Due to its unique characteristics, PTFE is an ideal choice for performance. Figure 1 shows the various characteristics of PTFE.
Figure 1. The various properties and the role of PTFE performance 
PTFE is mainly manufactured and supplied to the market in three forms, namely granular resin, fine powder and dispersion. Although they are both chemically high molecular weight polytetrafluoroethylene with extremely high melt viscosity, each requires different processing techniques.
Granular PTFE resins are most commonly processed by compression molding and ram extrusion. The compression molding process of PTFE includes the following three important steps: (1) Preforming; (2) Sintering; (3) Cooling. Ram extrusion is a process for producing continuous lengths of PTFE extrudates. The pelletized resin used for ram extrusion must have good flow characteristics so that they can be easily fed into the extruder die tube.
Table 1. Typical Properties of PTFE Granular Resins
|Resin||Bulk Density g/L||Specific Gravity||Particle Size, (average) μm||Tensile Strength, MPa||Elongation at Break, %||Shrinkage, %||Compression Ratio|
|Fine Cut||250–580||2.15–2.17||20–35||30–44||300–400||2.3–4.0||3.2:1 to 5.5:1|
|Free Flow||480–930||2.15–2.17||220–650||29–32||290–330||2.2 –2.8||2.2:1 to 2.5:1|
Fine powder resin is extremely sensitive to shearing, and the polymer after shearing cannot be processed. Therefore, they must be handled very carefully during transportation and processing. Generally, fine powder resins are processed in a "paste" form, which is prepared by mixing the powder with 15% to 25% hydrocarbon lubricants (such as kerosene, white oil, or naphtha).
Most fluoropolymers are produced by polymerization in an aqueous system, but in a subsequent step, the dispersion obtained during the polymerization process is coagulated into a solid form and converted into powder or granules. The aqueous dispersion of PTFE resin is a hydrophobic, negatively charged colloidal system that contains PTFE particles with a diameter of 0.05 to 0.5 μm suspended in water.
Figure 2. The mechanism of surface modification of TiO2.
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