Bio-based/green sandwich structures: A review

Sandwich panels are one of the most applied designs in the aerospace, construction and automotive structures due to their excellent stiffness-to-weight ratio. Recent advances in the design of eco-friendly sandwich structures with bio-based and/or recycled/recyclable components indicate a clear move towards reducing the environmental impacts of the resulting designs while preserving mechanical performance. This movement is driven by strict environmental legislation and the need to save material costs and fuel consumption, requiring the use of greener components in the transport and building sector with higher loading performance and a smaller environmental footprint. This work presents the most recent efforts in the development of eco-friendly sandwich structures by classifying different approaches to the environmental optimisation of structures. A consistent classification of sandwich panels as either eco-friendly, bio-based, or quasi/fully-green structures is proposed according to their amount of bio-based components. The main components of bio-based/green sandwich panel skins, cores, and adhesives are listed, identifying the most promising designs under different mechanical properties. The environmental benefits and limitations of bio-based/green components are balanced by considering the eco-efficiency of the structures and outlining the challenges that are expected in the future.