Radiation Measurements 40 (2005) 754 – 757 www.elsevier.com/locate/radmeas Activation energy of thermal decomposition of proton irradiated polymers R. Mishra a , ∗ , S.P. Tripathy a , D. Fink b , K.K. Dwivedi c a National Agency for Environmental Protection and Technical Services (APAT), Via. V. Brancati 48, Rome 00144, Italy b Hahn-Meitner Institute, Glienicker Strasse, 100, D-14109, Berlin, Germany c Department of Science and Technology, Embassy of India, 2536 Massachusetts Avenue, NW, Washington, DC 20008, USA Received 27 August 2004; accepted 1 February 2005 Abstract The ion irradiation of polymeric solids induces numerous modifications in the polymer properties, thus increasing their applicability in various fields. The present work looks into the aspect of thermal modifications induced in the irradiated polymers by using the thermogravimetric (TG) technique. It has been observed that the degradation of polymers is a multi-step process that involves sequential and competing processes, and obeys the Arrhenius kinetics, and this allows us to connect the rate constant with the absolute temperature and the activation energy. © 2005 Elsevier Ltd. All rights reserved. Keywords: Proton irradiation; Activation energy; Thermal decomposition; Polymers 1. Introduction The complexity of the chemical structure of polymers and the variability of their physical behaviour makes their thermal properties a function of the thermal pre-history of the sample and also of the heating rate (in dynamic experi- ments). Organic substances such as polymers are thermally sensitive due to the limited strength of the covalent bonds that make up their structures, which makes it possible to ex- plain their thermal sensitivity at the molecular level. More- over, scissions of chemical bonds under the influence of heat are the result of overcoming bond dissociation ener- gies (Melnik, 2002). Nevertheless, scission can occur either randomly or by a chain-end process, often referred to as an unzipping reaction. ∗ Corresponding author. Tel.: +39 06 500 72842; fax: +39 06 5007 2941. E-mail address: mishra@apat.it (R. Mishra). 1350-4487/$ - see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2005.02.022 Thermal conductivity is higher in the crystalline rather than in amorphous phase (the mean-free-path of phonons being longer in crystals than in amorphous phase, where it is limited by the disordered arrangement of atoms to a value of the same order as the inter-atomic distance). But at the same time, cross-linking of molecular chains increases the packing density of the macromolecules, thus increasing the effective mean-free-path of the phonons, i.e., increasing the thermal conductivity. As a result, the behaviour of ther- mal conductivity in irradiated samples depends on the rela- tive magnitude of these competing processes, mainly cross- linking and chain scission (Briskman, 2001). The effects of proton irradiation on different polymers have already been reported (Gagnadre et al., 1993; Lee, 1999; Tripathy et al., 2001,2002,2003). As an extension to our previous work on the modifications in thermal prop- erties of Makrofol-N (MFN) and Polyimide (PI) induced by 62 MeV protons (Mishra et al., 2003), the present work deals with the study of the activation energy of the ther- mal decomposition of these two polymers irradiated by