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 4: Adhesion Without Pretreatment
Good adhesion can be achieved by any of the following mechanisms namely:
-
Strong interaction across an interface
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Diffusion
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Mechanical keying
The magnitude of the interaction across an interface will be determined by (a) the degree of contact between the mobile phase, e.g., an adhesive and the substrate, and (b) the type of interaction between the two materials. A direct measure of wettability is given by surface energy (see Section 2).
Some values of surface energies for fluoropolymers are given in Table 1.
| Polymer | Chemical structure of monomer compared with ethylene | ? s d (mJ/m 2) | ? s p (mJ/m 2) | ? s (mJ/m 2) |
|---|---|---|---|---|
| Polytrifluoroethylene | 4H replaced by F | 18.6 | 0.5 | 19.1 |
| Poly(vinylidene fluoride) | 3H replaced by F | 19.9 | 4.0 | 23.9 |
| Poly(vinyl fluoride) | 2H replaced by F | 23.2 | 7.1 | 30.3 |
| Low density polyethylene | 1H replaced by F | 31.3 | 5.4 | 36.7 |
| - | 33.2 | - | 33.2 | |
| Key: | ? s d Dispersion component of surface energy | |||
| ? s p Polar component of surface energy | ||||
| ? s Total surface energy |
The 'non-stick' nature of PTFE can be explained by the lack of chemical functionality resulting in poor wetting and weak interfacial interactions. It will be noted later that weak boundary layers can also play an important role in the adhesion to fluoropolymers. Partially fluorinated polymers like PVF and PVDF have higher surface energies than PTFE and in particular possess...
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