Study On Synthesis Of Functional Nano-CaCO₃ Nanocomposite Materials

Calcium carbonate is one of the important fillers used in the industries of plastics, rubber, paint and so on. Such industrial applications require well-refined and dispersed calcium carbonate particles. These characteristics play a crucial role in calcium carbonate properties and their control is closely related with the method of its production and the process parameters. Various preparing methods of CaCO₃ have attracted much attention. How to control the preparation conditions to obtain the designed materials is the goal of the material chemists.Surface modification of calcium carbonate with hydrophobic species would lead to a great expansion in these applications, since mineral particles are hardly dispersed in a polymer matrix. The modification of the surface with surfactants has been extensively studied mainly for precipitated calcium carbonate (PCC) in order to improve its dispersibility in polymeric media. For example, the surfactants containing reactive functional groups such as silane coupling agents, titanate coupling agents or stearic acid can all improve the hydrophobic property of PCC. However, all the processes were conducted from the resultant PCC products rather than during the preparation of CC. Hence, an attempt was made to prepare the active and super-fine PCC directly. In this paper, we would like to report the resultsobtained.A carbonation process for the synthesis of active super-fine calcium carbonate panicles from Ca(0H)2 slurry at room temperature using a CO2-N2 gas mixture was investigated. The industrial octadecyl dihydrogenphosphate (A) was added as controlling-size additive and modifier in different reaction periods according to the pH of the medium. The analyses of the reaction products brought to the conclusion that the addition of A in the digestion period could inhibit the crystal growth of calcium carbonate, while the addition of A at pH=7 of the medium could modify the surface character of calcium carbonate particle which was found to exhibit hydrophobic property. From transmission electron microscope (TEM) observations, the hydrophobic property was attributed to the deposition of the calcium alkyl phosphates, produced in reaction mixture, onto the surface of calcium carbonate particle. IR spectra and TGA analysis of the obtained products indicated that A was bound onto the crystalline CaCC>3. The alkyl chains of A entirely shield the solid surface, decreasing dramatically its surface energy and hence facilitate the dispersion of the filler in a polyolefinic matrix and, on the other hand, enhance the compatibility between filler and matrix leading possibly to better mechanical performance of the composite.The encapsulation of inorganic particles with polymers is desirable in many applications in order to improve the stability of the encapsulated product, to improve the dispersibility in organic media, to reduce toxicity, and to facilitate storage or transport. Furthermore, the incorporation of inorganic materials on the nanoscale can enhance the fire retardancy and mechanical strength of organic polymers and coatings. In recent years, there has been increasing interest in thesynthesis of paniculate or colloidal polymer encapsulation.We have reported that hydrophobic calcium carbonate (CC) can be directly obtained by adding the octadecyl dihydrogen phosphate (A) during the preparation of CC. Here, we'd like to report another surface modifier, sodium oleate(SO), which owns C=C bond that can make it possible to be copolymerized with the styrene monomer, so that CC would be well encapsulated by polystyrene.Hydrophobic calcium carbonate has been in situ prepared via carbonation of Ca(OH)2 slurry in the presence of sodium oleate. We first used the DTG combined with the IR and TEM proved that the hydrophobic property was attributed to the deposition of the calcium oleate produced in the reaction mixture onto the calcium carbonate surface. The alkyl chains of calcium oleate shield the solid surface, making the CaCCb hydrophobic, dramatically decreasing its surface energy and hence facilitating the dispersion of the filler in a polyolefmic matrix and, on the other hand, enhancing the compatibility between filler and matrix, possibly leading to better mechanical performance of the composite. More important is that the alkyl chain owns C=C bond which can make it possible to be copolymerized with the styrene monomer, so that CC would be well encapsulated by polystyrene.In order to improve the property of calcium carbonate, surface modification is of importance. So far, most surface modificer is organic, for example, silane coupling agents, titanate coupling agents, stearic acid or alkyl dihydrogenphosphate, while inorganic surface modification of calcium carbonate is seldom reported. SiO2 was successfully coated on the surface of CaCCb by the method of chemical deposition. We studied the effect of coating that was influenced by pH, temperature, the time of stir and aging. XRD and IR analyses indicated that SiO2 coating wasamorphous and there were chemical interaction between CaCO3 and SiO2. The acid-resistance was improved greatly, which expanded the application of CaCC^.Titania has been widely used as the principal white pigment material in various branches of industry, because of its high refractive index, high dielectric constant, and chemical stability, even in strongly acidic or basic environments. With the development of manufacturing technology, it is possible for people to prepare nanosize titania which has much better properties than bulk titania because of the greatly decrease in size. A growing interest has been made in the applications of titania such as shielding of ultraviolet light, photocatalyst for photodecomposition and solar energy conversion because of its high photoactivity. Since Nanosize titania shows different electrical characteristics with oxygen, because it has a nonstoichiometric phase region, it can also be used as a humidity sensor or gas sensor. Together with the increasing use of of nanosize titania, there is a need for improved control over the crystalline phases, the mophology and the size of titania particles to make it functional in future applications.TiO2 was successfully coated on the surface of CaCCb by the method of chemical deposition, sol-gel method and absorption phase nanoreactor technique , which improved the mechanical, optical properties and expanded its application. XRD analysis indicated that the TiO2 coating was amorphous and its thickness was increased with the mass ratio of TiC>2 and CaCCb. The TiCVCaCOs composites were characterized by XRD, IR and TG. The results showed that the coating film was well distributed on the surface of CaCCb, so the TiCyCaCCb composites own some features of TiO2 and it can be substitute of TiCh in some field.CaCCypolystyrene inorganic/organic composite nanoparticles (80 nm) with acore/shell structure were obtained by in situ emulsion polymerization of styrene (St) on the surface of modified CaCO3 nanoparticles. Nanometer CaCCb slurry was prepared via carbonation of Ca(OH)2 slurry in the presence of sodium oleate at room temperature in order to introduce polymerizable groups onto its surface. TEM photographs of composite particles with well-defined core-shell structure gave direct evidence of encapsulation. In addition, TGA and FT-IR spectra of the products after extraction indicated tight encapsulation between PS and CaCO3.