Effect of mordants on colour variation in alpaca fibre dyed with dye extracted from the tankar stem (Berberis boliviana L.)

The objective of the research was to evaluate the effect of mordants on colour variation, textile characteristics, colour fastness, and Fourier‐transform infrared (FTIR) bands in alpaca fibre dyed with tankar stem extract. The white alpaca fibre was obtained from the company Inka Tops S.A. The mordants used were: alum (KAl(SO4)2·12H2O) at 20% and iron(II) sulphate (FeSO4) at 3%. Prior to dyeing, a pre‐mordanting process was carried out (86°C for 30 min), and dyeing was performed through thermal treatment at 70 and 86°C (30 and 60 min). The CIELab [L*, a*, b*, chroma (C*) and hue (h°)] coordinates and reflectance were evaluated using a spectrometer; textile characteristics were assessed with OFDA (optical fibre diameter analyser) 2000; chemical bands were analysed with an FTIR‐attenuated total reflectance (ATR) spectrophotometer, and colour fastness (light, washing, and rubbing) was evaluated using international American Association of Textile Chemists and Colorists (AATCC) standards. The results showed that luminosity (L*) significantly decreased after dyeing and pre‐mordanting with KAl(SO4)2·12H2O (81.47) and FeSO4 (70.47). Additionally, the b* value and C* value significantly increased at higher temperature and longer dyeing time, resulting in slightly different shades and hues in each treatment. The coefficient of variation (CV) and curvature index (CU) presented significant differences, with CU increasing at 86°C/60 min with FeSO4. Colour fastness to washing and rubbing showed acceptable values on the greyscale. In conclusion, the mordants used had a significant effect on colour variation, textile characteristics, colour fastness, and FTIR spectrum. The most intense shades were observed in fibres pre‐mordanted with FeSO4 (dull yellow‐green) and in dyeing without mordant (yellow).