Synergistic effects of micro- and macro-sized palm kernel shell fillers on the tensile properties of HDPE composites

In this study, high-density polyethylene (HDPE) composites reinforced with palm kernel shell (PKS) fillers with mixed particle sizes were prepared using melt-extrusion compounding. A 5-ton hydraulic hot-press machine was employed to fabricate samples for tensile testing, with a focus on understanding the influence of varying filler sizes on the mechanical properties of the HDPE/PKS composite. The 30 wt% PKS composites demonstrated an elastic modulus (E) of 1.08GPa, ultimate tensile strength (UTS) at 14.13MPa, yield strength at 8.6MPa, stress at failure 12.87MPa, and elongation at failure 5.16%. However, the incorporation of larger PKS particles (PKSL) had a detrimental effect on the tensile properties, with increasing PKSL content leading to significant reductions in tensile properties. For example, for 7.5 wt% PKSL, E decreased by approximately 18%, yield strength by 37%, UTS by 24%, stress at failure by 29%, and total elongation by 62%. Similar trends were observed for the composites containing 15 wt% and 22.5 wt% PKSL. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to assess the melting temperature ranges and thermal stability of the composites, respectively. Scanning electron microscopy (SEM) provided insights into the failure mechanisms, revealing weak filler-matrix interfacial bonding with larger particles, resulting in debonding and ultimately compromising the tensile properties of the composite.