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Light Stabilisation of Photochromic Prints Thesis for the Degree of Master in Science with a major in Textile Engineering The Swedish School of Textiles 2016-05-27 LIGHT STABILISATION OF PHOTOCHROMIC PRINTS Nikolina Brixland E-TEAM, European Masters Programme in Advanced Textile Engineering Description: Master Thesis for Master in Textile Technology Title: Light Stabilisation of Photochromic Prints Author: Nikolina Brixland Supervisors: Vincent Nierstrasz, Sina Seipel Examiner: Vincent Nierstrasz Abstract Light stabilisation of photochromic dyes is seen as the most challenging part in the development of photochromic dyes. The aim of this research is to compare stabilisation methods and their effect on the lifetime of a photochromic print on textile. The vision is to create a textile UV-sensor that detects current UV-light exposure in the surroundings and alarms the wearer by showing colour. The developed inks have been formulated for ink-jet printing as a novel production method with resource saving properties. UV-LED light curable ink formulations were prepared for two dye classes; a non-commercial spirooxazine, a commercial spirooxazine (Oxford Blue) and a commercial naphthopyran (Ruby Red). Two different stabilisation methods were applied; chemically by incorporation of hindered amine light stabilisers and physically by polyurethane coating. Fatigue tests were performed to evaluate and compare the stabilisation methods. The tests included were household washing, multiple activations and intensive sun-lamp exposure. As a result it was found that Oxford Blue and spirooxazine had an initial better resistance to photodegradation than Ruby Red. The coating reduced the ability of colour development in higher extend for Oxford Blue and spirooxazine compared to Ruby Red. Moreover, the photocolouration increased with the number of activations for Oxford Blue and spirooxazine in particular. In general, the physically stabilised samples showed a better or similar fatigue resistance compared to chemically stabilised samples. On the other hand the results are weak in significance. It is concluded that the developed coating method in combination with further optimising has potential. Key words: Photochromic dye, textile sensor, flexible sensor, lightweight material, light stabilisation, HALS, ink-jet printing, protective coating, spirooxazine, naphthopyran Popular abstract Today, we are more than ever aware of the harmful UV-radiation and its effects on human health. UV-light detectable sensor could be a useful tool to warn the wearer of current UV-light intensity in the surroundings by colours. Thanks to photochromic compounds, this is possible. Photochromic compounds show a reversible colour change trigged by external stimuli as UV-light. The higher photoelectric energy induced by irradiation changes the molecular arrangement, the absorption spectra and therewith shows a colour that is visible to the human eye. A smart flexible textile UV-sensor can be worn as an everyday application and alarm on cloudy days where harmful UV-radiation is not an obvious threat. This research gives light on photochromic dyes on textile substrate in a sensor application. The challenge is to improve their photostability to extend the lifetime of the dye and its function. Ways of stabilisation of the photochromic inks have been done chemically and physically and then evaluated by fastness tests. The testing has been tailored for textile applications and includes household washing, multiple and intensive activation of the prints. As a result, stabilisation was found for both methods. In the physically stabilised samples a lower degradation was found in comparison to chemically stabilised samples. Although, the trends are not significant for a real conclusion to be made, it is concluded that the developed coating method in combination with further optimising has potential. Acknowledgement A special thank to my thesis advisor PhD. Sina Seipel at the Swedish School of Textiles. The door to your office was always open whenever I needed a new perspective or had a question about my research or writing. This thesis would not have been the same without your support and valuable input throughout the whole project. I would also like to thank my supervisor Prof. Vincent Nierstrasz for feedback and reflections keeping my work at an academic level. Last but not least, a great thank to the team and students at the department for textile technology for excellent collaboration and support. Table of content 1 Introduction ................................................................................................. 1 1.1 Problem description ...................................................................................... 2 1.2 Research questions ........................................................................................ 2 1.3 Research objective ......................................................................................... 2 2 Literature review ....................................................................................... 4 2.1 Chromism .......................................................................................................... 4 2.2 Photochromism ............................................................................................... 5 2.2.1 Photochromic dyes ............................................................................................. 6 2.3 Effect of matrices ............................................................................................ 7 2.5 Photodegradation ........................................................................................... 9 2.6 Applications ................................................................................................... 10 2.7 Textile sensor ................................................................................................ 11 2.8 Colour difference ΔE ................................................................................... 11 2.9 Radiation curing ........................................................................................... 12 2.10 Chemical light stabilisation ................................................................... 14 2.10.1 Hindered Amine Light Stabilisers ........................................................... 15 2.11 Physical light stabilisation ..................................................................... 15 2.11.1 3D-printing ....................................................................................................... 16 2.11.2 Polyurethane coating ................................................................................... 17 3 Materials and methods ........................................................................... 18 3.1 Materials ......................................................................................................... 18 3.1.1 Fabric ..................................................................................................................... 18 3.1.2 Dyes ........................................................................................................................ 18 3.1.3 UV-light curable varnish ................................................................................ 18 3.1.4 Hindered Amine Light Stabiliser ................................................................ 19 3.1.5 3D-printing filament ....................................................................................... 19 3.1.6 Polyurethane coating ...................................................................................... 19 3.2 Methods ........................................................................................................... 20 3.2.1 Preparation of photochromic ink .............................................................. 21 3.2.2 Preparation of light stabilised ink ............................................................. 21 3.2.3 Ink characterisation ........................................................................................ 22 3.2.4 Preparation of samples .................................................................................. 22 3.2.6 UV-light curing ................................................................................................... 23 3.2.7 Preparation of 3D printed protective layer ........................................... 23 3.2.8 Preparation of knife coated protective layer ........................................ 23 3.2.9 Fastness tests ..................................................................................................... 24 3.2.10 Colour performance ...................................................................................... 25 3.2.11 Statistical analysis ......................................................................................... 26 4 Result ............................................................................................................ 27 4.1 Ink characterisation ................................................................................... 27 4.1.1 Viscosity ............................................................................................................... 27 4.1.2 Surface tension .................................................................................................. 28 4.2 Physical protection layer .......................................................................... 29 4.3 Colour performance .................................................................................... 30 4.3.1 Performance
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