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Study of thermal stability of (3- aminopropyl)trimethoxy silane-modified titanate nanotubes for application as nanofillers in polymers

Titanate nanotubes (TiNT) [1] are a mesoporous TiO2-based nanomaterial extensively studied over the last decade. In comparison to other nanotubular materials, TiNT exhibit some distinct advantages, including the ease with which they can be prepared in high purity and high yield, a low cost, a high specific surface area, a high density of surface OH-groups, and ion-exchange and semiconducting properties [1]. Due to the high density of surface OH-groups (in average, 5.8 OH- groups per nm2 [2]), TiNT are a promising material for surface modifications, particularly with functionalized alkoxysilanes, (RO)3Si−R’X, where R’X denotes an alkyl chain terminating with a functional group X. Depending on the nature of the group X, the physical and chemical properties of the TiNT surface can be varied and a range and the potential field of application of TiNT can be greatly expanded. Titanate nanotubes are a promising nanofiller for polymer composite materials. Their modulus is comparable to that of carbon nanotubes, they can be produced in large quantities, and the chemistry of their surface modification is the same as for conventional inorganic fillers. In this work [3], chemically modified TiNTs were studied. The aim was to prepare TiNT-H surface-modified with (3- aminopropyl)trimethoxy silane (APTMS) that can be further used for strengthening of polymers. Usage of prepared nanotubes for polymer reinforcement was also studied. Protonated titanate nanotubes (TiNT-H) were surface-modified with APTMS by novel method suitable for syntheses of large amounts of materials with low costs. Transmission electron microscopy was used for the investigation of the prepared nanotubes, while the polymer nanocomposite were examined by scanning electron microscopy (SEM) measuremets working in STEM mode. Since the thermal stability of nanofiller was important to preserve their functional properties, stability was studied by in situ high temperature Raman spectroscopy before inbuilt in polymer. The most temperature stable sample, 20 min silanized nanotubes, was used for preparation of epoxy-based nanocomposites (Fig. 1 a). All the APTMS modified titanate nanotubes were bond well with the epoxy matrix (Fig. 1 b) since amine groups on the TiNTs surface can react with epoxy group to form covalent bonds between the matrix and the nanofiller. This nanofiller form smaller (few hundreds of nm) and larger (few μm) aggregates in polymer (Figs. 1 c and d), where the amount of aggregates increase with addition of 102 nanofillers. Very small addition (0.19 – 1.52 wt%) of nanotubes significantly increased the glass transition temperature and the modulus in rubbery state of the epoxy based polymer. A smaller amount of added nanofiller provide larger increase in these parameters and therefore better dynamic mechanical properties due to the smaller amount of large aggregates. In this work APTMS modified tianate nanotubes were proved as promising nanofiller in epoxy based nanocomposits. References: 1. H. H. Ou and L. S. Lo Sep. Purif. Technol. 58 (2007) 179-91 2. V. D. Bavykin and C. F. Walsh, Titanate and Titania Nanotubes Synthesis, Properties and Applications, RSC Nanoscience & Nanotechnology Cambridge (2009) 100- 1. 3. M. Plodinec et. al. Nanotechnology 25 (2014) 435601-435614.

titanate nanotubes surface modified by (3-aminopropyl) trimethoxy silane; thermal stability; epoxy-based nanocomposites

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