Investigating the effect of dyeing on the surface of wool fibres with atomic force microscopy (AFM)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006.
Dyeing has an influence on the characteristic properties of wool fibres. This can result in changes in the final properties of the fibre including fibre elasticity, fibre strength and breaking elongation of the wool fibres, especially in the case of dark colours. Damage that occurs to the fibre surface due to the action of acid, alkali, dyestuff, water, heat, and mechanical stress during the dyeing process can thus have an affect on the fibre breaking elongation and the fibre strength. The aim of this project was to assess the effect of dyeing with different colours (ranging from light to dark) on the surface of wool fibres using atomic force microscopy (AFM). The results indicated that four different types of surface damage can be discerned: scale raising, scale chipping, fluting and pitting. The findings also indicate that the surface damage to the fibres was greater and more noticeable (especially the scale raising) on fibres dyed with dark colours than to fibres dyed with light colours. The same applied to the fibre strength and elongation, where generally the fibre breaking extension and the breaking load was smaller in the case of darker colours. The effect of dyeing with different colour shades on the fibre surface was observed with AFM. Several characteristic scale parameters of a statistical significant number of dyed and undyed fibres were measured in order to determine the surface damage caused by dyeing. The correlation between the surface damage, observed by AFM, and the loss in tensile strength and fibre elongation, determined by tensile tests, were investigated. This was done in order to determine the effect of the cuticle damage on the tensile stress/strain behaviour. The results show that AFM is a viable tool to study the effects of different dyes on the fibre surface and for detecting surface modifications with great accuracy. It was found that dyeing with dark colours caused greater damage to the surface than light colours, and it was possible to distinguish different lightness areas, which could be regarded as light and dark colours.