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A study conducted by Tristar examined the relative adhesion difference between untreated Rulon J and plasma-treated Rulon J.

It appears that plasma surface modification of Rulon-based polymers is a viable way to enhance adhesion prior to bond-up, lamination or over-moulding.

This study observed approximately a 117 per cent increase in lap shear bond strength after plasma treatment.

Rulon is an engineered tetrafluoroethylene polymer mixed with other proprietary materials.

Since a portion of the Rulon material is a fluorocarbon polymer, it is difficult to achieve good lap shear bond strength without some method of surface treatment.

Sodium naphthalene ammonia dips or liquid etching of fluorocarbons are effective ways to enhance the adhesion of fluorocarbon polymers, but these highly caustic and toxic methods are dangerous and can be difficult to control.

Moreover, the resulting surface of a dipped surface is discoloured to brown or black.

Plasma surface modification is as effective as this dip method, yet it is environmentally friendly, safe, controllable and repeatable without discolouration.

Plasma is a quasineutral cloud of ion, electrons and radicals.

The diffuse cloud produces the chemistry on the surface of materials that is unique, providing wettable or adherent surfaces on materials that are otherwise inert.

The Rulon J samples in this study were subjected to a specific plasma gas mixture to induce an adherent surface for a structural epoxy adhesive.

The results are as follows, showing untreated Rulon J values and untreated Rulon J respectively: contact angle – 110deg, 80deg; pull strength – 45.9psi, 100psi; extension – 1.23in, 6.35in.

It is important to note that the maximum pull strength of the treated sample was compromised by the deformation of the test specimen.

In summary, it is difficult to achieve strong lap shear bond strengths on fluoropolymers.

Traditional surface preparation methods are dangerous and discolour the material.

By using plasma surface modification, the bond strength has improved by approximately 117 per cent, without discolouration.

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