Jan 26 2015

Atmospheric Pressure Plasma Activation of Polymers and Composites for Adhesive Bonding: A Critical Review


Atmospheric Pressure Plasma Activation of Polymers and Composites for Adhesive Bonding: A Critical Review

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The strength of bonded joints is of great concern to the aerospace, automotive, medical device, and electronics industries [1]. Atmospheric pressure plasma acti-vation is rapidly gaining acceptance as a desirable method of surface preparation prior to bonding [1]. This technique provides an alternative to traditional methods of surface preparation by wet chemical cleaning and mechanical abrasion [1, 2]. Although these latter procedures are “tried and true,” they are time consuming manual processes. Moreover, in certain instances, they yield lower bond strengths, and can even result in damage to composites that are fabricated with high modulus fibers [1, 2]. Abrasion methods generate dust which is an environment, health, and safety concern. Consequently, there is a need to explore alternative, environ-mentally friendly approaches that activate the surface without damaging the bulk material. Atmospheric pressure plasmas show promise for fulfi lling this need.

This review article focuses primarily on atmospheric pressure plasmas that are self contained, and are suitable for the treatment of three-dimensional extruded parts, such as are common in many manufactured products. Plasmas used for this purpose are decoupled electrically from the workpiece. They produce an after-glow that contains neutral reactive species, which fl ow out and down onto the surface being activated. This may be contrasted to coronas and dielectric barrier discharges that are used to treat plastic fi lm. In this latter case, the polymer fi lm is passed between the powered and grounded electrodes in roll-to-roll fashion, and the fi lm is activated by contact with both ionized and neutral species. For more detailed information on the performance of these latter devices, the reader is referred to several excellent review articles [3–6].

In this paper, we examine published work using downstream, atmospheric pressure plasma to activate polymer and composite surfaces. First an overview of the physics and chemistry of atmospheric pressure plasmas will be given, along with a comparison of the different types of devices. Then, the efficacy of this technique for surface activation will be discussed in terms of the mechanical proper-ties, the water contact angle (i.e., surface energy), the surface roughness, and the surface composition. Lastly, we will consider the mechanism of polymer surface activation.

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