Surface modification of nano-silica by diisocyanates and their application in polyimide matrix for enhanced mechanical, thermal and water proof properties

Abstract In this study, 4,4′-methylene diphenyl diisocyanate (MDI) was used as a functionalizing agent to chemically grafting amino-functional groups on the nano-silica surfaces to achieve amino functionalized silica (SiO 2 -NH 2 ) nanoparticles. In situ polymerization technique was employed to fabricate PI/SiO 2 -NH 2 nanocomposite films followed by typical thermal imidization process. The mechanical and thermal properties as well as the water resistance of PI/SiO 2 -NH 2 composites were notably improved as compared to those of the original PI and PI/SiO 2 . The composite films shown a meaningful enhancement in both tensile strength and modulus up to 25.0% and 40.2%, respectively up on the addition of 2~10 wt% SiO 2 -NH 2 into the PI system when compared with the pristine PI. Likewise, the 5% and 10% weight loss temperatures were improved up to about 29.8 and 24.5 °C respectively, in comparison with the ones for pristine PI. The composites also exhibited a remarkably increased T g (glass transition temperatures) values up to 19% when 2~10 wt% SiO 2 -NH 2 nanoparticles were added to the matrix. The nanocomposites also demonstrated an astonishing decrease in water intake reaching up to 77% enhancement as the SiO 2 -NH 2 load in the PI medium increased from 0 to 10% implying that the hydrophobic property of the composite films was highly improved. As compared to the pristine silica particles, the SiO 2 -NH 2 nanoparticles showed excellent improvement in key performances of PI.