Abstract
The adsorption of two widely used fluorescent whitening agents (FWAs) on unbrightened cotton fabrics has been investigated as a function of temperature, hardness of the wash liquor, initial concentration of FWA in solution, and fabric to wash liquor ratio. Sorption efficiencies of FWAs have been studied using a UV spectrophotometry technique. A mechanistic model has been developed to describe the dissolution process of FWAs, convective mass transport into the fabrics, diffusion in the stagnant layer to the fabrics' surface, and adsorption of FWAs on cotton fabrics. Dual porosity of the fabrics (inter‐yarn and intra‐yarn porosity) has been considered by allowing two different regions (outer and inner areas of the cotton fabrics) where FWAs molecules can diffuse and adsorb. Good agreement between experimental and predicted whiteness benefit by the proposed mathematical model has been observed for the range of variables considered. © The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of 2017 American Institute of Chemical Engineers AIChE J, 64: 1305–1316, 2018
Highlights
Many organic fabrics such as cotton absorb in the short UVregion extending into the blue region of the spectrum which promotes a yellowing shade on the textiles
We investigated the adsorption of two widely used stilbene derivative fluorescent whitening agents (FWAs) on unbrightened and unbleached flat cotton fabrics as a function of temperature of the wash liquor, fabric to wash liquor ratio, initial concentration of FWAs in solution, hardness, and concentration of a commercial detergent with nil FWAs content
The adsorption isotherm of the FWAs is enhanced by the presence of salts in the wash liquor which may be due to electrostatic forces partially driving the process
Summary
Many organic fabrics such as cotton absorb in the short UVregion extending into the blue region of the spectrum which promotes a yellowing shade on the textiles. The extent of this shade depends on some properties of the polymer such as the number of conjugated systems, the degree of substitution, as well as the degradation products.[1] Bleaching of cotton textiles is carried out during its processing prior to dyeing and further finishing steps to remove the yellowish color and achieve a white appearance. The most common bleaching agent used industrially is hydrogen peroxide.[2,3] gradual yellowing and whiteness loss of used textile items occur over time due to several causes like accumulation and aging of unremoved oily soils such as human sebum or particulate soils.[4,5,6,7] during the washing process of textiles in a commercial washing machine, different whiteness maintenance transformations take place, namely (a) soil removal from fabrics’ structure, (b) suspension and antiredeposition of removed soil, (c) bleaching of soils remaining in fabrics, (d) deposition of shading dye actives, which are used to shift the yellowness of fabrics to a more preferred blue hue, and (e) deposition of Additional Supporting Information may be found in the online version of this article
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