FEG-ESEM investigation of micromechanical deformation processes in ultrafine monospherical SiO2 particle-filled polymer composites

Micromechanical deformation processes responsible for toughening mechanisms in ultrafine monospherical inorganic particle-filled polyethylene were inv estigated in situ by a field-emission gun-environmental scanning electron m icroscope (FEG-ESEM) with low-voltage techniques. In general, the ultimate properties of polymer composites are largely dependent on the degree of dis persion of filler particles into the matrix. Very often, the agglomeration is one of inevitable occurrences in polymer composites, mixed with ultrafin e filler particles. In the present work, the effects of agglomerates, consi sting of ultrafine monospherical filler particles, were reexamined in polym er composites on the toughening mechanism. The results show that the domina nt micromechanical deformation processes are the multiple debonding process es inside agglomerates, in which the ratio of the matrix strand and the siz e of agglomerate plays a great role of matrix yielding. In the specimen, wh ere the agglomerates are isolated in the matrix, deformation begins at the equatorial region of agglomerates and propagates through them. However, in the case of closely placed agglomerates, deformation occurs homogeneously w ithin the whole area inside the agglomerates. In both cases, in conjunction with the multiple debonding processes, the major part of energy during the deformation dissipates through the shear-flow processes of the matrix mate rial. In particular, the micromechanical deformation processes observed in this work confirm that the agglomerates do not always have negative effects on the mechanical properties-at least, in the shear deformable semicrystal line polymer matrices. The agglomerates may be effectively used for the imp rovement of toughness. Furthermore, the FEG-ESEM with low-voltage technique s offers an extremely promising and efficient alternative method to study t he morphology as well as in situ micromechanical deformation processes in n onconducting polymer systems. (C) 2001 John Wiley & Sons, Inc.