In the USA, Federal regulations still prohibit the use of composites in ship primary structure because requirements for non-combustion are not met. In contrast, the International Maritime Organisation’s High Speed Craft (HSC) Code accepts that composites can be included as an element of fire restricting materials used for lining compartments and bulkheads, subject to satisfactory performance in fire tests.

At a recent conference organised by RINA (the Royal Institution of Naval Architects), a presentation from the IMCB-Institute of Composite Materials and CNR-Biomedical National Research Council in Italy highlighted the beneficial flame retardancy achieved by adding zinc-based compounds to epoxy matrices.

Authors De Fenzo, Formicola, Antonnucci, Zarrelli, and Giordano pointed out that unaltered epoxy resin ignites at some 400°C, subsequently reducing to a char but producing large volumes of harmful smoke as it does so. The smoke is due to a high yield from the resin of flammable volatiles.

It is known that certain compounds of zinc and tin can be effective in suppressing these emissions and hence the harmful smoke. They do this by slowing down the combustion process, ’staging’ it so that there is a higher char yield than with neat resin. As a result, less of the material literally goes up in smoke. Tests carried out in Italy showed that zinc borate, zinc stannate and zinc hydroxystannate used as additives in a low-viscosity toughened epoxy resin intended for resin transfer moulding (RTM) and vacuum infusion proved effective as flame retardants. A model of the degradation process was developed.

A submission by the UK branch of classification society ABS on structural fire protection for fibre reinforced plastic (FRP) yachts outlined an intended theoretical model for predicting the behaviour of composite elements under specified heat loads. Successful validation of the model in actual fire tests would assist in developing draft standard to help designers provide effective protection against both resin ignition and harmful emissions after ignition. The ISO TC8/TC12/WG2 project team welcomes comments and input.
 

This article is an extract from the feature Marine composites – drawbacks and successes published in the July/August issue of Reinforced Plastics magazine. You can read the complete feature here.