This study developed compatible polymer composites based on a blend of high-density polyethylene (HDPE) and polypropylene (PP), modified with 1% maleic-anhydride-grafted polypropylene (PP-g-MAH) as a compatibilizer. Five formulations were prepared with HDPE/PP ratios of 100/0, 94/6, 89/11, 84/16, and 79/21, each containing 1 wt% (1% by weight) PP-g-MAH. The blends were comprehensively evaluated through morphological, mechanical, thermal, wettability, and bacteriological analyses to determine their suitability for sanitary water-pipe applications. Among all formulations, composite A2 (89% HDPE/10% PP/1% PP-g-MAH) demonstrated the most balanced and superior performance. It achieved a hardness of approximately 70 Shore D and an impact resistance close to 3.3 kJ/m2, while exhibiting enhanced thermal stability with a decomposition onset near 440 °C. Surface characterization revealed a smooth, homogeneous morphology and increased hydrophobicity, which contributed directly to its improved antibacterial behavior. Notably, A2 showed nearly a 30% reduction in E. coli adhesion compared to the control sample A0, confirming its hygienic advantages in potablewater environments. Overall, the synergistic effect of optimized polymer ratios and effective compatibilization produced a composite with high rigidity, excellent toughness, low thermal expansion, and reduced biofilm formation. These combined properties establish A2 as a highly promising and practical material for the fabrication of durable, thermally stable, and hygienically safe drinking water distribution pipes.
