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

Thermal insulation of polymeric composites using surface treatments

Fibre-reinforced polymeric composites for structural applications are required to conform to specific fire performance requirements and to retain their mechanical integrity after exposure to heat/fire. Many polymeric composites will lose their structural integrity when exposed to temperatures close to the glass transition temperature of the resin matrix. The most effective technique of protecting these materials against heat and fire is the use of surface coatings, which can inhibit or reduce the heat transfer from the fire/heat source to the underlying structure. In this PhD, novel thermal barrier coatings and techniques of their application on the surface of glass fibre-reinforced epoxy (GRE) composites were developed. These include: (1) commercially available intumescent coatings applied by paint brush and roller (2) nanoclays, dispersed in a solvent and sprayed on plasma activated GRE laminate surfaces (3) ceramic nano/microparticles dispersed in a flame retardant resin, applied by painting or K-bar application and (4) chemical coating obtained by applying phosphorus containing monomers (vinyl phosphonic acid) on a GRE surface by paint brush and polymerisation using UV radiation. Surface characterisation was carried out on each coating by scanning electron microscopy (SEM) and a water drop test. These results showed that the application method used plays an important role in determining the uniformity of the coating. Plasma treatment increased the hydrophilicity of the GRE composite surface, while in the presence of a resin binder, the coating established a hydrophobic surface. The effect of these coatings on the flammability of the composites was studied by a cone calorimeter at different heat fluxes, and the thermal barrier effect of the coatings was measured by insertion of thermocouples into the laminate during the cone experiments and measuring the time for the back surface temperature to reach the glass transition temperature of the resin. Intumescent coatings, as expected, showed the best performance and were used to set a benchmark for the performance of the other coatings. The nanoparticle and micro-ceramic particle coatings can act as thermal barriers. However, their concentration on the surface of laminates was not high enough to provide effective thermal protection for an extended period of time. The chemical (poly (vinyl phosphonic acid)) coating provided the best thermal barrier of the coatings due to its ability to form an intumescent char. Three point blending flexural and impact tests were used to study the effect of the coatings on the mechanical properties of the laminates. The contribution of the coating to the impact and flexural modulus of the laminates is related to the thickness of the coating and its mechanical properties. Thus, thin coatings showed better results than thick coatings. Each coating had a minimal effect on the mechanical properties of the GRE composite, while they improve the retention of mechanical property after exposure to heat, with the chemically coated samples performing the best, due to the formation of a thick intumescent char. A tape pull was performed to study the adhesion of the coatings on the GRE surfaces. All coatings containing resin binder or polymerized on the GRE surfaces were durable and did not peel off. The durability to water was tested by a water soak test. The nano/micro particulate ceramic coatings showed the best performance, whereas the chemical coatings showed the worst behaviour due to the highly hydrophilic nature of the poly (vinyl phosphonic acid)

Thermo-physical performance of organoclay coatings deposited on the surfaces of glass fibre-reinforced epoxy composites using an atmospheric pressure plasma or a resin binder

This work reports the thermal barrier and flame retardant efficiency of an organically modified clay (organoclay, OC), when deposited on the surface of glass fibre-reinforced epoxy (GRE) composites. Two approaches were undertaken: 1) the OC was deposited on the surface of the epoxy composite and then polymerised using an atmospheric argon plasma in the presence and absence of a silicon containing monomer and 2) the OC was dispersed in a phenolic resin binder and applied as a surface coating. Fourier transform infrared spectrometry confirmed the polymerisation of the silicon containing monomer by plasma treatment. The adhesion between the coating and the substrate was measured using the tape pull method, which indicated that the OC was tightly embedded in the resin matrix after plasma treatment or with the resin binder. The surface morphology of coated surfaces was studied using scanning electron and digital microscopies. The thermal barrier effect of the OC containing coatings studied by a cone calorimeter at 35 kW/m2 heat flux was demonstrated by increase in time-to-ignition and time-to-peak heat release rate, and decrease in the peak heat release of the coated samples compared to the control sample. However, for the coatings to be effectiveenough to be self extinguishing, the presence of an additional flame retardant element in the coating or on the surface layer of the GRE composite and beneath the clay layered coating is required

Evaluation of thermal barrier effect of ceramic microparticulate surface coatings on glass fibre-reinforced epoxy composites

In this work, three commercially available ceramic particles have been used as thermal barrier coatings on glass fibre-reinforced epoxy composites. The coatings have been prepared by dispersing 70 wt% ceramic particle in 30 wt% flame retarded epoxy resin. The thermal barrier efficiency of the coatings on the composites has been studied in terms of temperature gradient through the thickness of the sample while the surface is exposed to a radiant heat of varying heat fluxes. The tests have been performed in a cone calorimeter by inserting two thermocouples, one underneath the coating and the other on the reverse side of the sample during the experiments. This also allowed evaluating their flammability performanc

Ceramic particulate thermal barrier surface coatings for glass fibre-reinforced epoxy composites

This study investigates the thermal barrier efficiency of five commercially available ceramic nano and micro particles deposited on the surfaces of glass fibre-reinforced epoxy composites (GRE). Two approaches of application of deposition of ceramic particles have been undertaken, firstly where the ceramic particles were dispersed in a phenolic resin binder and applied on a GRE surface by a K-bar coater and the second where extra ceramic particles were sprayed on the first coating while the resin was partially cured to enable the surface to be completely covered by ceramic particles, leaving no resin exposed. The thermal barrier efficiency of these coatings was evaluated from the cone calorimetric parameters at incident heat fluxes of 35 and 50 kW/m2 as well as from temperature gradient through the samples’ thicknesses, measured by inserting thermocouples on the exposed and back surfaces during the cone tests. The morphology and durability of the coatings to water absorption, peeling, impact and flexural loading were also studied. The results showed that the surface layers of all coated samples were uniform and a strong adhesion between the coating and the substrate. Moreover, they did not adversely affect the mechanical properties of GRE composite while improving the mechanical property retention of GRE composites after exposure to heat

Fire reaction properties of flax/epoxy laminates and their balsa-core sandwich composites with or without fire protection

Fire reaction properties of flax/epoxy laminates and their corresponding balsa-core sandwich composites with/without fire protection were evaluated at an applied heat flux of 50 kW/m2. A strategy for improving the fire reaction properties of flax/epoxy composite materials without adversely altering their intrinsic mechanical properties was investigated. A thin glass fiber veil impregnated with ammonium polyphosphate was bonded onto the composite surface intended for heat exposure. There was no significant change in the time-to-ignition with the introduction of the fire retardant glass fiber veil. While similar PHRR values were measured in both flax/epoxy laminates and balsa-core sandwich composites, the total heat release was significantly higher in the later. It is noteworthy, the heat release rates (including the peak values) measured for fire-protected composites were significantly lower than those measured for their unprotected counterparts. Through-thickness temperature profiles across the sandwich composite revealed the effectiveness of the fire retardant veil in minimizing thermal damage of underlying substrate composites

Thermal protection of carbon fiber-reinforced composites by ceramic particles

The thermal barrier efficiency of two types of ceramic particle, glass flakes and aluminum titanate, dispersed on the surface of carbon-fiber epoxy composites, has been evaluated using a cone calorimeter at 35 and 50 kW/m2, in addition to temperature gradients through the samples’ thicknesses, measured by inserting thermocouples on the exposed and back surfaces during the cone tests. Two techniques of dispersing ceramic particles on the surface have been employed, one where particles were dispersed on semi-cured laminate and the other where their dispersion in a phenolic resin was applied on the laminate surface, using the same method as used previously for glass fiber composites. The morphology and durability of the coatings to water absorption, peeling, impact and flexural tension were also studied and compared with those previously reported for glass-fiber epoxy composites. With both methods, uniform coatings could be achieved, which were durable to peeling or water absorption with a minimal adverse effect on the mechanical properties of composites. While all these properties were comparable to those previously observed for glass fiber composites, the ceramic particles have seen to be more effective on this less flammable, carbon fiber composite substrate

Fire and mechanical properties of a novel free-radically cured phenolic resin based on a methacrylate-functional novolac and of its blends with an unsaturated polyester resin

A novel phenolic novolac resin bearing methacrylate functional groups has been synthesized by reaction of the novolac with methacryloyl chloride. This resin has been mixed with styrene and cured (crosslinked) free-radically under the relatively low temperature conditions used to cure unsaturated polyester/styrene mixtures, i.e. there is no need to employ the high temperatures and pressures that are required to cure conventional phenolic resins. Homogeneous cured blends of the methacrylated novolac with unsaturated polyester and styrene have been prepared also. The cured methacrylated novolac, and its blends with unsaturated polyester, are rigid materials with good mechanical strength, and have glass transition temperatures, thermal stabilities and flame retardancies superior to those of cured unsaturated polyester alone. Fire and mechanical properties of a novel free-radically cured phenolic resin based on a methacrylate-functional novolac and of its blends with an unsaturated polyester resin

The Effects of Thermophysical Properties and Environmental Conditions on Fire Performance of Intumescent Coatings on Glass Fibre-Reinforced Epoxy Composites

Intumescent coatings are commonly used as passive fire protection systems for steel structures. The purpose of this work is to explore whether these can also be used effectively on glass fibre-reinforced epoxy (GRE) composites, considering the flammability of the composites compared to non-flammable steel substrate. The thermal barrier and reaction-to-fire properties of three commercial intumescent coatings on GRE composites have been studied using a cone calorimeter. Their thermophysical properties in terms of heating rate and/or temperature dependent char expansion ratios and thermal conductivities have been measured and correlated. It has been suggested that these two parameters can be used to design coatings to protect composite laminates of defined thicknesses for specified periods of time. The durability of the coatings to water absorption, peeling, impact, and flexural loading were also studied. A strong adhesion between all types of coatings and the substrate was observed. Water soaking had a little effect on the fire performance of epoxy based coatings. All types of 1 mm thick coatings on GRE helped in retaining ~90% of the flexural property after 2 min exposure to 50 kW/m2 heat flux whereas the uncoated laminate underwent severe delamination and loss in structural integrity after 1 min