Periodic Reporting for period 1 - RED 4 MARS (Rubber & Elastomer Development for MArtian enviRonment applicationS)
Reporting period: 2022-03-01 to 2024-02-29
Imagine a truck-size Mars rover carrying a crew of astronauts and a decent amount of cargo. The weight of such a rover would have to be much higher than the weight of currently used rovers. Also, the rover’s speed needs to be much faster than the current maximum of 0.18 km/h. Therefore, such a vehicle will require high-performance tires and a damping system to ensure safe travel on the rocky surface of Mars and reduce vibrations, which might damage sensitive equipment. When a technical application requires both elastic and damping properties the obvious material of choice is rubber because of its unique visco-elastic properties. Tires are not the only ones where rubber elements can be applied. Rubber gaskets are needed for spacesuits and habitat sealing. Electric cables require elastic covers to provide insulation and protection. Finally, rubberized textiles will be needed for the pressurized Mars spacesuit design.
The environment on Mars is much more hostile than on Earth. The temperature ranges from -120°C to 30°C with a daily amplitude reaching 100°C. There is no ozone layer and magnetosphere to protect against UV and particulate radiation, respectively. Also, the pressure on Mars is around 150 times lower than on Earth. Because of this, rubber designed for Mars missions has to exhibit proper environmental resistance and the ability to preserve its performance in the challenging conditions of Mars.
To face these conditions, the RED 4 MARS project aims to develop butadiene (BR) / silicone rubber (VMQ) blends that can preserve viscoelastic properties in a wide range of temperatures. Both rubbers are characterized by the lowest glass transition temperature values from all elastomers, which makes them the most suitable ones to preserve elasticity at low temperatures on Mars. The designed BR/VMQ compounds are free of volatile ingredients to prevent outgassing on Mars and during space travel. Also, simulated radiation aging and low-temperature performance are tested to foresee their long-term behavior on Mars. However, blending BR with VMQ is very challenging because of their thermodynamic incompatibility. Also, the vulcanization of the blends is difficult due to the differences in the chemical structure of both elastomers. Therefore, this project aims to optimize the composition of the BR/VMQ compounds to maximize their performance in the Martian environment.
The main objective of this project is to design a family of rubber materials of high performance withstanding Martian conditions. There are also two secondary objectives: 1. Increased independency from materials transported from Earth and reduced costs by involving local materials in the design; 2. Ensured sustainable use of rubber by high recyclability of the materials.
The environment on Mars is much more hostile than on Earth. The temperature ranges from -120°C to 30°C with a daily amplitude reaching 100°C. There is no ozone layer and magnetosphere to protect against UV and particulate radiation, respectively. Also, the pressure on Mars is around 150 times lower than on Earth. Because of this, rubber designed for Mars missions has to exhibit proper environmental resistance and the ability to preserve its performance in the challenging conditions of Mars.
To face these conditions, the RED 4 MARS project aims to develop butadiene (BR) / silicone rubber (VMQ) blends that can preserve viscoelastic properties in a wide range of temperatures. Both rubbers are characterized by the lowest glass transition temperature values from all elastomers, which makes them the most suitable ones to preserve elasticity at low temperatures on Mars. The designed BR/VMQ compounds are free of volatile ingredients to prevent outgassing on Mars and during space travel. Also, simulated radiation aging and low-temperature performance are tested to foresee their long-term behavior on Mars. However, blending BR with VMQ is very challenging because of their thermodynamic incompatibility. Also, the vulcanization of the blends is difficult due to the differences in the chemical structure of both elastomers. Therefore, this project aims to optimize the composition of the BR/VMQ compounds to maximize their performance in the Martian environment.
The main objective of this project is to design a family of rubber materials of high performance withstanding Martian conditions. There are also two secondary objectives: 1. Increased independency from materials transported from Earth and reduced costs by involving local materials in the design; 2. Ensured sustainable use of rubber by high recyclability of the materials.
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.
♦ 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.
As a result of the conducted research a significant innovation in developing immiscible silicone-organic rubber blends was achieved. These are non-conventional polymer composites not available on the market, which exhibit unique properties providing very good dynamic mechanical properties combined with elasticity at very low temperatures. These blends could replace currently used materials in low-temperature applications leading to a longer lifetime of the elements made of them, which could result in lowering energy consumption, waste production and microplastics generation. The experimental results obtained within this project could also lead to establishing standards for Mars rubber properties, and their testing.