Investigating nonlinear viscoelastic properties of molten carbon black/poly(ethylene-co-butyl acrylate) composites, using Fourier transform rheometry and other test techniques

A series of molten carbon black (CB)/poly(ethylene-co-butyl acrylate) (EBA) composites were investigated through Fourier transform (FT) rheometry and other techniques. Filler loadings were above the critical percolation value, and consequently, strongly nonlinear viscoelastic properties were observed, with, in addition, an unusual complexity of carbon black effects when compared with other systems, for instance filled elastomers. FT rheometry appears particularly sensitive to such a complexity with typical variations of torque harmonics, as dynamic torsional strain is increased at constant frequency and temperature. How CB particles are distributed in the material appears as the key to understand experimental results. Indeed, in CB-EBA composites, filler particles concentrate in amorphous regions of the polymer, which are also butyl acrylate (BA)rich regions. At room temperature, such composites are basically dual-phase systems: ethylene segments (PE)-rich crystallites and CB-rich amorphous BA regions. Solid-state mechanical properties reflect this morphology. As temperature increases, crystallites melt down allowing a pseudofluid state to be eventually reached but the dual-phase morphology is essentially kept. It follows that, under increasing (dynamic) strain, such complex dual-phase molten systems exhibit a response that initially reflects a contribution from PE-rich regions, easier to deform than CB-rich amorphous BA regions, before the expected response of the filled BA phase is observed. (c) 2006 Wiley Periodicals, Inc.