Abstract
We obtained hydrophobic barite (BaSO4) and rutile titanium dioxide (TiO2) particles (as raw materials) by organic surface modification. Subsequently, TiO2-coated barite composite pigments were prepared via the hydrophobic aggregation of heterogeneous particles in a water medium. The pigment properties of the TiO2-coated barite composite pigments were characterized and evaluated by determining their hiding power, oil absorption value and whiteness. The optical properties were determined by obtaining their UV-vis diffuse reflectance spectra and using the CIE-L*a*b* method. The morphology and bonding properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (IR). The results show the similarity between the composite pigment and pure rutile TiO2: when the mass ratio of rutile TiO2 in the composite pigment was 60%, the hiding power of the TiO2-coated barite composite pigment was 90.81% of that of pure rutile TiO2. Moreover, the surfaces of the barite particles were uniformly and firmly coated by TiO2, with a hydrophobic association occurring between the hydrophobic carbon chains on the surfaces of barite and TiO2 particles.
Highlights
(XRD), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (IR)
When the TiO2 mass ratio increased to 60%, the hiding power and relative hiding power (R) of the TiO2-coated barite composite pigments were 12.08 g/m2 and 90.81%, respectively, nearly reaching the levels observed for pure rutile TiO2, for which the R value exceeds 30.81% (ΔR) compared with the mass ratio of TiO2 (R0)
Based on the aforementioned research and analysis, the composite mechanism of the TiO2-coated barite composite pigment prepared by hydrophobic aggregation can be described as follows: First, as Fig. 13(a) and (b) show, the sodium stearate used as a modifier is adsorbed on the barite and TiO2 particle surfaces via the reaction between C15H35COOH and the -OH groups on the surfaces of the TiO2 and barite particles
Summary
The L*a*b* parameters of representative specimens were measured using a portable integrating sphere spectrophotometer (X-Rite Sp60, X-Rite (Shanghai) International Trade Co., Ltd., China). The CIE-L*a*b* colourimetric method recommended by the CIE (Commission Internationale de l’Éclairage) was followed. The hydrophobic properties of the particles were evaluated based on the wet contact angle obtained by contact angle measurement (JC2000D, Shanghai Zhongchen Digital Technic Apparatus Co. Ltd., China). The images of TiO2-coated barite particles dispersed in an organic medium were obtained by an image analyser (BT1600, Bettersize Instruments Ltd., China). The surface functional groups were examined by infrared spectroscopy (Spectrum 100, PerkinElmer Instruments (Shanghai) Co. Ltd., China) using KBr as the medium. Further analysis was carried out using X-ray photoelectron spectroscopy (XPS, Escalab 250xi, Thermo Fisher Scientific USA) and X-ray diffraction (D/MAX2000, Rigaku Corporation, Japan)
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