This thesis describes the effects of different solvents have on the extraction profile of natural dyes from dye plants: madder, weld, golden rod, and chamomile. HPLC has been used to build a fingerprint of each dye plant profile and thus used to compare to the profiles of back extraction from textiles for natural dye identification in historical artefacts. The use of solid phase extraction is compared to extraction methods with no purification step which is favourable for anthraquinone dyes but results in a major loss of glycosidic compounds when using yellow dyestuffs. Supported by 1H and 13C NMR data, the conclusive X-ray crystal structure of the natural dye ruberythric acid is presented which has never been achieved prior to this research. In a collaboration with food science two of the main components of chamomile are fully characterised by 1D and 2D, 1H and 13C NMR. These compounds are usually referred to as ferulic acid derivatives in the literature but their actual structure is reported herein.
The thesis also discusses the relative dye uptake of anthraquinone compounds onto wool textiles which were measured by HPLC. Sorption isotherms for the main anthraquinones in madder; ruberythric acid, pseudopurpurin and alizarin are compared for more in-depth understanding on the method of adsorption of these compounds. Herein the glycosidic compounds in madder are shown to have a higher adsorption capacity than the aglycons. Ruberythric acid is shown to follow a Tempkin isotherm with the highest degree of correlation but both alizarin and ruberythric acid show good fitting with the Freundlich isotherm also. Pseudopurpurin was shown to follow a Freundlich isotherm with the highest degree of linearity but did also show some fitting to the Langmuir isotherm. The isotherms allow data to be collected on the energy of adsorption and draw conclusions on the effect the functional groups have on the dyeing capability which is studied herein for the first time on individual anthraquinone components.
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Studies were carried out on the acid-sensitive colorants present in madder which are degraded in the textile back extraction process. Anthraquinone aglycons alizarin and purpurin are usually identified in analysis following harsh back extraction methods, such as those using solvent mixtures with concentrated hydrochloric acid at high temperatures. Herein, a softer novel extraction method involving aqueous glucose solution was developed and compared to other back extraction techniques on wool dyed with root extract from different varieties of Rubia tinctorum.
A study into the breakdown compounds of the aglycon; lucidin under acidic conditions used for traditional back extractions was also undertaken. Here it is observed that lucidin is converted into xanthopurpurin in a retro aldol like mechanism. This report discusses some of the issues raised by using these harsh back extraction methods and the problems faced in using them to analyse historic artefacts
