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)
