Abstract:

Objective Photochromic textiles demonstrate changes in color under the irradiation of a specific wavelength of light, that is, through the change of optical conditions in the environment to achieve a reversible change in color. In the situation where there is light or other bands of light irradiation, photochromic textiles can restore the original color. This novel textile meets people's needs for color personalization, uniqueness and other aspects, and how to make textiles both functional and environmentally friendly has always been the goal of researchers.

Method Three photochromic microcapsules with different chromic effects were synthesized by in situ polymerization, which were added to the spinning solution of polyhydroxyalkanoate/polylactic acid(PHA/PLA). PHA/PLA fibers with photochromic function were obtained by microfluidic spinning technique. The influences of PLA concentration and the addition of microcapsules on fiber mechanical properties were investigated. Through the color mixing and color matching of the microcapsules, the fibers obtained more color-changing effect.

Results With spiroxazine as the core material and melamine formaldehyde as the wall material, the photochromic microcapsules that can change from white to blue under a specific wavelength light irradiation were synthesized by in situ polymerization method. Under the conditions that PVA concentration was 0.2%, the core wall volume ratio was 1∶1, and SDS concentration was 0.5%, the synthetic photochromic microcapsules demponstrated the best morphology and color change effect, and the average particle size was smaller. In addition, by replacing the photochromic compounds of the core material, the photochromic materials naphthopyran were used as the core materials, and the other two photochromic microcapsules with different color change effects (from white to yellow and from white to purple) were synthesized, which also showed good color change effect. Spinning was conducted by varying the PLA concentration (10%, 12%, 14%, and 16%). The results showed that the tensile strength of the PHA/PLA fibers was 50.68 MPa at the PLA concentration of 14%. In order to further improve the mechanical properties of the fibers, the fibers were collected on the plastic spool, and soaked in absolute ethanol for 24 h, and the mechanical properties of the treated fiber were significantly improved. With 14% PLA the concentration, the tensile strength of PHA / PLA fiber reached 66.10 MPa, a 30.4% increase compared with the untreated fiber, and the tensile elongation was also significantly increased. When the mass fraction of microcapsules was only 0.5%, the tensile strength of the fiber is 43.91 MPa, which is approximately 33.6% lower than that of the PHA/PLA fiber without microcapsules, and the tensile elongation is reduced by 56.46%. When the mass fraction of microcapsules reached 2%, the tensile strength of the fiber is only 20.65 MPa, and the tensile elongation is merely 11.14%.

Conclusion Three photochromic microcapsules with different color change effects were synthesized by in situ polymerization, using melamine-formaldehyde resin as the wall material and the photochromic compounds spirooxazine, naphthopyran, and spiropyran as the core materials, respectively. These microcapsules were then added to the PHA/PLA spinning solution, and photochromic PHA/PLA fibers were successfully prepared by microfluidic spinning. When the concentrations of PLA and PHA were 14% and 2%, respectively, the tensile strength of PHA/PLA fibers was 50.68 MPa. In addition, the mechanical properties of the PHA/PLA fibers were significantly improved after soaking in ethanol, and the tensile strength reached 66.10 MPa. The mechanical properties characterization found that once the microcapsule is added, the mechanical properties of the fibers will decrease significantly.

Key words: polyhydroxyalkanoates, polylactic acid, microfluidic wet spinning, microcapsule, photochromic fiber, smart fiber