The work carried out during the reporting period towards the achievement of the main objective “to design a family of rubber materials of high performance withstanding Martian conditions” is as follows:
♦ Investigation and improvement of radiation resistance of the rubbers constituting the main polymer phase was performed. In general, the radiation resistance of both rubbers is relatively good considering the ionizing radiation levels on Mars. The β and γ accelerated radiation aging test results showed that the mechanical properties and structural integrity of the unfilled raw rubbers after 50 thousand years would change maximally by 30% and 15%, respectively. However, the addition of mineral fillers can reduce these values down to maximally 9% and 5%, respectively.
♦ To improve the homogeneity of the immiscible butadiene and silicone rubber blends the following approaches were investigated:
1. Application of silicone rubber grades with grafted vinyl groups, which can co-vulcanize during sulfur-based curing of the blends.
2. Application of reinforcing fillers based on different Carbon Blacks (CBs) to improve the physical mixing effectiveness of the thermodynamically immiscible BR/VMQ blends.
♦ Improvement of mechanical and dynamic performance of the BR/VMQ blends. This was done by incorporation of different reinforcing fillers. The mechanical and micromorphological tests revealed that CB are the best reinforcing fillers providing improvement in tensile strength and elongation at break. The good reinforcing performance of CBs stems from their good dispersion in BR/VMQ matrix and good interfacial interaction with both rubber types.
♦ Depending on the chemical structure of BR macromolecules, BR can exhibit crystallization at around -60°C and melting at around -20°C, which are both within the daily Mars temperature range. The presence of a crystalline phase affects the thermal expansion coefficient of rubber compounds. The higher thermal shrinkage occurring with the crystallization can negatively affect the sealing performance of rubber gaskets used on Mars. Therefore the use of fully amorphous BR grades is preferred. However, the glass transition temperature of fully amorphous BRs is higher, which limits their low-temperature applications.
♦ Application of oligomeric rubbers as volatile oils replacement in BR/VMQ blends for Mars. The transportation of rubber to Mars through the vacuum of space and operation in much lower pressure of Mars’ atmosphere necessitates using non-volatile components in the BR/VMQ blend formulations. One of the main ingredients commonly used in rubber formulations are oils. Unfortunately, due to their volatile nature oils cannot be used in Mars rubber formulations. To find a suitable replacement, oligomeric BR were tested. Oligomers, due to their polymeric nature are not volatile but exhibit much lower viscosity than high-molecular rubbers. Based on the results, it can be noted that the oligomeric BR is a very effective oil replacement in the BR/VMQ formulations due to large plasticizing effect and perfect compatibility with the high-molecular BR. Also, the homogeneity of the blends was improved judging by improvement in the mechanical properties repeatability.
The work carried out during the reporting period towards the achievement of the secondary objective “Increased independency from materials transported from Earth and reduced costs by involving local materials (In-Situ Resource Utilization (ISRU)) in the design ” is as follows:
♦ Investigation on potential silica extraction from Mars soil using sodium hydroxide treatment of Mars regolith simulant revealed that the amount of extracted silica is nearly linearly proportional to sodium hydroxide concentration. The extraction performed resulted in a significant yield of 59.3% of silica. The purity of the obtained silica reached 93.67 % and the structural similarity to synthetic silica was confirmed by infrared spectroscopy.
