Effect of POSS on morphology and mechanical properties of polyamide 12/montmorillonite nanocomposites

Sodium-montmorillonite (MMT) was modified with two types of AP-POSS and OA-POSS and dual-surfactants (POSS with a ditallow-based second surfactant: 04AP-POSS/08DTDMA and 04OA-POSS/08DTDMA), respectively, via ion-exchange reaction. The interlayer space, interlamellar structure, thermal and surface properties of these organo-montmorillonites were investigated by X-ray diffraction, thermogravimetric analysis, and contact angle measurement. The interlayer space of POSS modified clay was strongly dependent on the arrangement of POSS surfactants, but less on the POSS concentration. The POSS modified montmorillonites have partially exchanged silicate surfaces and good thermal stabilities due to steric hindering and thermal stability of the POSS molecules. Dual-surfactant modified montmorillonites showed higher exchange ratio and possessed better compatibility with PA12 due to the lower interfacial free energy. Polyamide 12-montmorillonite nanocomposites were prepared by conventional melt compounding with the four POSS based organo-montmorillonites. The best dispersion of modified montmorillonite was observed for 3 mass% 04AP-POSS/08DTDMA/MMT filled PA12 nanocomposites, which resulted in the best mechanical performance with an increase of 60% in tensile modulus and 10% in yield strength, respectively, compared to that of pure PA12. Compatibility between montmorillonites and polymer was not the only key factor affecting dispersion, thermal stability and interlayer space were also crucial for good dispersion of montmorillonites in polymer matrix.