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Generation Of A Novel TiO2



The objective of this work was to explore the feasibility of generating a fiber-latex- TiO2-composite material that could be used as an additive in the papermachine wet end. By initially binding a cationic latex and subsequently anionic TiO2 to the fiber surface and then curing the latex, it was envisioned that the pigment would be strongly retained in a latex film on the fiber surface. This novel additive could be utilized in papermaking operations achieving high TiO2 retention and substantial cost-savings. Dispersion turbidity and microscopy were used to monitor experiments. Data were generated on the interaction between fiber and cationic latex, and a fiber-latex intermediate and TiO2. Retention levels of TiO2 in the range of the target value were achieved, and stability tests proved the material resistant to normal pH and shear stresses. However, the cured composite proved difficult to redisperse and a different approach for curing must be explored.

Opacity – the physical phenomenon

As light travels from one medium to another, its path is bent according to the difference in refractive index of the two media and the light is scattered. The incident light undergoes reflection by the surface and penetration into the sheet. The penetrating light is either absorbed or scattered by the particles in the structure. Light scattering in a non-filled uncoated paper will consequently depend on fiber and sheet properties, such as pulping method, sheet bulk, homogeneity and grammage. TiO2, improves sheet opacity when contained in paper.

Sheet opacity is defined as a “contrast ratio” 100(R0/R¥), where R0 is the reflectance of a single sheet backed by a non-reflecting surface and R¥ is the reflectance of an infinite number of sheets of the same material. TAPPI similarly defines opacity as a “contrast ratio” 100*(R0/R0.89), where R0 is defined as above and R0.89 is the reflectance of a sheet backed by a white material with 89 % reflectance (3,7). Thus, higher reflectance by the sheet surface and scattering of light within the sheet will result in higher opacities. Based on these observations, sheet opacites can be enhanced by producing layered sheets, incorporating filler particles into the fiber web or applying a pigment coating to the sheet. Layered sheets, mainly used in board applications, can include a dark central layer yielding high opacity (5). Pigment fillers generate a larger surface area within the sheet and introduce interfaces with larger differences in refractive index relative to the inherent ones between woodparticles and air. Pigment coatings drastically alter the sheet surface, essentially creating a more dense layered structure, improving among other things sheet opacity. However, fillers and coatings have negative effects on other paper properties like strength and bulk. Improper application or poor control can also have severe effects on the manufacturing process and final product quality.

Titanium dioxide – Properties and utilization

In terms of electronic structure (3d24s2), titanium is the simplest of the transition metals. It constitutes 0.6 % of the earth’s crust, mainly encountered as ores of FeTiO3 (ilmenite) and the binary metal oxides, TiO2 (rutile, anatase and brookite). The rutile polymorph is the most common of the TiO2 species, and accounts for about 90% of the TiO2 sold world wide (8,9). Global production in 1999 was 3,600,000 metric tons. About 396,000 metric tons (11%) went into the paper market. Industrial application in paints and plastics accounted for the bulk of the remaining consumption (9). Rutile is used in all industrial applications, and exclusively in paints and plastic due to its higher refractive index and non-reactive nature. Anatase is found in specialty products like food, cosmetics, and fibers. Both are used in paper with rutile having a more dominant role due to its better optical properties. The properties of synthetic titanium oxides are modified through the manufacturing process and are different from the inherent properties of the naturally occurring minerals.




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