Effect of γ-irradiation on the hydrolytic and thermal stability of micro- and nano-TiO2 based urea–formaldehyde composites
The hydrolytic stability and thermal behavior of organic–inorganic composites prepared by two-stage polymerization of urea–formaldehyde resin (UF) with micro- and nano-TiO2 before and after irradiation has been investigated. Composites of urea–formaldehyde and particles of TiO2 of different sizes were synthesized, namely: UF/micro-TiO2 and UF/nano-TiO2. The hydrolytic stability of the modified UF composites was determined by measuring the mass loss and liberated formaldehyde concentration of modified UF composites after acid hydrolysis. The studied modified UF composites have been irradiated (50 kGy) and the effect of γ-irradiation was evaluated on the basis of the percentage of liberated formaldehyde before and after irradiation. The minimum percentage (0.16%) of liberated formaldehyde was obtained in nano-TiO2 modified UF resin after γ-irradiation which indicated a significant improvement in the hydrolytic stability compared with micro-TiO2 modified UF resin (0.52%). The effect of γ-irradiation was evaluated also on the basis of the thermal behavior of the same modified UF composites before and after irradiation. The thermal behavior was studied by non-isothermal thermo-gravimetric analysis (TG), differential thermo-gravimetry (DTG) and differential thermal analysis (DTA) supported by data from attenuated total reflection infrared (ATR-IR) spectroscopy. DTG peaks of both composites are shifted to a higher temperature after irradiation, but UF/micro-TiO2 after γ-irradiation shows less change in the thermal behavior than nano-TiO2. In other words, UF/micro-TiO2 shows better radiation stability. Gamma irradiation causes a minor effect on the ATR-IR spectra, specifically the decrease of the intensities of some bands.