Recent advances in colour science
With thanks to Dr Muriel Rigout for reviewing this recent SDC event.
The SDC’s North of England region met for an interesting lecture evening on the 25th February 2015 at the University of Leeds. The committee are particularly indebted to Dr Christine Holdstock for, while the programme was advertising talks by Professor Lin (entitled Towards More Environmentally Friendly Coloration) and Dr Natalia Sergeeva (From Nanotechnology to Photomedicine – Functional Dyes Based Materials), Dr Sergeeva was unable to present due to personal circumstances. Dr Holdstock kindly agreed to present on a related topic, namely Functional and High-Tech Applications of Modern Specialised Dyes, at short notice.
The evening began with Dr Holdstock introducing us to the concept of specialised and functional dyes; that is to say colorants that, contrary to their conventional counterparts for which aesthetic properties are the raison d’être, have a function in high-tech applications. These can be subdivided into two sub-categories: specialty dyes for which colour is important and functional dyes that have a technical function and for which colour is not important. In terms of specialty dyes, Dr Holdstock first introduced us to chromic materials, that is to say colorants that change colour when a stimulus is applied. We were introduced in detail to the mechanism of colour change in leuco-dye based thermochromic colorants and photochromic colorants, with numerous examples of applications and some live demonstrations of chromic colorants in use. Dr Holdstock continued her talk explaining to us the mode of operation of fluorescent colorants, applications that include areas such as personal protection, anti-counterfeiting and solar energy harvesting. She then continued by introducing to us dyes for electronic applications, including liquid crystal displays, dyes in optical data storage and dye sensitised solar cells. To conclude, Dr Holdstock described to us the mode of action of dyes in photodynamic therapy, and shared with us the findings of recent publications in the field highlighting the effectiveness of this process in medical applications including cancer treatment, sterilisation of rooms and equipment, treatment of chronic wounds, and dental applications.
Following this overview of specialty and functional dyes, Professor Long Lin took the floor and introduced us to the work that he has been involved with over the past two to three years. He explained the urgent need for solutions to reduce the impact of textile manufacturing on the environment in Far East countries such as China. The premise is simple: the Chinese government has been moving towards tighter enforcement of its environmental standards. This seemingly simple move has had a drastic impact on regions with high concentrations of dye manufacturers, dyehouses and textile mills; where many textile processing factories had closed or relocated further away from the cities due to unsatisfactory compliance to release and emission standards. This dramatically reduced the number of entities working within the textile manufacturing supply chain over a relatively short period of time creating adverse social and economical impacts.
Professor Lin’s approach to resolve the challenge has been to consider reducing the pollution at source. More specifically, he proposes that this definition includes realising colorants with higher exhaustion, higher fixation, greater colour strength, less chemical use in dyebath, less water (or medium) used, recycling and reuse of dyebaths, recycling of water with or without treatment, and crucially reduction of costs.
Professor Lin went on to propose that he understood the wish-list of the textile industry to include high efficiency dye manufacturing (e.g. lower pollution in H-acid manufacturing), low loss of dye, low energy consumption, and low volume effluent during dye manufacture, salt-free and alkali-free dyeing, and simpler operational procedures. This wish-list has fed directly into the research projects that he is involved with at the University of Leeds, and he is therefore currently supervising one an MChem student looking at improving the light and wash fastness of natural dyes to match that of synthetic dyestuff. In addition, Professor Lin expressed his enthusiasm in the coloration of textiles in supercritical carbon dioxide, and he is supervising one PhD student and one MSc student researching novel dyes for the coloration of natural fibres. Professor Lin then introduced us to the jewel in his crown: a series of novel reactive dyestuff for natural fibres that can be applied under neutral conditions (alkali-free), with no salt addition (salt-free), which are not susceptible to hydrolysis, with comparable or improved exhaustion and fixation profiles, and fastness performance at least equal to that of commercial reactive dye systems. This new dye system, if used commercially, would thus reduce the impact of the coloration of natural fibres in a number of ways, for instance the possibility of reusing dyebaths, an effluent containing only dyestuffs and hence simpler to process, and simpler operational procedures likely to result in time saving as well as increased right-first-time or right-every-time dyeing, leading to cost, energy and water consumption savings.
To conclude, Professor Lin introduced us to a topic that he feels is very interesting, although deviating from the topic he had been following for the rest of his talk: hair coloration. Namely, he and his team have developed a process that can dye hair at ambient temperature, under two minutes and results in an unusual pearlescent effect.
The event finished after a period of discussions covering a range of related topics raised by the audience.
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