From the adhesion viewpoint, it is useful to divide fluoropolymers into fully and partially fluorinated examples.

Fully fluorinated polymers normally require a pretreatment. There are many methods that could be used to enhance such polymers but the two usually used commercially are sodium in liquid ammonia and sodium naphthalenide in an aprotic solvent. These two methods are both very effective but are undesirable from the environmental viewpoint. The use of sodium and liquid ammonia is clearly hazardous during the treatment stage. Sodium naphthalenide solutions are less hazardous and relatively stable proprietary products may be purchased. However, these are expensive, and when the treated polymer is washed with water naphthalene is liberated. The cleaning process results in an effluent typically consisting of naphthalene, THF, methanol, sodium hydroxide and sodium fluoride.

The existence of a low cohesive strength layer on PTFE is well established. To obtain good adhesion this layer must be removed, crosslinked to material of higher cohesive strength, or be chemically modified so that it can be absorbed by the adhesive. It may also be necessary to chemically modify the surface of PTFE to improve wetting and also increase the interaction across the interface where wetting has occurred.

Plasma treatment of PTFE has led to only moderate improvements in bondability. Many studies have reported introduction of substantial quantities of oxygen-containing groups and/or substantial improvements in wetting but only small to moderate improvements in adhesion. This is consistent with the incomplete removal of the weak layer on PTFE.

It has been...