Study On Surface Modification Of Fluoride Rubber Using Atmospheric Pressure Dielectric Barrier Discharge (DBD) In Air

Fluoride rubbers possess good properties such as good thermal and chemical resistance, and low electrical conductivity, which are based on the low polarizability of C-F bonds. The new kinds of the material with excellent performances become more and more important, and are widely used in the national defense, war industry, aerospace, automobile, petrochemical etc. However, fluoride rubbers are low polarizability materials with low surface energy and poor wettability, so it's very difficult for fluoride rubbers to wet, and the surface inertness has resulted in the poor adhesion of the polymer with various materials. In this connection, amount of researches have been devoted to the surface modification of fluoride rubbers.Dielectric barrier discharge plasma (DBD) technique develops quickly in recent years and it is adopted to modify the surface properties of many materials. The surface of fluoride rubber material was modified by the DBD technique in this paper. The result showed that the surface modification of the fluoride rubber affected the surface properties greatly.Surface modification of fluoride rubber films (F₂₃₁₁) had been done by an atmospheric-pressure plasma treatment using dielectric barrier discharge in air. The plasma-induced surface changes of F₂₃₁₁ film were investigated by fourier transform attenuated total reflection infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), the contact angle measurement and atomic force microscopy (AFM). Results showed that a short time air plasma treatment of few seconds leaded to morphology, wettability and chemical changes of F₂₃₁₁ film. After the plasma treatment, the oxygen containing groups were introduced, such as C=O,—OH, O—C—O etc, an additional C1s peak was introduced which appeared at 289.3-289.8eV , the water contact angle decreased from 98.6°to 32.0°. Air-DBD plasma had an obvious etching effect on F₂₃₁₁ films which were detected by AFM. The surface roughness increased remarkably. The peel strengh of the F₂₃₁₁ and silicon rubber increased from 3.3 to 6.0 N/cm. The preferable parameters of the air-DBD plasma were discharge power 40×2W, discharge distance 2mm and plasma irradiation time 120sec.The surface of F₂₃₁₁ was treated by the air-DBD plasma with the preferable treating condition, and then was modified functionally by the liquid-phase grafting method with acrylic acid, acrylic amide and acrylic acid/acrylic amide as a monomer. The result showed that the modification efficacy was the best when the acrylic amide and acrylic acid were adopted together. The grafting time and temperature affect the modified surface remarkably. The grafted surface became more uniform and wettable with the increasing of grafting time. The best grafting time of the AA/AAm monomer is 2h; the contact angle of the grafted surfaces decreases first and then increases with the increasing temperature, the best grafting temperature is between 50-60℃.The air-DBD plasma was adopted to modify the surface of F₂₃₁₁ with the first treating conditions, discharge distance 2 mm, 80 watts, 120s, and the second treating conditions, discharge distance 4 mm, 150 watts, 60s. The result showed that the modification efficacy was the best when the acrylic amide and acrylic acid were adopted together. The surface energy of the F₂₃₁₁ which passed through the secondary air-DBD plasma treated was increased greatly. After 60s treated the surface energy could reach 55.6 mN/m. From the point of treating time, the secondary air-DBD plasma grafting was more efficient compare to the liquid-phase grafting method.The grafted surface were much more flat, the roughness decreased compared to the surface modified by the air-DBD plasma only which were detected by the SEM. Both the XPS C1s spectra and O1s spectra showed there were new peaks assigned to some new groups, it could be the result of the graft, copolymerization and crosslink between the F₂₃₁₁ film and the acrylic monomers.