Development of novel parameters for characterising scale morphology of wool fibre and its correlation with dye diffusion coefficient of acid dye

Abstract

This paper reports the development of novel surface parameters which can be used to characterise the scale structure of wool fibres obtained from different breeds. Scanning electron microscopy and subsequent image analysis technique were used to study wool fibres from Leicester, Dartmoor, Ryeland and Herdwick breeds of sheep. Novel scale parameters related to wool fibre’s effective chemical diffusion pathway were developed. Namely, the total scale perimeter per 100 µm fibre length and scale perimeter index, which is the total scale perimeter per 100 µm length divided by the fibre diameter. Wool fibres obtained from different breeds showed significant differences in their scale pattern with the change in fibre diameter. The scale perimeter per 100 µm length increased with the fibre diameter and showed a polynomial correlation. It was also demonstrated that an increase in the diameter of the wool fibre resulted in an increase in the apparent dye diffusion coefficient, which contrasts the established theory that finer fibres are associated with a higher dyeing rate. The increase in effective diffusion pathway (total scale perimeter per 100 µm) for the wool fibres (among different breeds) resulted in a higher dye diffusion rate at the initial phase of dyeing (liquor to surface).

Investigation of the Thermodynamic and Kinetic Behavior of Acid Dyes in Relation to Wool Fiber Morphology

“…It was also reported that as the diameter of the fiber increases from Leicester to Ryeland to Dartmoor, the scale pattern shifts from coronal to coronal reticulate to reticulate . It can be proposed that as the scale pattern changes from coronal to reticulate, the area of the diffusion pathway decreases.…”

“…Finer fiber is associated with larger surface area compared to a coarser fiber, which can lead to a higher dye uptake, but this phenomenon is observed in synthetic fibers where the linear density of the fiber is almost constant . Wool is a very complex fiber, which does not possess a uniform diameter and has different scale patterns on the fiber surface, which could influence the dyeing sorption properties . The measurement methodology and results of mean fiber diameters of Leicester and Dartmoor have been reported by the authors in an earlier publication .…”

“…There may be other factors involved like differences in surface properties, morphological structure of the fibers, or amino acid composition of the fibers . The involvement of scale and surface morphology of the wool fiber in dyeing kinetics has been investigated in detail in an earlier publication by the authors . At the same time, at a higher concentration of dye, the sorption behavior may change depending on amino acid chemistry, i.e., the composition of basic amino acids (arginine, lysine, and histidine) within the wool fiber …”

“…This could highlight differential dyeing due to presence of different types of scale structure on the surface of the fiber. 29 Differential dyeing in wool fiber has been reported by modifying the wool fiber characteristics. 30,31 Researchers have claimed that changes in the amino acid content of wool fiber, obtained from specific breeds, can have an impact on the dyeing properties.…”

“…Despite variations seen in amino acid content in different breeds of wool, it has been observed that at equilibrium conditions, there is very little difference in the amount of acid dye uptake among wool fibers obtained from different breeds of sheep. , However, the reported merino wool fibers were dyed at lower concentration, and to investigate the maximum dye sorption capacity of a new breed of wool fiber, it is required to dye the fiber at higher dye concentrations and temperatures. This could highlight differential dyeing due to presence of different types of scale structure on the surface of the fiber …”