An in situ polymerization approach for functionalized MoS2/nylon-6 nanocomposites with enhanced mechanical properties and thermal stability

The enhancement in the thermal and mechanical properties of polymer/inorganic nanosheet composites depends strongly on their interfacial interaction. Herein, we exfoliated bulk MoS2 into nanosheets which was subsequently functionalized using lipoic acid. Nylon-6 (PA6) nanocomposites were prepared through in situ ring-opening polymerization of 3-caprolactam initiated by lipoic acid functionalized MoS2 (f-MoS2). MoS2/PA6 composites were prepared by melt blending of pristine MoS2 powder with PA6 in parallel with f-MoS2/PA6 composites. The morphology of MoS2/PA6 and f-MoS2/PA6 composites observed using scanning electron microscopy and transmission electron microscopy demonstrated that f-MoS2 exhibited a better dispersion state than pristine MoS2 within a PA6 matrix. The incorporation of f-MoS2 induced significant thermal stabilization in the PA6 matrix: with 1 wt% loading of f-MoS2, the T-5% and T-50% of the resultant PA6 nanocomposite were increased by 36 and 23 degrees C, respectively, relative to those of neat PA6. As demonstrated by the increase in the storage modulus and the glass transition temperature determined from dynamic mechanical analysis, f-MoS2 was more effective than MoS2 in terms of reinforcing mechanical properties of PA6. At very low fractions of f-MoS2 nanosheets (<= 1% by weight), PA6 nanocomposites exhibited up to 80% improvement in tensile properties compared to neat PA6 because of strong covalent polymer-filler interfacial interactions. These findings corresponded well with the nanoconfinement effect including a nanoscale interfacial layer that can support the superior reinforcements of f-MoS2 over pristine MoS2. The in situ polymerization approach proposed herein will open a new and exciting avenue for the development of transition metal dichalcogenide reinforced polymer nanocomposites.