Polytetrafluoroethylene (PTFE) acid neutralization, filtration and washing combined

 Low-molecular-weight polytetrafluoroethylene is used as an additive in plastics, inks, coatings, and lubricating oils (greases) to improve the non-stickiness and wear resistance of the base materials. The molecular weight of the said low-molecular-weight polytetrafluoroethylene is generally 1/100 of that of high-molecular-weight polytetrafluoroethylene. It can be well mixed with the base material, thereby endowing the base material with certain characteristics of polytetrafluoroethylene. In thermoplastics, elastomers and thermosetting plastics, it can enhance the wear resistance, non-stickiness and reduce the surface friction coefficient of the materials. In ink, especially in high-quality ink, it can help enhance surface gloss, increase wear resistance and reduce clogging. In non-stick coatings and wear-resistant coatings, it enhances the non-stickiness of the coating, reduces the coefficient of friction, and improves the anti-corrosion and wear resistance.

Unlike high-molecular-weight polytetrafluoroethylene, the preparation of low-molecular-weight polytetrafluoroethylene usually requires the use of organic substances that are harmful to the environment as molecular weight regulators and organic solvents. Conventional low-molecular-weight polytetrafluoroethylene resin is produced by emulsion polymerization. Deionized water is used as the polymerization medium, ammonium perfluorooctanoate as the dispersant, and dichloromethane as the chain transfer agent. Under the initiation of persulfate as the initiator, the tetrafluoroethylene monomer polymerizes. The resulting polymer liquid is then coagulated and continuously dried to obtain low-molecular-weight polytetrafluoroethylene resin This method can prepare low-molecular-weight PTFE resin of water emulsion type with excellent stability.

(1) The conventional process uses ammonium perfluorooctanoate as an emulsifier, which is difficult to degrade and may be harmful to the human body, and thus needs to be replaced.

(2) The chain transfer agent dichloromethane was used. This product has an anesthetic effect, mainly damaging the central nervous system and respiratory system, and is irritating to the skin and mucous membranes.

(3) Use molecular weight regulators of organic compounds. The use of this reaction medium inevitably has adverse effects on the environment and operators, and the molecular weight regulators of organic compounds will also affect the performance of the final product.

Research on the Two-in-One Technology of Acid Neutralization Reaction, Filtration and Washing of Polytetrafluoroethylene Resin (PTFE

The new preparation process of low-molecular-weight polytetrafluoroethylene resin does not use perfluorooctanoic acid and its salts, does not add chain transfer agents, and does not require high-temperature or radiation methods, thus posing no harm to the health of operators during the resin preparation process. The preparation method of low-molecular-weight polytetrafluoroethylene resin with a molecular weight of 30,000 to 600,000 includes the following steps:

Preparation of polytetrafluoroethylene dispersion system

Polymerize tetrafluoroethylene monomers for 2 to 3 hours at a temperature of 60 to 100 ° C and a pressure of 1.5 to 2.8MPa in the presence of water and 500 to 5000 PPM of fluorinated surfactants, 200 to 1000 PPM of carboxylic acids or their salts, and 100 to 1000 PPM of anionic non-fluorinated surfactants. The obtained polytetrafluoroethylene dispersion;

(2) Preparation of low molecular weight polytetrafluoroethylene resin

Nitric acid was added to the aqueous dispersion of low-molecular-weight PTFE. By applying intense mechanical shear force, the polymer coagulated and polytetrafluoroethylene resin was condensed.

(3) A two-in-one inorganic acid neutralization process of cylindrical and conical filtration and washing

In the cone-cylinder filtration and washing two-in-one process, the wet powder obtained is neutralized and washed with water, and then high-purity powder of low-molecular-weight polytetrafluoroethylene resin is filtered out.

(4) Drying process of low molecular weight polytetrafluoroethylene resin

The filter cake is dried in a special dryer for low-molecular-weight polytetrafluoroethylene resin, thereby obtaining low-molecular-weight PTFE powder.

The performance advantages of polytetrafluoroethylene resin (PTFE) acid neutralization reaction filtration and washing in one

The conical and cylindrical filtration and washing combined type is a filtration device composed of multiple layers of orifice plates and filtration media stacked inside the cone or cylinder. It is equipped with a stirring shaft and a variable-angle and variable-lead spiral stirring device inside. During filtration, it stirs, lifts and scrapes the material, and automatically pushes out the filter cake when unloading. This machine can perform vacuum filtration or pressure filtration. During the filtration process, the scraper inside the machine constantly scrapes off the filter cake on the filter screen, allowing the material to be filtered under the condition of a thin layer of filter cake, with a very high filtration rate.

The inorganic acid neutralization process of low-molecular-weight polytetrafluoroethylene resin can first filter the slurry dry in the machine, then add the washing liquid, and use the rotation and stirring of the scraper, agitator and extrusion screw in the machine to make the filter cake re-slurry. At this time, the re-slurry material is filtered into a filter cake by means of pressurization or vacuuming. By repeatedly filtering the slurry in this way, the material can be thoroughly washed, and finally all the filter cake can be extruded out of the machine.

(1) The fully enclosed system provides a very good operating environment and is particularly suitable for the filtration and washing of toxic, flammable, explosive and other dangerous products, as well as fresh and delicious food, biological products, medicines and biological products that are not allowed to be contaminated.

(2) Continuous operation with extremely low labor intensity. It has a large operational flexibility and can adjust the operation cycle by regulating the filtration pressure difference, rotational speed, screw extrusion lead, etc., to adapt to changes in process conditions.

(3) It can both concentrate and filter. Especially when it is necessary to wash the materials, the materials can be concentrated first and then thoroughly washed in a suspended state. Finally, they can be pressed and filtered. This can reduce the handling of materials, minimize waste, and there is no need for slurry during washing. The quality of the processed products is very high.

(4) This machine can form a very thin filter cake on the surface of the filter medium or perform filtration without a filter cake. The filtration rate per unit filtration area is very high, so the equipment is small and compact.

(5) It can conveniently and repeatedly filter and wash materials, enabling the functions of multiple unit devices to be accomplished on this one machine, thereby significantly reducing equipment costs, floor space, labor intensity, energy consumption, etc. When the cylindrical and conical filtration and washing are combined into one, it is particularly suitable for materials with high washing requirements that need to be repeatedly re-washed and filtered, and it can also save washing liquid.

(6) The material can be subjected to pressure filtration at a relatively high pressure, or vacuum filtration can also be carried out. A jacket is added to the outside of the filter to heat, cool or insulate the material for filtration, so as to meet the requirements of various process conditions.

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