International Journal of Adhesion & Adhesives 20 (2000) 361}366 Durability of APC2/Polyurethane adhesive joints for biomedical applications V. Barron*, M. Buggy, A. Mas, F. Schue Department of Materials Science and Technology, University of Limerick, Limerick, Ireland Laboratoire de Chimie Macromoleculaire, Universite de Montpellier II Sciences et Techniques du Languedoc, Place Eugene Bataillon, 34095 Montpellier, Cedex 5, France Accepted 10 February 2000 Abstract Thermoplastic polyurethane elastomer was thermally bonded to carbon "bre-reinforced polyetheretherketone (APC2) in the development of a biomedical device. Argon plasma treatment of the APC2 substrate was investigated as a means of enhancing bonding. Contact angle measurements were used to optimise the surface treatment and, it was observed that the wettability decreased on ageing. Kinetic analysis gave an activation energy of 25 kJ/mol, which was consistent with a bond rotation mechanism. Optimally treated substrates were bonded to polyurethane and bond stability at 373C was evaluated. While the bond was stable in air for over 1 year, storage in aqueous media lead to rapid deterioration of bond strength. This phenomenon was observed both in distilled water and in Ringer's solution. Measured di!usion rates for both environments were very similar and it is suggested that the observed faster rate of loss of bond strength in Ringer's solution is by the interaction of bu!ered components from the Ringers or solubilisation of low molecular weight material by the Ringers.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Polyurethane (A); Surface treatment by excited gases (B); Contact angle (C); Durability (D); Carbon "bre-reinforced polyetheretherketone 1. Introduction This work involved the bonding of elastomeric poly- urethane to carbon "bre-reinforced polyetherether- ketone (APC2) for a biomedical application. As no quali"ed adhesives were available, thermal bonding in- volving compression moulding was employed and the surface treatment technique of plasma ion bombardment was employed to achieve adequate bond strength be- tween the two materials. Previous workers have shown plasma treatment to be an e!ective method of surface treatment for APC2 for adhesive bonding [1}5]. It was found that this method of surface treatment reduced the contact angle, increased surface tension, and thereby enhanced the adhesion properties of APC2. By relating the water contact angle of untreated APC2 to plasma- treated APC2 the optimum treatment was developed. In * Corresponding author: Tel: #353-61-202301; fax: #353-61- 338172. E-mail address: valerie.barron@ul.ie (V. Barron). a previous study by Ameen [6] it was shown that these treatments are unstable, since the water contact angle increased with increase in storage time. Brennan et al. [7] and Munro and McBriar [8] believe that this change in surface behaviour is be due to the rotation of surface polar groups and migration of low molecular weight fragments into the bulk. This concept has been discussed by various researchers [9}11] including Chatelier et al. [12], who suggested that polymer surfaces can adapt to surrounding media by reorientation of the surface seg- ments and such surface segments can produce changes in contact angle measurements. Strobel et al. [9] observed a slight change in wettability in air corona-treated poly- propylene "lm on ageing and attributed this change to reorientation of oxidised functional groups within the surface region. In another study carried out by Strobel et al. [10], it was found that air corona-treated polypropylene and polyethyleneterphthalate "lms had di!erent responses to ageing. At ambient temperature the polypropylene exhibited only a slight decrease in wetta- bility on ageing, which was attributed to the reorienta- tion of oxidised functionalities within the surface region, 0143-7496/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 3 - 7 4 9 6 ( 0 0 ) 0 0 0 0 9 - 9