Organophilicity, degree

A partly hydrophobic and organophilic silica can be made very simply by a process patented by Goebel (507b). Fine silica powder is dehydrated and the surface dehydroxylated to an optimum degree by heating it for 1.5 hr in air at 470-530 C. The BET area was 297 m g" but the resulting specific hydroxylated area was 184 m g . When this powder was cooled and refluxed at 118 C in butanol at atmospheric pressure or even when simply exposed to butanol vapor in a closed container for a week, esterification occurred and the surface became about half covered with attached butoxy groups. 

Particles with both hydrophilic and organophilic areas obviously will collect at the oil-water interface. This stabilizes the boundary to an even greater degree than a surfactant alone. Though not usually us specifically as an emulsifying agent, sur-face>treated silicas often stabilize emulsion systems, as in paints, where the silica may also play other roles. 

As compared to purified bentonite, at which the maximum rate of decomposition is on the first step, at a temperature of 74 °C, the organophilized bentonite presents a shift of maximum decomposition rate towards higher temperatures (220-5-225°C for PB/ MA-VA nanocomposites and 220 -5-365 °C for PB/ MA-MMA nanocomposites), on the second step of decomposition, similar to maleic copolymers (Table 3). An increase of maleic copolymer concentration (from 50% to approximately 200% reported to bentonite) reflects into an increase of weight loss at the temperature range of 200 500 °C. The obtained results show the intercalation of maleic copolymers between the silicate layers. Thermal stability of obtained binary nanocomposites correlates with the degree of interaction between silicate and copolymer. We notice that in the case of PB/ MA-MMA nanocomposites the best thermal stability is obtained at 1 1 ratio while the best thermal stability for the PB/ MA-VA nanocomposites is obtained at 2 1 ratio. These results are in accordance with X-ray diffraction results. 

Amorphous silicates are produced by destabilization of soluble siUcates to yield amorphous discrete particles in varying degrees of aggregation. The high specific surface area in combination with an organophilic surface is responsible for the excellent ink adsorption characteristics. Amorphous silicate also has the potential to increase somewhat the bulk of the paper sheet. 

Therefore, understanding of the organomodification process of the clay and thus possible control of the degree of organophilization are of paramount importance. 

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