Abstract
This work investigates the effects of very small amounts of fumed silica on the morphology and on the rheological and mechanical behaviour of polypropylene nanocomposites and on their photo-oxidation behaviour. Polypropylene nanocomposites were prepared using a twin-screw corotating extruder with 0, 1 and 2 wt/wt% of SiO2. Morphological, mechanical, thermomechanical and rheological properties were examined. It was found that the viscosity of the matrix is reduced by the presence of the silica nanoparticles, suggesting a poor adhesion between the two phases and probably some lubricating effect. On the contrary, the mechanical and, in particular, the thermomechanical properties of the matrix are considerably improved by the presence of the silica. In particular, elastic modulus and tensile strength increases remarkably, and this effect becomes more and more remarkable with an increasing temperature. As for the photo-oxidation behaviour, the presence of silica improves the photostability of the polypropylene matrix. This effect has been attributed to both the barrier to the oxygen and to the absorbance of the UV radiation from the silica nanoparticles. Finally, no significant effect of the silica nanoparticles has been put in evidence on the crystallisation behaviour of the polypropylene. As for the effect of the silica content, the difference in the properties of the two nanocomposites is relatively small and all the measured properties depend much less than linearly with its amount. This has been correlated with the reaggregation of the nanoparticles that, having a larger size, decrease the contact area between the matrix and the filler.
Highlights
Nowadays, polymer nanocomposites have attracted the attention of many groups in both the scientific community and industry
This work investigates the effects of very small amounts of fumed silica on the morphology and on the rheological and mechanical behaviour of polypropylene nanocomposites and on their photo-oxidation behaviour
Polypropylene is a thermoplastic material used widely in industrial applications because of its excellent processing ability, low cost and, especially, recyclability. It can be produced with different molecular chain structures under controlled conditions, the most commercially attractive form is still the isotactic form, which is a semicrystalline polymer characterised by high tensile strength, low density, low thermal and abrasion resistance
Summary
Polymer nanocomposites have attracted the attention of many groups in both the scientific community and industry. Several studies have shown that incorporating very small amounts of nanoparticles into thermoplastic materials can improve properties, such as mechanical properties, [1,2] thermal, [3,4] barrier, [5,6] and dielectric [7]. Polypropylene is a thermoplastic material used widely in industrial applications because of its excellent processing ability, low cost and, especially, recyclability. It can be produced with different molecular chain structures under controlled conditions (stereospecific), the most commercially attractive form is still the isotactic form, which is a semicrystalline polymer characterised by high tensile strength, low density, low thermal and abrasion resistance. Several nano-reinforcing materials have been introduced in polypropylene, such as calcium carbonate [8,9,10], nano-clay [11,12], graphene [13,14,15,16] and nano-silica as well [17,18]
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