Search

The electron probe microanalyzer is a device often used in the field of geology or in the glass and steel industries. However, it is barely known or used in the polymer field. Thus, in this paper, we investigate the use of electron probe microanalyzer for polymer microanalyses and compared it with a scanning electron microscope equipped with an energy dispersive spectrometer. To show the unique potential of this technique only develop in our lab for polymer application, three different samples were studied: (i) a fire protective epoxy-based coating submitted to aging in salt water, (ii) the distribution of organometallic catalysts into a thermal isolative silicone polymer, and (iii) the fouling growth of milk protein (biopolymer) on a stainless steel surface. Compared to an energy dispersive spectrometer, with an electron probe microanalyzer it is possible to quickly create X-ray mappings of low concentration elements at a good resolution, as well as allowing the interpretation of the mechanism of action for the three samples which was impossible using only an energy dispersive spectrometer because of its too low detection resolution. Copyright © 2015 John Wiley & Sons, Ltd.

Using a polyurethane of methylene diphenyl isocyanate and 1,3-propane diol, several new non-halogenated aromatic boron and phosphorus flame retardants were evaluated for heat release reduction potential using the pyrolysis combustion flow calorimeter (PCFC). The polyurethanes were prepared in the presence of the potential flame retardants via solvent mixing and copolymerization methods, and were then analyzed via spectroscopic methods to determine if the flame retardant was still present in the final product. PCFC testing on the resulting products showed that the flame retardant molecule can have different effects on heat release depending upon how it is mixed into the polyurethane. Some materials showed strong effects on heat release reduction when reacted into the polyurethane during copolymerization, while others were more effective at heat release reduction when simply solvent blending into the polyurethane. The results from this screening study show that flame retardant chemical structure and its environment in the polymer (covalently bonded vs. noncovalent interactions) greatly affects flammability behavior. From the combined data, aromatic boronates were found to be very effective at reducing heat release and inhibiting melt flow during thermal decomposition, as were some aromatic phosphonic acid terephthalic acid and terephthalate derivatives.

The fire performance of curable silicone-based coatings containing expandable graphite, organoclay, and calcium carbonate is evaluated in cellulosic fire scenario (standard ISO834) using a lab-scale furnace test. It is shown that the use of organoclay and calcium carbonate allows achieving same insulative performance when compared with organic commercial intumescent coating. The mode of action of these silicone-based coatings is fully investigated using thermal analyses and spectroscopic analyses including X-ray photoelectron spectroscopy. It is shown that the high fire performance of intumescent silicone-based coatings is due to (1) interactions between calcium carbonate and silicone matrix increasing the thermal stability of the resin and (2) the formation of calcium silicate embedding the top of the char and permitting the formation of an additional protective ceramic layer.

The fire performance of a curable-silicone based coatings containing expandable graphite (EG) and an organoclay is evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. It is shown that the use of organoclay allows achieving better performance. The influence of the clay as additional filler is investigated on the fire performance and on the mechanical properties of the char. It is shown that the clay increases significantly the mechanical properties of the char and hence, the fire performance of the silicone based coating. In a next part, the silicone/clay material was characterized by electron microscopy, wide-angle X-ray scattering and solid state 29 Si nuclear magnetic resonance (NMR). It evidences the nanodispersion of the clay into the silicone matrix and two main interactions: (i) intercalation of some silicate layers and (ii) chemical reactions between the hydroxyl groups of the clay and the silicone matrix. Finally, X-ray fluorescence of the residue after fire testing shows the organoclay is present uniformly throughout the thickness of the char, due to the previous interaction, and hence increasing the cohesion of the char.

The fire performance of two curable-silicone based coatings containing 25% expandable graphite (EG) are evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. In this paper, the influence of the catalyst on the fire performance are investigated. Two organometallic titanium based- and tin based catalyst are used to make the curable silicone crosslink. When titanium based catalyst is used, the fire performance are higher and the mechanical properties of the char is better than that when tin is used as catalyst. To explain this surprising different fire behavior, the two residues after the furnace test were analyzed by X-ray photospectroscopy. It has been demonstrated that in the case of titanium based catalyst, the char is composed of graphite embedded by crosslinked silicone structure compare to linear silicone structure in the case of tin based catalyst. The two silicone resins were characterized by Fourier Transform Infrared spectroscopy, 29Si NMR, thermogravimetric analyses, EPMA (electron probe microanalyses). It was highlighted that the tin migrates into the surface during the crosslinking of the matrix leading to a low thermal stability and, thus, low fire performances. Whereas, when titanium based catalyst is used, it participates to the silicone network with the formation of Si–O–Ti bounds increasing the thermal stability of the matrix and so enhancing the fire performance of the silicone/EG based coating.

The fire performance of curable-silicone based coatings containing expandable graphite (EG) is evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. From 5% to 25% of expandable graphite is incorporated in the silicone matrix to make the coating swell during the fire experiment. Fire performance of 25%EG/silicone-based coating is better than that of commercial intumescent paint used as reference. This is explained by a high swelling velocity (18%/s), a high expansion (3400%), an impressive cohesion of the char and a low heat conductivity at high temperature (0.35 W/K m at 500 °C). To elucidate this way of charring, the residue after fire testing was analyzed by scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray photoelectron spectroscopy and X-ray diffraction. It is shown that the char is composed of two main parts: the top is composed of quartz and amorphous silica which coat graphite flakes and the heart of the char is composed of graphite flakes embedded in degraded silicone forming a complex structure. It is shown that, the good cohesion of the char is due to: (i) the presence of the undegraded silicone matrix; and (ii) the coating of graphite pellets by silicone.

This paper deals with the thermal degradation and fire performance of silicone-based coatings for protecting steel. In this study, the fire performance of silicone coatings as virgin or formulated materials is evaluated using two homemade fire testing methodologies: one similar to the “torch test” fire testing method and the other using a heat radiator test. It was shown that the performance of the silicone-based coating used as thermal barrier can be improved incorporating a modifier (a mixture of polydimethylsiloxane and silica coated by a silane). In this case, silicone-based coating swells and exhibits same fire performance as commercial intumescent coating at the torch test. It is shown that the incorporation of modifier in the silicone makes it to swell upon heating resulting in the formation of expanded material exhibiting low heat conductivity. Thermal degradation of the coating is also investigated: it occurs in three main steps leading to the formation of a tridimensional network characterized by the formation of Q4 structure at high temperature. Copyright © 2012 John Wiley & Sons, Ltd.

This paper deals with the thermal degradation and fire performance of polysilazane (PZane) based coatings. PZanes are silicon–nitrogen backbone polymers and can be used in a wide range of applications. In this study, the fire performance of PZane coating as virgin or formulated materials were evaluated using a homemade fire testing methodology similar to the “Torch Test” fire testing method. It was shown that the performance of the PZane coating can be improved incorporating fire retardant additives. Degradation of the coating is then investigated. The mechanism of degradation of the PZane was elucidated analyzing the gas and condensed phases during the degradation. It was shown that the degradation occurs in three steps leading to the formation of SiN4 and charring at high temperature. The kinetics of degradation of the three steps of degradation was also modeled in order to predict the degradation of the PZane coating in a fire scenario.

International audience; The thermal degradation of aluminium diethylphosphinate (AlPi) with aluminium trihydrate (ATH), two flame retardant additives, was investigated. The interactions between the additives were characterized using thermal analysis (TG). The evolved gas were analysed by TGA–FTIR and the degradation products formed in the condensed phase were fully characterized using solid state NMR analysis, and in particular 2D NMR, as well as XRD analyses. Decomposition pathways have been determined and it was proposed that chemisorption of the phosphinate on alumina resulting from the ATH dehydration, activated by the temperature increase, influences the degradation of the mixture. As a consequence, the degradation products of AlPi differ in presence of ATH since the formation of aluminophosphonate is prevented.