Evidence of a monoclinic-like amorphous phase in composites of LDPE with spherical, fibrous and laminar inorganic particles as studied by infrared spectroscopy

Well-dispersed nanocomposites of LDPE with spherical silica and laminar and fibrous silicates have been prepared by melt compounding with nanofiller compositions ranging from 50 to 5 wt%. Spatial dispersion and size domains of the aggregates in the composites series have been evaluated by electron microscopies (SEM and TEM). The methylene rocking (700-740 cm(-1)) and bending (1400-1480 cm(-1)) modes of LDPE in these composites were studied by FTIR spectroscopy. When the nanofiller is present in a 40 or 50 wt%, the amorphous phase of polyethylene adopts a monoclinic arrangement. This arrangement is due to the confinement induced by the nanofillers on the polymer matrix. When the fibrous silicate or the spherical silica are used as nanofillers, a dilution of the concentrated composite or annealing bring about a relaxing of the amorphous structure of the polymer, and the monoclinic-like conformations disappear. When the nanofiller is a laminar silicate, dilution or annealing only partly eliminate the monoclinic-like structure, which remains in all cases an important fraction of the polymeric matrix. (C) 2008 Elsevier Ltd. All rights reserved.