formaldehyde - Sciencemadness Dot Org

366*
FORMALDEHYDE
spiration can be obtained by treatment of the dyed fabric with formaldehyde.
Direct colors whose molecule? contain two or more hydroxyl groups,
one or more amine groups, and one or more azo (X:X—) linkages are
highly soluble in water and tend to bleed easily in water or alkaline solution.
It is this type of dye which is claimed to be particularly susceptible to
improvement by an after treatment of the fabric with formaldehyde 38 .
It is probable that formaldehyde acts as a color stabilizer by reacting with
the hydroxyl or amino groups of the dye molecules to form methylene
derivatives of low solubility 43 . There is also the possibility that formaldehyde
may actually couple the cellulose to the dye. According to Geigy 34
cotton dyed with an azo dye should be immersed after washing in a solution
of 0.5 kg of 40 per cent formaldehyde in 200 liters water and allowed to
stand for one-half hour at room temperature. The formaldehyde treatment
may also he carried out at elevated temperatures, in slightly acid
media, or in alkaline solution. Another method 23 employs a warm bath
containing 3 of 35 per cent formaldehyde and 1 to 2 per cent bichromate in
which the dyed fabric is soaked for 20 to 30 minutes, washed, and dried 41 .
Quirnr^ states that the insolubilising action of formaldehyde on the amino
groups of special direct colors appears to give better wash fastness on filament
and spun viscose rayon than on cotton and mercerized cotton. The
fastness of dyed cellulose fibers to water, acid boil, and wet ironing is also
reported to be improved by treatment with condensation products of a
polyethylene polyamine7 e.g. diethylenetriamine, formaldehyde, and a
ketone such as acetone 58 .
Miscellaneous Effects. A large number of special effects other than
those which have already been mentioned can be obtained by formaldehyde
treatment of a wide variety of cellulosic fibers including esters, ethers,
and other special derivatives. The following examples based on the claims
of patent processes are illustrative:
Fabrics containing warp and highly twisted weft yarns of an organic
cellulose derivative are treated with, e.g., 1 per cent, formaldehyde to
harden the warp yarns 22 .
The elasticity of cellulose acetate fibers is increased by treatment with
thiourea, guanidine or dicyandiamide, and formaldehyde or hexamethylenetetramine
18 . Cellulose acetate fabrics are treated with formaldehydeurea
resins to increase their resiliency 17 .
Cellulose acetate fibers are curled by treatment with a hot aqueous solution
containing hexamethylenetetramine and urea 19 .
Formaldehyde derivatives are often employed to render various finishes
more lasting. It is claimed, for example, that: (a) starch finishes may be
improved by applying a 1 per cent methyoxymethylpyridinium chloride
solution to the finished fabric, drying and baking 21 , (b) flame-proofing