Sustainable manufacturing of 3D-printed polylactic acid parts reinforced with walnut shell/epoxy composites

The mechanical properties of hybrid composites prepared by 3D-printing Polylactic Acid (PLA) injected with a syringe with a compound comprising 35% walnut shells and epoxy resin are evaluated in the current research and aligned with the Sustainable Development Goals (SDGs) attentive to responsible consumption and responsible production (SDG 12) and climate action (SDG 13). The study encourages recycling of agricultural waste in order to enhance sustainability in production. There are nine samples that are formed with different design parameters, such as the printing angle (450, 50, 55, 20), infill density (10, 15, 20), and the number of wall thickness (1, 2, and 3) each wall is 0.4 mm thick. Tensile tests, flexural tests, and impact tests are mechanical tests that are conducted to test the characteristics of the synthesized samples. The results indicate that model (L5 has (angle of print 50°, Infill percentage 15%, and three walls)) attains a maximum tensile strength of 30.9 MPa, which is a 31% reduction compared to the pure PLA. Specifically, this is an improvement of 37% than the epoxy and 35% walnut shell composite. Moreover, the L5 displays an elongation at break of 4.5%. Model L7 (angle of print 55°, Infill percentage 10%, and three walls) achieves a maximum flexural strength of 42.5 MPa and elastic modulus of 2147.6 MPa. This is corresponded to reductions of 24% and a 46% if compared to pure PLA. When the maximum flexural strength is compared to the sample of the walnut and epoxy composite, this increases by almost 73%. Checking the highest impact strength of 5 kJ/m 2 , this is possible in case of model L5, which is a 27% decrease as compared to pure PLA, yet 21% higher than the walnut and epoxy composite. The Taguchi method is employed to make a systematic evaluation of the contribution of each variable. This indicated that the wall thickness is the main factor influencing tensile and flexural strength, while printing angle is the key factor affecting impact test. The multi-criteria decision-making (MCDM) approach is incorporated to weight the relevant mechanical properties. This shows different weight factors of 33% for impact strength, 33% for flexural strength, and 34% for tensile strength. Clearly, model L5 is found to be the optimal model following this analysis, presenting the potential for sustainable manufacturing practices that support SDGs by combining waste materials into high-performance products.