Abstract


Achieving the wash fastness specified by any retail organisation is not a straightforward exercise in the case of applying reactive dyestuffs to Cellulosic substrates.


Some of the problems involved are discussed in the full text.


Evidence, in the form of a practical working example, is presented to illustrate the value of understanding the basic principles involved.



Parameter

Before Dyehouse Audit

After Dyehouse Audit

Dyes Used


Procion H-EXL

Same Procion H-EXL

Time of Dyeing Method

275 min

155 min

Time of Wash-Off Process

390 min

124 min

Volume Effluent Produced

20,000 litres

10,000 litres

M&S C4A Test @ 60 C

Fail

Pass

Tensile Strength

Poor

Perfect



Full Article


2.1 Background


The consumer requires the assurance of all clothing and home textile purchases that they keep their appearance and fastness through domestic laundry, drying and ironing.


The dyer and finisher require the assurance of all dyes that he uses that they meet the fastness demands of the customer he is serving.


These fastness assurances are provided by the dyestuff supplier in their published literature.


With the majority of dyestuff classes, the claims of the dye supplier are relatively easy to achieve in practice.


The exception to the rule occurs in the case of the application of reactive dyes to Cellulosic fibres.


Firstly, not all the reactive dye which is applied exhausts on to the fibre.

Some remains in the bath.

Secondly, not all the dye which exhausts onto the fibre is chemically fixed to the fibre.

There is therefore, a significant amount of unfixed dye which must be washed off the fibre before the optimum fastness properties of the dyed fibre can be realised.


The fastness properties claimed by the reactive dye supplier are obtained under ideal conditions in which all the hydrolysed dye has been washed off the fabric.

This will be on small scale dyeings; and it is far easier to achieve a perfect wash-off on this scale than it is in bulk production.


Furthermore, the degree of fixation achieved in bulk production will not necessarily match that achieved on smaller scale dyeings.


The degree of fixation achieved in practice can even vary from one bulk dyelot to another; even on the same dye recipe on the same substrate.


The difficulties in achieving the optimum fastness properties are compounded even further when the substrate is varied.