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Purpose Powder bed additive manufacturing processes are widespread due to their many technical and economic advantages. Nevertheless, the disposal of leftover powder poses a problem in terms of process sustainability. The purpose of this paper is to provide an alternative solution to recycle waste PA12 powder from HP multi jet fusion. In particular, the opportunity to use this material as a dispersion in three-dimensional (3D) printed clay is investigated. Design/methodology/approach A commercial fused deposition modelling printer was re-adapted to extrude a viscous paste composed of clay, PA12 and water. Once printed, parts were dried and then put in an oven to melt the polymer fraction. Four compositions with different PA12 concentration were studied. First, the extrudability of the paste was observed by testing different extrusion lengths. Then, the surface porosities were evaluated through microscopical observations of the manufactured parts. Finally, benchmarks with different geometries were digitalised via 3D scanning to analyse the dimensional alterations arising at each stage of the process. Findings Overall, the feasibility of the process is demonstrated. Extrusion tests revealed that the composition of the paste has a minor influence on the volumetric flow rate, exhibiting a better consistency in the case of long extrusions. The percentage of surface cavities was proportional to the polymer fraction contained in the mix. From dimensional analyses, it was possible to conclude that PA12 reduced the degree of shrinkage during the drying phase, while it increased dimensional alterations occurring in the melting phase. The results showed that the dimensional error measured on the z-axis was always higher than that of the XY plane. Practical implications The method proposed in this paper provides an alternative approach to reuse leftover powders from powder bed fusion processes via another additive manufacturing process. This offers an affordable and open-source solution to companies dealing with polymer powder bed fusion, allowing them to reduce their environmental impacts while expanding their production. Originality/value The paper presents an innovative additive manufacturing solution for powder reuse. Unlike the recycling methods in the body of literature, this solution does not require any intermediate transformation process, such as filament fabrication. Also, the cold material deposition enables the adoption of very inexpensive extrusion equipment. This preliminary study demonstrates the feasibility and the benefits of this process, paving the way for numerous future studies.

The adoption of natural‐based fibers in place of inorganic reinforcements is an effective approach to reduce the environmental and economic impact of composite materials. In particular, hemp is an attractive solution due to its mechanical, physical, and growing properties. The present article deals with the manufacturing of thermoset hemp‐reinforced composite materials. In particular, the investigation moves into the production by resin transfer molding and by resin powder molding with the use of epoxy polymeric material. To describe the effects of the technological cycle onto the characteristic of realized products, different manufacturing parameters have been combined during the braiding of reinforcement and the polymerization of the final composite. Computed tomography, microscopical analysis, and tensile tests have been used to observe the main effects of the manufacturing process and mechanical properties of the materials. Furthermore, elastic moduli of the materials have been estimated by means of modified rule of mixture and Halpin‐Tsai models in order to verify their effectiveness in forecasting stiffness of the hemp‐reinforced composites in the early design phase. The article extends the existing knowledge base on hemp‐reinforced thermoset composites manufactured with different processes. Results also illustrate relations existing between error introduced by calculation models and the intrinsic variability in mechanical properties.

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