Preparation And Application Study Of TiO₂@CaCO₃ Composites

TiO₂ is the most outstanding white pigment in the world due to its excellent physical and chemical properties, which can be widely applied in paint, paper making, plastic, rubber, ink, cosmetics, medicine, and so on. Approximately 60% of worldwide TiO₂ has been used in coating industry. The situation including relatively unadvanced mining-technology and lower technology level has brought out serious waste and environmental contamination problems. In addition, the demands of special anatase TiO₂ and rutile TiO₂ for the coating, ink, plastic, rubber and other flourish industries are increased. However, the yield rate of rutile TiO₂ is far lower than the foreign countries in China and the technology of the preparation of rutile Ti O₂ almost requires high-temperature calcination at present with high energy consumption. As to the applications of TiO₂, its high catalytic activity will accelerate the decomposition of polymer matrix, the TiO₂ surface needs some treatments to curb its photocatalytic activity in order to improve the properties of light fastness, weather resistance, chemical stability.Waterborne polyurethane（WPU） possesses the properties of nontoxic, nonpollution, environmental, energy security, safe, resistant to chemicals, low temperature resistant and wear resistant. WPU materials have been developed rapidly in recent years as a kind of water-based materials, which can used in coating, printing and dyeing, wood, leather, textile and so on. However, the low mechanical strength and poor self-thickening of WPU makes it slightly worse than solvent-based polyurethane. As an important biopolymer materials, microcrystalline cellulose（MCC） owns rich resources, high mechanical properties, high surface area, low density and so on, which provides a great prospect for the research of WPU composites.It is well known that the effect of pigment depends on the outer layer of the particles. So it is necessary to select the appropriate inorganic material as a core and prepare the composite with similar properties to TiO₂ in this papaer. The composite with silica surface coating can totally or partly substitute TiO₂, which can effectively solve the problem of the reduction of titanium resources and environmental pollution. In this paper, microcrystalline cellulose used as a high reinforcing filler material modify WPU to improve its mechanical and other properties.Firstly, commercial TiO₂ can be disaggregated to nanoparticles（NPs） under the effects of alkaline Ca（OH）2 slurry and mechanical stirring. Rutile TiO₂@Ca CO₃ composites were synthesized by the deposition of disaggregated TiO₂ NPs on the surface of CaCO₃ particles during the process of CO₂/N2 gas-bubbling. The results of FESEM, XRD, EDS, thermal gravimetric analysis and acid-resistance confirmed that a coating layer of rutile TiO₂ nanoparticles was formed on the surface of calcite Ca CO₃. TiO₂@CaCO₃-15 performed good coating effect and uniformity among different mass ratios of TiO₂ to Ca CO₃ for TiO₂@CaCO₃ composites. Moreover, the whiteness and UV-visible absorption of TiO₂@Ca CO₃-15 were similar to TiO₂. The TiO₂@Ca CO₃-15 with silica surface treatment was studied by FESEM and XRD, which clarified that epidermis-like dense amorphous hydrated silica layer was formed on the surface of TiO₂@Ca CO₃. Compared with TiO₂@Ca CO₃, the UV-Visible absorption has been significantly improved. In addition, the mechanism of TiO₂@Ca CO₃ were analyzed.Secondly, MCC/WPU composite film was prepared by the method of in-situ polymerization and MCC was successfully embedded into the WPU film with good dispersion according to the results of FESEM, AFM and XRD. The study of TGA showed that thermal decomposition temperature of the soft segment of MCC/WPU higher than WPU, so it can be concluded that MCC can improve the heat resistance of WPU film. Within a certain range, an increase in MCC loading led to the improvement of tensile strength, but the breaking elongation would firstly increased and then decreased. MCC/WPU wood adhesives met the standard ofâ…¡class bond strength of plywood in GB/T 9846-2206, therefore MCC/WPU can be used in wood adhesives. The TiO₂@Ca CO₃ composites were originally added ino the MCC/WPU wood adhesives in the plan of this paper. However, the data of the TiO₂@Ca CO₃ composites in MCC/WPU wood adhesives were not listed in this paper due to the results of the TiO₂@CaCO₃ composites in MCC/WPU wood adhesives were further improved.Finally, the as-prepared TiO₂@CaCO₃ was applied in interior emulsion coatings and PVC profiles. When the percentage replacement of TiO₂@CaCO₃ to commercial TiO₂ was selected as 40%, the performance of the interior emulsion coatings with TiO₂@Ca CO₃ was up to the standard of GB/T 9756-2009 and the contrast ratio and scrub resistance increased effectively. The TiO₂@CaCO₃ composites used as the substitution of TiO₂ in PVC profiles whose photooxidation aging stability improved significantly. Therefore, TiO₂@Ca CO₃ could partly substitute TiO₂ in interior emulsion coatings and PVC profiles.