Flammability Performance of Bio-derived Composite Materials for Aircraft Interiors

Abstract

Composite materials are increasingly being used in applications where their fire response is a critical consideration. Environmental concerns motivate the use of natural fibres, but they represent an additional fuel source for combustion, and their resulting composites will perform worse in flammability testing compared to synthetic alternatives. This research investigates the flammability implications of using natural fibres in composite material systems through a combination of experiments and numerical modelling. Flax fibres and glass fibres were selected for the natural fibre reinforcement and synthetic counterpart respectively, along with an epoxy resin system for the composite matrix. An initial set of experiments using glass fibre reinforced composites found that the permeability and fibre architecture significantly influenced the flammability properties of their respective specimens. An experimental study was also conducted, which compared flax fibre reinforced epoxy specimens to composites formed from glass fibre reinforcements of similar architecture, reinforcing the same resin system. The results demonstrated that flax fibre reinforced composites ignited earlier, released greater levels of heat, and took longer to extinguish than their glass fibre counterparts. A significant amount of structural deformation also occurred during the combustion process, with expansion of up to 2.5 times the original thickness in the vertical plane and up to 30 % shrinkage in the horizontal plane. The effects of key properties on the flammability of natural fibre reinforced composite systems were investigated using cone calorimetry in a parametric study, which varied specimen thickness, fibre volume fraction, incident heat flux, fibre type, fibre architecture, and composite matrix retardancy. Key trends were identified in flammability properties such as heat release rate, smoke production, ignition time, and time to extinguishment when the parameters were varied. A predictive one-dimensional finite difference model was developed from first principles to predict trends in the material behaviour during the combustion of natural fibre reinforced composite materials under cone calorimetry testing conditions. The model was successfully compared to available analytical data in literature for synthetic composites, as well as the data obtained during the parametric study.