Preparation Of TiO₂ Nanosol And Study Of Its Application In Decelerating UV-Photodegradation Of Aramid Fibers

Aramid is a kind of photosensitive material and it is prone to degrade under ultraviolet radiation. Wavelength of 280³20nm, corresponding to UV radiation, is most sensitive to aramids. Therefore, aramid fibers can be protected from photodegradation and prolonged their longevity of use by addition of proper anti-UV agers capable of inhibiting light within wavelength. A lot of studies have discovered that TiO₂ of nano size can provide good protective benefit by reflecting, scattering or absorbing harmful UV rays. Current studies focus on adding TiO₂ to spinning solution to produce anti-UV fibers or dispersing in certain medium with dispersants as coating to protect fibers. However, it is difficult to add inhibitor in the spinning process of aramid. Therefore, it has to use finish method to form a coating in protecting aramid against UV irradiation. It is known that nano TiO₂ is hard to disperse in the medium and easily congregate, even with a proper dispersant. To form a proper coating on the surface of aramid fibers, sol-gel, a wet chemical method is used in the present study to make nanoparticles disperse evenly in the coating to sheathe the surface of aramid fibers as an anti-ager. This study includes the preparation of TiO₂ nanosol, the characterizations of TiO₂ sol and coating prepared by this method, the change of mechanical propertiesand the surface structure of TiC>2 coated aramid fibers under accelerated UV-aging treatment.Some conclusions are summarized as following:1. Stable TiO2 sol has been prepared by using titanium alkoxide as precursor and water as solvent, while adding acetic acid for the purpose of moderating the rate of hydrolysis. The effects on the sol particle size distribution and the properties of TiO2 nanosol and coating are studied.1) The formula of the TiO2 sol is established with considering the influence of acetic acid, hydrochloric acid and water, i.e. TTB:HAc: H2O:HC1 = l:(4¹0): 166:0.15 in molar ratio.2) The quantity of HAc and aging time are two key factors influence on the size distribution of TiO2 sol particles. By careful selection of these factors TiO2 sols with 20 to 50nm is prepared. It shows a good UV inhibition result and the absorption band-edges for these sols are at about 370nm.3) The uniform transparent TiO2 thin coating having excellent shielding effect on UV radiation less than 320nm is prepared on glass substrates. Red shift of the threshold is observed in the UV spectra with the increase of coating thickness. Moreover, when treated at 80 °C, the anatase of TiO2 coating on the sample has been observed.2. The anti-aging effect of the TiO2 coating is studied by accelerated aging test with a UV lamp. During the period of aging, the mechanical properties of the coated fibers with TiO2 are studied in comparison with uncoated ones, including tensile strength and extension. The micro fractures of the fibers are also analyzed by SE1VL ATR and XPS. The results show that the TiO2 coating decreases the intensity of UVlight on aramid fibers resulting in the deceleration of photodegradation of the fibers.1) In the process of degradation, the tensile strength and elongation rate of the uncoated aramid fibers are decreased significantly. While for the coated ones, the mechanical properties are decreased but with less degree due to the protection effect of TiC>2 coating. Verifying the data of the tensile properties by means of statistics. The results show that the maximum confidence interval range of tensile strength and elongation at rapture between the coated fibers and uncoated ones reach to ( 9.64cN, 11.15cN) and (1.55%, 1.65%), respectively.2) The analysis results of SEM and XPS show that the quantity of carboxylic acids as the major products for coated fibers clearly lower than the one for uncoated fibers. It means that the TiO2 coating on aramid fibers can protect amide bonds against photocleavage by means of UV absorption, preventing or decelerating the photodegradation of aramid fibers.3) The condition of preparing TiO2 coating have certain effects on the properties of inhibiting UV radiation. The TiO2 coating on aramid fibers is characterized with better improvement of the properties of resistance to UV irradiation, which is provided by TiO2 sol (about 25nm) and via heat treatment at 80°C and 1³ coating cycles.