Low Creep/Low Relaxation Polymer Composites, Year 2

The goal of this research is to develop novel low-creep and low-stress-relaxation polymer composites for inflatable and deployable space structures like solar sails, solar arrays, antennas, payload booms, Mars/Moon habitats and planetary decelerators. To do this, we a) select rigid monomer structures, b) control cross-linking density, c) add second phase components and d) create strong interfaces between polymer molecules and reinforcements. Candidate resin formulations designed during the 1st year effort. The new polymer composite will provide high reliability to deployable and inflatable space structures. 

Innovativeness: 

Our approach to developing a novel low creep and low stress relaxation polymer composites for inflatable and deployable space structures includes: (1) Designing new, stiff molecular structures containing aromatic rings that can only rotate around their bond axes. With these structures, bond torsions do not lead to changes in the chain configuration. In the 1st year, it was confirmed that a polyimide resin with a rigid molecular structure showed about 20% less stress relaxation than an epoxy resin. An even more rigid polymer structure can be synthesized from monomers such as 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 1,4-phenylenediamine (PDA) and 9,9-bis(4-aminophenyl)fluorene (BAFL). A polyimide with a rigid backbone also offers an inherently low coefficient of thermal expansion (CTE). (2) Using reactive functional groups to add crosslinks while keeping a good balance between restriction of molecular rearrangement and material brittleness. Candidate monomers with reactive functional groups are diphenyl methane diisocyanate (MDI), 4,4'-diamino-3,3'-dihydroxybenzidine (HAB) and 1,3'-diaminobenzoic acid (DAB). (3) Adding second-phase components to restrict large scale rearrangements of polymer molecules. One candidate second phase is sol-gel derived sub-nano-sized silica. Silica can be chemically bonded to isocyanate groups on the polyimide via hydroxyl or amine groups. Bonded or physically adsorbed chains are restricted from sliding past one another. During the 1st year, it was confirmed that fumed silica particles (5%) or epoxy-based fortifiers (35 phr) reduced stress relaxation by about 20% in an epoxy resin. (4) Securing strong interfaces between reinforcing fibers and the polymer matrix by chemical bonding to prevent slippage under load. The temperature-dependent creep and stress relaxation properties of the developed material will be characterized to predict lifetime creep behavior of the system.

Impact:

The successful completion of the proposed research will provide an improvement in creep/relaxation by a factor of 5 compared to state-of-the-art carbon-fiber-reinforced polymer composites. The latter would creep ~10% during 5 years' storage at 30\xb0C [2]. The new materials will benefit various NASA missions by offering low creep/low stress relaxation in composites for deployable and inflatable space structures such as deployable booms for solar sail and drag sail deorbiting systems, lightweight solar arrays and antennas for satellites and spacecraft, lightweight planetary decelerators for human and robotic exploration, and lightweight inflatable habitats for long-duration human exploration. In addition, this technology can be used in a range of terrestrial applications in the aeronautics industry, automobile industry, and civil engineering. 

Alignment with the Agency/Center/Product Line strategies (Langley STIP Topic):

The proposed research supports In Space Autonomous Assembly and Operations by providing novel low creep low relaxation polymer composite deployable structures. In addition, this project provides guidelines for the fabrication of dimensionally-stable deployable habitats for radiation shielding to support Safe Human Travel Beyond Low Earth Orbit (LEO)

References

[1] J. S. Dai et al. (eds.), Advances in Reconfigurable Mechanisms and Robots I, Springer-Verlag, London, 2012.

[2] W.K. Goertzen et al., Materials Science and Engineering A, 421, 217 (2006).

[3] F. Daver, et al., Polymers, 8, 437 (2016).

[4] x. Hao, et al., Composites Part B, 89, 44 (2016).

[5] S.-S. Michardi\xe8re et al., The Journal of Physical Chemistry C, 120, 6851 (2016).