Preparation And Properties Of Flexible Photochromic Membranes Based On Bacterial Cellulose

Photochromic material is a kind of new functional material. Its optical properties change after appropriate light irradiation, which makes it has broad potential applications in many fields. Spirooxazine, as a new type of photochromic compound, has good fatigue resistance and light stability. In addition, it also has the advantages of fast response and stable chemical properties, which is very promising into the applications. However, photochromic compounds are generally small molecules. It is difficult to achieve a wide range of applications, while polymer material just has a great advantage in this respect, which can make up for the shortcoming.As a new type of natural polymer materials, bacterial cellulose (BC) has unique nano-dimensional network structure with excellent physical and chemical properties. In addition, bacterial cellulose is easy to be modified because of a large number of hydroxyl groups on its surface. Composites with bacterial cellulose and spirooxazine would have the excellent properties of bacterial cellulose as well as the special photochromic properties, and may have potential applications in the field of modern optoelectronic materials.The detail researches are as follows:(1) Spirooxazine compounds containing hydroxyl and carboxyl were synthesized respectively. The structures were characterized by FT-IR,’H-NMR and MS. The effect of different external factors on photochromic properties was studied. The synthesized pirooxazines had no photochromic phenomenon under crystal state, but good photochromic properties in solution. As the solvent polarity increased, the color of spirooxazine solution after irradiation blue shifted and its maximum absorption wavelength red shifted. At different pH values, the color of spirooxazine solution changed reversibly. With the reduction of temperature, the color of spirooxazine solution after irradiation became darker and the recovery became slower.(2) Bacterial cellulose membrane was carboxyl modified by the TEMPO/NaClO/NaBr oxidation system. The effect of activation and buffer solution on carboxyl content was studied. Under the optimal oxidation conditions, the dosage of NCIO was8mmol/g and reaction time was2hours, the carboxyl content was1.22mmol/g. Oxidation process had little influence on the structure and properties of bacterial cellulose membrane.(3) Bacterial cellulose and spirooxazines were composited by hydrogen bonding. The photochromic properties of composite membrane were studied. With the increase of spirooxazine content, the thermal property of composite membrane improved. The spirooxazine containing hydroxyl had better light response and stability in oxidized bacterial cellulose. Its optical density only decreased by4.9%after100color-decolor cycles, showing excellent fatigue resistance.