Improved Fire Resistance Research Articles

Fire Retardance in Polyamide-6,6. The Effects of Red Phosphorus and Radiation-Induced Cross-Links

The combustion performance of polyamide-6,6 (PA-6,6) can be improved by the addition of red phosphorus provided it is intermolecularly cross-linked upon irradiation with 60Co-γ-rays in the presence of triallyl cyanurate (TAC). At a content of 5 wt.-% the latter promotes cross-linking, both in the presence and absence of O2, by a factor of about 100. From a variety of combustion tests with samples containing red phosphorus and having been γ-irradiated in the presence of TAC it turned out that an improved fire resistance of PA-6,6 is achieved if the red phosphorus content is at least 7 wt.-%. In this case test samples were self-extinguishing and the UL 94 rating corresponded to V-0. IR analysis of the solid residue brought about evidence for the reaction of red phosphorus with the polymer.

Fire retardance in polyamide‐6. The effects of red phosphorus and radiation‐induced cross‐links

AbstractRed phosphorus contained in non‐irradiated polyamide‐6 at concentrations up to 12.5 does not significantly improve the fire resistance of the polymer. It weakens the thermal stability of the polymer as reflected by a decrease in the onset temperature for mass loss from 407°C to 363°C, but causes char formation as indicated by mres=13 wt%, the non‐volatile residue at 600°C. Irradiation of polyamide‐6, loaded with red phosphorus, with 60Co‐γ‐rays generates intermolecular cross‐links resulting in an improved fire resistance. However, the absorbed dose necessary to achieve improvement is too high (>1 MGy) from a practical point of view. This inconvenience is overcome by applying triallyl cyanurate (TAC) as a cross‐linking promoter. Typically, polyamide‐6 containing 5 wt% TAC and 12.5 wt% red phosphorus exposed to a γ‐ray dose of 22 kGy yields a V‐0 rating (in the mode A UL 94 test) concurrently with a small increase in the onset temperature for mass loss and a drastic increase in the residue non‐volatile at 600°C. Copyright © 2002 John Wiley & Sons, Ltd.

Impact of high temperature on PFA concrete

After being subjected to high temperatures, the residual properties of pulverized fly ash (PFA) concrete have been investigated. Both mechanical and durability properties of concrete were tested on concretes made with different water to binder ratios and PFA contents. Microscopic techniques were then employed and the pore structure and microhardness values of hardened cement paste (hcp) were determined. The results of rapid chloride diffusion tests revealed that concrete durability deterioration commences after exposure to temperatures which are lower than those at which compressive strength deterioration commences. The rise in compressive strength, which occurs after exposure to 250°C, may be largely due to the hardening of cement paste caused by drying and the further hydration of cementitious materials. The simultaneous loss of durability, however, can be explained by a weakened transition zone between hcp and aggregate, and by the concurrent coarsening of the hcp pore structure. When PFA is included, an improvement of fire resistance as characterized by the residual compressive strength was observed, and this relative improvement over non-PFA concrete was the most pronounced for maximum exposure temperatures of 450°C and 650°C.

Effect of hydroxides and hydroxycarbonate structure on fire retardant effectiveness and mechanical properties in ethylene-vinyl acetate copolymer

The flame retardant effect of inorganic hydroxides, like aluminum hydroxide and magnesium hydroxide in ethylene vinyl acetate copolymer, was evaluated and compared with that of other inorganic fillers such as boehmite and hydrotalcite. The thermal decomposition of the fillers and the mixtures with EVA polymer were analysed by differential scanning calorimetry (DSC), Thermogravimetry (TG) and X-ray diffraction (XRD). The most significant flame retardant effects, observed using a mass loss calorimeter, indicated that the EVA polymer filled with 50 wt.% of hydrotalcite has the slowest heat release rate and the lowest evolved gas temperature. XRD data, combined with thermal analysis results, indicated that the layered structure of hydrotalcite may play a role in the degradation mechanism. The improved fire resistance of EVA filled with hydrotalcite also results from its intumescent behaviour.

Recent developments in fire design

Developments in fire safety engineering now allow a better assessment of fire risk and consequently better design of steel structures for improved fire resistance. By using numerical modelling the various physical phenomena occurring in a fire can be predicted with a fair degree of accuracy. These models cover fire development, temperature distribution within heated structural elements and the mechanical behaviour of structures at elevated temperatures. With such tools it is possible to assess the global behaviour of steel structures, taking into account the real risk of fire and considering the thermal elongation effect and possible redistribution of loads between hot and cold members. The fire parts of Eurocode I (actions in case of fire) and of Eurocode 3 (structural fire design of steel structures) cover a large part of this fire engineering discipline. Some useful definitions are given at the end of this review.

Advances in US Air Force hydraulic fluids

The US Air Force Wright Laboratory's Materials Directorate has been involved with the development and transition of advanced fluids and lubricants since the 1950s. The driving force for the development of new hydraulic fluids has primarily been and still is, improved fire resistance, although biodegradability and low toxicity have become increasingly important. This paper briefly traces the use of military aircraft hydraulic fluids from the beginning to the current state-of-the-art.

Laser pyrolysis of polymers and its relation to polymer fire behaviour

Laser-pyrolysis; time-of-flight mass spectrometry has been applied to the study of rapid thermal degradation of polymethymethacrylate (PMMA) and rigid polyurethane foams. The heating rate has little influence on the mechanism of PMMA degradation. In both the laser and low heating rate experiments, monomer was the major pyrolysis product. Laser pyrolysis of rigid polyurethane foams resulted in the evolution of polypropylene glycol as the major species together with low molecular weight species such as CO 2 etc. It is considered that polypropylene glycol and its further decomposed species act as fuel for the flame in a real fire situation. The ratio of polypropylene glycol to CO 2 in the evolved gases decreased with the increase of isocyanate index. This is associated with the improvement of fire resistance at a high isocyanate index.

Development of new materials with improved fire resistance, reduced smoke and toxicity (BREU CT91-0466)

New alternative halogen free thermoset polymers that meet processing, thermal, flammability and environmental requirements have now become necessary for mass transport applications. Based on the synergistic effects of nitrogen and phosphorus compounds, new telechelic phosphorylated crosslinkable monomers (reactive phosphine oxides, reactive phosphazenes..) have been synthesised as an alternative to the hazardous fire retardant systems commonly used. New formulations have been produced and selected on the basis of simple thermomechanical characteristics, fire performance, predictive toxicity assessment and parallel fundamental investigations on their degradation mechanisms. They have been used for further fibre impregnation of composite test samples and demonstration pieces. This work has been performed in the BRITE-EURAM Programme BREU CT91-0466 (BE 4412) under the Authority of EC-DG XII. The results obtained are described in other articles, presented by the different partners of the BRITE 4412 consortium.

New Phosphorus-Containing Flame Retardants for Poly-Urethanes and Polyesters

Abstract New phosphorus - containing monomers and oligomers from tetrakis(hydroxymetyl)phosphonium chloride and dialkylphosphites are synthesized. On the basis of new products phosphorus-containing polyesters, polyurethanes and polyuretanesemicazbazides with improved fire resistance are obtained. The dependence of fire resistance of the polymers on the structure of the use flame retardants is investigated.

Improved Fire Resistance for Interior Wood Panels

Abstract The background for considering decorative wood panels in the overall evaluation of materials and products which may contribute to fire hazard is briefly reviewed. State-of-the-art approaches to fire resistance for these products are summarized, with reference to the broader subject of fire retardants for wood. Some areas for potential development, and specific research needs are suggested.

Improved Fire Resistance of Insulation and Jacketing Materials for Electric Cables

Abstract The increasing use of synthetic organic polymers as insulation for wire and cable has led to some concern regarding the flammability of these materials, which may contribute to propagation of an electrically initiated fire. An analysis of statistical data for 1977–1979 reported through the National Fire Incident Reporting System (NFIRS) to the National Fire Data Center of the U.S. Fire Administration [1] has revealed that wire and cable insulation is involved in 59% of the fire incidents in which a plastic material is ignited first, accounting for a considerable percentage of the “civilian injuries” recorded by the data system for plastic products' fires. Wire and cable insulation thus poses a significant, albeit unusual flammability hazard, as well as complex technical problems relating to the selection of materials and designs for improved flame resistance. The magnitude of these problems is reflected, for example, in the proceedings of workshops held under the aegis of the National Research Council, with contributions from many experts in the field. Technical reports covering these workshops have been issued by the National Materials Advisory Board [2] and by the Electric Power Research Institute [3], and they demonstrate that overviews of materials and technology employed in wire and cable insulation, and approaches to flame resistance, can provide only an introductory discussion of a difficult and multifaceted subject. In the context of these limitations, the present paper presents a brief review of the polymeric materials and flame retardants currently used in the industry, and of some advanced state-of-the-art approaches that have been developed to enhance fire resistance in wire and cable products.