Effective exfoliation of expanded graphite in rigid poly(methyl methacrylate) and its dispersion and enhancement in poly(Vinylidene Fluoride)

Initial high-level loadings of expanded graphite (EG, 20 wt%) was intensively melt-extruded with poly(methyl methacrylate) (PMMA) using a small screw extruder. The enriched graphite concentrate (enri-G) was then introduced into poly(vinylidene fluoride) (PVDF) matrix to produce PVDF/GNP nanocomposites by a solution diluting method. The morphology and structure of the graphite concentrate and PVDF/GNP nanocomposites were characterized by scanning electron microscopy and X-ray diffractometer. The results show that the tangled EG flakes have been successfully exfoliated into individual graphite nanoplatelets (GNP), but the pristine structure of graphite still remain unchanged. Moreover, the resulting PVDF/GNP nanocomposites exhibit an almost 60% lower percolation threshold of 4.0 vol% than that of direct melt-compounded PVDF/EG system (6.07 vol%) due to excellent dispersion of GNP in PVDF matrix. The melting and crystalline temperature as well as the crystallinity of PVDF change slightly at low loadings of enri-G (<20 wt%), whereas they decrease significantly at high loadings due to the presence of the noncrystalline phase of PMMA. In addition, the storage modulus of the resulting PVDF/GNP nanocomposite increase with increasing enri-G contents, indicating excellent reinforcing effect of graphite.