Dyeing With Basic Dye

(ACRYLIC )

About Basic Dye These are salt of organic bases had free basic

amino groups capable of reacting with acids Also known as cationic dyes

In aqueous solution dye ionizes into coloured cations and colourless anions

Basically insoluble Converted into their hydrochlorides, sulphates

etc. to impart solubility Generally used to dye Acrylic, modacrylic, wool

& silk Poor colour fastness properties with wool &

silk and not used now

Properties of Basic Dyes Basic Dye is an Ionic Dyes with POSITIVE

CHARGE (D+)GOOD WATER SOLUBILITY – best below

pH 7 Posses high colour value (TINCTORIAL

VALUE) Almost UNLIMITED SHADE RANGE - Many dyestuff have F L U O R E S E N C E

P R O P E R T I E S - L i g h t f a s t n e s s on acrylics v a r i e s from

POOR TO GOOD. On other fibers it can be VERY P O O R .

W a s h f a s t n e s s is g e n e r a l l y GOOD - C h l o r i n e f a s t n e s s is POOR - High strike rate - Poor l e v e l i n g Combines with tannic acid to form INSOLUBLE

COMPOUND Do not have affinity towards cotton

Requires mordanting with tannic acid These are made specially to dye acrylic fibres

Produces all round fastness

Properties of Basic Dyes

Chemical structures of some typical cationic dyes

Acrylic Fibre (CH2=CH-CN)

100 % Polyacrylonitrile is very difficult to dye

• No Dye accepting group.• Glass transition temperature is very

high.• Highly compact structure.

So copolymer of colour attracting group are used to dye Acrrylic fibre.

Dyeing with Basic Dye – Dye Mechanism

Basic dye can be used depending upon the kind of dye sites introduced into the fibre during co-polymerisation

Co-monomers with anionic group are used which will attract the cationic coloured radical of a basic dye molecule

Ac = Acrylic fibre polymerSO3

- = Negatively charged sulphonate group

AcSO3- = Acrylic fibre polymer containing negatively

charged sulphonate group which is the acidic group and also the dye siteD+ = Dye cation

Dyeing with Basic Dye – Dye Mechanism

AcSO3- + D+ = AcSO3

-+D

The colouring component of basic dyes is the cation

The dye cation is adsorbed on the fibre surface which is negatively charged The negative potential of the fibre is thus

neutralised Diffusion of the dye from the surface to the fibre

interior Ion exchange with the dye sites inside the fibre

Other Chemicals used during dyeing

Acetic acid Acetic acid is used to dissolve the dye completely.

Otherwise aggregates can be formed with aqueous solution

Cationic retarder To prevent uneven dyeing of acrylic fibres with

basic dye a cationic retarder is added to the dye liquor Cationic retarder competes with the cationic

retarder Prevents the dye on rushing onto the fibres Ensures more level dye

Dyeing Acrylic Fibres With Cationic Dyes

Dyebath preparation: The dye powder is usually pasted with acetic acid (2-5gpl) and then mixed with boiling water. Preparation of a paste with methanol and addition of warm or hot water is sometimes a useful alternative. Some cationic dyes are not stable in boiling water. Many react with alkali to give colorless products.

Dyeing procedure: The dye solution is often prepared by pasting with acetic acid, and a stable pH of 4.5 to 5.5 can be obtained by addition of sodium acetate to buffer the solution.

A typical procedure for dyeing acrylic material

A typical procedure for dyeing acrylic material

If dye additions are needed to give the correct shade, the bath temperature is first slowly reduced to below 80 °C. Acrylic materials are quite thermoplastic. They easily form crack marks and creases and texturised acrylic filaments also readily lose their characteristic bulk. After dyeing is complete, the bath is slowly cooled to 50–60 °C to avoid these problems. Rapid cooling by addition of cold water to the dyebath can be disastrous as it causes immediate setting of creases in the goods.

The material is finally rinsed, and possibly given a mild scour with a non-ionic detergent and a little acetic acid plus a softening agent.

Fastness Properties of Basic Dye

FastnessBasic dye on acrylic have an excellent

light fastness

Have a very good wash fastness Due to very good affinity between the basic

dye and the acrylic fibre and the hydrophobic nature of acrylic

The wash fastness rating is around 4 - 5

Questions??

Why are basic dyes called so? State any four properties of basic / cationic dye.

Explain how cellulose may be dyed with a basic dye using tannic acid

Explain the mechanism of dyeing of acrylic fibres with cationic dyes