Biofilaments from recycled high-density polyethylene and rice husks for fused filament fabrication

The benefits of green technology have industrial use of composites reinforced with biofibers garner attention. They are replacing conventional plastics due to their capability to solve environmental issues. Despite this shift in material development, the synthesis of biodegradable biocomposites still poses a challenge due to their wide range of properties. This work focuses on developing biofilaments for fused filament fabrication from recycled high-density polyethylene and rice husk waste in varying proportions to study the effect of their different ratios on the biofilaments. High-density polyethylene though very popular, has not been widely explored in fused filament fabrication due to warping challenges and high thermal shrinkage of printed parts upon solidification. The addition of organic fillers has been proposed as a way to reduce these challenges. Rice husk waste has been used as a filler in polyethylene for conventional processes such as extrusion, injection molding, and pressing but not widely in additive manufacturing. In this study, a particle size of less than 75 μm and the use of a compatibilizer improved its miscibility in the polymer's matrix. The highest composition of the biofilament achieved was 35 % rice husks, 35 % recycled high-density polyethylene, and 30 % compatibilizer, an improvement of the rice husk filler from previous studies. Printability was attained up to a biofilament composition of 40 % recycled high-density polyethylene, 30 % rice husks, and 30 % compatibilizer. The maximum tensile strength, tensile modulus, and maximum tensile strain of this biofilament were 8.53 MPa (standard deviation of 1.32 MPa), 6.6 % (standard deviation of 0.03 %), and 128.56 MPa (standard deviation of 13 MPa), respectively. Though the addition of rice husk filler reduced the tensile strength, there was an improvement in the crystallinity of the biofilament which improved the shrinkage and warpage of the printed part. This work thus demonstrated an improvement in the rice husk content as a filler in biofilaments made from recycled high-density polyethylene with enhanced biodegradability.