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Fire Performance of Flax Laminates and their Hybrids

In the current age of growing environmental awareness, natural fibre composites have gained wide acceptance in various facets of engineering. However, in industries, such as aerospace and mining, their acceptance is primarily dependent on them meeting the stringent fire test requirements. In this paper, symmetric laminates consisting of only glass, glass/flax hybrid and only flax as reinforcements in thermoset matrices were tested for their time to ignition, heat release rate and smoke constituents as per standard ASTM E 1354 in a cone calorimeter. Four fire retardant versions of resin systems, were used in this study. The laminates were manufactured using wet hand-layup technique that was vacuum bagged and cured between hot platens of a hydraulic press. A constant fibre volume fraction of 0.5 for all the laminates was obtained by maintaining a constant laminate thickness of 4mm. The results from the cone calorimeter tests were compared to examine the influence of natural fibres on the fire properties of the laminates. It was observed that the degree of fire retardance in the polyester based composites decreased with the increase in the flax fibre content; however, in the modified urethane composites, flax fibre composites performed better by exhibiting higher ignition time compared to the hybrid and glass fibre composites. Another important observation was that the carbon monoxide emissions during testing decreased with the increase in flax content in the composites, no matter what resin system was used. These preliminary tests suggest that, by judiciously incorporating natural fibres in a synthetic system, a hybrid system could be designed to sustain loads in environments with high fire risks.