Micropowders dispersions

Micropowders are added to a wide variety of material used in industry, where they provide nonstick and sliding properties. They are incorporated into the product by blending and grinding. To disperse weU, the powder must have good flow properties. Conditions that make the powder sticky should be avoided. 

PTFE micropowders or fluoroadditives (e.g., Zonyl TE-3887, DuPont) are available in aqueous dispersions with 50% to 60% solids. They have very small particle size, typically in the range of 2 to 20 pm, and contain typically 6% of nonionic wetting agent and stabilizer. Usual pH of these dispersions is 10. PTFE micropowders are used as additives to paints and coatings, for demolding, and for lubrication (for details see Publication L-13812, 01/07, DuPont). 

Particle size and surface area are important properties for many micropowder applications and each micropowder application has its own requirements. Due to their small primary particle size, the powders from dispersion polymerization are the more easily suspended in low viscosity media. However, some applications require a larger particle size. Particulate additives can increase the viscosity of fluids or even polymer melts and the effect is a function of the additive surface area. This can be a positive or negative factor depending on the application. 

As noted above, surface area is an important property for many micropowder applications. The only directly polymerized low MW PTFE available commercially is based on dispersion polymerization (high surface area) so either irradiated granular or thermally degraded PTFE is employed when a low surface area is preferred for the application. 

Method of synthesis granular resin, water dispersions, and powdered resins are produced by free radical polymerization in aqueous medium TFE polymerizes linearly without branching micropowders are produced by irradiation of PTFE by high energy electron beam or polymerization controlled to produce lower molecular weight Diobny, J G, Fluoroplastics, Rapra, 2006. 

The micropowder of chitin is dispersed at room temperature using CaClj THjO saturated methanol solutions. When this is refluxed for several hours, a consistent and clear dope is obtained. After being degassed, the film is immersed in a 20% mixed sodium formic acid aqueous solution and ethylene glycol (1 1 v/v) overnight, resulting in a chitin gel after calcium is removed. 

Uses Rub resist, aid in printing inks flatting agenL antisetUing agent in paints/coatings dispersant, color enhancer in color cones. hardener in wax compds. bik. heel mark resist, aid in floor polishes lubricant for plastics processing Properties Micropowd. sol. in nonpolar solvents insol. in water dens. 0.94 vise. 

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