Multiscale modelling techniques in life cycle assessment: Application to nanostructured polymer systems in the maritime industry

One of the major challenges of Life Cycle Assessment is in the generation of life cycle inventories for complex or novel materials. This paper aims at broadening the perspective in Life Cycle Assessment methodology, exploiting multiscale modelling towards the generation of inventory data during an early-stage product design. Our approach involves the usage of molecular modelling techniques, such as electronic, atomistic or mesoscale models, in combination with continuum models, such as process simulation or finite element methods, to provide data for the generation of life cycle inventories of nanostructured materials. In particular, each simulation is performed at a specific length and time scale through specific software, passing information from the lower to the upper scale. We applied our procedure to a comparative Life Cycle Assessment among suitable materials for the production of a set of cylinder head cover of a marine engine, i.e., aluminium alloys and nano-engineered thermoplastic polymers. Engineering judgment, Ashby charts and maritime regulations led the initial identification of suitable materials. As a result, polyamide 6,6 reinforced with 30% wt. glass fibers and mixed with phosphate-based flame retardants have been identified as promising candidate for the replacement of aluminium traditional covers. Nonetheless, we introduced nanoclays, i.e., exfoliated montmorillonite, as a replacement for a quota of conventional flame retardant, aiming at reducing the usage of pollutant chemicals. We then resorted to atomistic and finite-element techniques to investigate the compliance of nanocomposite materials with several Key Performance Indicators. The nanocomposite formulations obtained from simulations have been finally employed as input data for life cycle inventories of material alternatives. Using a Life Cycle Assessment approach, we could identify the most environmental-friendly nanocomposite formulation, which was then compared with traditional aluminium through an additional comparative cradle-to-grave study. Among the suitable nanocomposite formulations, the material with the minimum amount of traditional flame retardant exhibited the lowest scores among the majority of Environmental Footprint impact categories. To account for the entire lifetime of the marine engine, a set of four nanocomposite covers has been compared with a set of three aluminium covers made by two different metal alloys. Four recycling scenarios for aluminium covers have been examined, assuming an incremental number of end-of-use products reintroduced into a circular life cycle, while nanocomposite ones were disposed into landfill. In turn, if the aluminium products are insufficiently recycled, our results promote the usage of nano-engineered polymer products. As the amount of reused metal covers increases, indeed, polymer-based covers become unfavorable with respect to aluminium cast alloy products. Accordingly, an increasing amount of post-consumer aluminium diminishes the need of primary metal, yielding considerable advantages in terms of environmental footprint. Consequently, stakeholders should commit in recycling metal components not only at ship dismantling, but also during ordinary maintenance. Our study showed how multiscale molecular modelling proved to be useful for providing necessary inventory data for complex nanostructured materials. This preliminary study paves the way for future development of the proposed framework, in which in-silico techniques based on distinct paradigms can mutually contribute towards an improvement of products ecodesign.