Polymerization of Composite Materials in Free Space Environment
DEFOORT, B¹; PASQUET, JC¹; LACOUR, DOMINIQUE¹; COQUERET, X²; MILLE, M.²; Langlois, S^3
1Astrium Space Transportation; ²RSA - Université de Reims Champagne Ardenne; ³ESA-ESTEC

The development of original concepts such as inflatable and rigidizable structures for satellite equipments and spatial habitats is driving the need for new in-orbit rigidization technologies. Lightinitiated curing of composite in free space environment appears as one of the most promising processes to turn a foldable, inflatable package into a rigid, load-bearing structure.

Fiber-reinforced composites materials with organic matrices are indeed widely used in space applications and a variety of composites are qualified for in-orbit use. However many design and processing requirements are associated with the curing in free space environment of composites with complex structure. In-orbit polymerization of composite materials can be basically induced by thermal energy or by radiation (UV, visible or ionizing radiation). The curable systems can be accordingly formulated including monomers and prepolymers, hardeners (in the case of thermal curing) and / or initiation packages (photopolymerizable systems, for example). Typical start-point compositions will be presented and discussed from the viewpoints of chemistry and of processing.

The report will focus on the specific constraints of free environment conditions on the polymerization of epoxy resins initiated with visible light, and optional amplification by limited thermal post-curing. The behavior of model formulations will be presented and discussed from the viewpoints of chemistry and of processing. Various photo-initiation packages and resin formulations were tested and compared to enable the multi-criteria selection of promising materials with suitable curing conditions.

The crucial issue of curing will be detailed by presenting various chemical options, including direct or photosensitized cationic polymerisation of epoxy resins. The influence of thermal post-curing will be exemplified by the extensive characterization of epoxy polymer networks cured under well-defined conditions. Kinetic modelling of the initiation with visible light and following polymerization steps will be proposed on the basis of spectroscopic and thermomechanical data. The successful manufacturing and testing of breadboards will substantiate the readiness level and potentiality for industrial application of the materials currently under development. Long shelf life, low out-gassing systems based on proprietary chemistry and processes were shown to be cured with a low energy budget and to yield rigidized materials with satisfactory mechanical properties.