Sustainable and environmentally friendly composites: Development of walnut shell powder-reinforced polypropylene composites for potential automotive applications

Abstract

Abstract In order to lessen carbon emissions, preserve natural resources, and enhance the planet’s sustainability for future generations, environmentally friendly and sustainable composites offer a promising solution that combines technological innovation and environmental responsibility. Therefore, the current study focused on the development of walnut shell (WS) powder as a natural reinforcing additive for polypropylene (PP) composites as sustainable materials for potential automotive applications. Different particle sizes (150, 212, and 300) μm and particle content (10, 20, 30, and 40 wt%) of WS-reinforced PP composites were investigated. This investigation involved two strategies: The first strategy was to determine the best WS size and loading in the PP matrix. The second strategy involved the development of additives by applying dual treatment methods on the WS: alkaline and microwave as chemical and physical treatment at the same time. Under fixation microwave conditions, different NaOH concentrations of 3, 5, and 7% were applied. The extrusion and hot compression processes at fixed operating conditions were used to combine all dosages of WS/PP composites. The mechanical properties of tensile, flexural, and impact for all the composite dosages for the strategies were studied according to ASTM standards D638, D790, and D256, respectively. To confirm the mechanical properties, the influence of treatment techniques on the WS powder and WS/PP composites was also investigated using physicochemical characterization Fourier transform infrared spectroscopy, scanning electron microscope, and X-ray diffraction. Furthermore, the best WS/PP composite was compared with the real automotive part (automobile steering airbag cover [ASAC]) to confirm the mechanical properties of the new WS/PP composites. The results showed that the first strategy obtained a 212 μm, 20 wt% composites that achieved the highest tensile strength, which increased about 1.2 times the tensile strength of the PP matrix. The second strategy showed composite that had treated WS with 7% NaOH (WS7Comp) attained the best mechanical properties throughout other WS/PP composites. In addition, the mechanical properties of the new WS/PP composites were adjusted to the ASAC mechanical properties. Therefore, the improved composites could be a promising alternative material for automotive applications.