Influence of micro and nano particles on the mechanical, morphological and thermal properties of HDPE/PP blends.

Improving the mechanical performance of high-density polyethylene (HDPE) and polypropylene (PP) blends remains a significant challenge in materials science. Due to their inherent immiscibility and weak interfacial adhesion, these blends require suitable additives to enhance interfacial interaction and improve mechanical properties for practical applications. In this study, a series of HDPE/PP blends with HDPE contents of 25, 50, and 75 wt%, in addition to neat HDPE and PP were examined to determine the optimal base composition. The blend containing 75% HDPE was selected as the optimal composition due to its balanced mechanical performance. This blend was subsequently modified with silica, carbon black, Ethylene propylene diene monomer (EPDM), and their hybrid combinations at 5 wt% to evaluate their effectiveness in enhancing the overall performance of the material. In addition, fumed nano-silica was incorporated at 1, 3, and 5 wt% to examine its influence on the morphological, mechanical and thermal behavior of the blends. Mechanical performance was evaluated using tensile, hardness tests and impact tests, while phase morphology was investigated by scanning electron microscopy (SEM), and thermal behavior was evaluated by thermogravimetric analysis (TGA). The results demonstrate that micro-silica improved yield strength, elongation, and toughness by approximately 17%, 43%, and 72%, respectively, compared with the neat blend, while carbon black mainly enhanced yield strength by 19%. In contrast, EPDM led to an overall reduction in mechanical performance. Nano-silica produced the most significant enhancement, even at low concentrations. At only 1 wt%, nano-silica increased yield strength, elongation and toughness by nearly 11%, 98% and 120%, respectively, whereas the 3 wt% nano-silica formulation achieved the highest overall improvement, with yield strength, elongation and toughness enhanced by 13%, 120% and 150%, respectively. Thermogravimetric analysis revealed that the thermal stability of HDPE/PP blends influenced by both composition and additive type. Nano-silica exhibited the most pronounced stabilizing effect compared to micro-additives. These findings demonstrate that nano-silica is a highly efficient modifier for HDPE/PP blends and provides a practical route for producing high-performance and functional polyolefin materials for engineering and industrial applications.