Evaluation of the physico-mechanical properties of activated-carbon enhanced recycled polyethylene/polypropylene 3D printing filament

In this study, recycled polymer feedstocks (high-density polyethylene, HDPE and polypropylene, PP) were added with different percentages of activated carbon (AC) made from coconut fiber waste – 0, 2, 4, 6, and 8%. The melting temperatures of the recycled HDPE and HDPE/PP filaments were 113 and 170°C, respectively. The addition of AC improved the thermal stability of the recycled filaments up to 28% while decreased the crystallinity of the filament produced, resulting in a more uniform surface with less crazing. Incompatibility of the recycled HDPE and AC was observed. However, the presence of PP greatly enhanced the compatibility of AC with the HDPE polymer. With the addition of 8% AC to the recycled HDPE/PP, the elongation at break of the recycled HDPE/PP filament reached 54.2%, about 10 times higher than that without AC, which could be due to the passive local interfacial bonding of AC with the methyl group of the PP matrix. The improved elongation at break would in turn aid in 3D printing of products with better elasticity.