# Regolith-Rich PEEK Composite Bricks: Steps Towards Space-Ready Lunar Construction Materials
## 1 Introduction
### Organic Phase Selection
Moreover, experimental conditions, such as radiation sources and doses, differ across studies. For consistency, this paper compares the properties of the materials in their original state with those measured after exposure to a standardized dose of 1 MGy, if available. A study on high-performance plastics [35] demonstrated that both PEEK and PEI exhibit exceptional radiation resistance. PEI maintained its mechanical properties after a 1 MGy dose. Similarly, PEEK showed no significant degradation up to 5 MGy. Further confirmation of the stability of PEEK up to 8 MGy was provided in [36], along with that of PPS, which retained its tensile strength even after irradiation. Polyimides also display excellent radiation resistance as demonstrated by studies on Kapton [37] and AURUM [38], which showed no loss of tensile strength up to doses of 12 MGy. In contrast, PTFE is highly sensitive to radiation, with its mechanical properties deteriorating rapidly at relatively low doses [39; 40]. No tensile strength data were available for PTFE at the 1 MGy level due to its fast degradation. However, the literature reports a significant reduction in tensile strength to 10.3 MPa after exposure to a dose of just 12 kGy [41]. To enhance the understanding of their performance across various criteria, Table 1 summarizes the properties discussed. When considering the full spectrum of temperature performance, PEEK exhibits the most favorable properties overall, alongside TPI. With PEEK, its slightly lower melting point, glass transition temperature, and TML further enhance its suitability. While TPI demonstrates superior tensile properties at elevated temperatures, these benefits appear to be achieved through commercial grades specifically formulated for such conditions. Furthermore, PEEK is already extensively used in extreme environments [42; 43]. In the aerospace industry, PEEK plays a crucial role in high-performance components such as seals, gaskets, and insulation for jet engines and rocket propulsion systems, where it withstands extreme temperatures and mechanical stress. The material's resistance to radiation and its stability in a vacuum make it indispensable in space exploration, being used in components for satellites, spacecraft, and lunar rovers. In the oil and gas sector [44], PEEK is found in seals, bearings, and valve seats for drilling equipment operating in deep-sea environments and at high temperatures, often above 250 \({}^{\circ}\)C, where it resists exposure to corrosive chemicals and intense pressures. Additionally, PEEK is used in applications involving intense thermal cycling, such as in high-performance electronics and military-grade equipment. Beyond these considerations, it is worth mentioning that polymers are generally susceptible to photodegradation when exposed to UV radiation, which can result in material deterioration [57]. To enhance UV resistance, UV screeners are often used. [PERSON] et al. [58] demonstrated that incorporating TiO\({}_{2}\) particles into PEEK slows and confines photodegradation to the material's external surface. Notably, TiO\({}_{2}\) is naturally abundant in lunar regolith, constituting approximately 10% of its composition in weight [59]. Furthermore,