Natural Dyeing and UV Protection of Raw and Bleached/Mercerised Cotton

Abstract

Dyeing with natural dyes extracted from curcuma, green tea, avocado seed, pomegranate peel and horse chestnut bark was studied to evaluate the dyeability and ultraviolet (UV) blocking properties of raw and bleached/mercerised cotton fabrics. 20 g/l of powdered plant material was extracted in distilled water and used as a dyeing bath. No mordants were used to obtain ecologically friendly finishing. The colour of samples was measured on a refl ectance spectrophotometer, while UV-blocking properties were analysed with UV-Vis spectrophotometer. The results showed that dyeing increased UV protection factor (UPF) to all samples, however much higher UPF values were measured for the dyed raw cotton samples. The highest UPF values were obtained on both cotton fabrics dyed with pomegranate peel and green tea extracts, giving them excellent protective properties (UPF 50+). The lowest UPF values were obtained by dyeing cotton with avocado seed extract and curcumin. Dyeing with selected dyes is not stable to washing, so the UV-blocking properties worsen after repetitive washing. However, raw cotton samples retain their very good Uvblocking properties, while bleached/mercerised cotton fabrics do not provide even satisfactory UV-blocking properties. No correlation between CIE L*a*b*, K/S and UPF values were found.

Keywords

• UV protection
• dyeing
• natural dyes
• cotton