Structural evolution of a constrained epoxy functional polyethylene network crosslinked by a bio-based reactant Ruben D. Briceño Garcia a,b,c , Laurent Keromnes c , Yannick Goutille c , Philippe Cassagnau a,⇑ , Françoise Fenouillot b , Philippe Chaumont a a Ingénierie des Matériaux Polymères, UMR CNRS 5223, Université Claude Bernard Lyon 1, 15 Boulevard Latarjet, 69622 Villeurbanne Cedex, France b Ingénierie des Matériaux Polymères, UMR CNRS 5223, INSA de Lyon, 17 Avenue Jean Capelle, 69621 Villeurbanne Cedex, France c Nexans Research Center, 29 rue Pré Gaudry, 69007 Lyon, France article info Article history: Received 29 March 2014 Received in revised form 4 September 2014 Accepted 13 October 2014 Available online 22 October 2014 Keywords: Crosslinking Copolymer Aging Thermoporosimetry Epoxide abstract Epoxy-ethylene copolymers were thermally crosslinked by using an amino-acid agent to create covalent cross-links between epoxide functions. Two different systems were stud- ied: a pre-constrained network and a non-constrained one. Samples were aged for 6, 16 and 24 h. The study of the network structure before and during the aging was done by dif- ferent techniques such as: swelling ratio measurement, Fourier transform infrared spec- troscopy (FTIR) and thermoporosimetry analysis. For the constrained-network system two different mechanisms of aging have been identified: a chain scission phenomenon dur- ing the first 6 h and a cross-linking effect in the latest stages. Chain scission was found to be probably related to the increasing of the rate of the C–C breaking during thermo-oxidative aging as a consequence of a heterogeneous structure formed when crosslinking takes place before relaxation. On the other hand, crosslinking reactions in the latest hours of aging were attributed to reactions of etherification between epoxy and hydroxyl functions as well as the thermo-oxidation of ethylenic chains. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, study of epoxy-functionalized polyeth- ylenes (epoxy-grafted or copolymers) has gained large attention in many domains [1–4]. It is well known that polar nature of the oxirane group brings to polymers useful properties such as oil resistance [5], low gas permeability [6] and enhance compatibility with polar polymers [3,4]. Ethylene polymers are usually crosslinked by peroxides formulations [7,8] and silane-water methods [9,10] how- ever epoxy-functionalized copolymers may be alterna- tively crosslinked via ring opening of oxirane groups. Crosslinking of functionalized polyethylenes by epoxy chemistry has not been extensively studied in the litera- ture. Some studies have been done with a very industrial approach [11–13] however, recent works have been done with a basic research approach by Pire et al. [14,15]. By contrast, crosslinking conditions between epoxy functions and numerous functional groups such as hydroxyl, car- boxyl and amine are well known [16–18]. On the other hand, use of bio-based and non-harmful curing agents for epoxy resins is quite recent in the literature. Acid modified lignin (a chemical complex generally derived from wood) as well as some amino acids (particularly lysine and tryp- tophan) have been recently studied as epoxy hardener [19–22] but no previous study of using a bio-based curing agent on ethylene-epoxy copolymers was found on the literature. http://dx.doi.org/10.1016/j.eurpolymj.2014.10.003 0014-3057/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Ingénierie des Matériaux Polymères, UMR CNRS 5223, Université Claude Bernard Lyon 1, 15 Boulevard Latarjet, 69622 Villeurbanne Cedex, France. E-mail address: philippe.cassagnau@univ-lyon1.fr (P. Cassagnau). European Polymer Journal 61 (2014) 186–196 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj