Recent developments in fire retardation and fire protection of fibre-reinforced composites

This article reviews recent work on fire retardation and fire protection of fibre-reinforced composites carried out in the laboratories of the Fire Materials Group at the University of Bolton. This work has concentrated mainly on the effects of fire-retardant additives and coatings on the fire performance of unsaturated polyester, vinyl ester and epoxy resin composites reinforced with glass fibres

Thermal degradation behaviour of flame retardant unsaturated polyester resins incorporating functionalised nanoclays

This paper discusses the effect of nanoclays on thermal degradation of unsaturated polyester resin with and without conventional flame retardants. Unsaturated polyester nanocomposites were prepared by in-situ polymerization with exfoliated structures. Simultaneous DTA-TGA analysis showed that nanoclays reduce thermal stability of the unsaturated polyester resin below 6000C and after that there was no change. Nanoclays also reduce the onset of degradation temperature of the resin. Above 600 0C, char formation is enhanced but not to the same extent as reported in literature for other polymer (e.g., nylon, polystyrene, etc.) – nanocomposite structures. The effect of conventional flame retardants - ammonium polyphosphate, melamine phosphate with and without dipentaeythritaol and alumina trihydrate on thermal degradation of resin was also studied. All these flame retardants enhance char formation of the resin above 4000C and presence of nanoclays promotes further increase. Analysis of the thermogravimetric data indicates that this enhancement in char formation is not as much as expected when compared with similar other polymer - nanocomposite structures

Fire-resistant flax - reinforced polypropylene / polylactic acid composites with optimised fire and mechanical performances

Fabrics from commingled natural (flax) –thermoplastic (polypropylene (PP) / poly lactic acid (PLA) polymeric fibres were fire retarded with an oragnophosphonate flame retardant (FR). The fire retarded flax/PP and flax/PLA fabrics were melt pressed to prepare respective thermoplastic composites. The effect of FR concentration on the fire and mechanical properties of composites were studied and the results analysed in terms of concentration of FR elements in the composites. While the UL-94 test was used as a benchmark to achieve a V-0 rating, cone calorimetric parameters were used for in-depth analysis of fire performance. The results show that flax/PP and flax/PLA composites require a minimum 0.9 and 0.6 % phosphorus (P), respectively to achieve a V-0 rating in the UL-94 test. Mechanical properties, evaluated in tensile and flexural modes are however slightly impaired, most probably due to the acidity of the FR solution (pH = 3.2). In order to improve the mechanical properties, a buffer solution was used to change the pH to 6.0, which while having a minimal effect on mechanical properties of flax/PP, significantly reduced those of flax/PLA, and increased flammability of both composites and hence overall showed no benefit

Synthesis and thermal analytical screening of metal complexes as potential novel fire retardants in polyamide 6.6

The development of new flame retardants is of ever increasing importance because of ecotoxicity concerns over existing systems and related regulatory pressures. From a range of low-toxicity, water-insoluble reagents, a total of 151 metal complexes were assessed for their potential to impart flame retardant behaviour in polymer matrices. These were successfully synthesised on a small scale and possible interactions were explored with a model engineering polymer, namely polyamide 6.6 (PA66). Powder mixtures of each complex with PA66 in a 1:3 mass ratio were analysed under air using TGA/DTA. Based on the stability of each at the typical processing temperature of 290 °C and its char forming potential (the final residue requirement at 580 °C being > 25%), selected mixtures were then analysed further using a differential mass loss technique. Metal complex/PA66 mixtures in which the differential residual mass above 470 °C was >10% with respect to the theoretical value were considered to have a positive char forming interaction. Only eight of the metal complexes passed this last criterion including aluminium, tin (II) and zinc tungstates, three tin (II) phosphorus oxyanion complexes, iron (II) aluminate and iron (III) hypophosphite. These selected compounds were synthesised on a larger scale (c.a. 100 g), characterised and compounded into PA66 at 5 wt% for flammability assessment using LOI, UL94 and cone calorimetry. Of these, only aluminium tungstate and iron (II) aluminate showed some degree of FR behaviour with LOI values ≥ 23.0 vol% compared with PA66 (LOI = 22.9 vol%) and the former almost achieved a UL94 V-2 rating. However, while up to 32% reductions in total heat releases and up to 49% reduction in PHRR in cone calorimetric tests were observed for the metal complex/PA66 composites generally, those for Al2(WO4)3 were 6 and 29% respectively and for Fe(AlO2)2 were 18 and 45% respectively

Organophosphorus and organo-inorganic hybrid fire retardant coatings for polymers

Thin coatings of crosslinked poly(vinylphosphonic acid) display good adhesion and excellent fire-retardant barrier properties when applied to the surfaces of a typical thermoplastic, such as poly(methyl methacrylate), but perform relatively poorly in water-soak tests. Water-soak test performance can be significantly improved however by various hydrophobic modifications without detriment to fire performance

Quantification of thermal barrier efficiency of intumescent coatings on glass fibre-reinforced epoxy composites

In this work, the thermal barrier efficiency of three commercial intumescent coatings of varying thicknesses on glass fibre-reinforced epoxy (GRE) composites has been studied using cone calorimetric parameters and temperature profiles through the thicknesses, obtained by inserting thermocouples in the sample during the experiment. The methodologies developed to measure char expansion of the three coatings during the cone experiment as well under slow heating conditions using an advanced rheometric expansion system have been discussed. While the expansion ratios in the two experiments were different, the trends were similar. Thermal conductivities of the chars as a function of time were measured, which could be related to the intumescence steps of respective coatings. The accurate measurements of these parameters are important in predicting the surface requirements of an ideal coating that can enable a given composite structure to survive a defined thermal threat for a specified period of time

Novel flame retardant thermoset resin blends derived from a free-radically cured vinylbenzylated phenolic novolac and an unsaturated polyester for marine composites

A phenolic novolac resin has been chemically reacted with 4-vinylbenzyl chloride to introduce polymerizable vinyl benzyl groups. The modified novolac spontaneously polymerizes like styrene, is physically and chemically compatible with a typical unsaturated polyester (UP) resin, and can be free-radically cured (crosslinked) alone and in mixtures with UP using styrene as a reactive diluent. The cured vinylbenzylated novolac and co-cured blends of it with UP show superior flame retardance to cured UP alone and have potential applications as matrix resins in glass-reinforced composite laminates especially for marine structures

Surface modification of fabrics for improved flash‐fire resistance using atmospheric pressure plasma in the presence of a functionalized clay and polysiloxane

Improving flash fire resistance of otherwise flame resistant fabrics is a recognised challenge within the civil emergency and defence communities. Simulation of the flash fire condition using cone calorimetry has demonstrated the effectiveness of atmospheric plasma treatments in which either a functionalised nanoclay, a polysiloxane (poly(hexamethyldisiloxane)) or both are deposited on to plasma-activated fibre surfaces. Textile substrates comprised flame retardant (Proban®) cotton and a poly (meta-aramid) (Nomex®). Results show that the generated surface layer has a measurable effect on fabric ignition and burning characteristics when exposed in a cone calorimeter at heat flux levels up to 70 kW/m2. Reductions in peak heat release (PHRR) values are observed for all substrates especially for argon/clay and argon/clay/polysiloxane, plasma-treated samples, with reductions of over 50% being observed for Proban® cotton and smaller reductions (≤ 20%) for Nomex® fabrics. Both scanning electron microscopic and cone calorimetric studies show that these properties are retained after a simulated washing process including the argon/clay plasma-treated Proban® and Nomex® fabrics in which no potentially binding polysiloxane was present. This suggests that plasma-activated fibre surfaces in the presence of a functionalised clay enables relatively strong binding forces to be generated. The results provide further evidence in addition to our earlier reported studies, that atmospheric plasma treatment of fabric surfaces in the presence of a nanoclay produces an inorganic coating that confers reduced flammability at the high heat fluxes used suggesting increased resistance to flash fire ignition