Laurent Ferry

Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer

The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/ talc) has been investigated. The release of water from Mg(OH) 2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH) 2 , appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH) 2 loading in ternary compositions.

Red phosphorus/aluminium oxide compositions as flame retardants in recycled poly(ethylene terephthalate)

Abstract The mechanical properties and fire resistance of a recycled poly(ethylene terephthalate) were improved by using a specific treatment of the waste material and the incorporation of encapsulated red phosphorus in combination with co-additives. The use of red phosphorus has to be limited due to a negative influence on impact resistance and rate of heat release. Among several metal oxides, Al 2 O 3 acts as a good co-synergist at a total loading of 5 wt.% due to its reactivity, high specific surface area and aluminium phosphate formation. The complementary use of glass fibres can also generate intumescence by improving the mechanical stability of the char layer.

From a bio-based phosphorus-containing epoxy monomer to fully bio-based flame-retardant thermosets

In this work, phloroglucinol was used as a renewable resource to prepare an epoxy monomer and phosphorus containing reactive flame retardant (FR). These building blocks were reacted with diamines to obtain partly or fully bio-based flame retardant epoxy resins. It was highlighted that the glass transition temperature of the materials was tightly related to the functionality of the reactive monomers and the resulting crosslink density. Thermal stability and char yield of the thermosets seems to be mainly governed by the aromaticity of the monomers, the linking rate of the aromatic ring and the phosphorus content. Phosphorus FR are more efficient in intrinsically poorly charring matrices. It was evidenced that the flammability of bio-based epoxies can be monitored by two strategies: (i) choosing bio-based monomers with high charring ability and low combustion energy, (ii) incorporating bio-based phosphorus-containing reactive FR in the polymer network.

Incorporation of a grafted brominated monomer in glass fiber reinforced polypropylene to improve the fire resistance

Glass fiber reinforced polypropylene composites have been flame retarded using a brominated acrylate as both monomer (PBB-MA) and polymer (PBB-PA), associated with Sb2O3 (Sb/Br) and Mg(OH)2. We have shown that the brominated monomer can react either by grafting onto the polymer matrix or onto the glass fibers or by polymerizing around the Sb2O3 particles. We have highlighted that the efficiency of this FR system is connected to its high bromine content and to its reactivity with polypropylene. We have observed that grafting of brominated monomer onto glass fibers does not strongly modify the fire properties of the composites. We have demonstrated that the action of PBB-MA/Sb2O3 can be improved in reinforced PP by combination with Mg(OH)2, which delays ignition. Improvement of the fire properties of the composites has been achieved to the detriment of mechanical properties which are strongly affected by the presence of the brominated polyacrylate.

Fire behavior of halogen-free flame retardant electrical cables with the cone calorimeter

Fires involving electrical cables are one of the main hazards in Nuclear Power Plants (NPPs). Cables are complex assemblies including several polymeric parts (insulation, bedding, sheath) constituting fuel sources. This study provides an in-depth characterization of the fire behavior of two halogen-free flame retardant cables used in NPPs using the cone calorimeter. The influence of two key parameters, namely the external heat flux and the spacing between cables, on the cable fire characteristics is especially investigated. The prominent role of the outer sheath material on the ignition and the burning at early times was highlighted. A parameter of utmost importance called transition heat flux, was identified and depends on the composition and the structure of the cable. Below this heat flux, the decomposition is limited and concerns only the sheath. Above it, fire hazard is greatly enhanced because most often non-flame retarded insulation part contributes to heat release. The influence of spacing appears complex, and depends on the considered fire property.

Synthesis of biobased phosphate flame retardants

Abstract An approach to prepare some biobased flame retardant (FR) compounds is presented. The adopted strategy consists in functionalizing an aromatic biobased phenolic compound, the phloroglucinol, with different phosphate groups in order to promote a charring effect. Different chlorophosphates were grafted onto phloroglucinol hydroxy groups and the functionalization of the hydroxy groups was quantitative. The synthesized biobased FR were incorporated into an epoxy matrix as additive to estimate their flame retardant properties. The influence of different parameters was studied such as the phosphorus content of the thermoset or the nature of the R group of the used phosphate P-O-R. MEB/EDX observations proved the influence of this R group on the compatibility between the FR and the matrix and its importance to obtain homogeneous thermoset. Thermogravimetric analyses of the phosphorus-containing thermosets showed a small decrease in thermal stability accompanied by a char yield almost tripled for a 3 %wP-containing thermoset compared to that of the thermoset without any FR. Pyrolysis combustion flow calorimetry was also used to evaluate the flammability of the modified epoxy thermoset. A significant decrease in peak of heat release rate and total heat released was observed compared to thermoset without FR. These results demonstrate the good flame retardant properties of these biobased phosphates in an epoxy matrix. In addition these results show the potential of the biobased phenolic compounds as raw material for flame retardants syntheses.

In-line ultrasonic characterization of shear dispersion processes of polydisperse fillers in polymer melts

Shear break-up processes of polydisperse fractal clusters are investigated by the ultrasound scattering technique. Within the framework of fractal aggregation and the hybrid approach model for polydisperse correlated scatterers, the concept of variance in the local filler concentration is used to derive a new expression for the scattering cross-section for polydisperse fractal aggregates in the Rayleigh scattering regime. Considering the scaling laws for the shear-induced disruption of the clusters, the shear stress dependence of the ultrasound scattered intensity for polydisperse fractal aggregates is also derived. The fractal scattering regime is further discussed for both monodisperse and polydisperse clusters of size larger than the wavelength. In-line ultrasonic measurements for the shear disruption processes of silica fume fillers compounded with polypropylene during extrusion are investigated. A critical disaggregation shear stress is determined and is found to decrease with the filler surface treatment concentration. This stress is representative of the particle adhesiveness and aggregate dispersion in the matrix. This is confirmed by the improvement in impact resistance tests. On the basis of the scaling laws and the self-consistent-field approximation usually used in the microrheological models, the shear-thinning behaviour of silica fume clusters is successfully simulated.

Thermal degradation and flammability of polyamide 11 filled with nanoboehmite

Abstract The flame-retardant effect of rod-like nanoboehmite was evaluated in biobased polyamide 11. Thermal analysis reveals that hydrated nanofillers modify the degradation pathway of polyamide 11 turning from a two-step to a single-step mechanism. The polymer thermal stability is increased due to interactions between polar groups and filler surface hydroxyl groups. Despite this improved thermal stability, polyamide 11/nanoboehmite composites exhibit shorter times to ignition in cone calorimeter. The phenomenon was attributed to changes in thermoradiative properties leading to a faster heating of the polymer surface. The most significant flame-retardant action is a reduction in heat release rate that was related to a barrier effect while endothermic water release seems to play a minor role.

Contribution to the study of particle resuspension kinetics during thermal degradation of polymers

Experimental results are reported on the resuspension of particles deposited on polymer samples representative of glove boxes used in the nuclear industry, under thermal degradation. A parametric study was carried out on the effects of heat flux, air flow rate, fuel type and particle size distribution. Small-scale experiments were conducted on 10 cm × 10 cm PolyMethyl MethAcrylate (PMMA) and PolyCarbonate (PC) samples covered with aluminium oxide particles with physical geometric diameters of 0.7 and 3.6 μm. It was observed for both polymer (fuel) samples that heat flux has no effect on the airborne release fraction (ARF), whereas particle size is a significant parameter. In the case of the PMMA sample, ARF values for 0.7 and 3.6 μm diameter particles range from 12.2% (± 6.2%) to 2.1% (± 0.6%), respectively, whereas the respective values for the PC sample range from 3.2% (± 0.8%) to 6.9% (± 3.9%). As the particle diameter increases, a significant decrease in particle release is observed for the PMMA sample, whereas an increase is observed for the PC sample. Furthermore, a peak airborne release rate is observed during the first instants of PMMA exposure to thermal stress. An empirical relationship has been proposed between the duration of this peak release and the external heat flux.

Flame Retardancy of Natural Fibers Reinforced Composites

Due to numerous advantages (high specific mechanical properties, low density, biosourcing, …), natural fibers from plants are considered as credible alternatives to glass or carbon fibers for composites industry. Nevertheless, their relatively high flammability limits their potential applications. Many researches have been carried out to improve the flame retardancy of composites reinforced with natural fibers. This chapter attempts to establish the state-of-art of these researches.