Development of melt-stretching technique for manufacturing fully-recyclable thermoplastic honeycombs with tunable cell geometries

Highlights: • Honeycomb panels with integral face sheets were created by stretching a polycarbonate melt between perforated platens. • Cell geometries were demonstrated to be controllable and repeatable, including mixed cell geometries within a single panel. • Contrary to analytical predictions, out-of-plane compressive strengths were found to be independent of cell geometry. • The new honeycombs demonstrate competitive mechanical performance to conventionally-produced thermoplastic honeycombs. • Melt-stretched honeycombs are composed of a single material and so are fully and easily recyclable. Honeycomb sandwich panels of several cell geometries were created by stretching polycarbonate melts between opposing platens. Perforations for air ingress through one of the platens were employed to enable and direct the formation of cells within the honeycomb, demonstrating a simple means to produce complicated architectures. Platen temperature, consolidation pressure, and platen movement speeds were each investigated to establish a range of effective process parameters. Honeycomb panels were successfully produced with areal densities of 0.18 g cm^{- 2} to 0.42 g cm^{- 2} and panel thicknesses ranging from 6 mm to 32 mm. The cell geometries were found to be effectively modeled by Voronoi diagrams seeded by the perforations used for air ingress. This model was validated by the successful production of hexagonal-, square-, and triangular-celled honeycombs, as well as an architecture combining all three cell shapes. Analysis of several samples via computed tomography provided insight into the internal distribution of material. Out-of-plane compressive testing was used to probe the mechanical performance of the structures. Minimal variation in buckling strength was found between the different honeycomb geometries, but post-failure behavior was dependent on cell shape.