Adhesion to Fluoropolymers
Of interest to those who already use fluoropolymers and those who are considering using them, this book is mainly concerned with the wide variety of methods available to pretreat fluoropolymers.
TABLE OF CONTENTS Adhesion to Fluoropolymers
Chapter 5: Pretreatments
5.1 Summary
Effective pretreatments for PTFE were developed in the 1950s. These were sodium in liquid ammonia (a.4) and sodium naphthalenide in tetrahydrofuran (THF) (a.5). Many other treatments for PTFE have since been investigated including plasma treatment, direct electrochemical reduction, treatment with an alkali metal amalgam and reduction with benzoin dianion. In recent years the vast majority of research studies have centred on plasma treatment. This is reflected in the account of pretreatments given next.
5.2 Wet Chemical Treatments
5.2.1 Treatments with Solvated Electrons and Radical Anion Salts
Sodium in liquid ammonia and sodium naphthalenide in THF are both powerful reducing agents, i.e., they are capable of acting as powerful electron donors as shown in Equations (4) and (9):
| (4) |  |
| (5) |  |
A possible mechanism of reduction of the carbon halogen bond in fluoropolymers is outlined next:
| (6) |  |
| (7) |  |
| (8) |  |
| (9) |  |
The first step, Equation (6), involves electron transfer from a solution of solvated electrons, or a naphthalenide radical anion or a cathode to the fluorinated polymer with elimination of a fluoride ion to produce a neutral radical. This then reacts further to produce new carbon-carbon bonds resulting in crosslinking as shown in Equation (7) or the radical may accept a second electron to form a carbanion which in turn reacts with a protic solvent (HS) to yield carbon-hydrogen bonds as shown in Equation (8), or undergoes elimination of a fluoride ion with formation of carbon carbon double bonds as shown in Equation (9).
The treatment of fully fluorinated polymers with...
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