Effect of temperature on the low-velocity impact response of environmentally friendly cork sandwich structures

Impact events are common in every-day life and can severely compromise the integrity and reliability of high-performing structures such as sandwich composites that are widespread in different industrial fields. Considering their susceptibility to impact damage and the environmental issues connected with their exploitation of synthetic materials, the present work aims to propose a bio-based sandwich structure with an agglomerated cork core and a flax/basalt intraply fabric as skin reinforcement and to address its main weakness, i.e. its impact response. In-service properties are influenced by temperature, therefore the effect of high (60 °C) and low (-40°C) temperatures on the impact behavior of the proposed structures was investigated and a suitable comparison with traditional (polyvinyl chloride) (PVC) foams was provided. The results highlighted the embrittlement effect of decreasing temperature on the impact resistance of the sole cores and skins and of the overall structures with a reduction in the perforation energy that shifted, in the last case, from 50-60 J at - 40 °C up to more than 180 J at 60 °C. A maleic anhydride coupling agent in the skins hindered fundamental energy dissipation mechanisms such as matrix plasticization, determining a reduction in the perforation threshold of all composites. In particular, neat polypropylene (PP) skins displayed a perforation energy of 20 J higher than compatibilized (PPC) ones at 60 °C, while agglomerated cork sandwich structures at 60 °C were characterized by a perforation threshold higher of at least 50 J.