The HM3D project, funded by the German Federal Ministry of Education and Research under the ProMat KMU‑Innovativ programme (grant number 03XP0292C), ran from 1 August 2020 to 31 January 2023. It was carried out by the Institute for Polymers and Composites at the Technical University Hamburg (TUHH) together with Ludeko GmbH and CompriseTec GmbH, with MBJ Solutions providing additional support in the early phase. The consortium’s goal was to replace conventional thermoplastic filaments used in fused filament fabrication (FFF) with a new, REACH‑compliant hardener‑based material that could be extruded into filament while retaining the ease of use of standard desktop 3D printers. Five main work packages guided the effort: (1) identification of material parameters and demonstrator requirements, (2) formulation of the base material, (3) development of functional filaments, (4) adaptation of the FFF process, and (5) production of an application‑oriented demonstrator part.

Technically, the project succeeded in producing a solid epoxy filament that can be printed at a temperature below 100 °C, a substantial reduction compared with typical thermoplastics such as PLA or ABS, which require 180–260 °C. The filament’s viscosity was tuned to match the extrusion characteristics of commercial thermoplastic filaments, allowing it to be used in standard FFF printers without any hardware modifications. No heated build plate or chamber was necessary, which cuts energy consumption and enables the use of inexpensive printer components. The material’s density was measured at 1.15 g cm⁻³, and it exhibited a tensile strength of at least 58 MPa and a Young’s modulus of 2130 MPa in the 0° direction, meeting the design targets set in the requirement specification. The glass‑transition temperature was above 105 °C, and the heat‑distortion temperature (HDT Type B) exceeded 97 °C, ensuring dimensional stability during use. Surface resistance was below 109 Ω, satisfying electrostatic discharge requirements. Importantly, the filament remained chemically stable and elastically compliant for at least three months when stored at or below room temperature, with a residual reaction enthalpy of 0.9 % or less.

Functionalization was achieved by incorporating short‑walled carbon nanotubes (SW‑CNTs) into the epoxy matrix, providing electrical conductivity and potential for sensor integration. The hardener formulation was designed to be tough and ductile by adding low‑molecular‑weight aliphatic or aromatic additives and a long‑chain hardener or rubber component, thereby mitigating the brittleness typical of cured epoxies. The resulting printed parts displayed isotropic mechanical properties, a significant improvement over the anisotropic behavior of conventional thermoplastic prints caused by inter‑layer bonding issues. A demonstrator part was fabricated that met the application‑specific load and environmental criteria, confirming the material’s suitability for functional components.

The project’s scientific outcomes were disseminated through an open‑access publication titled “Solid epoxy for functional 3D printing with isotropic mechanical properties by material extrusion” by Drücker et al., which detailed the formulation, processing, and mechanical testing. Additional results were reported in the TUHH funding overview and in the project’s success‑control report. The collaboration between academia and industry proved essential: TUHH supplied the polymer chemistry expertise and testing facilities, Ludeko GmbH contributed to the extrusion process development and filament production, and CompriseTec GmbH performed comprehensive material characterization at both filament and part levels. The project’s achievements lay a foundation for future production of functional, isotropic components using inexpensive FFF printers, potentially expanding the market for additive manufacturing beyond prototyping into serial production.