Premium
Relation between Physical State and Rate of Fading of Dyes
Author(s) -
Baxter G.,
Giles C. H.,
Lewington W. J.
Publication year - 1957
Publication title -
journal of the society of dyers and colourists
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.297
H-Index - 49
eISSN - 1478-4408
pISSN - 0037-9859
DOI - 10.1111/j.1478-4408.1957.tb02210.x
Subject(s) - fading , chemistry , substrate (aquarium) , chemical engineering , materials science , channel (broadcasting) , telecommunications , oceanography , computer science , engineering , geology
A theoretical analysis of curves expressing the rate of fading of dyes in different physical forms is given, illustrated by typical examples of the fading of dyes in transparent films, measured spectrophotometrically. Molecularly dispersed dye fades according to an approximate first‐order law (exponential decrease of rate), and dye in large particles according to an approximate zero‐order law (constant rate). In aggregated particles fading probably occurs only at the surface. First‐order fading occurs with some water‐insoluble dyes in “solid solution” in a hydrophobic substrate (collodion), and some surface‐active dyes in a hydrophilic substrate (methylethylcellulose) appear to exist mainly as molecular dispersions, since they also give first‐order fades. In contrast, entirely aggregated dyes, e.g. water‐insoluble dyes prepared in substance and incorporated in hydrophilic films, show zero‐order fades. The form of the fading‐rate curves of most water‐soluble dyes, however, suggests that the dyes are present in both forms, i.e. as a heterogeneous mixture of single molecules and aggregated material, the proportion of each varying according to the physical properties of the dye. The heat generated during irradiation causes some of the larger aggregates to break up. This may lead to a slight initial rise in depth of colour or, in special cases, to a fading rate which increases with time. The forms of the appropriate fading‐rate curves show that a disaggregating agent (phenol) and a cationic surface‐active dispersing agent, when mixed with acid dyes in films, decrease the amount of dye aggregate present. The fading rates of the Procion (ICI) reactive dyes in cellulose film are of the same form as those of most water‐soluble dyes, and appear to demonstrate that most of the dye is in some form of aggregated state or is enmeshed in crystalline regions of the fibre. The results explain why the light‐fastness grading of dyed fabrics may differ with the extent to which fading has progressed when the assessment is made.