Study On Photoaging Behavior Andprotection Of Vectran Fibers

Vectran fibers belong to aromatic polyester fibers, which are high-performance thermotropic liquid crystal fibers developed recently. Given their excellent properties, they can be widely used in military and aerospace industries. However, they are susceptible to degradation and undergo structural changes when exposed to strong light irradiation. The focus of this work is to investigate the photochemical aging behavior of the Vectran fibers. The changes of morphologies, mechanical properties and chemical structures under Xenon lamp irradiation have been studied. Based on the situation that the anti-photoaging properties of Vectran fibers are poor, the effective coating protection method were proposed to slow down the degradation of fibers. The nano-TiO2protective coatings were prepared on the surface of Vectran fibers using several different methods, to obtain nano-TiO2particles with good dispersion and small size, thereby improving the coating protection effect. The inorganic/organic hybrid protective coatings were prepared on the fiber surface using organic UV absorbers and nano-TiO2together. The performances of fibers after protecting with different anti-photoaging coatings such as microstructure, and morphology, filament strength and anti-UV aging were evaluated.The photoaging degradation behaviors of Vectran fibers were studied. The filament strength decreased quickly when the fibers are exposed to Xenon lamp irradiation, and the morphology of the fiber surface was damaged. X-ray diffraction analysis illustrated that the degree of the fiber structual ordering was decreased due to irradiation. Fourier transformed infrared analyses and X–ray photoelectron spectroscopy analyses of the accelerated aged fibers proved the chemical structural changes of the fibers. For the first time, the possible photodegradation process of Vectran fiber is proposed in both air and N2environments. The rate of degradation and number of chain scissions are greater in air than that in N2. The radicals generated by chain scissions can directly abstract a hydrogen atom or can react with O2creating-OH and-COOH end groups in air atmosphere. The diaryl ethers may be formed due to the replacement of the H atoms in aromatic rings for linking up two aromatic rings.The anti-photoaging coating was formed on the surface of Vectran fiber with the prepared TiO2nano-sol using sol-gel method. The results showed that there existed aggregation of TiO2, and the adhesion was poor. To improve this phenomenon, the PSS/TiO2coatings were prepared on the fiber surface through layer-by-layer method, and the dispersion and adhesion were improved. The filament strength of fiber coated with PSS/TiO2after Xenon lamp irradiation was higher than that of coated fiber by sol-gel method. However, the strength was still very low after photoaging for a long time, and the aggregation problem of TiO2needed to be further improved.The OH terminated hyperbranched polyester (HBPE) was used to modify the TiO2nano-material in-situ synthesized via a sol–gel method with butyl titanate as precursor, and the average particle size of TiO2was smaller than10nm. X-ray diffraction analyses and thermogravimetric analyses illustrated the interactions of the OH terminated HBPE with the products of TiO2hydrolysis. The modified nano-TiO2hybrid sols were used in Vectran by surface coating and a continuous uniform TiO2coating on the Vectran fiber surface was achieved. The strength remain of the coated fiber after aging for336h was22%, which increased by6%over PSS/TiO2coated fiber, indicating the positive role of the nano-scaled titania coating with good dispersion and small size in improving the anti-photoaging performance of fiber, which laid the foundation for preparation of nano-TiO2/organic UV absorber hybrid protective coating.The benzotriazole absorber UV-1130, triazine absorber Tinuvin477, and hindered amine light stabilizer Tinuvin123were used to mix with TiO2nano-sol to prepare protective coatings for photoaging. Hybrid coatings performed much better than TiO2coating in protecting fibers from UV. Among them, UV-1130was especially feasible to reinforce the UV protecting ability of TiO2coating, by showing a stronger absorbance of UV. In another hand, although the performances of Tinuvin477were doing less well when they were combined with TiO2alone, they showed excellent synergistic effect when used together with UV-1130and Tinuvin123, which further improved the protective ability of coating.The organic UV absorbers with the best formula were used to mix with the OH terminated HBPE-modified TiO2, and the adhesion between the hybrid coating and fiber was improved effectively by ultrasonic assisted impregnation process. The hybrid coating could ensure the zero transmission in the UV range of200~380nm. The strength remain of the fiber coated with hybrids after aging for336h increased by49%over the uncoated fiber, indicating that the hybrid coating effectively improved the protective efficiency against photoaging of Vectran fiber.