Circular bio-filled composites for additive manufacturing: reinforcing photopolymer resin with walnut shell particles via digital light processing

Purpose This study aims to investigate the development of sustainable composites reinforced with walnut shell particles for additive manufacturing applications. The primary goal is to evaluate the influence of different walnut shell concentrations on the mechanical properties, including tensile strength, flexural strength and hardness. Design/methodology/approach Composites were fabricated using a Digital Light Processing (DLP) system. Mechanical characterization was performed through Shore-D hardness, tensile and three-point bending tests, while Fourier Transform Infrared Spectroscopy, X-ray Diffraction and Scanning Electron Microscopy were used to examine structural, thermal and morphological characteristics. Findings The incorporation of walnut shell particles enhanced the mechanical performance of the matrix, with the optimal reinforcement observed at 1.0 Wt.% walnut shell content. At higher concentrations (1.5 Wt.% and 2.0 Wt.%), particle agglomeration and poor dispersion led to reduced mechanical performance. The Shore-D hardness increased progressively with reinforcement content, indicating improved surface rigidity. Originality/value This research highlights the potential of walnut shells, an eco-friendly agricultural by-product, as a sustainable reinforcement material for composites. The use of DLP as an additive manufacturing technique provides a precise and resource-efficient method for composite production, aligning with global efforts toward sustainable and environmentally responsible manufacturing practices.