Studies on characterization and cryogenic mechanical properties of polyimide-layered silicate nanocomposite films

Polyimide/layered silicate nanocomposites were prepared via in situ polymerization process from PMDA-ODA and organo-MMT in a solution of N,N-dimethylacetamide. XRD, FTIR, UV-vis analyses showed that at the content of 1 wt% MMT, MMT were well intercalated, exfoliated and dispersed in polyimide matrix. As the MMT content is more than 3 wt%, MMT agglomerates became severe as shown by the transparency and transmittance of the hybrid films. The cryogenic mechanical properties of the films at 77 K were studied and compared with those at room temperature. The cryogenic tensile strength showed the highest value at 1 wt% MMT content, and its strength, modulus and elongation at break were simultaneously increased than the pure PI film. The cryogenic elastic modulus exhibited an increasing trend until the MMT content reached 10 wt%. The cryogenic failure strain of hybrid films with 1-3 wt% MMT contents was greater than 10%, showing good ductility at 77 K. The tensile strength and modulus of the hybrid films at 77 K were generally higher than those at room temperature except at 20 wt% MMT for the strength.