Poly Fep Film Surface Modification Of Epdm Rubber Bonding

Poly (tetrafluoroethylene -co-hexafluoropropylene) (FEP), a perfluorinated polymer, is widely used in anticorrosion field due to its excellent chemical stability, resistance to strong acid, alkali and strong oxidizer. Ethylene-Propylene-Diene Monomer (EPDM), made by solution or suspension copolymerization with ethylene, propylene and a small amount of non-conjugated double olefin, is widely used as sealing material because of its excellent chemical stability and good elasticity after vulcanization. The composite materials composed of FEP and EPDM, have excellent anticorrosion and sealing performance, can be used in heavy anticorrosion fields which need anticorrosion and sealing such as the ion-exchange membrane electrobath in chlorine-alkali industry. However, as a perfluorinated polymer like polytetrafluoroethylene (PTFE), FEP has minimum surface polarity and is difficult to bond with other materials. Thus, it is necessary for FEP to perform surface modification before bonding with others. Up to now, most of the researches upon the surface modification of perfluorinated plastics focus on PTFE, and it's relatively few on FEP. Moreover, the report of adhesion between FEP and EPDM is few. Therefore, the work focuses on the less studied aspects in this paper. Taking ideas from the former researches for reference, the conventional chemical method and electron irradiation grafting are adopted in this paper to study the surface modification of FEP films. Also, the author has discussed the modification mechanism of FEP films and studied the adhesive property between FEP and EPDM in this paper.For conventional chemical method, the sodium-naphthalene solution which takes tetrahydrofuran (THF) as solvent is used to modify the surface of FEP films. This method is widely adopted due to its simple operation, fast and direct effects. However, this method also has many disadvantages such as the solution rapid failing in open-air, difficult controlling as its quick reaction and easy volatilizing, the films changing brown after modification,, and the solvent having certain extent of toxicity. Therefore, the stable and innoxious non-ether organic liquid l,3-Dimethyl-2-imidazolidinone (DMI) is taken as solvent to prepare the sodium-naphthalene solution in this paper. After this, a comparison of modification effects has been made between sodium-naphthalene solutions using THF and DMI as solvents. It was found that the adhesive strengths between vulcanized EPDM and FEP films modified by both of solutions were almost equal except for a little advantage of the treating solutions with THF as solvent in wetting property. However, the time from successful preparation to failure of the treating solutions with DMI as solvent was superior to those of the treating solutions with THF as solvent. In addition, this paper also studied the effects of the treating solutions' concentration on surface modification. The result showed that both the wetting angle and adhesive strength approached their optimum values at the same concentration. This paper considered that part of the F atoms on the surface of FEP films were replaced by H atoms and formed CH₂ which improved the surface property through the analysis of RA-IR spectra of FEP films.Electron beam irradiation is one of the irradiation methods. In addition, other high energy rays also can be used to perform irradiation. Electron beam with proper irradiation dose and energy can produce anionic free radicals on the surface of FEP films. These free radicals are unstable and can be used to graft with single olefin molecule. This paper performed irradiation with the dose of 300kGy and 250kGy respectively on FEP films using electron beam with the energy of 1.2MeV. After irradiation, the grafting was conducted with acrylamide and methacrylic acid respectively. The modified FEP films were analyzed by XPS, and the modification effects were measured. The XPS results showed that other atoms except for C, F were introduced into FEP films' surface after irradiation grafting treatments, especially that the atom N appeared in the FEP films' surface after grafting with acrylamide. It confirmed that acrylamide had grafted to the surface of irradiated FEP films, and the atomic ratio of F/C decreased from 1.95 before modification to 0.914 after modification. The wetting property of modified films was improved significantly, and the wetting angle of distilled water decreased from 128.4°before modification to about 85°after modification. Although the adhesive property was improved to some extent, the adhesive strength was not enough. Further researches are needed.