Study of the Influence of the Surface Roughness of Knitted Fabrics from Natural Fibres on the Light Fastness of Their Colours

The article examines the influence of the surface properties of knitted fabrics from cotton and wool of various knitted structures on the light fastness of their colours. The surface properties of knitted fabrics of single plain, 1×1 rib and French piqué knitted structures were evaluated by determining their roughness using a non-contact optical method for processing digital images of the knitted fabric’s surface. The roughness profiles of the corresponding knitted fabric samples were obtained, and the main indicators of surface roughness were calculated: the profile height at ten points Rz and the arithmetic mean profile deviation Ra . Cotton knitted fabrics were dyed with the Bezaktiv Cosmos dye brand, which are bifunctional reactive dyes with monochlorotriazine / vinyl sulfone active groups, and wool knitted fabrics were dyed with acid dyes. The light fastness of the samples was evaluated after exposure to the Light Fastness Tester (Mercury-Tungsten Lamp) RF 1201 BS (REFOND) with a PCE-TCR 200 colorimeter. Colour measurements were averaged for each sample. Total colour difference (dE) was measured on the dyed cotton knitted fabrics samples after light exposure. According to the obtained roughness profiles of cotton and wool knitted fabrics, it can be concluded that the studied knitted fabrics are characterized by different roughness, which depends on their knitted structures. At the same time, a relationship was found between an increase in the roughness of knitted fabrics and the photodestruction of colours by reactive and acid dyes on cotton and wool knitted fabrics, respectively. The results show that the surface structure of knitted fabrics, that is the knitted structure, impacts the process of colour photodestruction and that the amount of dye that has undergone photodestruction increases with the increasing surface roughness of the knitted fabric.