Experimental Investigation into the Effect of Adhesion Properties of PEEK Modified by Atmospheric Pressure Plasma and Low Pressure Plasma Sangeeta Jha, 1 Shantanu Bhowmik, 2 Nitu Bhatnagar, 1 Nayan Kamal Bhattacharya, 1 Utpal Deka, 1 Hafiz Mohammad Salim Iqbal, 2 Rinze Benedictus 2 1 Sikkim Manipal Institute of Technology, Sikkim Manipal University, Majitar Sikkim, India 2 Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands Received 18 June 2009; accepted 27 November 2009 DOI 10.1002/app.31880 Published online 19 May 2010 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: High performance polymer, Polyether Ether Ketone (PEEK) (service temperature 250  C to þ300  C, ten- sile strength: 120 MPa) is gaining significant interest in aero- space and automotive industries. In this investigation, attention is given to understand adhesion properties of PEEK, when surface of the PEEK is modified by two differ- ent plasma processes (i) atmospheric pressure plasma and (ii) low pressure plasma under DC Glow Discharge. The PEEK sheets are fabricated by ultra high temperature resist- ant epoxy adhesive (DURALCO 4703, service temperature 260  C to þ350  C). The surface of the PEEK is modified through atmospheric pressure plasma with 30 and 60 s of exposure and low pressure plasma with 30, 60, 120, 240, and 480 s of exposure. It is observed that polar component of surface energy leading to total surface energy of the poly- mer increases significantly when exposed to atmospheric pressure plasma. In the case of low pressure plasma, polar component of surface energy leading to total surface energy of the polymer increases with time of exposure up to 120 s and thereafter, it deteriorates with increasing time of expo- sure. The fractured surface of the adhesively bonded PEEK is examined under SEM. It is observed that unmodified PEEK fails essentially from the adhesive to PEEK interface resulting in low adhesive bond strength. In the case of sur- face modified PEEK under atmospheric pressure plasma, the failure is entirely from the PEEK and essentially tensile failure at the end of the overlap resulting in significant increase in adhesive bond strength. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 173–179, 2010 Key words: polyether ether ketone (PEEK); epoxy adhesive (DURALCO 4703); low pressure plasma; atmospheric pressure plasma; SEM; adhesive bond strength INTRODUCTION Various industrial sectors like automotive, aviation, space etc. is constantly striving for high strength light weight materials. These materials are often fab- ricated by adhesive bonding to form desired struc- tural components. Adhesive bonding is advanta- geous than other ways of joining especially riveting. 1–3 Riveting of components results in stress concentration and reduces the overall load capacity of the structure. 4 Adhesive bonds are more effective in assembling composite structures than other me- chanical joining methods, as they provide more uni- form stress distribution, lower stress concentration and better fatigue life and corrosion resistance. 5 Ad- hesive joint can distribute the applied load over the entire bonded area and is suitable for joining dissim- ilar materials with low manufacturing cost. 6 The use of adhesive bonding for high performance applica- tion is still challenging due to low thermal and me- chanical properties of adhesives. However, due to the development of high performance adhesives the limitations in terms of thermal and mechanical prop- erties have overcome considerably. 7,8 It is established that for successful application of polymeric composite materials to form structural parts using adhesive bonding, they need to have special surface properties like hydrophilicity. 9 Recent advances in the use of polymers and the resulting need for hydrophilic surfaces for adequate adhesion has fueled the development of the plasma surface modification industry. 10 Low-pressure plasma meth- ods have been investigated, but they are difficult to apply on a industrial scale as they require vacuum and consume considerable amounts of energy. More- over, these treatments can only be carried out in a batch mode, which increases the overall treatment time. New methods based on atmospheric plasma Correspondence to: S. Jha (sangeetajha66@yahoo.co.in). Contract grant sponsor: Aerospace Material, Faculty of Aerospace Engineering, Delft University of Technology, The Netherlands, Sikkim Manipal Institute of Technology (Sikkim Manipal University), India, and Birla Institute of Technology, Mesra, Ranchi, India. Contract grant sponsor: AICTE New Delhi, India; contract grant number: F.NO.8023/BOR/RID/RPS-243/ 2008-09. Journal of Applied Polymer Science, Vol. 118, 173–179 (2010) V C 2010 Wiley Periodicals, Inc.