Synergistic Effects on the Mechanical, Thermal, and Morphological Properties of <scp>HDPE</scp> Composites Reinforced With Walnut Shell and Nano‐Calcium Carbonate

Abstract

ABSTRACT In this study, the thermal, mechanical, and morphological properties of high‐density polyethylene composites reinforced with wal1nut shell and nano‐CaCO 3 were investigated. Composites with a fixed walnut shell content (20%) and varying nano‐CaCO 3 concentrations (1%, 3%, and 5%) were prepared by extrusion and injection molding. The results showed that increasing filler content raised crystallization temperatures, while melting temperatures (T m ) slightly decreased, and crystallinity was lower compared to pure HDPE. The lowest T m (128.2°C) and crystallinity (27.3%) were found in the PECCWS4 and PECCWS5 composites. Thermogravimetric analysis (TGA) revealed that the initial degradation temperature (T 5 ) increased from 452°C to 457.8°C, and the temperature for 50% weight loss (T 50 ) shifted from 481.8°C to 486.5°C. Residual weight at 600°C increased from 1.1% for PECCWS1 to 9.5% for PECCWS5, indicating improved char formation. Scanning Electron Microscopy and Transmission Electron Microscopy showed improved filler distribution and enhanced filler‐matrix interaction. The combination of walnut shell and nano‐CaCO 3 improved certain mechanical properties such as tensile strength and modulus; however, elongation at break decreased in tensile testing, indicating reduced ductility. These findings highlight the synergistic effect of walnut shell and nano‐CaCO 3 in enhancing HDPE composites' thermal and mechanical properties, showing potential for improved performance.