Effect of tungsten disulfide (WS2) nanotubes on structural, morphological and mechanical properties of poly(L-lactide) (PLLA) films

Abstract

Poly(L-lactide) (PLLA) is a semicrystalline, biocompatible and biodegradable polymer widely employed in many applications (food packaging, biomedical devices, drug delivery systems). This work deals with nanocomposites of PLLA and tungsten disulfide (WS 2 ) nanotubes (NTs) as a novel material to obtain thinner and stronger bioresorbable vascular scaffolds. We studied the influence of WS 2 NTs on the mechanical properties of PLLA-WS 2 films. Polarized optical microscopy reveals a high degree of orientation of the polymer molecules in stretched films that further increases with a post-stretching annealing treatment. At the same time, X-ray diffraction (XRD) and Raman spectroscopy confirm enhancement of the crystallinity induced by the WS 2 NTs.

Effect of tungsten disulfide nanotubes on crystallization of polylactide under uniaxial deformation and annealing

“…The mechanical properties of solvent cast PLA-WS 2 films measured at room temperature have been recently reported by Shalom et al showing a large increase of elastic modulus (50% for 0.7 wt%), yield strength (about 70% for 0.7 wt%), and elongation (about 70% for 0.5 wt%) with increasing concentration of WS 2 NTs [24]. On the other hand only our previous work [25] reports on the crystallization process induced by stretching PLA-WS 2 films at temperatures above the glass transition of PLA (T g~5 5-65°C) but the effect of the WS 2 concentration on the crystallization of PLA was not analyzed at the time.…”

“…This result indicates, first of all, the presence of chains in conformation 10 3 [36], typical of α and α' forms [39] in the ST0 series; hence some level of crystallization is induced by the stretching process without further annealing. Moreover, the increase of the Raman signal of the 924 cm − 1 band with the nanotube concentration confirms the nucleation activity of WS 2 NTs [21][22][23][24][25] towards the increase of crystallinity of PLA that makes the stretching process more effective. The Raman intensity of the 924 cm − 1 band for the series ST3 and ST10 is higher than the ST0 series and independent on the WS 2 concentration, suggesting that prolonged annealing (above 3 min) does not promote further crystallization.…”

“…Despite these advantages, to the best of our knowledge, only a few studies are reported in literature on PLA-WS 2 nanocomposites, mainly focused on thermal properties of samples obtained by melt-mixing [21][22][23][24][25]. These studies show that WS 2 NTs remarkably influence the kinetics of nucleation and growth of the PLA during the cold crystallization.…”

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

“…In agreement with previous studies, the WS 2 NTs disperse very well within the PLA matrix. 43,48,69,70 Nevertheless, APTES functionalised WS 2 NTs are much more uniformly dispersed as clearly seen from these images suggesting increased surface interaction and compatibility between APTES modified WS 2 NTs and the PLA matrix. Extensive SEM imaging of the composites of PLA and APTES modified WS 2 NTs (Fig.…”

Poly(L-lactic acid) Reinforced with Hydroxyapatite and Tungsten Disulfide Nanotubes

“…It remains to be seen if other specific functionalization processes of the nanotube surface could further improve their interfacial interaction with the matrix and influence the mechanical behavior of the nanocomposite without sacrificing its biocompatibility. In the absence of a specific interaction between the nanotubes and the polymer-HA, their large surface area and aspect ratio (50-100) as well as their mechanical strength (10-22 GPa), large strain (10%) [77], nontoxic nature [21], and their facile dispersion make them ideally suited for reinforcing biodegradable polymers, even if added in minute amounts (~0.2 at%, ~0.6 wt%) [36,78,79]. Beyond this limit the nanotubes start agglomerating and their effectiveness in the polymer matrix is gradually impaired.…”