The inﬂuence of electron beam irradiation conducted in air on the thermal, chemical, structural and surface properties of medical grade polyurethane Kieran A. Murray a , James E. Kennedy a , Brian McEvoy b , Olivier Vrain b , Damien Ryan b , Richard Cowman b , Clement L. Higginbotham a,⇑ a Materials Research Institute, Athlone Institute of Technology, Dublin Road, Athlone, Co. Westmeath, Ireland b Synergy Health Applied Sterilisation Technologies, IDA Business & Technology Park, Sragh, Tullamore, Co. Offaly, Ireland article info Article history: Received 17 December 2012 Received in revised form 27 February 2013 Accepted 25 March 2013 Available online 8 April 2013 Keywords: Electron beam irradiation Surface, structural and thermal properties Chain branching/crosslinking Chain scission Polyurethane abstract It is well known that polyurethane (PU) provides good irradiation resistance; however, extremely high irradiation doses can alter the structure and/or function of macromole- cules, resulting in oxidation, chain scission and crosslinking. In this present study, modiﬁ- cations to the material characteristics resulting from irradiation were extensively examined through a broad array of analytical techniques. Fourier transform infrared spec- troscopy (FTIR) revealed that there were a number of changes to the chemical structure after electron beam irradiation while dynamic frequency sweeps identiﬁed an occurrence of crosslinking particularly in the higher irradiation doses. The degree of crosslinking was further analysed by implementing the crosslink density experiment, which illustrated a high level of crosslinking at 200 kGy only. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) identiﬁed an increase in phase segregation and as a consequence it could lead to soft segment mobility. This increase in mobility could be responsible for an increase in the degree of chain orientation. Surface morphology of the electron beam irradiated material was determined using scanning electron microscope (SEM) imagery and this pro- vided evidence that the surface of the material had clearly transformed with the develop- ment of additional ridges. The inﬂuence of such modiﬁcations initiated a signiﬁcant reduction in the contact angle at the upper irradiation dose regime. Overall, this study demonstrated that the medical grade PU was highly affected by radiation exposure, partic- ularly at high irradiation doses. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Polyurethane (PU) elastomers are ﬂexible biomaterials that have numerous end use applications, owing to its combination of excellent oxidative bio-stability, biocom- patibility, processability and desirable mechanical proper- ties such as abrasion resistance, toughness, ﬂexibility, durability and tensile strength [1]. PUs are often referred to as segmented block copolymers as they consist of a hard and soft phase which either mix or segregate due to their immiscibility and produce phase mixed or phase separated morphologies. Each of the hard and soft segments is con- nected by means of urethane linkages, where the hard seg- ment provides the physical crosslinks within the soft segment matrix [2,3]. Implant devices which contain such elastomers have signiﬁcantly degraded in vivo after 0014-3057/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.eurpolymj.2013.03.034 ⇑ Corresponding author. E-mail addresses: kmurray@research.ait.ie (K.A. Murray), jkennedy@ ait.ie (J.E. Kennedy), Brian.Mcevoy@synergyhealthplc.com (B. McEvoy), Olivier.Vrain@synergyhealthplc.com (O. Vrain), Damien.Ryan@ synergyhealthplc.com (D. Ryan), Richard.Cowman@synergyhealthplc.com (R. Cowman), chigginbotham@ait.ie (C.L. Higginbotham). European Polymer Journal 49 (2013) 1782–1795 Contents lists available at SciVerse ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj