Durability of Sustainable Composites in Ship Design for Enhanced Environmental Performance: a Multiscale Approach

The marine industry is one of the largest consumers of composite materials. According to Composite Insights, the demand for composite materials in global marine-composites industry is set to grow 5.8% per year between 2013 and 2018 [1]. Given the rising prices of fossil fuels and the increasing global environmental awareness, there is now pressure on the reduction of the use of crude-oil-based composites. The harsh marine environment represents a unique challenge for the use of sustainable bio-alternatives. Thus there is an interest in the long term structural performance of sustainable alternative fibres and resins for such materials. To certify safe performance of sustainable composite structures it is necessary for the users to know the material properties, processability, and their capacity to sustain loads and retain stability during the whole life cycle. In recent years bio-derived fibres have received much attention and as a result a substantial amount of research has been conducted in order to better understand and quantify their properties [2]–[5]. In the public domain, however, there is still little information to aid the designer about sustainable resins (especially epoxies) and hence composite materials utilising them are not typically considered as a technically viable option. Failure mechanisms during the design life of the material can be identified but the root cause behind its degradation remains unclear. Malmstein at al. [6] reported that after 20 + weeks of hygrothermal ageing the glass/linseed oil specimens lost 72% of their dry strength and that this might be caused by the UV-curing and chemical reactions between water and linseed oil resin and/or fibre–matrix interface. They also revealed that the properties of glass/conventional epoxy kept degrading while the moisture content remained constant indicating chemical degradation of the composite. Reportedly, glass/linseed degraded rapidly during the first 2 weeks of immersion but after 4 weeks until the end of the testing period suffered no further degradation. Only when knowing both the physical and chemical properties of the resin system can one use the material with full confidence. Furthermore, this knowledge would allow modification (redesign) of the resin in order to yield better physical properties, thus improving the performance of the whole composite material. The aim of this study is to bring chemistry and engineering together to achieve the similar level of understanding of the degradation processes of a sustainable epoxy resin system in a harsh marine environment as has taken place for conventional marine epoxy.