Preparation And Characterization Of Nano Rutile TiO₂ Used For High Polymers Modification

As an excellent inorganic ultraviolet(UV) shielding and absorbing agent, nano rutile TiO2, which can not only scatter UV that entries into materials, but also absorb UV effectively by its electronic transition, has been widely used in polymer materials UV-resistance modification. However, the surface of nano-TiO2 particle is hydrophilic due to its absorption of a large number of hydroxyl groups. So nano-TiO2 particle has a poor compatibility with most polymers and is prone to aggregation and phase separation. In order to improve the dispersibility of nano-TiO2 particles in polymer materials, nano-TiO2 particle surface modification has become the focus of this area. Traditionally, before surface modification, TiO2 powder was dispersed in some kind of solvent, which has a poor result as its aggregation during dispersing. In order to solve this problem, a new way to prepare surface modified TiO2 was proposed in this thesis. Nano rutile TiO2 was prepared at a low temperature, adding organic surface modifier during the late process, which can realize improved dispersibility of nano-TiO2 particles in polymer materials. The main contents are as follows:(1) Preparation of nano rutile TiO2 at low temperatureTo prepare nano rutile TiO2, tetrabutyl titanate was used as raw material and hydrolyzed in nitric acid solution. Effect of water content, nitric acid concentration, reaction temperature and time on TiO2 crystal structure was studied. Serial comparative experiments of Self-made TiO2 with commercial product (MT-500B provided by Imperial Chemical) on structure and UV-resistance ability were carried out. The results showed that:pure rutile TiO2 with grain size in the range of 70～100 nm can be obtained when tetrabutyl titanate hydrolyzed in nitric acid solution with a concentration of 4 mol/L (the molar rate of water and tetrabutyl titanate is 35) at 45℃for 5 hours. Compared with commercial TiO2 product, self-made TiO2 has larger number of active hydroxyl groups on the grain surface, while equal UV absorption performance was obtained.(2) Surface modification of nano rutile TiO2A-151 silane was introduced to modify the prepared nano rutile TiO2 particles (existing in suspension) by direct blending method. The reasonable amount of modifier was discussed. Further more, the micro structure and macroscopic properties of modified TiO2 particles were characterized. The results show that: A-151 silane is grafted onto the surface of TiO2 particles by reacting with hydroxyl groups to form Si-O-Ti bond. When the molar ratio of A-151 between TiO2 is 0.15, the amount of organic groups grafted onto the surface of Tio2 particles will be saturated, the contact angle of modified TiO2 with water is 144°in this case. Surface modified TiO2 of highly improved dispersibility in xylene together with a relatively high UV absorbability is obtained.(3) UV-resistance modification of polypropyleneTiO2/polypropylene composite prepared by a certain mixing process was then compressed into thin film. Accelerated aging test of the samples were carried out with self-made equipment. The dispersibility of TiO2 in polypropylene was examined and the UV-resistance ability of the composite was characterized based on carbonyl index. The results showed that:The dispersibility of surface modified TiO2 particles in polypropylene improved significantly. When TiO2 content is 2 wt%, best UV-resistance ability of the composite can be obtained.