1. Introduction One of the most important consequences of the incorporation of nanofillers in molten polymers is the significant change in their viscoelastic proper- ties [1]. The reduction of the filler size down to nanometric scale can produce substantial differ- ences in the rheology and dynamic of filled poly- mer in comparison to micron sized particles [2–7]. In fact, polymer composites reinforced with sub- micron fillers generally show significant enhance- ments in the viscoelastic properties compared to microcomposites at similar filler contents, associ- ated to the appearance of a secondary plateau for the dynamic storage modulus (G′) in the low fre- quency regime [3, 6–10]. These effects can be explained considering that the extremely large sur- face area provided by nanoparticles can intensify the effect of particle-particle and/or polymer-parti- cle thermodynamic interactions [4, 5, 11–14]. When filler-filler interactions dominate, it is believed that the rheological response of the mate- rial is influenced by the destruction and reconstruc- tion of a filler network and/or agglomerates during mechanical loading [8, 9, 15, 16]. On the other hand, when polymer-filler interaction is the driving factor, the viscoelasticity of the melt is controlled by the dynamics of the stick-slip motion of the polymer chains around the filler surface [17–22]. During the past few years, the linear viscoelastic behaviour in the molten state of polymer nanocom- posites filled with organically modified clays has been widely investigated [23–31], and the subject 115 * Corresponding author, e-mail: andrea.dorigato @ ing.unitn.it © BME-PT Linear low-density polyethylene/silica micro- and nanocomposites: dynamic rheological measurements and modelling A. Dorigato * , A. Pegoretti, A. Penati Department of Materials Engineering and Industrial Technologies, University of Trento, 38123 Trento, Italy Received 13 October 2009; accepted in revised form 12 December 2009 Abstract. Linear low-density polyethylene (LLDPE) based composites were prepared by melt compounding with 1, 2, 3 and 4 vol% of various kinds of amorphous silicon dioxide (SiO2) micro- and nanoparticles. Dynamic rheological tests in parallel plate configuration were conducted in order to detect the role of the filler morphology on the rheological behaviour of the resulting micro- and nanocomposites. A strong dependence of the rheological parameters from the filler surface area was highlighted, with a remarkable enhancement of the storage shear modulus (G′) and of the viscosity (η) in fumed silica nanocomposites and in precipitated silica microcomposites, while glass microbeads only marginally affected the rheologi- cal properties of the LLDPE matrix. This result was explained considering the formation of a network structure arising from particle-particle interactions due to hydrogen bonding between silanol groups. A detailed analysis of the solid like behav- iour for the filled samples at low frequencies was conducted by fitting viscosity data with a new model, based on a modifi- cation of the original De Kee-Turcotte expression performed in order to reach a better modelling of the high-frequency region. Keywords: nanocomposites, polyethylene, silica, modelling, rheology eXPRESS Polymer Letters Vol.4, No.2 (2010) 115–129 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2010.16