126 



H. E. SCHROEDER AND S. N. BOYD 



AFFINITY OF ANIONS FOR WOOL 



a 



SO: 



oy 



S03" 





o 



z 



CO 



< 





03S 



S03 - 



CI2H25S03 



Oh^==n-(>n=n-A^ 



S03- 9 



Q-N = N 



Cr 



C5^N=N 



<9 



Z 



m 



< 



u 



Fig. 16 



i' dicated schematically in the graph (Fig. 15). It may be assumed that this 

 irxrease in the proportion of organic moiety decreases the water solubility of 

 the dye. As a result under dyebath conditions involving acid and some salts, 

 the thermodynamic activity or effective concentration of the dye may be in- 

 creased in the aqueous phase, and the equilibrium shifted in the direction of the 

 fiber. There are also indications that as the organic moiety becomes larger, the 

 dye molecule is held increasingly by forces in addition to the simple coulombic 

 ones, quite probably by the simple solution forces observed for ethylene tere- 

 phthalate or the associative forces so important in the case of cellulose. 



As the dye gradually acquires an ability to associate with the wool molecule, 

 its affinity increases to the point where it is not necessary that all the amine 

 groups be protonated. In fact pH can for certain classes of colors be raised to 

 the isoelectric point and for others to neutral conditions. This change with 

 structure is illustrated in Fig. 16. 



DYEING MECHANISMS 



POLYESTER CELLULOSE PROTEIN 



POLARITY OF ATTRACTIVE FORCE 



Fig. 18 



