Silane functionalization of WS 2 nanotubes for interaction with poly(lactic acid).

Functionalisation of nanofillers is required for the promotion of strong interfacial interactions with polymers and is essential as a route for the preparation of (nano)composites with superior mechanical properties. Tungsten disulphide nanotubes (WS 2 NTs) were functionalized using (3-aminopropyl) triethoxysilane (APTES) for preparation of composites with poly(lactic acid) (PLA). The WS 2  NTs : APTES ratios used were 1 : 1, 1 : 2 and 1 : 4 WS 2 NTs : APTES. The APTES formed siloxane networks bound to the NTs via surface oxygen and carbon moieties adsorbed on the WS 2 NTs surface, detected by X-ray photoelectron spectroscopy (XPS) studies and chemical mapping using energy dispersive X-ray spectroscopy in the scanning transmission electron microscope (STEM-EDS). The successful silane modification of the WS 2 NTs was clearly evident with both significant peak shifting by as much as 60 cm -1 for Si-O-Si vibrations (FTIR) and peak broadening of the A 1g band in the Raman spectra of the WS 2 NTs. The evolution of new bands was also observed and are associated with Si-CH 2 -CH 2 and, symmetric and assymetric -NH 3+ deformation modes (FTIR). Further evidence for functionalization was obtained from zeta potential measurements as there was a change in surface charge from negative for pure WS 2 NTs to positive for APTES modified WS 2 NTs. Additionally, the thermal stability of APTES was shifted to much higher temperatures as it was bound to the WS 2 NTs. The APTES modified WS 2 NTs were organophilic and readily dispersed in PLA, while presence of the pendant amine and hydroxyl groups resulted in strong interfacial interactions with the polymer matrix. The inclusion of as little as 0.5 wt% WS 2 NTs modified with 2.0 wt% APTES resulted in an increase of 600% in both the elongation at break (a measure of ductility) and the tensile toughness relative to neat PLA, without impacting the stiffness or strength of the polymer.