Manufacturing of Lightweight Sandwich Composites with Bio-Based PU Foam Core and Cellulose Fiber Network Skin

Abstract: The use of lightweight material are at an increasing demand in our society. Particularly, PU foams are used as lightweight insulation and support in sandwich composites for a wide range of products such as walls, packaging and car bumpers. This project aims to improve the mechanical properties of bio-PU foam by reinforcing the pre-resin with nanofibrillated cellulose (NFC). A lightweight sandwich panel was manufactured in a vacuum infusion process with carrot NFC-reinforced bio-PU foam core. Fine Kraft paper was used as skin and epoxy resin was used as adhesive. The sandwich was tested and compared to a non-reinforced PU foam core sandwich in terms of compressive, flexural and cellular properties. The result was a sandwich panel with improved mechanical properties, smaller cell size structure and lower open cell content. Moreover, the results were evaluated in a material selection process by means of minimizing merit indices. A trend in the behavior of compressive properties of the foam and flexural properties of the sandwich panels could be established thanks to this evaluation method. Overall, the results indicate that the mechanical properties of bio-PU foam can be improved by reinforcing the pre-resin with small amounts of wet carrot NFC. Ultimately, this work show a positive trend suggesting NFC- reinforced bio-PU foam has a great potential for use in commercialized products or structural components in future constructions.