PAPERmaking! g FROM THE PUBLISHERS OF PAPER TECHNOLOGY Volume 2, Number 1, 2016
was used as a reference sample. The prepared titanium dioxide nanopigments were used at 30 and 50pph in conjugation with clay. The coating mixtures were prepared in three steps. First, the pigment was dispersed in water in a high shear mixer for 20 min at 50% solids content with sodium hexametaphosphate dispersant. Second, the pre-dispersed binder was gradually added, over a 5-min period to the pigment slurry; for this step the impeller speed was reduced to a moderate speed. Finally, water was added to obtain the desired solids content. The pH was adjusted to 8.5 by adding few drops of 1M sodium hydroxide solution to the coating mixture. Preparation of coated paper samples A K-bar semiautomatic coater (model NOS k101, R&K print coat instruments Ltd, United Kingdom) was used for applying the coating mixtures. A wire-wound coating bar was chosen to give a 6ml thick wet film. Paper samples to be coated were cut to overall dimensions of 200 x 300mm using strip cutter, and were coated under standard conditions of temperature and humidity 23 ± 1°C and 50 ± 2% RH according to ISO 187. Characterisation of the prepared pigments and coated paper samples The crystal structure, phase identification, purity, crystallinity and crystallite size for the prepared pigments were done by X-ray diffraction (XRD; Bruker axs D8, Germany) using Cu- Kα (k = 1.5406Å) radiation and secondary monochromator in the range 2 Θ from 10 to 80. Crystallite size is automatically calculated from XRD data. Bonding structures were analysed using Fourier Transform Infrared spectrometer (FTIR-460plus, JASCO model 6100, Japan). The pigment samples were ground with KBr (1:100 ratios) and mounted as a tablet to the sample holder in the cavity of the spectrometer. The spectra were recorded on a single-beam spectrometer with a resolution of 4cm -1 at room temperature in the range 400 – 4,000cm -1 . The specific surface area (SBET), pore volume and pore size distribution of the prepared samples were determined by N 2 adsorption desorption technique using BET surface area analyser (Auto Sorp-1-Mp surface area 2008). The samples were degassed at 250°C for 3 h before analysis, and the N 2 isotherms were obtained at 196°C. The morphological structure of the pigment samples was investigated using scanning electron microscopy (SEM, Jeol-JSM-5410, Japan) and high resolution analytical transmission electron microscopy (TEM, Jeol, JEM-2010, Japan) operating at a maximum of 200kV. The optical properties of the prepared pigment materials were measured in air at room temperature. The UV – visible absorption spectra were recorded in the wavelength range of 200 – 800nm using a spectrophotometer (UV – Vis, JASCOV-570, Japan). Photoluminescence (PL) spectra were collected in the scan range from 300 to 900nm using a luminescence spectrometer (RF-5301) with xenon lamp as the excitation source. UV – Vis and PL spectra were measured using a quartz cuvette (Q10) of 1cm path length. Ultrasonically dispersed TiO 2 nanopowders in ethanol solution were introduced into the cuvette and exposed to source light. As the UV light could be absorbed pretty quickly so the sample suspensions should be very dilute. The properties of coated papers including the prepared nanopigments were evaluated using standard tests for physical and optical properties. The surface microstructure is observed by scanning electron microscope (XL30, Philips). Gloss is a property that refers to the quality of lustre, or ability of the surface to show an image. A micro glossmeter was used, at an angle of 75°, to measure the gloss of coated paper samples. Paper brightness is referred to the overall reflectivity i.e., visual efficiency of the paper. The measurements were conducted on brightness and colorimeter instrument (model 68-59-00-002, Buchel-
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Article 3 – Titanium Coating Pigments
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