The influence of structural properties on the dye diffusion and dyeabilty of PA 6 fibres

The relationships were investigated between the structural and dyeing properties of different structurally modified PA 6 fibers. PA 6 monofilament yarn samples were applied having different crystalline degrees and different content of alpha, respectively gamma crystalline modification. The diffusion coefficients of two different acid dyes were determined together with the content of dyestuff absorbed (under specific conditions) by fiber samples. In order to estimate colorimetry method from the viewpoint of polymer structural change detection, the colors of the dyed PA 6 samples were determined (L*, a*, b*, C*, h coordinates) and the color differences (ΔL*, Δa*, Δb*, ΔC*, ΔH*, ΔE*) were calculated between untreated standard and structurally modified samples. The dyeability of PA 6 fibers depended mainly on the way in which crystallinity had been achieved, i.e. on the material's history. Different crystalline modifications caused different sorption properties and fiber dyeability. Smaller increases (app 20%) of crystallinity degree caused a decrease in diffusion coefficients. Contrary to expectations, the significant increase of crystallinity degree (app 50%) had an influence on the increase of dyeability, presumably owing to the formation of larger empty spaces in the structure. The results achieved by colorimetry were in good correlation with dye absorption measurements. The colorimetry of dyed fiber samples was sensitive enough to detect even small differences in the quantities of absorbed dyestuff.