Artificially light-aged, black-dyed harakeke fibres: Understanding the correlations between chemical composition and fibre properties using vibrational spectroscopy and chemometrics

The IR and Raman spectra for a series of traditionally black-dyed (with iron-tannate) harakeke (New Zealand flax, Phormium tenax) fibres have been measured. Such fibres are used to make numerous cultural materials by indigenous (Māori) communities in New Zealand. The fibres were subjected to artificial light-aging to determine the changes that occur due to fibre degradation. Fibres could be distinguished using IR spectroscopy based on whether they were dyed, and which form of iron-tannate dye was used, made with either a condensed or hydrolysable tannin (hinau, Elaeocarpus dentatus or manuka, Leptospermum scoparium). Raman spectroscopy differentiated dyed and non-dyed fibres and the type of dye based on the nature of the tannins used. For IR spectroscopy, it was possible to observe spectral changes with aging for the non-dyed and hinau-dyed samples. For non-dyed fibres the aging changes reflected an increase in cellulose crystallinity. For the hinau-dyed samples, the changes appeared to reflect increased oxygen content and higher acidity levels. These are important constituent changes that lead to degradation of fibres.