Fabrication of lightweight, high-strength rigid polyphenylene oxide/polyamide foam via supercritical CO₂

Polyphenylene oxide (PPO) exhibits excellent heat resistance, flame retardancy and low dielectric constant. However, the chain rigidity of PPO results in significant brittleness in its foams. In this work, PPO was blended with polyamide6 (PA6) to enhance the toughness and processability of its foams. Innovatively, maleic anhydride-grafted PPO (PPO-g-MAH) and triglycidyl isocyanurate (TGIC) were synergistically utilized as compatibilizers and to construct a crosslinked network. PPO-g-MAH served as a bridge connecting PPO and PA6, TGIC functioned as a crosslinking agent for PA6 and PPO-g-MAH, forming a long-chain entangled and crosslinked structure that interpenetrates the matrix. Supercritical CO 2 foaming was employed to prepare the PPO/PA rigid foam. At 30 phr PA6 content, the synergistic compatibilization led to a refined co-continuous phase morphology and yielded a low density of 0.203   g/cm 3 . At a density of 0.251   g/cm 3 , the average cell size was approximately 22   µm and exhibited a uniform distribution, which contributed to a high flexural strength of 47.29   MPa. Additionally, the foam demonstrated a low dielectric constant of 2.05. This research presents a viable approach for fabricating rigid foams that are lightweight, high strength, and heat-resistant. It showed significant potential for lightweight structural components in automotive engineering, and high-frequency insulating layers in construction.