Monomatrix thermoplastic sandwich structures through in-situ foaming technology

Polymeric sandwich structures are conventionally based on either thermosetting (skin matrix, foamed or honeycomb cores) or thermoplastic (foamed cores) components, bonded through the use of adhesives. A new technology has been developed in the framework of the CESPERT project, which allow the production of a monomatrix thermoplastic sandwich structure in which the core is directly foamed between skins and consolidated without the use of adhesive layers. In order to show the potential of this technology, a nanocomposite based on poly(ethylene naphthalate), PEN, and expanded graphite, EG, was developed as matrix and a glass fiber fabric was used as reinforcement. PEN is a thermoplastic polyester characterized by a high glass transition temperature (125 °C), comparable to that of PEEK (143 °C), but with a significantly lower melting temperature (265 °C vs 345 °C). Its physical and chemical properties are very promising for applications in transport industry and aeronautics. The polymer was melt blended with expanded graphite by means of extrusion process and its effects on the foaming properties were investigated through solid state foaming process. Reinforced composites were prepared by means of film stacking technique by using the same nanocomposite matrix. Main results of developed technology on morphological, mechanical and impact properties of sandwich structures are presented.