Lightweight Recyclable Sandwich Composite Materials: Interface Mechanism, Mechanical Enhancement Effects, and Electromagnetic Shielding Properties

ABSTRACT In this study, a recyclable polymethyl methacrylate (PMMA)‐based sandwich composite was fabricated by vacuum‐assisted resin infusion, with upper and lower layers of single‐layer carbon fiber fabric (CFF) (0°/90°) and a hollow glass microsphere (HGM)‐filled PMMA foam core. The effects of HGM content on density, mechanical performance, electromagnetic shielding performance, and recyclability were systematically examined. Incorporating HGM reduced the density from 1.14 to 0.8 g/cm ³ and improved bending (357.33 MPa), impact (49.08 kJ/m ² ), and tensile strengths (134.54 MPa) by 3.6%, 36.9%, and 4.6%, respectively, while the bending (22.69GPa) and tensile (14.67GPa) moduli increased by 34.5% and 14.2%, respectively. Micromechanical simulation revealed that improved interfacial bonding mitigates stress concentrations and promotes effective load transfer, consistent with the experimental results. The composite also showed a 30.5% increase in electromagnetic shielding effectiveness (SE) (61.45 dB) and an 86% increase in specific shielding effectiveness (SSE) (76.81 dB/(g/cm ³ )), driven by the synergistic reflection–absorption effects of the CFF and HGM. Furthermore, a methyl methacrylate (MMA)‐based separation enabled efficient recovery of CFF, PMMA, and HGM, and the regenerated sandwich panel retained over 96% of its original strength and modulus.