Polypropylene foams are attractive lightweight thermal insulation materials; however, their practical application is often limited by the intrinsic trade-off between low thermal conductivity and mechanical degradation induced by foaming. In this study, a surface-alkylated zeolitic imidazolate framework–based hybrid composite was developed to achieve enhanced thermal insulation while preserving mechanical integrity. Surface alkylation of ZIF-94 improved filler dispersion and interfacial compatibility in the nonpolar PP matrix, promoting heterogeneous nucleation during chemical foaming and resulting in a refined and uniform cellular structure. Owing to the combined effects of intrinsic microporosity, stabilized foam morphology, and increased interfacial thermal resistance, the optimized AZIF/GF/PPF exhibited a low thermal conductivity of 0.070 W m–1 K–1, as measured by laser flash analysis. Despite the presence of a porous structure, the composite retained a high tensile strength of 45.6 MPa, demonstrating effective mitigation of foaming-induced mechanical deterioration. Thermogravimetric analysis confirmed that the incorporation of AZIF and glass fiber did not compromise the thermal stability of the PP matrix under melt-processing conditions. Overall, this study demonstrates that surface alkylation of ZIF fillers is an effective strategy for simultaneously controlling cellular morphology, interfacial structure, and heat-transfer pathways, providing a promising route for designing lightweight PP-based foam composites with balanced thermal insulation and mechanical performance. These results indicate that surface alkylation is an effective interfacial engineering strategy for simultaneously improving cellular structure, thermal insulation performance, and mechanical stability in PP-based foam composites.
Kim et al. (Tue,) studied this question.