A colorant is a substance that penetrates and remains coloring in a uniform way a textil fabric. “Remaining” means that the colorant will retain the same tone and concentration during the fabric´s life time. Each colorant has to be selected to fulfill the quality standards required for the final fabric´s use, because every piece of fabric has a defined purpose.
For the colorants chemist, a colorant is a non staurated structures combination containing certain groups known as Chromophores and Auxochromes.
Chromophores give color to the molecule and Auxochromes intensify color and improve the colorant´s final afinity by fiber.
Some of the more common Chromophores and Auxochromes are listed in the next table:
Pigments in Fabrics:
CHROMOPHORES AUXOCHROMES
The combination of Chromophores and the non saturated structure is called a Chromogenous: two benecic rings are bonded by a group called Chromophore (-N-N). AZO Group has a yellow color, but when there are Auxochromes missing, it has a dark red low tone and a very few afinity or maybe none for the fiber. Through Auxochromes adittion is possible to obtain a commercial colorant.
This colorant has afinity for fiber, the obtained color is way more intense than the equivalent Chromogeneus and besides there is a Barochromic effect in its tone (the abstortion´s peak shows a longer wave´s longitude than its equivalent Chromogeneus).
There have been a lot of efforts and research looing for a relation between color and its chemical constitution.
Generally, intensity is directly proportional to the molecular resonance and the colors resistant properties are connected to the molecule´s physical and chemical stability as well as temperature, light, pH, etc.
Industrial Colorants Chemist “plays” with Chromophores and Auxochromes looking forward building blocks to creat a maximum intensiy - resistant colorant at the lowest cost.
COLORANTS CLASIFICATION
There are two ways to classify colorantes. The first one is based on the Chromophoric Systems´ chemical constitution, and the second one is based on the application methods.
None of these systems is completely satisfactory because there are included colorants in the same Chromophoric sistem that completely differ from its application.
Colorants utilites are determined by: molecular size, solubility groups, protons acceptance groups, chain´s longitude, etc. Depending on the chemical constitution, there are around 25 different colorant types.
Maybe the best way of getting into colorants chemistry is going to the classification in a higher detail in its application function, listing them in the next order:
