Investigation of Influence Factors in Electron Beam Curing of Epoxy Resins Using a Calorimetry Technique J. H. Chen, 1 A. Johnston, 2 L. Petrescue, 2 M. Hojjati 1 1 National Research Council of Canada, Institute for Aerospace Research, Aerospace Manufacturing and Technology Center, Montreal, Quebec, Canada H3T 2B2 2 National Research Council of Canada, Institute for Aerospace Research, Structures, Materials and Performance Laboratory, Ottawa, Ontario, Canada K1A 0R6 Received 17 November 2006; accepted 3 August 2008 DOI 10.1002/app.29170 Published online 19 November 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Because of the complexity of the electron beam (EB) curing process, current understanding of EB curing of polymer resins and composites is limited. This article describes an investigation of different factors affect- ing EB curing of epoxy resin such as dose rate, time inter- val between irradiation doses, moisture, and photoinitiator concentration using a calorimetry technique. Results show that higher dose rate resulted in a higher and faster tem- perature increment in the uncured resin samples, and thus a higher degree of cure. In the multiple-step EB irradia- tion, a shorter time interval between irradiation doses resulted in higher temperature in the resin samples and therefore higher degree of cure. Results indicate that mois- ture could delay crosslinking reaction in the early stages of the cure reaction, but accelerates it later in the curing process. Given a reasonable percentage of photoinitiator, experiments confirmed that samples with higher photoini- tiator concentration reach higher degree of cure under same EB irradiation conditions. V V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2318–2327, 2009 Key words: EB curing; epoxy; calorimetry INTRODUCTION Electron beam (EB) curing of composites is a tech- nology that offers significant potential in manufac- turing of cost-effective composite structures. During EB curing process, high-energy electrons are used to initiate cure reactions of polymer resins. In compari- son with conventional composites curing processes, EB curing has many advantages such as reduced cycle time, long resin shelf life, and low temperature curing. 1 Although significant progress has been made in improving properties of EB-cured compos- ite materials in recent years, 2,3 due to the complexity of process, the basic mechanisms of EB curing and the influence of processing conditions on material properties are still largely unknown, presenting a significant barrier to progress. 4 To improve the prop- erties of EB-cured composites and to produce high quality parts, efforts have to be made to control and optimize the curing process. Therefore, it is impor- tant to investigate the factors that could influence the EB curing of resins and composites. It has been confirmed by many researchers that various factors such as total dose, dose rate, temper- ature, photoinitiator concentration, and moisture can influence EB curing of resin and composites. First of all, the investigation of the influence of EB irradia- tion dose has been a subject of many research stud- ies. Research has shown that the total EB irradiation dose can influence the degree of cure, 5–7 glass transi- tion temperature, 6,8–10 mechanical properties, 7,11,12 and fiber/matrix interfacial properties. 11,13 However, a more important factor in EB curing is the dose rate. Dose rate can influence the temperature rise in the part, processing time, and total dose required for full cure of composite part. It is understandable that even with same irradiation dose, if the dose rate were different, the properties of the cured part could be totally different. Also, in EB curing, an appropri- ate dose rate (kGy/s) has to be selected to avoid overheating the part to be cured. Currently, less in- formation is available about influence of dose rate (kGy/s) on the EB curing process, and on the prop- erties of EB-cured resin and composites. Although the influence of dose/pass has been reported, 11,14–16 dose/pass is not equivalent to dose rate since the rate of dose application in a given pass can vary Journal of Applied Polymer Science, Vol. 111, 2318–2327 (2009) V V C 2008 Government of Canada. Exclusive world wide publication rights in the article have been transferred to Wiley Periodicals, Inc. Correspondence to: J. H. Chen (jihua.chen@nrc-cnrc.gc.ca). Contract grant sponsors: Canadian Department of National Defence, New Initiatives Fund of the NRC Institute for Aerospace Research.