René Delobel

Carbonization mechanisms resulting from intumescence-part II. Association with an ethylene terpolymer and the ammonium polyphosphate-pentaerythritol fire retardant system

Abstract In this work we study the carbonization resulting from an intumescence phenomenon of the fire-retardant formulation: ethylene terpolymer-ammonium polyphosphate/pentaerythritol. Characterisation of the intumescent coating is carried out using infrared spectroscopy and MAS-NMR of the solid state. The study shows the formation of organic phosphocarbonaceous esters, which limits depolymerisation or the evolution of gaseous hydrocarbons. These esters prevent the development of condensed polyaromatic structures. These latter are bridged by the polyethylenic links, which provide the mechanical properties of interest in the protective shield.

The origin and nature of flame retardance in ethylene‐vinyl acetate copolymers containing hostaflam AP 750

The aim of the study is to investigate new intumescent materials based on ethylene-vinyl acetate copolymers. Hostaflam AP 750 is used as a flame-retardant system. Fire testing and thermal analyses have shown that the incorporation of AP 750 leads to the formation of an intumescent coating which provides good fire barrier properties. Spectrochemical analyses have shown that the coating consists of polyethylenic chains issued from the polymer. Polyaromatic structures and phosphorus oxides are also observed in the coating.

4A zeolite synergistic agent in new flame retardant intumescent formulations of polyethylenic polymers: study of the effect of the constituent monomers

4A type zeolite adducted in the intumescent ammonium polyphosphate (APP)/pentaerythritol (PER) system, additives in fire retardant (FR) polyethylenic-based formulations (ethylenic co/terpolymers), leads to a synergistic FR effect. This study concerns ethylenic co- or terpolymers. It shows the part played by the polymeric matrix on the fire-proofing performances which depend on the chemical nature and amount of comonomer in the polymer. Further, the thermal analyses confirm the effect of the polymeric matrix and show the participation of oxygen in the formation of the intumescent coating. Measurement of the performances using the cone calorimeter puts forward that the zeolite causes different degradation of the intumescent materials and thus the formation in fire of a more thermally stable coating.

Elaboration of EVA–nanoclay systems—characterization, thermal behaviour and fire performance

In this study, the effect of several parameters (nature of clay and clay loading) on the fire retardancy of the nanocomposite is investigated. It is observed that the nature of the cations, which compensates the negative charge of the silicate layers, affects the fire performance even though they are improved for both investigated montmorillonite-type fillers. The clay loading also affects the fire properties. In a second part, the materials are characterized using thermogravimetric analysis and small-angle X-ray diffraction in order to better understand the obtained fire retardant performance. It is observed that the degree of dispersion determined by X-ray diffraction can be correlated with the fire performance of the polymer clay composite.

Thermal degradation of polyurethane and polyurethane/expandable graphite coatings

Abstract This study deals with the thermal degradation of polyurethane (PU) and polyurethane/expandable graphite (PU/EG) coatings. EG represents a new generation of intumescent additives which provides good fire retardancy to various materials and in particular to PU. The thermal analyses have shown that the thermo-oxidative degradation as well as the pyrolysis of PU are not affected by the presence of EG. On the other hand, they have enabled the determination of the temperatures which correspond to different steps of the development of the intumescence : formation, stabilisation and degradation of the intumescent shield. Spectroscopic analysis of the residues resulting from each of these steps has demonstrated that the structure of the char is similar for PU and PU/EG and consists in a carbonaceous polyaromatic species. However, the results have suggested that the char formed from PU/EG may contained trapped free radicals.

Charring of fire retarded ethylene vinyl acetate copolymer — magnesium hydroxide/zinc borate formulations

Abstract Zinc borate has been used as a synergistic agent in EVA-Mg(OH)2 flame retardant (FR) formulations. Solid state NMR of carbon in the residues collected after thermal treatment allows the study of the charring of the flame retardant system. The study has shown that polymer fragments are in the char layer. It is suggested that zinc borate slows the degradation of the polymer, creating a vitreous protective residual layer which could act as a physical barrier and a glassy cage for polyethylene chains.

Carbonization mechanisms resulting from intumescence association with the ammonium polyphosphate-pentaerythritol fire retardant system

Abstract In this work we study the thermal behavior of an ammonium polyphosphate-pentaerythritol mixture, fire-retardant additive for polyolefins and most particularly the carbonization process resulting from an intumescent phenomenon. The study has been carried out using Micro-Raman and 13C, 1H, 31P NMR of the solid state spectroscopies. It is shown that the structure consists in phoscarbonaceous and polyaromatic species. These latter form an anisotropic structure above 280°C. This structure grows when the temperature increases. Finally, a reactional scheme of the carbonization of the intumescent system is proposed.

Synergistic effect of zeolite in an intumescence process: study of the carbonaceous structures using solid-state NMR

This work deals with the chemical effect of zeolite 4A added to the intumescent ammonium polyphosphate (APP)–pentaerythritol (PER) system [fire retardant (FR) polyethylene-based formulation]. The study of the thermal behaviour of the system using thermogravimetric (TG) analysis shows that the presence of the zeolite leads to an increase in the stability of the material at high temperature (T > 500 °C). Chemical analysis and cross-polarisation dipolar-decoupled magic-angle spinning (CP–DD–MAS)13C NMR reveals that the materials resulting from the thermal treatment of the APP–PER and APP–PER/4A systems are formed by carbonaceous and phosphocarbonaceous species and that the zeolite enhances the stability of the phosphocarbonaceous species. DD–MAS 31P NMR indicates that this stability may be due to an absence of pyrophosphate species in the heat-treated APP–PER/4A system. Micro-Raman spectroscopy and 1H NMR of the solid state provides information on the structure of the carbonaceous material. Thermal treatment led to the formation of a ‘turbostatic carbon’ with a local structure of this ‘carbon species’, with the zeolite permitting retention of the comparatively unorganised carbon species in the high-temperature range. Moreover, a low-resolution solid-state 1H NMR study of the spin–lattice and spin–spin relaxations of the samples allows an evaluation of the size of the slow relaxation domains using the Goldman–Shen procedure. It is shown that the zeolite hinders the formation of small molecules in the polyaromatic network. Finally, the relationship between the formation of a coherent macromolecular network and the improved FR performance of the APP–PER/4A system is proposed.

Synergistic effect of zeolite in an intumescence process. Study of the interactions between the polymer and the additives

The chemical effect of the zeolite 4A added to the intumescent ammonium polyphosphate (APP)–pentaerythritol (PER) system in a fire retardant (FR) ethylene–butyl acrylate–maleic anhydride terpolymer (LRAM3.5)-based formulation has been studied. Thermogravimetric (TG) analysis defines the different steps of the degradation of the formulation and shows that the presence of the zeolite leads to an increase in the stability of the material at high temperature (T > 550 °C). Spectroscopic characterisations, mainly 31P, 13C, 1H and 27Al NMR of the solid state, demonstrate that there are interactions between the polymer and the additives. In the case of the LRAM3.5–APP–PER formulation, the protection arises principally from the additives which make a thermal barrier between the flame and the material. When zeolite is present it plays an essential role, because it allows the formation of structures stabilising the polymer which can then participate in the formation of the intumescent protective shield and hence in its own protection. Moreover, we prove that the FR properties of the protective material obtained from the formulations depend on the ‘quality’ of the intumescent coating obtained from the additives. In particular, the presence of the zeolite decreases the size of the amorphous domains of the carbon.

XPS study of an intumescent coating: II. Application to the ammonium polyphosphate/pentaerythritol/ethylenic terpolymer fire retardant system with and without synergistic agent

Abstract Fire retardancy of polymer may be due to the formation of protective surface coating, i.e. a swollen char layer (intumescence). The intumescent coatings resulting from thermal treatments of the association of ammonium polyphosphate (APP) and pentaerythritol (PER) with or without zeolite 4A (used as synergistic agent) in a polyethylenic terpolymer (LRAM3.5) are studied by X-ray photoelectron spectroscopy. The O 1s , P 2p , C 1s and N 1s spectra are discussed. The formation of pyridinic and pyrrolic nitrogen and quaternary nitrogen in polyaromatic groups in the intumescent structures is shown. The oxidised nitrogen (nitro groups and pyridine N-oxide) are only observed up to 350°C and then are evolved as NO x species. It is then proposed that the pyridinic function, observed only in the case of the system with zeolite at all temperatures, participates in the improvement of the fire proofing properties of the materials.