Manufacture, repair and recycling of thermoplastic composite boats

Abstract

The design and construction of boats using thermoplastic composites (TPCs) is an emerging industry derived from the advantages these materials offer. Short manufacturing cycle times, virtually infinite shelf life, increased toughness, no volatiles emission, and the ability to be re‐processed and recycled, lead to improved processes and open new and more sustainable manufacturing possibilities for boats and other structures. However, the manufacture, repair and actual recycling of TPCs still present a number of technical challenges. This thesis addresses the five most important of these challenges, from both the academic and industrial points of view. The manufacturing of TPC structures involves the impregnation of reinforcing fibres with melted resin. This process, known as consolidation, is still to be fully understood. In order to contribute to this understanding, a consolidation model based on existing and newly developed sub‐models was developed and applied to experimental data. The results obtained proved that the non‐isothermal consolidation of laminates of a thickness typical of boatbuilding, can be approached by applying this model locally on a discretised laminate, fitting well experimental data. The choice of a cost‐effective moulding material is one of the factors currently preventing the widespread use of TPCs in boatbuilding. The vacuum forming of TPCs requires moulds which have considerable strength, and allow high service temperatures and the shape freedom which is typical of boat moulds. A review of commercial and experimental materials and laboratory experimentation on a novel glass‐reinforced ceramic composite was carried out, showing that a range of metals and composites are useful for TPC‐capable moulds, and that a cost‐effective free‐shape mould capable of processing any TPC is achievable. After hull shell manufacturing stiffeners and other internal structure are often required. The manufacturing of such a reinforced and subdivided hull involves the use of a joining technology. Adhesive joining, widely used in thermosetting resin composite boats, cannot be easily used on TPCs due to their low energy surfaces. However, the re‐melting ability of thermoplastic resins enables the use of welding, fusion bonding and other joining methods involving molecular diffusion at the bond line. Experiments carried out on lap and T‐joints showed that vacuum‐assisted local heating can be used for structural assemblies such as reinforced boat hulls, obtaining strengths that are comparable to existing thermosetting designs. A TPC boat manufactured and assembled in such way would still require a suitable repair technique that provides a long product life. An emergency repair method capable to return the boat to the water in less than 24 hours without using any mould was devised and tested on a prototype TPC rigid inflatable boat. This was achieved by fusion bonding the edges of a pre‐manufactured flat panel to the hull. The flat panel adapted to the hull double curvature by means of vacuum pressure, delivering the required bond quality and strength. Finally, the disposal of a TPC boat must be addressed after the end of its service life. Current policies and innovative business thinking are leading companies into reusing and recycling instead of landfilling materials. While the mechanical recycling of TPCs, achieved by means of resin re‐melting, has been largely studied, the recycling of a real boat containing paint and core material raise questions on how these materials would affect the recyclate. An experimental study on the recycling of a TPC real boat was carried out to answer these questions, revealing that despite the deleterious effect of core and paint, the final properties of injection moulded samples were in the region of those of virgin materials.