Perfluoroether rubber (FFKM) is composed of a tetrafluoroethylene (PTFE) main chain and perfluoromethyl vinyl ether (PMVE) side chains and bridging parts. It not only has excellent properties of high temperature resistance and chemical corrosion resistance (resistant to more than 1.600 chemicals), but also has the elasticity of rubber. FFKM products are mainly used in aviation, aerospace, petroleum, chemical industry and atomic energy industries [1]. Most of them are seals and can be used in rocket engine fuel, hydrazine, oxidizer, nitrogen tetroxide, fuming nitric acid and Freon-21. At present, my country's FFKM synthesis process is still in the experimental research stage. Zhonghao Chenguang Chemical Research Institute has successfully developed an important raw material for synthesizing perfluoroether rubber - perfluoromethyl vinyl ether, but its synthetic rubber process is still in the experimental stage. This experiment selected perfluoroether raw rubber for formulation and process research to develop a perfluoroether compound rubber with good high temperature performance, low compression permanent deformation and excellent medium resistance. I. Materials and Methods
I. Selection of Compounding Agents
1.Vulcanization System. Perfluoroether rubber is a highly saturated fluorine-containing polymer. It cannot be vulcanized with sulfur. Mixing a small amount of sulfur will make the fluororubber completely scrapped. Generally, organic peroxides, organic amine derivatives, and dihydroxy compounds are used as vulcanizers or radiation vulcanization is performed. Radiation vulcanization has not yet been put into industrial production. In general industrial production, the rubber compound produced by the bisphenol AF/BPP vulcanization system has good stability, is not easy to burn, has good fluidity, and has small compression permanent deformation [3]; the rubber compound produced by the bisphenol 25+TAIC vulcanization system does not burn or shrink, and has good corrosion resistance and high-temperature steam resistance. At present, rubber generally uses the peroxide vulcanization system of bisphenol 25+TAIC.
2.Reinforcing filler. Perfluoroether rubber is a self-reinforcing rubber with high strength. Reinforcing fillers are mainly used to improve process performance, reduce costs, and control product hardness, heat resistance, and compression permanent deformation. Semi-reinforced carbon black is generally used as a filler.
3.Additives. In order to improve the comprehensive performance of perfluoroether rubber, Solvay has developed special additives. A small amount of addition can greatly improve the mechanical properties and processability of the compounded rubber.
II. Processability research
1.Key points for quality control of perfluoroether rubber compounded rubber
(1) Pay attention to whether the rubber mixer and the surrounding environment are clean. It is best to use a dedicated rubber mixer. Otherwise, the rubber mixer must be cleaned before mixing.
(2) Turn on the rubber mixer and open the cooling water valve to about 1/2.
(3) Requirements for the rubber mixing process: Adjust the roller spacing to about 1mm, thin the raw rubber three times and then wrap it around the front roller. Wait until the raw rubber is evenly wrapped around the roller on the open mill to ensure that there is an appropriate amount of accumulated rubber on the roller; slowly add the pre-mixed powder along the roller gap of the open mill in batches, and be careful not to cut during mixing. If there is too much accumulated rubber, gradually and slowly increase the roller spacing; clean the material plate of the open mill and add the cleaned material to the rubber; after the powder is eaten, pull the cutter left and right once, adjust the roller spacing to about 1mm, thin the rubber and make a triangle wrap three times each; adjust the roller spacing to about 3.5mm, and unload the sheet.
(4) Heat is generated during the mixing of perfluoroether rubber, which can accelerate the dispersion of carbon black and compounding agents. However, be careful not to let the roller temperature exceed 50℃; if the temperature is too high during mixing, wait for the roller to cool down slightly before operating.
(5) The mixed rubber is spread out and naturally aired to room temperature before being put into storage. The rubber cannot be stacked to prevent the temperature in the middle of the rubber from accumulating and causing scorching. As shown in Table 2. the specific information of the perfluoroether rubber compounding process is shown.
2.Performance test
The perfluoroether rubber compounding was prepared according to the designed formula. Under the selected vulcanization molding process conditions, the test pieces and small beans (Φ10×10 ) were pressed. The performance was tested according to GB/T528-1998 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber" and GB7759-87 "Physical test methods for vulcanized rubber". The test results were compared with those of other brands of rubber compounds, and the medium resistance of the new perfluoroether rubber compound within 30 days was tested.
III. Results and analysis
The newly developed perfluoroether rubber compounding has the following characteristics:
1.The room temperature tensile strength and elongation at break are higher than those of other perfluoroether rubber compounds, indicating that its mechanical properties are excellent;
2.The high temperature compression permanent deformation is greatly reduced compared with other rubber compounds, and the high temperature performance is excellent. It can be used reliably at 280 ℃;
3.The medium resistance is excellent and it is first-level compatible.
Ⅳ. Conclusion
The newly developed perfluoroether rubber compound has a scientific and rational formulation, good processability, and excellent high-temperature performance and media resistance. It achieved the research objectives and can be used to manufacture seals for media-resistant and high-temperature resistant products.
