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

Abstract

Tungsten disulfide (WS2) nanotubes (NTs) are examined here as a filler for polylactide (PLA) for their ability to accelerate PLA crystallization and for their promising biocompatibility in relevant to biomedical applications of PLA-WS2 nanocomposites. In this work, we have studied the structural and thermal properties of PLA-WS2 nanocomposite films varying the concentration of WS2 NTs from 0 (neat PLA) to 0.6 wt%. The films were uniaxially drawn at 90 °C and annealed at the same temperature for 3 and 10 min. Using wide angle x-ray scattering, Raman spectroscopy and differential scanning calorimetry, we probed the effects of WS2 NT addition on the structure of the PLA films at various stages of processing (unstretched, stretching, annealing). We found that 0.6 wt% of WS2 induces the same level of crystallinity in as stretched PLA-WS2 as annealing in neat PLA for 10 min. These data provide useful insights into the role of WS2 NTs on the structural evolution of PLA-WS2 composites under uniaxial deformation, and extend their applicability to situations where fine tuning of PLA crystallinity is desirable.

Interaction of Poly L-Lactide and Tungsten Disulfide Nanotubes Studied by In Situ X-ray Scattering during Expansion of PLLA/WS2NT Nanocomposite Tubes

“…neat PLLA to PLLA/WS 2 NT, Figure 7 , second column, solid orange curves). This difference in crystallization clearly reveals that WS 2 NTs promote the nucleation of PLLA crystals, as reported in both quiescent [ 57 ] and flow-induced crystallizations [ 60 ]. When T ann is increased from 60 °C to 70 and 80 °C (corresponding to an increase in the tube temperature from ~70 °C to ~85 and 100 °C based on the calibration curves in Figure S4 ), the rate of neat PLLA crystallization increases by an order of magnitude [ 64 ].…”

“…In addition to the effect of WS 2 NTs on the nucleation of PLLA crystals and the deformation behavior near T g , we believe that the strong orientation of WS 2 NTs in the extruded tube is also a consequence of the favorable interaction between PLLA and WS 2 NTs. The strength of the alignment of WS 2 NTs in the extruded tube can be seen in the narrow orientation distribution of the WS 2 (002) diffraction peak (5° FWHM, Figure 8 a and Figure S8c , initial value; unlike the ring observed in WAXS patterns of randomly oriented WS 2 NTs in PLA [ 60 ]) and the sharpness of the horizontal streak in PLLA/WS 2 NT’s initial 2D SAXS pattern ( Figure 5 c, t = −10 s; Figure 8 a and Figure S8d , initial value). This high degree of alignment is reminiscent of a nanocomposite drawn fiber [ 66 , 67 ] and is unusual for a history of shear flow, where nanotubes that have a higher affinity for each other than for the polymer matrix (like CNT) tend to agglomerate and tumble [ 9 , 10 ].…”

“…This high degree of alignment is reminiscent of a nanocomposite drawn fiber [ 66 , 67 ] and is unusual for a history of shear flow, where nanotubes that have a higher affinity for each other than for the polymer matrix (like CNT) tend to agglomerate and tumble [ 9 , 10 ]. However, if the particles have a high aspect ratio and behave as individual particles, as is expected for WS 2 NTs based on evidence of their good dispersion in PLA [ 57 , 59 , 60 ], alignment is expected in shear flow [ 68 , 69 ]. The remarkable alignment of WS 2 NTs in the extruded tube sets the stage for the lack of reorientation observed during tube expansion.…”

“…WS 2 NTs are a promising choice of nanofiller because of their established synthesis methods [51,52], high aspect ratio, excellent mechanical properties [53], and lack of known cytotoxicity [54][55][56]. Moreover, recent studies on PLA/WS 2 NT nanocomposites blended by melt mixing showed the capacity of WS 2 NTs to easily disperse in the polymer matrix, promote PLA crystallization, and reinforce PLA at low loading (0.5 wt%) [57][58][59][60]. As an additional advantage, WS 2 could confer enhanced radiopacity to a PLLA-based BVS [61] due to the higher atomic number of tungsten (compared to the carbon and oxygen atoms of the PLLA), which would enable X-ray imaging of the BVS during implantation and follow-up treatment.…”

Sustainable polymer composites: functionality and applications

“…PLA crystallisation can be induced by nucleation agents [24]. This special collection contains a study led by Di Luccio and Kornfield (Caltech, USA) [25] on the effect of tungsten disulphide (WS 2 ) nanotubes as a filler on the crystallisation of the PLA films at various stages of processing (unstretched, stretching, annealing) (DOI: https:// doi. org/ 10.…”