Study On The Modification Conditions Of Titanium Dioxide

In this dissertation, TiO₂ was modified facing pigment and paper industry via wet chemical surface modification method, taking the oil absorption value and hiding power as the main index. The appropriate modifiers were selected respectively and the modification conditions were optimized as well. The TiO₂/PS composite microspheres were synthesized through miniemulsion polymerization using Octadecyl trimethyl ammonium chloride （OTAC） modified TiO₂ as monomer and PS as the carrier. The main conclusions were obtained as follows:（1） Modified TiO₂ sample with good lipophilicity was produced using OTAC as modifier. The optimized surface modification conditions were obtained through single-factor and orthogonal experiments as follows:modification temperature 50℃, modification time 105 min, dose of OTAC 4%wt and pH value 7. Under this condition, the oil absorption value of the as-produced modified TiO₂ decreased from 22.00% to 13.35% comparing to non-modified TiO₂, showing obvious enhancement in lipophilicity. The resistivity of water extract liquid of modified TiO₂ sample increased from 35 Ω·m to 78Ω·m, and the pH value of water suspension was 7.69, meeting the requirements of TiO₂ pigment （the resistivity of water extract liquid not lower than 50 Ω·m and the pH value of water suspension between 7-8）. FT-IR analysis showed that OTAC was successfully coated on the surface of TiO₂; XRD and particle size analysis showed that compared to the non-modified TiO₂, the crystal structure of modified TiO₂ did not change significantly and the micro particle size increased slightly; the modified TiO₂ showed less agglomeration and better dispersion from the SEM observation.（2） Modified TiO₂ sample with higher hiding power was produced using polyethylene glycol 20000 （PEG 20000） as modifier. The optimized surface modification conditions were obtained through single-factor and orthogonal experiments as follows:modification temperature 55℃, modification time 75 min, dose of PEG 20000 2%wt and pH value 8. Under this condition, the hiding power of the modified TiO₂ sample decreased from 32.00 g/m2 to 17.81 g/m2 comparing to non-modified TiO₂, showing better hiding power.（3） The TiO₂/PS composite microspheres were synthesized through miniemulsion polymerization using the OTAC modified TiO₂ as monomer and PS as the carrier. When TiO₂ dosage was 4%wt （based on oil phase）, styrene concentration was 40%wt （based on whole system） and emulsifier concentration was 11.56 mmol·L-1 （based on aqueous system）, after 20 min of ultrasonic emulsification time, the as-prepared TiO₂/PS composite microspheres had more uniform size distribution with an average diameter of 50～70 nm. The composite microspheres showed good regularity from SEM observation.