I'm studying the extraction of xylan from hardwoods and I see many different colours. Some colours are specific to each tree species, but I observe colour changes before and after pretreatments and also colour changes at different pHs. So knowing which are the compounds that give colouration to wood would help me a lot to understand these phenomena.
Natural materials from organic sources such as wood mainly consist of complex fibrous polymers called lignins. The chemical structure of such polymers typically includes repetitive alternating single and double-bond atomic valency linkages. Each such chain of alternating links has an electronic resonance frequency property, and a consequential frequency-specific wavelength of light absorption, that is characteristic of a given chain length. As chain length grows, the light-absorption of the resonance band moves from the UV into the visible spectrum and thus changes the observed colour. The pH related colour change indicates the presence of ionic as well as covalent atomic structures in the lignin.
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