Sustainable 3D printed composites from recycled ocean plastics and pyrolyzed soy-hulls: Optimization of printing parameters, performance studies and prototypes development

This research work focuses on the utilization of waste ocean plastics with waste agro-industrial pyrolyzed biomass to develop complex shaped value-added prototypes through additive manufacturing. Fused Filament Fabrication (FFF)-based three-dimensional (3D) printing of recycled HDPE/PP blends was challenging due to significant warpage-related problems during printing. Reinforcing these blend plastics with fillers played a significant role in the efficient 3D printing of complex-shaped objects. In this research, a blend of these recycled HDPE (70%) (rHDPE) and recycled PP (30%) (rPP) collected from the ocean shores was reinforced with pyrolyzed soy hulls-based biocarbon (20%) to fabricate filaments employed for developing specimens through injection molding as well as FFF-based 3D printing. The design of experiments (DOE) using Taguchi method was performed to determine the optimized 3D printing parameters to obtain the defect-free printed specimens. The results suggested that the injection-molded samples showed better mechanical properties as compared with 3D printed samples. However, an improvement (34%) in Young's modulus of the 3D printed rHDPE/rPP (70/30) blend was observed in comparison with injection-molded counterparts. The 3D printed rHDPE/rPP/20% Biocarbon composite showed an improvement of ∼11 and ∼15% in Young modulus and flex modulus, respectively as compared to rHDPE/rPP. Combining ocean plastics and agro-industrial wastes could generate value-added products that would contribute to the circular economy approach for sustainable product development for different applications such as prototyping and automotive, while helping to protect ocean marine life. Two prototypes, elliptical gears with shaft and spectacle frame, have also been developed by using sustainable recycled HDPE/PP-based composites.