Preparation And Responsive Property Of Spiropyran Photochromic Microcapsules

As society becomes more aware of the novelty and versatility of textiles,the demand for color in textiles is gradually shifting from the original ornamental and practical to more specific display properties.This has led to an increase in research on photochromic textiles in China and abroad.Organic photochromic materials have highly influential applications in the fields of optical switching and reaction sensing due to their ability to switch colors rapidly and reversibly under light irradiation in a special wavelength range,presenting vivid and variable colors.However,based on the fact that such compounds are highly susceptible to be affected under external conditions of uncertainty or different organic solvents,problems such as short service life,poor fatigue resistance,instability and color variation of photochromic materials arise.This project proposes a method of microencapsulating photochromic materials,which can effectively prolong their performance and ensure their stable performance,and is one of the more suitable solutions to this problem today.In this thesis,photochromic compounds with hydroxyl(SP-OH),carboxyl(SP-COOH)and methyl(SP-CH₃)as chain segments were firstly produced by means of hydroxyl-formaldehyde condensation reactions,respectively.By comparing the color development properties and thermal stability of the three different spiro-pyran type photochromic compounds,SP-CH₃was selected as the substrate for the subsequent study.Subsequently,photochromic microcapsules with fast color response were successfully prepared by in situ polymerization using methyl methacrylate(MMA)as the wall material and SP-CH₃dissolved in butyl stearate as the core material.The photochromic textiles were successfully produced by applying the synthesized microcapsules to polyester fabric using a green water-based polyurethane(WPU-6638)as the binder.The main findings and results of the study are as follows:(1)Three spiro-pyran type photochromic compounds,SP-OH,SP-COOH and SP-CH₃,were prepared by hydroxyl aldol condensation reactions.The synthesis of the target product was successfully demonstrated using a series of characterization It was also explored that SP-CH₃has the advantage of the best photo-responsiveness and ring opening stability,and has excellent thermal stability properties.Therefore,SP-CH₃was used as a substrate in the subsequent process discussion of the article.(2)Photochromic microcapsules with fast color response were prepared by in situ polymerization using SP-CH₃and butyl stearate solvent as the core material and polymethyl methacrylate(PMMA)as the wall material.By analyzing the effect of different process parameters on the microcapsules,the optimum process conditions for the preparation were determined as follows:emulsifier SDS content of 2 wt%,core to wall material mass ratio of1:2,SP-CH₃content in the core material of 3.75%and emulsification rate of 2000 r/min.The results showed that the microcapsules had successfully coated SP-CH₃and butyl stearate,and the particles were spherical in shape with smooth surface morphology and a particle size of about 550 nm.The results of thermogravimetric analysis(TG-DTG)and differential scanning calorimetry(DSC)showed that the microcapsules had good thermal stability and energy storage.(3)polyurethane(WPU-6638)with synthetic photochromic microcapsules to form a slurry and applying it to polyester fabrics by screen printing.The photochromic polyester fabrics were investigated for their color properties,light responsiveness,fatigue resistance and applications.It is shown that the color of the fabric changes rapidly when irradiated by365nm UV light,and the color reaches its maximum depth at 12s.The fabric also faded reversibly under dark,heated or visible light(green light)conditions.After 20 cycles of irradiation,the absorbance of the photochromic polyester fabric was found to decrease slightly,but this had little effect on the fatigue resistance of the fabric.In addition,after 20cycles of standard washing,the absorbance of the polyester fabric decreased,but still had good wash resistance.In summary,the results of this thesis provide new ideas in terms of microencapsulation and properties of photochromic materials.