Preparation And Properties Of Photochromic Fabric Based On Microcapsule Technology

With the gradual enhancement of people’s awareness of the functionalization of textiles,the pursuit of textile colors has also changed to achieve more novel and avant-garde effects as the goal,and the research on photochromic textiles is also increasing.Organic photochromic materials have broad application prospects in the textile field because they have the advantages of sensitive color change and bright colors.However,they are very susceptible to the influence of the external environment and lead to poor photochemical fatigue resistance.And the microencapsulated photochromic material is an effective method to solve this problem.Its dense shell realizes the effective barrier between the core material and the external environment to achieve the purpose of improving the fatigue resistance.This subject first synthesized the photochromic spiropyran derivatives with alkenyl functional groups.Subsequently,spiropyran was used as the core material,chitosan as the wall material,and glutaraldehyde as the crosslinking agent to successfully prepare photochromic microcapsules.The microcapsules are arranged on the fabric and are divided into two parts.One is the successful preparation of photochromic hydrophobic cotton fabrics using PDMS and microcapsule blend coating on cotton fabrics,and the other is the use of electrostatic layer-by-layer self-assembly method to arrange the microcapsules and sodium alginate on the fabric to prepare a self-assembled photochromic fabric.The main research results are as follows:（1）Synthesis of photochromic spiropyran derivative with alkenyl functional group1-allyl-6-nitro[2H]-1-benzopyran-2,2’-indoline.Characterization methods such as ultraviolet spectroscopy（UV）,infrared spectroscopy（FT-IR）,proton nuclear magnetic resonance spectroscopy（¹H-NMR）,and carbon spectroscopy(¹³C-NMR)proved the successful synthesis of the target compound.（2）Using the above-mentioned spiropyran compound as the core material and chitosan as the wall material,photochromic microcapsules were prepared by the emulsification-chemical cross-linking method.The surface morphology of the photochromic microcapsules was analyzed by scanning.electron microscope（SEM）and it was found that the microcapsules appeared regular microsphere shape,smooth outer wall and good compactness.Through the laser particle.size analyzer test,it is found that the particle size distribution of the microcapsules is uniform and the average particle size is 0.71μm.The sub-micron structure also shows that it is suitable for the coating method and the electrostatic layer-by-layer self-assembly method used in the process of finishing onto the fabric.（3）Since PDMS has high light permeability,viscosity and hydrophobicity,the above-mentioned microcapsules and PDMS are blended and coated on cotton fabrics to prepare photochromic hydrophobic cotton fabrics.It changes color instantly under ultraviolet light（5 W,365 nm）irradiation,and the maximum color depth can be reached in 10 seconds.Under green light（5 W,532 nm）irradiation for 20 s,standing in an environment of 80℃for 1 min,and standing at room temperature and darkness for 50 min,it can be reversibly returned to the original state.After 20 sets of UV-green light recovery cycles,the photochromic effect can still be maintained at the original 96.36%,which is higher than the 88.24%of the same photochromic compound without microencapsulation.It can be concluded that the microencapsulated photochromic material has a significant effect on improving its fatigue resistance.It is also because of the use of PDMS that the prepared coated fabric has a static water contact angle of more than 138°,which has a good hydrophobic and antifouling effect and superior washing durability.（4）Under the condition of pH=5,the amino group on the wall.material of the microcapsule is positively charged,the carboxyl group on the sodium.alginate is negatively charged,and the two kinds of materials mentioned above are self-assembled on the anionized cotton to prepare a self-assembled photochromic cotton fabric.Scanning electron microscopy（SEM）analysis proved that the loading of microcapsules on cotton fabric increased with the increase of assembled layer numbers,and infrared spectroscopy（FT-IR）proved the successful loading of microcapsules on cotton fabric.Methylene blue（cationic dye）dyes fabrics in different assembly processes,and its K/S and Lab values show regular"odd-even"changes,which proves the surface charge changes caused by the alternate deposition of microcapsules and sodium alginate on anionized cotton.The self-assembled cotton fabric assembled with 5 microcapsule layers（MPC-5）reaches the maximum color depth under 12 s of UV light irradiation,and returns to the original status after 90s green light irradiation.The excellent photochromic effect（94.65%）can still be maintained after20 sets of cyclic tests,proving its excellent fatigue resistance.After linear fitting,it is found that the photochromic effect of self-assembled cotton fabric increases proportionally with the increase of the assembled layer numbers,which proves that the photochromic microcapsules are uniformly deposited on the fabric.In addition,its excellent UV protection effect and erasable/rewritable characteristics also indicate potential applications in the field of UV protective clothing and optical information storage.The research results of this paper provide a new way to improve the fatigue resistance of photochromic materials and broaden the preparation methods of photochromic textiles.