Surface modification of polytetrafluoroethylene for adhesive bonding

The chemical bonding at metal–polymer interface is believed to play an important role in adhesion. The interfacial bonding and consequently adhesion are directly influenced by the way in which the interface is formed. Modification of a polytetrafluoroethylene surface (PTFE) has developed into an attractive way to chemically alter a polymer. Such synthetic approaches potentially can maintain a polymerʹs desirable bulk properties but can provide new different interfacial properties. There are many methods by which polymer surfaces can be chemically modified. Most common examples of this chemistry are reactions that introduce a single metal atom, a single type of functional group or mixture of functional groups. This paper briefly summarizes some existing as well as some newer examples from our laboratory of an alternative metal coating chemistry by which PTFE surface has covered with a thin and uniform metal sodium layer. In order to study the nature of the bond formation at metal/polymer interface, we have investigated the interaction of sodium atoms with a polytetrafluoroethylene fragment. Our results suggest that sodium bound to a PTFE polymer chain is energetically favorable. The compound formation is accompanied by charge transfer between sodium and polymer. PTFE with new interfacial properties is well recognized in many areas. Requirements to join dissimilar materials are more and more frequent in new technologies. The paper also deals with a study of a joint between aluminium pieces and polytetrafluoroethylene (PTFE) pieces. The way of their joining is described. The joint was performed through soldering with adhesive that covered the joining surfaces of the pieces, processed at a certain roughness, in a well established thickness layer. The joint was achieved through particular procedure of soldering, simultaneous with plastic deformation of the metal. Various tests of the joint were carried out under conditions simulating service conditions. A piece joint was tested in terms of its strength, thermal resistance and tightness. The tests showed a very good tightness of the joint at high vacuum (1.333 × 10−9 mbar), in conditions of repeated thermal shocks, in the range of temperatures between − 195.5 and 270 °C. The study took into account the requirements of the particular tests and relevant foreign standards, including ASTM and DIN.