| In papermaking industry, it has long been a goal to increase the filler content of graphic papers. The cost of filler is approximately four to seven times less the price of market kraft pulp. According to the survey, a1%increase in filler content is estimated to save37yuan/ton raw material cost. Increasing filler content also has the potential to improve sheet optical properties, surface smoothness and printability. Titanium dioxide, calcium carbonate, Kaolin, Talc and so on are common fillers in papermaking industry. CaCO3can raise the paper whiteness, softness, and gloss. Talc can improve the ink absorption performance of paper. Kaolin can enhance the paper smoothness, opacity and printability. TiO2can effectively improve the paper whiteness, gloss and hiding power, and is a kind of relatively expensive papermaking fillers. Since TiO2itself has such advantages as high whiteness, gloss, light reflecting performance, small particle size, and has better physical and chemical stability. But due to high price, TiO2is only for high-grade paper and specialty paper production.Considering from the effects of paper and cost of raw material, the author propose two-compound system preparing method:CaCO3as sediment layer Kaolin-CaCO3composite; TiO2as coating layer Kaolin-TiO2composite; synthesis core-shell nanocomposite CaCO3@TiO2. For the composite powder, its pigment performance is manifested by the optical properties of the surface material. And deposition TiO2coating of composite powder can fully demonstrate the optical properties. But for Kaolin-CaCO3composite powders, the ratio of two raw materials can be regulated according to desired effect. In this paper, carbonation method is chose to synthesis Kaolin-CaCO3. Titanium sulfate is used as Ti source, urea as precipitant, to take a simple chemical precipitation method for preparing Kaolin-TiO2, CaCO3@TiO2. Structures, UV characteristics and retention effect of composite powders were studied.At first, Kaolin-CaCO3composite powders are produced via carbonation method. Through XRD and FT-IR results commonly show that carbonation method can realize Kaolin and CaCO3inter reacting, and Kaolin-CaCO3may combine by Al-O-Ca or Si-O-Ca bond form. SEM results show that the cubic morphology calcium carbonate particles are attached onto the surface of Kaolin. Retention and whiteness tests results show retention rate of composite fillers will increase with Kaolin content raised, while the whiteness increases with Kaolin amount decreasing. Analyzing from experimental results, Kaolin mass fraction ranging from20%to60%of composite powder could be used as paper fillers. In addition, the presence of CaCO3can improve the viscosity of Kaolin, it expected to expand the Kaolin-CaCO3composite powders in papermaking coating applications.Secondly, by comparing blending and dropping method, which is chose to prepare Kaolin-TiO2. This chapter inspect in quantitative Kaolin and urea conditions, the variable Ti(SO4)2impact on coating effect. By XRD analysis showed that when the volume of Ti(SO4)2was5mL, which was the minimum value to completely achieve coating quantitative Kaolin (0.8g). Then the mass fraction of TiO2in Kaolin-TiO2composite powders reaches33.3%. FESEM and particle size analysis shows that a large number of circular TiO2particles deposited on sheet surface of Kaolin, the composite particles size decreases with decreasing in the content of TiO2. FT-IR results shows that the calcined Kaolin with-OH on the surface of TiO2may incorporate by dehydrating and form the bond Si-O-Ti, and Al-O-Ti. Through slurry Zeta test, whiteness, and filler retention rate measurements show that when Kaolin content is about40%, Kaolin-TiO2composite has the maximum whiteness, the growth degree is closed to2.8%(compared with the pure Kaolin), and the retention rate is also appropriate. From the perspective of practical production, the Kaolin content in40%of Kaolin-TiO2composite powder may be more conducive to reduce costs.Last, two-step process is used to prepare CaCO3@TiO2composite powders, namely impregnation and coating. Due to CaCO3is easily soluble in an acidic solution, and high concentration of Ti(SO4)2solution having a strong acidity. However, TiO2don’t dissolve in acid and alkali solutions. Therefore low concentrations Ti(SO4)2is used to impregnate carbonate calcium. Owing to Ti4+hydrolytic characteristic leading TiO2as a cladding layer to precipitate at the surface of CaCO3, thereby preventing high concentrations Ti(SO4)2reacted with CaCO3in coating step. In this chapter, the reaction among different content of Ti(SO4)2and quantitative amount of impregnated CaCO3and urea was examined. Through XRD, when the dosage of titanium sulfate is between in1.25×10-2～7x10-3mol, that can obtain a good coating effect. FESEM testing results show spherical TiO2significantly precipitated in the surface of CaCO3, and never change the morphology of CaCO3. XPS results verify the conclusions of FESEM, and prove chemical bonds combination environment of surface TiO2have changed. That imply a new inter action between in CaCO3and TiO2is existed. Meanwhile, UV test results confirm the UV absorption capacity of CaCO3@TiO2composite powder is similar to pure TiO2, that is to say, the composite powder can serve as a good UV-shielding material. Analysing by zeta potential, retention rate and Whiteness measurements show when the amount of CaCO3reached40%, the retention rate and Whiteness are both optimum. At last, the reacting mechanism of CaCO3and TiO2is analyzed.’... |
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