Nanocomposite Materials with Poly(l-lactic Acid) and Transition-Metal Dichalcogenide Nanosheets 2D-TMDCs WS2

Abstract

Layered transition-metal dichalcogenides (TMDCs) based on tungsten disulfide nanosheets (2D-WS2) were introduced via melt processing into poly(l-lactic acid) (PLLA) to generate PLLA/2D-WS2 nanocomposite materials. The effects of the 2D-WS2 on the morphology, crystallization, and biodegradation behavior of PLLA were investigated. In particular, the non-isothermal melt-crystallization of neat PLLA and PLLA/2D-WS2 nanocomposites were analyzed in detail by varying both the cooling rate and 2D-WS2 loading. The kinetic parameters of PLLA chain crystallization are successfully described using the Liu model. It was found that the PLLA crystallization rate was reduced with 2D-WS2 incorporation, while the crystallization mechanism and crystal structure of PLLA remained unchanged in spite of nanoparticle loading. This was due to the PLLA chains not being able to easily adsorb on the WS2 nanosheets, hindering crystal growth. In addition, from surface morphology analysis, it was observed that the addition of 2D-WS2 facilitated the enzymatic degradation of poorly biodegradable PLLA using a promising strain of actinobacteria, Lentzea waywayandensis. The identification of more suitable enzymes to break down PLLA nanocomposites will open up new avenues of investigation and development, and it will also lead to more environmentally friendly, safer, and economic routes for bioplastic waste management.

Nanocomposite Materials Based on TMDCs WS2 Modified Poly(l-Lactic Acid)/Poly(Vinylidene Fluoride) Polymer Blends

“…As such, it would suggest that the nanofillers provoked nucleation in both polymeric components, with the effect being more pronounced for PLLA. In contrast, 2D-WS 2 nanosheets have been shown to slow down the crystallization rate of PLLA [ 25 ]. Such differences suggest that the nanoparticle shape plays a fundamental role in PLLA crystallization.…”

“…In this way, Lisuzzo et al demonstrated that the chitosan coating of halloysite nanotubes driven by electrostatic interactions can be considered a suitable strategy to obtain drug delivery systems with tunable properties [ 20 ]. Of particular interest is the use of layered transition metal dicalcogenide (TMDC) nanostructures, such as tungsten disulfide (WS 2 ) and molybdenum disulfide (MoS 2 ), which are broadband semiconductors with multidimensional structural anisotropy, 0D (IF), 1D (INT), and 2D [ 21 , 22 , 23 , 24 , 25 , 26 ]. These environmentally friendly and biocompatible TMDCs nanoparticles also have demonstratable processing, performance, design, and cost advantages over nanoclays, CNTs, etc.…”

The Effect of WS2 Nanosheets on the Non-Isothermal Cold- and Melt-Crystallization Kinetics of Poly(l-lactic acid) Nanocomposites

“…In this regard, elaborate methodologies have been previously reported for the synthesis of PLA/MoS 2 -NH 2 nanocomposites [ 29 ]. In our case, the WS 2 nanosheets exhibited better dispersion and semi-exfoliated structure in the solution samples than the melt-processable counterparts [ 26 ]. The good dispersion and strong interfacial adhesion may support a significant stress transfer to reinforce the properties of PLLA nanocomposites.…”

“…In a similar manner to the 2D-WS 2 nanosheets, the addition of inorganic fullerenes (IF-WS 2 ) to polyphenylene sulfide (PPS) was also found to exert significant influence on the crystallization kinetic of PPS, but in ways unexpected for polymer nanocomposites [ 39 ]. In contrast, 2D-WS 2 has been shown to reduce the crystallization rate of melt-processable PLLA nanocomposites at any concentration [ 26 ]. This discrepancy is likely related to several factors, including the nucleation efficiency (NE) and morphology of the filler, its surface energy, roughness, and state of dispersion within the matrix as well as on the filler’s ability to form the critical nucleus [ 22 , 23 , 24 , 39 ].…”

“…On the other hand, the effects of 2D-WS 2 on the melt-crystallization and biodegradation of melt-processable PLLA nanocomposites have recently been investigated. Promising results for the biodegradation behavior of a standard PLLA commercial grade have been recently reported [ 26 ], especially the addition of 2D-WS 2 into the PLLA matrix to facilitate the enzymatic degradation of poorly biodegradable PLLA using a promising strain of actinobacteria, Lentzea waywayandensis .…”