Carbon black-filled polyurethane foam as a core for sandwich panels

This study presents the development and characterization of rigid polyurethane foams (RPUFs) reinforced with carbon black (CB) particles (0.5%, 1.0%, and 3.0% wt.), engineered as lightweight core materials for structural sandwich panels. The novelty lies in the use of CB as a cost-effective nanofiller to improve both mechanical and morphological properties of RPUFs while reducing density. The foams exhibited closed-cell, anisotropic structures, with the 0.5% and 1.0% CB formulations showing enhanced cell alignment and reduced cell size. Significant mechanical improvements were achieved: compressive strength increased by 41.7% and 45.8%, and compressive modulus by 33.3% and 9.5% for the 0.5% and 1.0% CB foams, respectively, compared to neat RPUF. These enhancements are attributed to effective filler–matrix interaction and optimized foam microstructure. In contrast, the 3.0% CB foam displayed poor dispersion, leading to structural defects and reduced mechanical performance. When applied as sandwich panel cores, the 0.5% CB formulation led to improvements of 54.5% in specific flexural stiffness and 37.5% in core shear strength. These results demonstrate that low CB contents can simultaneously reduce density and improve mechanical efficiency, highlighting their potential for use in lightweight, high-performance structural applications in automotive, construction, and insulation systems.