Colour of flax fibres in regard to different pretreatment and dyeing processes

Abstract

The main objective of this work was to compare the colour of different pretreated (alkaline, acidic and enzymatic) and dyed (conventional and ultrasonic‐assisted) flax fibres, to establish the impact of various parameters on dyeing kinetics. Flax fibres were dyed using two direct dyes of different chemical structures and molecular mass. Diffusion profiles were established by the application of Fick’s Law and dyeing behaviour was studied by means of online spectrophotometry. Finally, the dyed samples were colorimetrically evaluated and colour differences and colour strengths were subsequently calculated. The results provided evidence that a dye molecule’s size has a greater influence on the exhaustion degree, migration and diffusion than individual pretreatment processes. The determined diffusion coefficients indicated superior dye mobility and faster diffusion into the fibres when ultrasonic power was used in comparison with conventional process. Nevertheless, the colour depth obtained was found to be low after ultrasonic dyeing using a larger dye molecule, implying part degradation of CI Direct Red 80 (and total degradation of small‐size dyestuff, CI Direct Red 81).

Modeling of the linen fabric dyeing after previous preparation

“…Because of the smaller dye molecule, and hence better diffusion, the exhaustion curves show greater slopes during the first division of the dyeing process than on the earlier graphs, although stronger migration of the dye is presented. During the ultrasonic-assisted dyeing of different pretreated samples, the degradation of dye 2 was observed after 60 min after the processes had started, which is not evident [6].…”

“…The final exhausted dye 1 after 92 min of dyeing was 94% for acidic and enzymatically pretreated fibers, followed by 95% for alkali-scoured fibers. Generally, final amounts of dyestuff exhausted over ultrasound assistance were higher, and the time attaining equilibrium was shorter [6].…”

“…A similar study focused on the colors of different pretreated flax fibers (alkaline, acidic and enzymatic), dyed both conventionally and ultrasonically using two red direct dyes with different molecular mass, in terms of the exhaustion rate etc. Dyeing was accomplished according to both a conventional dyeing procedure (without the ultrasound power) and an ultrasonic technique, using two direct dyestuffs: CI Direct Red 80 (dye 1) and CI Direct Red 81 (dye 2) [6].…”

“…The obtained results demonstrate that different pretreatments of flax could influence the dyeing behavior depending on the time and, above all, the type of the dyeing procedure. During conventional dyeing, the dyeing rate slightly increased in the first stage of the process (the first 30 min), most likely on account of very strong repulsion forces between the large dye molecule and the fiber [6].…”

“…Many fibers impurities, like lignin, pectin etc., require the preparation that is long lasting and divided in many individual processes, and they are related to high costs. Flax contains almost 20% more impurities compared to cotton [6,7].…”