In 2004, a single-crystalline graphite film of atomic thickness was isolated [1]. The researchers responsible for this revolutionary work, Novoselov and Geim, were shortly thereafter awarded the Nobel Prize in Physics for 'innovative experiments with graphene' in 2010. Several researchers have used graphene (Gr), graphene oxide (GO), and reduced graphene oxide (rGO) as mechanically reinforcing nanoparticles in polymeric matrices. The insertion of these two-dimensional (2D) materials considerably improves the mechanical properties of the polymers. They also increase the thermal and electrical conductivity and the dimensional stability of the composite when compared to the polymer matrix [2-7]. Important challenges still need to be overcome to produce polymer nanocomposites based on two-dimensional particles (graphene-based materials, molybdenum disulfide, hexagonal boron nitrite, and phosphorene among others) on a large scale. Essentially, there are three strategies for nanocomposites preparation: 1) solution mixing, 2) in situ polymerization, and 3) melt mixing. The first two options achieve excellent results in terms of particles dispersion, however,

Molybdenum disulfide is a highly esteemed 2D material with interesting applications in nanoelectronics, composites, biotechnology and beyond.

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This study aimed to investigate how an ultralow content of a molybdenum disulfide (MoS2) two-dimensional particle affects the photodegradation mechanism of polystyrene (PS). Here, an accelerated weathering study was presented on neat polystyrene and its nanocomposites produced with 0.001, 0.002, 0.003 and 0.005 wt% of molybdenum disulfide (MoS2) exposed for various irradiation intervals (up to 8 weeks). The polymer photo-transformations were monitored using size exclusion chromatography (SEC), infrared spectroscopy (FTIR), and UV-Vis spectroscopy. The FTIR and UV/Vis results indicate that the PS degradation mechanism was not altered by the presence of MoS2 particles; however, the degradation reactions were slowed down at higher MoS2 contents (>0.003%). The SEC results proved the stabilizer effect due to MoS2 particles, where M¯n, M¯w, and M¯w/M¯n values after 8 weeks were less modified when compared with the neat PS results. The MoS2 acted as a UV stabilizer, and these two-dimensional particles acted by deactivating the free radicals generated by the PS matrix, even considering the low amount of the filler (<0.005 wt%).

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