Flexural behaviours of nanophased rigid polyurethane foam core sandwich composites

Reinforcing foam cored sandwich composites with nanoparticles occupies an important place in expending the utility of sandwich structures with multifunctional properties. This study focuses on improving the flexural properties of foam cored sandwich structures by addition of carbon nanotubes (CNT) and nanosilica (nSi) particles to the polyurethane (PU) foam. The increased surface area in PU foams cores makes them promising candidates over honeycomb with enhanced bonding between core and skin. By effective dispersion and distribution of CNTs and nSi at various weight fractions, the compressive strength of nanophased PU foams increased up to 32.2% for CNTs and 10% for nSi followed by a rise in density, as well. Through morphological and micromechanical characterizations, it is also found that the geometry of nanomaterial has a significant effect on the reinforcing mechanism through formation of cellular characteristics of foams. Using CNTs as rod like nanostructures, the cell edge length is increased and high surface energy causing cells to stretch through the longest direction of nanoparticle during cell growth. Compared to CNTs, nSi showed tighter cell packings with decreased cell edge length, respectively. As a result, PU foam cored sandwich composites have shown an enhancement more than 5% in core shear yield strengths of both nSi/PU and MWCNT/PU cores under three-point bending tests.