Suspension resin, Dispersion resin, Dispersion, what is the difference between these forms of PTFE?
PTFE (polytetrafluoroethylene) has excellent solvent resistance, chemical stability, and extremely low surface friction coefficient. It is the best fluoroplastic product with the best comprehensive performance, capacity, and dosage. Usually, fluorine chemical manufacturers supply three types of PTFE: suspended PTFE resin dispersed PTFE resin and PTFE dispersion. What is the difference between them? This starts with the preparation process of PTFE...
PTFE manufacturing process
As a polymer compound, PTFE is polymerized from a tetrafluoroethylene (TFE) monomer. The industrial polymerization method of TFE is mainly suspension polymerization and dispersion polymerization, the former obtaining a suspension PTFE resin, and the latter obtaining a dispersion PTFE resin and a PTFE dispersion.
Both methods use an aqueous phase as a polymerization medium, and a water-soluble persulfate, peroxide or oxidation-reduction system as an initiator. In the polymerization, an aqueous initiator solution is added to the reaction vessel, and the reaction vessel is ensured to be sealed. After the oxygen is discharged, the TFE monomer is gradually charged, and the TFE dissolved in the aqueous phase is initiated to be polymerized. Since PTFE is insoluble in water, the polymerized product is precipitated from water to form primary particles. If there is no dispersant in the water, the primary particles will aggregate into coarse particles, which is commonly known as suspension polymerization. When a small amount of dispersant (such as perfluorooctanoate) is dissolved in the aqueous phase, and the concentration is lower than the critical micelle concentration, the primary particles are alternately protected, and the system is a temporarily stable dispersion, which is a dispersion polymerization.
Suspension polymerization product
The PTFE resin obtained by suspension polymerization can be pulverized to obtain a granulated product.
After coarse pulverization, a product having a particle diameter of 100 to 180 μm is obtained as a medium PTFE resin. This product is relatively fluid and is usually processed into a simple cylindrical, rectangular blank product by molding or extrusion.
The product was pulverized by a jet stream to obtain a fine PTFE resin having a particle diameter of 20 to 40 μm. It has a smaller particle size and is therefore softer and is commonly used to make molded and extruded articles with better mechanical properties.
The product processed by dry or wet granulation process using fine or suspended pellets as raw material is called granulated PTFE resin, which is characterized by good fluidity and is suitable for automatic molding and plunger extrusion methods. Produce rod-shaped products, thick-walled tubes, etc.
After drying, the medium pellets are first sintered at a temperature higher than 300 ° C. The product with certain fluidity is called pre-sintered PTFE resin, which is suitable for thin-walled products and small-diameter bars of the plunger extrusion process.
Suspension polymerized PTFE is commonly used in the manufacture of seals, gaskets and valves, expansion joints, pipes, protective liners, electrical insulators, and electrical tapes that can be made by compression or extrusion.
Dispersed polymer product
PTFE dispersion polymerization products mainly include PTFE concentrated dispersion and dispersion resin. The PTFE dispersion concentrate, that is, the concentration of the product is concentrated to about 60%, and can be directly applied. At this time, PTFE is present in the form of primary particles, and the particle diameter is generally between 0.05 and 0.5 μm. After the PTFE dispersion is coagulated and dried, a powdery resin-dispersion resin having an average particle diameter of about 450 μm is obtained.
It is worth noting that the dispersed PTFE is processed by paste extrusion, especially when the temperature is above 19 °C, the resin will become soft and sensitive to mechanical shearing, and the pre-fibrillation will easily cause the material to agglomerate and not easily broken and separated. Therefore, in the post-treatment production preparation process, various shearing effects are minimized and stored at a low temperature.
PTFE dispersion polymerization products can be used to impregnate glass or plastic fabrics and can be applied to construction, electrical and electronics, semiconductor, filtration systems, food processing, and fuel cell gas diffusion layers, etc., which require weather resistance, chemical resistance, and high dielectric strength.