| Photochromophore often can change color sensitively and reversibly under sunlight(UVVis light source), and presents bright color via metachromatism which can endow textiles and clothing various color and pattern changing effect. Moreover, it enables the potential applications in functional textiles, apparel and accessories, decoration materials, anti-counterfeit materials and optical glasses due to the characterizations of photochromophore. Photochromophore often can rapidly change absorption spectral and turns into rather bright color under definite spectrum light irradiation, the existing scope of chromatography includes yellow, red, blue, sky blue and orange, a wide range of chromatography can be obtained by color blending of double-shell polyurethane-chitosan microcapsules. It’s susceptible to be affected by the dyeing and finishing as well as environmental factors such as p H, light, temperature, solvent and oxidation, which lead to the losing of reversible color change ability as a result of unreversible color change reaction and poor photochemical fatigue resistance. Encapsulation photochromophore or adding hindered amine light stabilizer, antioxidant or UV-absorbent in dyeing and finishing process can effectively enhance the fatigue resistance of photochromophore. However, hindered amine light stabilizer belongs to an alkaline radical scavenger, there exists antagonism for acidic matrix and additives, including acid environment can affect the properties of photochromophore, and it also presents shortcomings of more volatile, blooming, migration and extraction, etc. Therefore, encapsulation of photochromophore is one of the main methods to resist the effects of dyeing and finishing as well as environmental factors, meanwhile, the optical effect intensity that photochromophore accepted can be changed by double-shell structure to further enhance the fatigue resistance of photochromophore. Moreover, double-shell encapsulation plays an important role in preventing the lossing of reversible color change property resulted by unreversible color change reaction. The outer shell possess functional groups that can be used to make photochromic microcapsules covalent bonded onto cotton fabric by crosslinking, which provides a new way for the application of photochromic microcapsule onto fabric, and plays an important role in the development of new type functional textiles.The emulsifier type and its dosage, core/wall weight ratio, homogenization speed, stirring speed and synthesis temperature can directively affect the average properties and distribution of photochromic microcapsules. The influences of the factors on the particle size of the microcapsules were investigated. The effect of single/double shell structure on the changed leakproofness and the optical mechanism of photochromophore as well as photochromic properties of photochromic microcapsules were studied incorporating with the characterization methods, such as SEM, TEM, absorption spectrum before and after irradiation and absorbance, etc. Furthermore, the photo-responsive coloration and decoloration processes as well as the effect of single/double shell microencapsulation on improving fatigue resistance and reversible color change times were also studied. Double-shell polyurethane-chitosan photochromic microcapsules were treated onto cotton fabrics via covalent bonding by coating method. The effects of citric acid concentration and microcapsule concentration on color performance of microcapsules treated cotton fabric were discussed. The washing resistance and thermal stability of the covalent bonding between double-shell polyurethane-chitosan photochromic microcapsules and cotton fabric were studied. Double-shell microcapsules and the color blending double-shell microcapsules were treated onto cotton fabric and applied in outdoor clothing sun light irridiation indicating identification pattern design, which possess quick-response to outdoor ultraviolet intensity besides decoration function.Polyurethane was used as wall material, photochromophore was dispersed in butyl acetat as core materials. The photochromic microcapsules coated by polyurethane were prepared via in-situ polymerization, the average particle size of the photochromic microcapsuoles was about 714 nm. The influences of emulsifier type and its dosage, core/wall ratio, homogenization speed, stirring speed and synthesis temperature on the particle size of the microcapsules were investigated. Peregal O emulsifier was more suitable for the preparation of polyurethane microcapsules than Tween80, OP-10 and PVC, the average particle size of microcapsules decreased from 0.6171 um to 0.5236 um as the Peregal O concentration increased from 5% to 15%. With the reduction of the core/wall weight ratio in the range from 1:1 to 1:8, the average particle size increased from o.4731 um to o.7147 um. The average particle size of the microcapsules was inversely proportional to the homogenization and stirring speed. 20~60 ℃ prepolymerization temperature and 90-100 ℃ chain extension temperature were appropriate for normal proceeding of polymerization as well as gentle and stable decrease trend of microcapsules average particle size.In order to compare the photochromic properties of photochromophore before and after encapsulated using polyurethane as wall material, photochromic properties as well as fatigue resistance of photochromophore dissolved in ethanol and polyurethane photochromic microcapsules dispersing were compared. The polyurethane microcapsules slowed down the colourization process for 12 s compared with photochromophore dissolved in ethanol, however, the absorbance of azo compound increased by 29.7% in polyurethane microcapsules. The absorbance of photoisomer decreased by 50% of the initial and photostationary value during 60 s in polyurethane microcapsules and 14 s in ethanol, and the color depth of polyurethane microcapsules was higher at the end of decolorization process. The half-life of polyurethane microcapsules and azo compound were 135 min and 280 min, respectively. The photo-reversible color change times of photochromophore was 17 times, increasing to 29 times of polyurethane microcapsules. Comparing with unencapsulated azo photochromophore, the polyurethane photochromic microcapsules showed advantages in improving the fatigue resistance and photo-reversible color change times.Double-shell polyurethane-chitosan photochromic microcapsules with good leakproofness were prepared by in situ polymerization. The coloration and decoloration processes of photochromophore and double-shell polyurethane-chitosan microcapsules were studied. FTIR and TEM characterized that chitosan-glutaraldehyde copolymer formed by imine and combined with polyurethane photochromic microcapsules. The polyurethane-chitosan microcapsules exhibited a near-spherical shape, and the average particle size of microcapsules was around 1.2 μm. The half-life of photochromophore increased from 135 to 340 min after encapsulated in polyurethane-chitosan microcapsules. The optical switching of photo-response can be repeated for numerous times without any apparent “fatigue” effects or photobleaching until the 36 th UV-Vis cycles. The double-shell polyurethane-chitosan microcapsules delayed the coloration process for 14 s compared with azo compound in ethanol, however, the absorbance of azo compound increased by 17.15% in polyurethane-chitosan microcapsules. It decreased from 0.3486 to 0.1738 in ethanol during 20 s, however, it decreased from 0.4084 to 0.2625 in polyurethane-chitosan microcapsules in 55 s when it reached steady state during decoloration process.Double-shell polyurethane-chitosan photochromic microcapsules were covalent bonded onto cotton fabrics by coating method. FTIR indicated that acylamino group and ester group formed between hydroxyl of cotton fabric and amino group of chitosan shell. The surface morphology of microcapsules treated cotton fabrics revealed the uniform bonding of double-shell polyurethane-chitosan microcapsules on cotton fabrics. Factors affect the covalent bonding such as citric acid(CA) and double-shell polyurethane-chitosan microcapsules(DSPCM) concentration were studied. The K/S value of treated fabric by using 9wt% CA increased for 157.0% compared with 5% CA. The color properties of samples treated with 8wt% concentration microcapsules increased for 44.72%. The K/S value decreased for 8.55% after 50 launderings. The surface morphology of treated cotton fabric after 50 launderings remained almost the same as the original ones. It can be speculated that the covalent bonding fastness between DSPCM and cotton fabric is good. Additionally, it possesses good thermal stability. It can be concluded that 9% citric acid concentration and 8% DSPCM concentration are available to obtain bright and uniform color.In order to obtain broad chromatography, double-shell polyurethane-chitosan microcapsules were color blended according to 2-(4’-N,N-dimethylamine benzene azo) anthraquinone yellow/red/blue double-shell photochromic microcapsules weight ratio for obtaining multicolors to satisfy the multi-color microcapsules application in textiles and clothing. The color blended double-shell microcapsules obtained from red double-shell microcapsules adding into yellow double-shell microcapsules as well as blue double-shell microcapsules adding into red double-shell microcapsules present distinct absorbance and colorimetric performance changes under various irradiation intensities, besides good color identification, possessing rather dark and bright color. Double-shell microcapsules were applied to design out door clothing sunscreen detection indicator pattern, which present quick photo-response and good color identification after being irradiated under various irradiation intensities, which endows outdoor clothing ultraviolet intensity of sun light irradiation display and warning function. |
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