Progress in Organic Coatings 51 (2004) 139–144 Mechanical, dielectric and enthalpic relaxation of a thermosetting powder coating based on carboxyl-terminated polyester and triglycidylisocyanurate X. Ramis a , Y. Calventus b , A. Cadenato a , F. Roman b , J.M. Morancho a , P. Colomer b , J.M. Salla a , S. Montserrat b,∗ a Laboratori de Termodin` amica, ETSEIB, Universitat Polit` ecnica de Catalunya, Diagonal 647, 08028 Barcelona, Spain b Laboratori de Termodin` amica, ETSEIT, Universitat Polit` ecnica de Catalunya, C/Colom 11, 08222 Terrassa, Spain Received 24 February 2004; accepted 4 March 2004 Abstract The  relaxation associated with the glass transition region of a thermosetting powder coating was studied within a range of measur- ing frequencies (f) between 100 kHz and 3 mHz. The thermoset was based on a carboxyl-terminated polyester crosslinked with a trigly- cidylisocyanurate. The relaxation was studied by dielectric analysis (DEA) (1 Hz–100 kHz), dynamic mechanical thermal analysis (DMTA) (10 mHz–100 Hz), and temperature-modulated differential scanning calorimetry (TMDSC) (3–33 mHz). Additionally, experiments of intrin- sic cycles by DSC were performed to study the structural relaxation and to determine the reduced apparent activation energy, which was 126 kK. The correlation of data was studied in a relaxation map, in which the ln(average relaxation time 〈τ 〉)(〈τ 〉 = 1/(2πf) was plotted against the reciprocal of the relaxation temperature, which was determined by the maximum in tan δ and the loss permittivity ε ′′ by DMTA and DEA, respectively, and by the midpoint of the variation in the modulus of the complex heat capacity by TMDSC. The relaxation times obtained by TMDSC appear as an extrapolation of those obtained by DEA, while the DMTA relaxation times are slightly higher than those of DEA. The DMTA results were fitted to a Williams–Landel–Ferry equation (C 1 = 7.905 K and C 2 = 51.46 K) and the dielectric data to a Vogel–Tamman–Fulcher equation (ln A = -30.33 s, B = 1552 K and T 2 = 305 K). The curves of both equations were coincident within the range of the highest relaxation times. © 2004 Elsevier B.V. All rights reserved. Keywords: Thermosetting powder coating; Relaxation process; Glass transition 1. Introduction Powder thermoset coatings, which are made up of a reac- tive resin mixed with fillers and pigments, are used for dry finishing processes, during which a thin layer of fine powder is deposited on the surface to be coated. The most commonly used chemical families are epoxy resins, polyester resins and hybrid systems based on polyester and epoxy, whose proper- ties are better than those of coatings based solely on epoxy or polyester resins. The advantages of these systems include the reduction of the required curing temperature, durable finishes ∗ Corresponding author. Tel.: +34 937 398 123; fax: +34 937 398 101. E-mail address: montserrat@mmt.upc.es (S. Montserrat). and a decrease in the coating’s thickness [1–3]. The powder coatings are solids and the curing reaction does not eliminate volatiles, which contributes to reduce the environmental con- tamination. The powder coating acquires the widest range of properties by a curing process that involves heat or radia- tion from ultraviolet light. The curing conditions depend on the chemical structure of the components and the preparation process. The powder coating is prepared by mixing the com- ponents, which are submitted to fusion and passed through an extruder at a temperature lower than the curing tempera- ture. At room temperature, the powder is a glassy solid, whose glass transition temperature must be at least 50 ◦ C. The curing temperature is strongly limited by the T g , the fusion tempera- ture, and the viscosity of the system before crosslinking [4,5]. 0300-9440/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2004.03.011