Getting a better insight into the chemistry of decomposition of complex flame retarded formulation: New insights using solid state NMR N. Hansupo a, d , G. Tricot b, d , S. Bellayer a, d , P. Roussel c, d , F. Samyn a, d , S. Duquesne a, d , M. Jimenez a, d , M. Hollman e , P. Catala e , S. Bourbigot a, d, * a Univ.Lille, ENSCL, CNRS, UMR 8207, UMET, Unit e Mat eriaux et Transformations, 59 000 Lille, France b Laboratoire de Spectrochimie Infrarouge et Raman (LASIR), UMR-CNRS 8516, 59655 Villeneuve d’Ascq, France c Unit e de Catalyse et Chimie du Solide (UCCS), UMR-CNRS 8181, 59655 Villeneuve d’Ascq, France d Universit e Lille Nord de France, 59000 Lille, France e Hempel, S.A.U, Carretera de Sentmenat 108, 08213 Polinya, Barcelona, Spain article info Article history: Received 13 February 2018 Received in revised form 13 April 2018 Accepted 20 April 2018 Available online 23 April 2018 Keywords: Solid state NMR Characterization Intumescent char Amorphous borosilicate and borophosphate species abstract This paper aims at developing an innovative approach to characterize the char residue of an intumescent coating obtained after a UL1709 furnace test. The intumescent formulation is based on an epoxy resin and contains numerous additives including zinc borate, ammonium polyphosphate and silicate fibers. The purpose is to characterize the numerous reactions that can occur upon burning using crossed methods including Electron Probe Micro-Analysis (EPMA), X-ray diffraction (XRD) and 1D/2D solid state Nuclear Magnetic Resonance (NMR). In particular, it emphasizes the potential of the advanced NMR technique namely two-dimensional Dipolar Heteronuclear Multiple Quantum Correlation (2D D-HMQC) NMR. As a result, EPMA evidenced that B/P and B/Si are located in the same domain suggesting the formation of boron-phosphorus and/or boron-silicone containing compounds on the sample surface. H 3 BO 3 was identified by XRD as a main crystalline specie, additional species (e.g. SiO 2 , Zn 4 O(BO 2 ) 6 ) were also identified. The borate, silicate and phosphate chemical species were then characterized using 1D NMR but no definitive assignments could be given. To specify those assignments, 2D D-HMQC NMR was performed and the formation of amorphous borophosphates and borosilicates was evidenced empha- sizing the chemical reactivity between the ingredients of the formulation. It was suggested that these species allow reinforcing the char and improving the fire protective properties of the coatings. This work highlights the particular interest of advanced NMR technique, which provides unique information on the characterization of intumescent char. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction The protection of human life and infrastructures against fire is an important issue, that is the reason why fire protections have been developed. Among them, intumescent coating appears as a solution of choice since it can be included as a part of in- frastructures with instant and quick response to a fire [1 ,2]. It can also be used as a conventional coating without destroying the aesthetic aspect of the structural frameworks. Such coatings have been widely used to protect steel (e.g. buildings, skyscrapers, offshore platforms) against fire for many decades. An intumescent coating is designed to expand when exposed to a fire and to form a carbonaceous char structure, which can protect an underlying substrate such as steel. It principally contains ‘active’ ingredients dispersed in a binder. Three ‘active’ ingredients are generally: a carbon source (e.g. pentaerythritol), a blowing agent (e.g. melamine) and an acid source (e.g. borate and/or phosphate) [3]. Additional ingredients can be incorporated such as a synergist (e.g. titanium oxide) [4] and reinforcing agents (e.g. fibers) [5] to fine tune the properties of the formulations. A commercial intu- mescent coating contains more than ten ingredients to meet all specifications required by its applications [6]. The complete * Corresponding author. Unit e Mat eriaux et Transformation (UMET), UMR-CNRS 8207, 59652 Villeneuve d’Ascq, France. E-mail address: serge.bourbigot@ensc-lille.fr (S. Bourbigot). Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab https://doi.org/10.1016/j.polymdegradstab.2018.04.028 0141-3910/© 2018 Elsevier Ltd. All rights reserved. Polymer Degradation and Stability 153 (2018) 145e154