Fire retardant behaviour of halogen-free calcium-based hydrated minerals

Environmentally Friendly Hybrid Organic-Inorganic Halogen-Free Coatings for Wood Fire-Retardant Applications

Wood and wood-based products are extensively used in the building sector due to their interesting combination of properties. Fire safety and fire spread, however, are of utmost concern for the protection of buildings. Therefore, in timber structures, wood must be treated with fire-retardant materials in order to improve its reaction to fire. This article highlights the flame retardancy of novel hybrid organic-inorganic halogen-free coatings applied on plywood substrates. For this purpose, either a huntite-rich mineral (H5) or its modified nano-Mg (OH)₂ type form (H5-m), acting as an inorganic (nano) filler, was functionalized with reactive oligomers (ROs) and incorporated into a waterborne polymeric matrix. A water-soluble polymer (P (SSNa-co-GMAx)), combining its hydrophilic nature with functional epoxide groups, was used as the reactive oligomer in order to enhance the compatibility between the filler and the matrix. Among various coating compositions, the system composed of 13% polymeric matrix, 73% H5 and 14% ROs, which provided the best coating quality and flame retardancy, was selected for the coating of plywood on a larger scale in one or two layers. The results indicated that the novel plywood coating systems with the addition of ecological coating formulations (WF-13, WF-14 and WF-15), prepared at two layers, reached Euroclass B according to EN13501-1, which is the best possible for fire systems applied to wood.

Evolutive Models for the Geometry and Heat Conductivity of an Intumescent EVA-ATH Composite during Its Thermal Degradation

Reliable predictions from numerical simulations in fire safety applications require knowledge of the combustible materials’ properties in their initial and thermally degraded states. The thermal conductivity of the sheath material of electrical cables, present in massive amounts in industrial plants, is addressed here. An evolutive conceptual model is proposed for the morphology of this intumescent polymer composite during its thermal degradation. It accounts for the multiscale structure and anisotropy observed during a thorough characterization based on tomographic images of samples at representative stages of the degradation. The evolution of the geometrical characteristics during the process is linked to chemical advancement parameters according to a reasoned scenario based on physical arguments and balance considerations. The anisotropic thermal conductivity tensor can be deduced from the geometry by a nested application of classical models. Ultimately, the conductivity is obtained as an analytic function of the chemical advancement and temperature. The model predictions were validated by comparisons with direct numerical solutions of thermal problems in the fully described geometry provided by the tomographies, and with measurements from the literature. The methodology and conceptual tools can be of interest for the treatment of other materials and in other contexts of application.

The Flame Retardancy of Polyethylene Composites: From Fundamental Concepts to Nanocomposites

Polyethylene (PE) is one the most used plastics worldwide for a wide range of applications due to its good mechanical and chemical resistance, low density, cost efficiency, ease of processability, non-reactivity, low toxicity, good electric insulation, and good functionality. However, its high flammability and rapid flame spread pose dangers for certain applications. Therefore, different flame-retardant (FR) additives are incorporated into PE to increase its flame retardancy. In this review article, research papers from the past 10 years on the flame retardancy of PE systems are comprehensively reviewed and classified based on the additive sources. The FR additives are classified in well-known FR families, including phosphorous, melamine, nitrogen, inorganic hydroxides, boron, and silicon. The mechanism of fire retardance in each family is pinpointed. In addition to the efficiency of each FR in increasing the flame retardancy, its impact on the mechanical properties of the PE system is also discussed. Most of the FRs can decrease the heat release rate (HRR) of the PE products and simultaneously maintains the mechanical properties in appropriate ratios. Based on the literature, inorganic hydroxide seems to be used more in PE systems compared to other families. Finally, the role of nanotechnology for more efficient FR-PE systems is discussed and recommendations are given on implementing strategies that could help incorporate flame retardancy in the circular economy model.

Ecological Ammonium Thiocyanate-Modified Geopolymeric Coating for Flame-Retarding Plywood

An ecological ammonium thiocyanate (NH4SCN)-modified geopolymeric coating was facilely prepared for flame-retarding plywood. The effect of NH4SCN on the flame resistance was preliminarily investigated using cone calorimeter (CC), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermal gravimetry (TG). The results show that 1 wt.% NH4SCN as dopant is of paramount importance to generate a compact and continuous coating. The formation of a smooth, intact, and uniform-swelling siliceous layer during combustion facilitates enhanced fire resistance, evidenced by the increased fire performance index (FPI), reduced fire growth index (FGI), and 39.7% decreased value of peak heat release rate (pHRR), in comparison to those of the sample without NH4SCN. Because of the reducibility of O2-consuming NH4SCN, the compact shielding-layer containing carbonate and sulfate, as well as the release of NH3, the NH4SCN-modified geopolymeric coating exerts an enhancement on the flame-retardant efficiency.

Improving the flame retardancy of ethylene vinyl acetate composites by incorporating layered double hydroxides based on Bayer red mud

Nowadays, reducing the hazards of bayer red mud (BRM) is an important research direction in the fields of environmental and safety. In this article, Mg/Al/Fe ternary layered double hydroxides (Mg/Al/Fe-LDHs) were synthesized successfully by a co-precipitation method based on introducing Mg2+ into the BRM suspension. The thermogravimetric analysis (TGA) results showed that the decomposition rate of LDHs is higher than that of BRM, which indicates that LDHs can absorb more heat than BRM during the decomposition process. Subsequently, BRM and LDHs were added into the ethylene vinyl acetate (EVA) to investigate its effects on reducing flammability of the composites. The cone calorimeter test (CCT) results demonstrated that 50 wt% LDH-B can make the peak value of HRR (PHRR) decrease from 1694.8 kW/m2 (EVA) to 199.2 kW/m2 (ELDH2). The smoke density test (SDT) results showed that the luminous flux of ELDH2 is nearly 95% at the end of test with a pilot flame, which is much higher than that of EVA and EBRM. The thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) results confirmed that LDHs can improve the thermal stability of composites and reduce the production of some toxic gases. Compared with BRM, the improved flame retardancy of Mg/Al/Fe-LDHs is ascribed to the introduction of Mg2+, which offering an enhanced catalytic carbonization capability, as well as the physical barrier effect of char residue layer catalyzed by the lamellar LDHs