# Regolith-Rich PEEK Composite Bricks: Steps Towards Space-Ready Lunar Construction Materials
## 2 The Manufacturing Process and Parameter Refinement  
The manufacturing process builds on the methodology validated in [5], where PLA was used as a binder and EAC-1a as a lunar regolith simulant. EAC-1a is the lunar regolith simulant currently in use at the European Astronaut Centre. While it shares several physical and chemical similarities with lunar regolith, as with all simulants, it exhibits distinctions that, in principle, may influence its applicability. Detailed analyses of its grain size distribution and chemical composition are provided in [60]. The EAC-1a particle size distribution falls within the upper and lower boundaries observed in Apollo lunar regolith samples, although it exhibits a higher median grain size. Its particles display a variety of shapes similar to lunar regolith but lack the extreme angularity and features caused by space weathering, which might lead to differences in cohesion and compaction behavior. From a chemical standpoint, major mineralogical components are shared between EAC-1a and lunar regolith samples, but the simulant contains higher levels of alkali components (K\({}_{2}\)O and Na\({}_{2}\)O), feldsparheads, quartz, and chlorite, rare or absent in actual samples. These components, particularly the crystalline water in chlorite, could influence specific processes such as sintering and oxygen extraction. Additionally, EAC-1a features ilmenite in its oxidized state and lacks the reduced ilmenite and nanophase iron typical of lunar regolith, potentially impacting its magnetic properties. Despite these differences, the authors expect EAC-1a to perform effectively in particle binding processes, as the binder acts as the primary adhesive, while the simulant primarily serves as an inert filler. Transitioning to a PEEK-based process requires refining several processing parameters, leveraging insights gained from the PLA-based process to focus on key factors. The core phases of the process and their respective refinements are detailed below; in addition, Figure 2 highlights the differences in the manufacturing steps between PEEK- and PLA-based samples. Drying : Both the regolith simulant and the binder are dried to remove moisture. For PEEK, drying is performed at 80 \({}^{\circ}\)C for 12 h, and for EAC-1a at 250 \({}^{\circ}\)C for 2 h, using a Memmert UN30 universal oven. Sieving: The regolith simulant is sieved to ensure that only particles within a specific size range are included in the process. The previous study demonstrated that a heterogeneous particle size distribution enhances the mechanical properties of the parts, especially when all particles are below 500 \(\upmu\)m. Consequently, this threshold is set during sieving, performed using a Nexopart EML 200 sieve machine. Mixing and Mold Filling: The dried regolith simulant and binder are mixed in the desired weight percentage (wt%) for a few minutes before being transferred into a metallic mold for shaping. Figure 2: Manufacturing steps for PEEK- and PLA-based samples: The blue boxes indicate the process parameters specific to PLA, highlighting where they differ from those used for PEEK. Compaction: The mixture within the mold is compacted using a press at the specified pressure level. Depending on the sample size and compaction pressure, the mixture is compacted using either a toggle press with a 2 kN load sensor or a 10-ton Unicraft WPP 10 hydraulic press. Curing: The compacted green body undergoes heating to a temperature above the melting point of the binder. PLA-based samples show no significant differences within a narrow range above its melting point. For PEEK, curing is conducted at 400 \({}^{\circ}\)C using a Carbolite Gero STF 15/450 tube furnace. A preliminary study shows no significant variation in the material properties at higher temperatures, though shorter curing times are achievable. Both air and vacuum curing are examined, with a uniform curing time of 3 h chosen for consistency. For vacuum curing, an Edwards RV3 vacuum pump is used to maintain pressures of 0.17-0.23 mbar.