PTFE: What is the difference between molding powder, fine powder and dispersion?
PTFE (polytetrafluoroethylene) has excellent solvent resistance, chemical stability and very low surface friction coefficient, and it is currently the fluoroplastic variety with the best comprehensive performance, the largest production capacity and dosage. Fluorochemical manufacturers typically supply three types of PTFE: PTFE molding powder, PTFE fine powder, and PTFE dispersions.?Next let’s explore what is the difference between them ?
PTFE manufacturing process
As a high-molecular compound, PTFE is polymerized from tetrafluoroethylene (TFE) monomer. The polymerization methods of TFE in industry are mainly suspension polymerization and dispersion polymerization, the former to obtain suspended PTFE resin(PTFE molding powder), and the latter to obtain dispersed PTFE resin(PTFE fine powder)?and PTFE dispersion.
Both methods use the aqueous phase as the polymerization medium and use water-soluble persulfates, peroxides, or oxidation-reduction systems as initiators. During polymerization, an aqueous solution of initiator is added to the reaction kettle, and the reactor should be sealed, and after oxygen is discharged, the TFE monomer is gradually filled, and the TFE dissolved in the aqueous phase is initiated by polymerization. Since PTFE is insoluble in water, the polymerized product will precipitate from the 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 (e.g., perfluorooctanoate) is dissolved in the aqueous phase, and its concentration is lower than the critical micelle concentration, the primary particles are alternately protected, and the system is a temporarily stable dispersion, which is dispersion polymerization.
Suspension polymerization?products
PTFE resin obtained by suspension polymerization can be mashed to obtain a granular product.
After coarse grinding, the product with a particle size between 100~180μm is medium-grain PTFE resin. This kind of product has poor fluidity, and usually processed into simple cylindrical and rectangular blank products by molding or extrusion.
After airstream grinding, the product with a particle size of 20~40μm is fine-grained PTFE resin. Its smaller particle size makes it softer, and it is often used to make molded and extruded products with better mechanical properties.
Taking fine-grained PTFE resin?or medium-grained?PTFE resin?as the raw material, the products processed by dry or wet granulation process are called granulated PTFE resin, which is characterized by good fluidity, suitable for automatic molding and plunger extrusion methods, and can be used to make rod-shaped products, thick-walled pipes, etc.
After drying medium-grained?PTFE resin?, it?is firstly?sintered at a high temperature of more than 300 °C,?the product with a certain fluidity is called?pre-sintered?PTFE resin, which is suitable for thin-walled products and small-diameter bars in the plunger extrusion process.
Suspension polymerized PTFE is commonly used in the manufacture of seals, gaskets and valves, expansion joints, pipes, protective linings, electrical insulators, and electrical tapes, which can be molded or extruded.
Dispersed polymerization products
There are two main types of PTFE dispersed?polymerization products: PTFE concentrated dispersion and dispersion resin. PTFE dispersion is concentrated to about 60%, which can be directly applied, at this time, PTFE basically exists in the form of primary particles, and the particle size is generally between 0.05~0.5μm. After condensing and drying the PTFE dispersion, a powdered resin is obtained, with an average particle size of about 450 μm.
It is worth noting that dispersed PTFE is processed by paste extrusion, especially when the resin is above 19 °C, it?will become soft, sensitive to mechanical shear, and pre-fibrosis?can easily make the material agglomerate, and not easy to break apart. Therefore, in the post-processing production and preparation process, it is necessary to minimize all kinds of shearing and store at low temperatures.
PTFE dispersed?polymerization products can be used to impregnate glass fiber or plastic fabrics, and can be applied to flexible materials such as construction, electrical and electronics, semiconductors, filtration systems, food processing, and fuel cell gas diffusion layers?etc?that require weather resistance, chemical resistance, and high dielectric strength.
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