Abstract

Reprocessable, repairable, and recyclable thermoset composites have the potential to improve the circularity of composites and ensure their sustainability. Disulfide-based epoxy matrices are under development to meet the specifications of key sectors (transport, wind energy, etc.). The manufacturing of reinforced composites by different techniques (infusion, prepregs, etc.) has been validated (TRL 4-5). The incorporation of new functionalities, such as fire resistance, and the validation of recycling are now on the table. Conventional chemical recycling separates the reinforcement from the composite for reuse, leaving aside the polymer matrix. The new functionalities incorporated require recovery and validation of the matrix. Dynamic resins allow milder conditions to be applied during recycling, and the challenge remains to find new applications that reuse these recycled products. On the other hand, the rational use of resources demands for new recycling routes that do not require separation of the components, apply few steps, be economically viable, and maintain the value of the reinforcement and the matrix. Vitrimers allow the thermoforming of composite parts through the application of heat and pressure. This process opens the way from reusing final parts with new shapes to generating short new fibre composites from mechanical pre-crushing. This communication will present the latest developments and objectives of several European projects funded under the HE framework (SURPASS, GA no. 101057901; MC4, GA no. 101057394) in which work on the maturity of the technologies is in progress.

Abstract

Pyrolysis is a technically suitable process for recovering fibres from reinforced plastic waste that may also contain other types of materials (wood, foam, lacquer, etc.), such as wind turbine blades at the end of their useful life. The economic profitability of the pyrolysis recycling process depends mainly on the value of the recovered fibres, since pyrolysis liquids currently have no industrial application (and are therefore hazardous waste) and the gases are usually used to partially supply the energy requirements of the process, which is endothermic. Given that the wind turbine blades currently being retired are mainly made of glass fibres, which have low economic value, the profitability of the pyrolysis recycling process for this type of blade is a critical issue. This paper presents an analysis of the increase in the profitability of a wind turbine blade pyrolysis process that includes a treatment stage to improve the properties of the liquid and gaseous products. To this end, the investment required for this treatment (additional process units) has been defined and the energy costs and liquid waste management costs have been quantified in scenarios with and without treatment, including in the latter case the income from the sale of hydrogen. With this information and the amortisation expense, the incremental income statements derived from carrying out the treatment have been prepared, obtaining the net cash flows (NCF). The NCF has been used to calculate the net present value (NPV) of the investment project, as this is the best criterion from a financial point of view for evaluating a project. Finally, a sensitivity analysis was performed taking into account deviations in the investment to be made, income and costs. The results show that the cost of managing liquid waste is the parameter with the greatest influence on profitability, meaning that implementing the treatment increases the profitability of the recycling process.

Abstract

Thermosetting matrix composites are by far the most use composite solutions in the market. Thermosetting matrices are not currently possible to recycle by convenient means, which makes them a poor sustainable solution. In environmental terms, these matrices materials are also more harmful due to gas emissions during the curing process that can be considered harmful to the workers. Thermoset composites also have some disadvantages from the point of view of mechanical behaviour, being less ductile and resistant when compared to thermoplastic matrix composites. Despite the very high viscosity of thermoplastic materials that is a main problem regarding composite processing, they have advantages such as being recyclable, cleaner workspaces and greater availability, as well as a longer shelf life. This paper aims to be a contribution to increase use of thermoplastic matrix composites as alternative to the more traditional thermosetting based composites. First, thermoplastic matrix prepregs were produced in tape form by dipping the fibres into a molten polymer bath. Carbon and glass fibres are used as reinforcement material, testing their combination with thermoplastic polymers and recycled polymers. The use of prepregs is more attractive on the market as the process of mixing and selecting the raw materials is carried out prior to their application in a consolidation process. The prepregs were then processed by pultrusion, which is characterised by its continuous nature, allowing the manufacturing of constant cross section profiles for structural applications. The pultrusion of thermoplastic composites is still a novelty and therefore presents challenges. The determination of the best combination of operational parameters was also conducted in this study. Finally, the produced profiles were subjected to mechanical tests as a way of assessing the quality of the processed composites. The mechanical properties obtained will be compared to those predicted by the application of micromechanical models using experimentally obtained mass fibre fraction content.

Abstract

If we want to maintain, or even increase, the current level of use of high-performance composite materials, some major challenges need to be solved: reduction in the cost of the final structure, reduction in energy consumption during the manufacturing cycle from the base material to the final structure, and develop strategies following the “5Rs Circular Economy” approach: Rethink, Refuse, Reduce, Reuse and Recycle technologies to produce materials and structures with high added value. This communication has the intention to show Airbus work on the reuse of multilayer uncured prepreg scrap generated in AFP, to be used for the manufacturing of non-loaded parts by BMC (Bulk Moulding Compound). We will deal with the problem understanding; multilayer prepreg scrap represents an important part of the fresh scrap generated in the manufacturing plants and no feasible technology has been yet developed to treat this type of residue due to the difficulty of separating layers without completely damaging the composite prepreg. We will also detail the multilayer prepreg scrap treatment, part production, material characterization, and the opportunities to introduce parts made of reuse prepreg on real aircraft.