WS₂ Nanotubes as a 1D Functional Filler for Melt Mixing with Poly(lactic acid):Implications for Composites Manufacture

Abstract

Multi-walled WS 2 nanotubes (NTs) with lengths ranging from 2 to 65 μm and widths from 50 to 110 nm were synthesized in a horizontal quartz-made reactor by a process yielding NTs with aspect ratios (ARs) between ∼40 and >1000. The NTs obtained were thermally stable in air up to 400 °C but were oxidized within the temperature range 400−550 °C to produce yellow WO 3 particles. Critically, 400 °C is well above the temperature used to mix additives with the majority of meltprocessable polymers. The hydrophilic WS 2 NTs were easily dispersed in poly(lactic) acid (PLA) using a twin-screw extruder, but the shear stresses applied during melt mixing resulted in chopping of the NTs such that the AR decreased by >95% and the tensile mechanical properties of the PLA were unchanged. Although the as-extruded unfilled PLA was >99% amorphous, the much-shortened WS 2 NTs had a significant effect on the crystallization behavior of PLA, inducing heterogeneous nucleation, increasing the crystallization temperature (T c ) by ∼3 °C and the crystalline content by 15%, and significantly increasing the rate of PLA crystallization, producing smaller and more densely packed spherulites. The reduction in the AR and the nucleating effect of WS 2 NTs for PLA are critical considerations in the preparation, by melt mixing, of composites of rigid 1D NTs and polymers, irrespective of the target application, including bone tissue engineering and bioresorbable vascular scaffolds.

Silane functionalization of WS2 nanotubes for interaction with poly(lactic acid)

“…S1†) and the relevant atomic percentages are listed in Table 2. The atomic percentages are in agreement with our previous studies 64 confirming successful grafting of silane through carbon and oxygen. Both are loosely attached to the surface of the NTs due to atmospheric conditions, while Si and N are also detected for the WS 2 NTs : APTES samples.…”

“…Figures S1) and the relevant atomic percentages are listed in Table2. For neat WS 2 NTs the atomic percentages are in agreement with our previous studies[64] confirming successful grafting of silane…”

“…3 We reported the structure and morphology of the WS 2 NTs in great detail in our previous work. 64 From high resolution STEM images, (Fig. 5(d) and (e)), the APTES is seen to clearly coat the surface of the WS 2 NTs, an observation confirmed from EDS mapping.…”

“…d)), with lengths as small as 0.64µm observed, most likley due to the sonication process during sample preparation [3]. We reported the structure and morphology of the WS 2 NTs in great detail in our previous work [64]. From high resolution STEM images, (Figure 5.…”

Polyelectrolyte Complexation of Chitosan and WS2 Nanotubes

“…Additionally, WS 2 NTs have been shown to be nontoxic and biocompatible. [33][34][35] WS 2 NTs have been studied as a functional filler when added to certain biodegradable polymers including, poly(hydroxyalkanoate)s (PHAs), [36,37] poly(ethylene succinate) (PES), [38] poly(propylene fumarate) (PPF), [39] and poly(lactic acid) (PLA), [40][41][42][43][44][45] as well as for application in vascular bioresorbable scaffolds (VBS). [46,47] WS 2 NTs have been clearly shown to readily disperse in these biopolymers as well as enhance the thermal and mechanical properties of the polymer matrix.…”