Fabrication and Characterization of Boron Nitride‐Reinforced Polypropylene Composite Foams via Chemical Foaming

ABSTRACT In this study, polypropylene (PP) foams reinforced with boron nitride (BN) particles were produced via chemical foaming to evaluate the effect of chemical blowing agent (CBA) content on cellular morphology, melt flow behavior, mechanical performance, and thermal properties. Increasing CBA content enlarged the average cell size from approximately 0.1–0.3 mm, while the expansion ratio rose from 1.06 to 2.04. Conversely, cell density decreased from 2.67 × 10 4 to 0.86 × 10 4 cells/cm 3 due to excessive gas generation and cell coalescence at higher CBA levels. The maximum CBA addition resulted in a density reduction of about 50%. Melt flow index (MFI) measurements indicated reduced flowability with BN incorporation, attributed to increased melt viscosity and enhanced polymer–filler interactions. Hardness decreased by approximately 13% at the highest CBA loading, which was associated with thinning of the solid skin layer (measured as 0.844 mm). Impact strength declined with increasing BN content, likely due to particle agglomeration. In contrast, heat deflection temperature (HDT) values exhibited a measurable increase, confirming improved thermal stability. Overall, BN acted as an effective heterogeneous nucleating agent, promoting closed‐cell formation while the CBA content governed pore growth and structural integrity of PP foams.