JOURNAL OF MATERIALS SCIENCE 26 (1991) 5708 5716 Characterization of polyethylene/EPDM/silicon dioxide multicomponent composites by solid-state dynamic mechanical spectroscopy C. SCOTT, H. ISHIDA Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH 44106, USA F. H. J. MAURER DSM Research BV, P.O. Box 18, Geleen, The Netherlands Various composites of polyethylene, ethylene propylene diene rubber (EPDM), and filler are milled and analysed by solid-state dynamic mechanical spectroscopy. The filler used is silicon powder with an oxidized surface. This filler is a model for materials with siliceous surfaces. The torsion pendulum measurements show that the multicomponent composites exhibited complex viscoelastic behaviour. For composites of polyethylene and silicon dioxide, there is evidence of particle-particle interactions. In composites which include polyethylene, rubber and filler, interactions of the polyethylene and especially of the rubber with the filler surface are significant. Treatment of the filler surface with gamma-aminopropyltfiethoxysilane (~/- APS) or gamma-methacryloxypropyltrimethoxysilane (~,-MPS) has a significant influence on the resultant composite dynamic mechanical spectrum. Maleic anhydride grafting of the EPDM rubber also changes the character of the composites. These composites appear to exhibit com- plex morphologies, which may be controlled to a certain extent by filler surface treatment and grafting to the rubber. There is evidence for a chemical reaction between the maleic anhydride modification of the EPDM and y-APS during processing on the roll mill. Prediction of the composite properties using the extended van der Poel model is qualitatively useful. 1. Introduction Composites including high modulus particulates and rubbers have attracted increasing attention both in- dustrially and academically over the past few years. It is well known that the addition of a high modulus component to a plastic matrix enhances the composite modulus, but generally results in increased brittleness. On the other hand, addition of a rubbery component often increases the impact strength but reduces the composite modulus. It is believed that careful incorp- oration of both high-modulus and rubbery materials in a composite could result in an improvement of both the modulus and impact strength. Only a few publi- cations have been concerned with such systems [14]. Comitov et al. [2] studied multicomponent com- posites of calcium carbonate and styrene-butadiene- rubber or butadiene-styrene-latex in polypropylene. They found that the impact strength was increased with the addition of the rubber modifier. Pukanszky et al. [3] studied systems of EPDM and calcium carbon- ate in polypropylene. They measured the stress-strain behaviour, shear modulus, impact strength and dy- namic mechanical properties of these composites. Dy- namic mechanical spectra and scanning electron micrographs (SEM) showed that in these systems the rubber partly covered the filler particles and/or filled in the voids in filler agglomerates. This morphology was critical in determining the properties of these composites. The addition of rubber was also found to restrain the deteriorating effect of the filler addition on composite impact strength. Pukanszky et al. [4] fol- lowed the torque and temperature against time curves during milling of PP/EPDM/CaCO3 multicompo- nent composites. Multicomponent composites incorporating a ma- trix, rubber and filler are expected to exhibit quite complex behaviour. Filler-matrix, filler-rubber and rubber-matrix interfaces and/or interphases may be involved. The use of coupling agents in such com- posites would result in the presence of even more interfaces/interphases. The morphology of these com- posites is also expected to be quite complex. Many different morphologies may be imagined. One possib- ility is a composite where the filler and rubber existed as separate, non-interacting particles within the ma- trix. Another morphology might involve filler particles encapsulated by the rubber inside the matrix. The composite properties of these two extreme cases 5708 0022-2461/91 $03.00 + .12 1991 Chapman & Hall