The increase in HDPE (High Density Polyethylene) and PP (Polypropylene) plastic waste encourages the reuse of these materials into products with functional value. This study aims to analyze the effect of variations in the composition of HDPE, PP, and coconut shell powder on the mechanical properties and macrostructure of composites produced using the hot press method at a temperature of 160°C and a pressure of 20 bar. The composition variations were determined using the Design of Experiment (DOE) method, which resulted in 13 mixture combinations. Characterization was conducted through tensile testing based on the ASTM D638 Type IV standard, Shore D hardness testing, and macrostructure observation using a stereo microscope. The results showed that material composition affected the characteristics of the resulting composite. The highest tensile strength of 12.22 MPa was obtained at a composition of 60% HDPE, 30% PP, and 10% coconut shell powder, while the lowest value of 5.78 MPa was obtained at a composition of 50% HDPE, 40% PP, and 10% coconut shell powder. Macrostructure observation showed that uniform filler distribution and good interfacial bonding contributed to the improvement of the mechanical properties of the composite. The results showed that the composition of the material mixture is an important factor in determining the quality of waste plastic-based composites.

Keywords: HDPE, PP, coconut shell powder, composite, tensile test, macrostructure.