Influence of reactive dyes on ultraviolet protection of cotton knitted fabrics with different fabric constructions

The influence of coloration on ultraviolet (UV) protection of cotton knitted fabrics with different knit structures incorporated with the three major stitch types, namely knit, tuck and miss stitches, are studied in four approaches. The effects of color depth and knit structures on the ultraviolet protection factor (UPF) of fabrics are investigated. The influences of hue and color depth on the UPF of fabrics are also compared. Since UV protection offered by dyes mainly depends on their chemical structures, the UPF and color strength of fabrics colored by reactive dyes that varied in reactive groups, such as mono-functional and bi-functional reactive dyes, are examined. The correlations between UPF and the CIELAB color coordinates, color strength (K/S-sum), are analyzed. The results show that light-colored fabrics with compact structures achieve similar or even better UV protection than the dark-colored fabrics with loose structures. This implies that color property might not be a reliable indicator for UV protection of knitted fabrics and the effect of coloration on UV protection is affected by fabric construction. The results also denote that the chemical structure of reactive dyes affects the UV protection of fabrics in a qualitative approach that depends on the unique ultraviolet radiation blocking ability of the chemical constituents. Among the color coordinates investigated, only lightness (L*) and K/S-sum are found to be correlated with the UPF of the fabrics, but the strength of correlations is not very strong. This is because the fabric characteristics that have significant impacts of UV protection are mostly not involved in the measurement of color properties.