Page 281 - Handbook of Adhesives and Sealants

Surfaces and Surface Preparation 247

turers, and adhesive developers. ASTM D 2093 describes recom-
mended surface preparations for plastic adherends. Appendix C-2 lists
common recommended surface treatments for plastic adherends. Table
6.15 provides a comparison of general surface treatment techniques.
Solvent and heat welding are methods of fastening plastics that do
not require chemical alteration of the surface although cleaning or
degreasing is recommended. These welding procedures will be dis-
cussed in Chapter 15 of this Handbook. The plastic materials com-
monly used in bonded structures, their unique characteristics, and
successful surface treatments and bonding process are more fully de-
scribed in Chapter 16.

6.6.3 Polymeric composite adherends
All of the surface preparations described in Appendix C-2 for poly-
meric substrates are also applicable for when they are reinforced and
made to form a composite material. However, care must be taken so
that the liquid surface preparation chemicals do not wick into the com-
posite along the interface between the fibers and the resin matrix. As
a result, immersion treatments are usually not used. Surface wipe
with a solvent or cleaning agent and abrasion followed by another
surface wipe is usually all that is necessary for treating the high en-
ergy composite substrates prior to bonding. For low energy composite
substrates, chemical etching (protecting the cut edges of the compos-
ite) or plasma treatment are sometimes used.
Plasma treatment has been found to give significantly improved
adhesion properties to thermoplastic based carbon composites (poly-
etheretherketone and polyphenylene suflide). Whereas, thermosetting
composites (e.g., epoxy) provide sufficient joint strength with only light
abrasion and solvent cleaning. 48
The nature of the composite surface treatment will depend on the
resin matrix, the permanence characteristics required, the nature of
the cut surfaces where reinforcement may be exposed to the environ-
ment, and the production facilities that are available.
Many surface roughening approaches have been tried for compos-
ites, and all have some merit. One method that has gained wide ac-
ceptance is the use of a peel ply. In this technique, a densely woven
nylon or polyester cloth is used as the outer layer of the composite
during its manufacture (Fig. 6.12). This ply is then torn or peeled away
just before bonding. The tearing or peeling process fractures the resin
matrix coating and exposes a clean, virgin, roughened surface for the
bonding process.
In the cases where the peel ply is not used, some sort of light ab-
rasion is required to break the glazed resin finish on the composite