MadSci Network: Chemistry

Re: Difference between absorption and covalent bonding of pigments?

Date: Thu Feb 28 12:21:37 2002
Posted By: Keith Allison, , dept: New Product, Technology & Development, Binney & Smith, Inc. (Crayola)
Area of science: Chemistry
ID: 1014078882.Ch

     When coloring fabric, the type of dye used depends on the type of 
fabric that is being dyed.  In general, the proper dyes bond covalently to 
the specific fabric.  For instance, negatively-charged dyes will bond to 
fabric containing positive charges.  Pigments, on the other hand, can also 
be used to color fabrics.  Pigments generally attach via absorption.
     Fiber-reactive dyes work differently in comparison to all other dyes: 
they are not bonded directly to fabric.  Instead, they are anchored to the 
fabric.  Specifically, dyes whose molecular structures contain hydroxy (-
OH) or amine (-NH2) groups are reacted with cyanuric chloride (C3N3Cl3).  
Cyanuric chloride serves as the anchor.  The dye covalently bonds to 
C3N3Cl3 by replacing one of the chlorines (Cl).  The resulting product of 
the reaction is called a "Procion dye".  When the Procion dye is put in 
contact with fabrics that also contain -OH and/or -NH2 groups in its 
structure, the remaining two chlorides on the cyanuric part of the Procion 
dye are replaced with the fabric via covalent bonds.  Thus, fiber-reactive 
dyes are covalently bonded to the cyanuric chloride which is, in turn, 
covalently bonded to the fabric.

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