Preparation of gram quantities of high-quality titanate nanotubes and their composites with polyamide 6

Gram quantities of high-quality titanate nanotubes (Ti-NT) were prepared and melt-mixed with polyamide 6 (PA6), which then exhibited a 35% increase in elastic modulus. Ti-NT with high aspect ratio were prepared by hydrothermal synthesis from TiO2. In the next step, dried Ti-NT nanopowder could be employed in preparation of polymer composites by a standard melt mixing. Impact of various drying procedures (air drying, vacuum drying, freeze-drying) on morphology and structure of Ti-NT was investigated by a number of microscopic, diffraction and thermal methods. FESEM and TEM microscopy proved that the best nanopowder with well-dispersed, non-merged and unbroken single nanotubes resulted from freeze-drying. EDX analysis confirmed that the nanotubes were stable in both alkaline and neutral suspensions. SAED, HRTEM and PXRD showed that drying procedures did not influence the specific Ti-NT crystalline structure. DSC confirmed that Ti-NT were stable at elevated temperatures (260 °C), used during melt mixing. Model system of polymer PA6 containing 5 wt% of freeze-dried Ti-NT exhibited a 35% increase in elastic modulus (in comparison with pure PA6; measured by DMA), which was considerably higher than in the case of analogous composites with commercial TiO2 nanopowder (14%) or micropowder (9%).