Introduction The formulation of low curing temperatures epoxy powder coatings (using new initiators and cross-link- ers) has become one of the main lines of research in industries and related research centres. One of the main objectives of this research is to obtain epoxy systems with low curing temperatures so that they can be applied on different substrates sensitive to temper- ature (mainly different types of organic ones like plastics), and of course to reduce energetic costs. Properties of the paints (mechanical, thermal, anticorrosive and so on) are specially influenced by the kind of epoxy network-structure (which depends on the cross-linker and initiator employed in its for- mulation). Powder coatings are currently the fastest growing section of industrial paints, because of their favourable environmental attributes and performance advantages. They are well-adapted for the main strategic goals of the paint industry, namely corrosion protection, improved durability, increased transfer efficiency, elimination of organic solvents, reduction of toxic waste, conservation of energy and reduction of costs. Since they are fully solid, and without volatile organic emissions, powder coatings are considered to be the best alternative for the reduction of the volatile organic contents (VOCs) of solvent-based paints, among the emerging coating technologies (powder coatings, high solid coatings and waterborne ones) [1, 2 ]. Compared to liquid paints, the film formation process of powder coatings is different since it is occurring in the molten phase. Melting, flow, gel point and cure completion are the principal stages in film formation of powder coatings and determine both the aesthetic and protective properties of the paint. The duration of these stages is directly affected by the paint composition, e.g., type of binder and cross-linker, pigmentation (nature and particle size, packaging and distribution), catalyst, and additives, curing and application conditions. These factors, in turn, determine important coating characteristics such as levelling, adhesion, gloss, chemical resistance and exterior durability [3–12]. Catalysts are important in polymerization processes because they decrease the activation energies and accelerate the reaction. They can be stimulated by heating or photoirradiation but, from the practical point of view, heating is the easier 1388–6150/$20.00 Akadémiai Kiadó, Budapest, Hungary © 2006 Akadémiai Kiadó, Budapest Springer, Dordrecht, The Netherlands Journal of Thermal Analysis and Calorimetry, Vol. 83 (2006) 2, 429–438 CATIONIC CROSSLINKING OF SOLID DGEBA RESINS WITH YTTERBIUM(III) TRIFLUOROMETHANESULFONATE AS INITIATOR S. J. García 1,* , X. Ramis 2 , A. Serra 3 and J. Suay 4 1 Área de Ciencia de los Materiales, Deparment d’Enginyeria de Sistemes Industrials i Disseny, Universitat Jaume I, Avda Vinent Sos Baynat s/n, 12071, Spain 2 Laboratori de Termodin´mica, Escola TÀcnica Superior Enginyeria Industrial Barcelona, Universitat Polit Àcnica de Catalunya Diagonal 647, 08028 Barcelona, Spain 3 Departament de Q. Analítica i Q. Org´nica, Facultat de Química, Universitat Rovira i Virgili, C/Marcel·lí Domingo s/n 43007 Tarragona, Spain 4 Centro de Biomateriales, Universitat Polit Àcnica de ValÀncia, Camino de Vera s/n, E-46071 Valencia, Spain Solid bisphenol-A epoxy resin of medium molecular mass was cured using a Lewis acid initiator (ytterbium(III) trifluoromethanesulfonate) in three different proportions (0.5, 1 and 2 phr). A kinetic study was performed in a differential scanning calorimeter. The complete kinetic triplet was determined (activation energy, pre-exponential factor, and integral function of the degree of conversion) for each system. A kinetic analysis was performed with an integral isoconversional procedure (free model), and the kinetic model was determined both with the Coats–Redfern method (the obtained isoconversional value being accepted as the effective activation energy) and through the compensation effect. All the systems followed the same isothermal curing model simulated from non-isothermal ones. The growth-of-nuclei Avrami kinetic model A 3/2 has been proposed as the polymerization kinetic model. The addition of initiator accelerated the reaction especially when 2 phr was added. 0.5 and 1 phr showed very few kinetic differences between them. Keywords: epoxy resin, initiator, kinetics (polym.), ytterbium triflate * Author for correspondence: espallar@sg.uji.es