A DRIFTS study of reactive dye states on cotton fabric

Abstract

A diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) investigation was performed on a series of poplin cotton fabrics treated with a bifunctional reactive dye of unknown chemical structure and composition, and in different states on the substrate (unfixed or fixed to the cotton substrate as well as chemically treated). The cotton-cellulose bands (log 1/ R) dominate the spectra of the dyed fabric samples, and this leads to difficulties in the discrimination and matching of such spectra. However, it is demonstrated that qualitative discrimination is achieved by using principal component analysis (PCA). The dye state is the basis for this; also, within the % dye concentration series separation of spectra is observed according to the amount of the dye present. Exploratory quantitative analysis of such samples, attempted with partial least squares (PLS) regression, shows that it may be possible to predict the % concentrations with larger calibration sets. Further, series of fabrics were dyed with different reactive dyes and again treated to obtain various reactive dye states. The DRIFT spectra of these fabrics were submitted to PCA, with qualitative discrimination being achieved on the basis of dye colour and the reactive dye state. It is shown that the spectra of the unfixed dyes are similar to those of the neat dye powders. This study indicates that DRIFTS may be useful for matching, discrimination and prediction of reactive dyes on cotton substrates even if the dye structure is unavailable. This points to potential applications in the dye and general textile industry as well as specific forensic cases involving relatively large samples. In addition, it is clear that further carefully designed experiments may lead to a clarification of the details of binding of polyfunctional reactive dyes on cotton.