for dyeing cellulosic fibres like cotton but not applied for wool because caustic soda is used in this process and wool being soluble in caustic soda makes it impossible to dye them with vat dyes. Vat dyes are less suitable for dyeing of nylon and polyester fibres.
Basic dyes are mainly used in colouration of paper. These are water soluble cationic dyes. They are applied to acrylic fibres. Usually acetic acid is added to the dye bath of basic dyes, it helps in the absorption of the due into fibres easily and effectively.
Disperse dyes are water insoluble types of dyes. These dyes are mainly used to dye substances like nylon, cellulose acetate, acrylic fibres etc. High temperature and high pressure is applied during dyeing via disperse dye.
Azo dyes are used in the azoic dyeing process. During the azoic dyeing process, fibres are treated with both diazo and coupling components in order to produce the required insoluble azo dye. Thus, azo dyes are directly produced onto fibres during azoic dyeing process. But the usage of this dye is limited due to the highly hazardous and toxic nature of chemicals being used.

Thus, the correct option is A. Vat dyes are not used to dye nylon and polyester fibres.

Note:
Sulphur dyes are cost effective and mainly used for dyeing of cotton with mainly dark colours. During this dyeing, fabric is treated with nitrophenol derivative and sulphide. Example: sulphur black1.