Design and preparation of shape memory phenol–formaldehyde foam composites with excellent thermal stability and mechanical properties

Phenolic resins equipped with flame retardant and exceptional ablative properties show considerable potential for thermal protection applications. However, phenolic resins typically exhibit poor mechanical properties, as they are brittle, easily pulverized, and difficult to deform. In this study, shape memory phenol–formaldehyde resins (SMPRs) were synthesized through chemical cross-linking reactions and prepared shape memory phenol–formaldehyde foams (SMPFs) using physical foaming techniques. SMPFs exhibited good shape memory properties and deformation capabilities. Compared with other shape memory polymer foams, the SMPFs presented superior thermal stability, and a superior residual carbon rate. Shape memory polymer foam composites (SMPFCs) reinforced with SiO₂ or Al₂O₃ nanoparticles demonstrated improved thermal stability, and were capable of completing a self-expanding and self-folding process. SMPFs and SMPFCs have the potential to be applied in flexible fireproof materials owing to their excellent deformation properties and high-temperature resistance.