Effect of Polymer-Filler and Filler-Filler Interactions on Dynamic Properties of Filled Vulcanizates

Abstract

In the past few years, an enormous amount of work has been reported on the progress in the application of conventional fillers and the development of new products to improve the reinforcement of rubber, dynamic properties in particular. While all agree that the filler as one of the main components of the filled-rubber composite, has a very important role in improving the dynamic performances of the rubber products; many new ideas, theories, practices, phenomena, and observations about how and especially why the filler alters the dynamic stress-strain response have been presented. This, of course, suggests that not only is the real world of the filled rubber complex and sophisticated but also multiple mechanisms may be involved. However, it must be admitted that the possibility exists for explaining the effect of all fillers on rubber properties ultimately in similar and relatively nonspecific terms, i.e., the phenomenon related to all filler parameters should follow a general rule or principle. It is the author's belief that, with regard to the effect of filler on the dynamic properties of a given polymer and cure system, filler networking, both its architecture and strength, is the main (although not only) parameter to govern the behavior of the filled rubber. From the thermodynamic and kinetic points of view, filler network formation is especially related to filler-filler, polymer-filler, as well as polymer-polymer interactions. As mentioned in the introduction, this paper is an attempt to review the effect of filler characteristics on dynamic properties in connection with processing conditions and additives. Since the polymer-filler interaction is not only affected by filler, what is also important are the characteristics of polymers such as chemical composition, chain microstructure including molecular weight and molecular weight distribution, configuration, stereoregularity, monomer unit distribution and sequence, and their functionality. All of these have a substantial influence on the physical and/or chemical interactions with other additives and filler surfaces, as well as on the interaction between polymer molecules themselves, which would impact not only the filler network formation but also the viscoelastic response of the polymer matrix. In addition, the polymer network structure which was formed during vulcanization and characterized by crosslink density, crosslink structure, and chain modification, is equally important in contributing to the overall dynamic properties of the filled rubber. In this paper, only some of these aspects have been discussed relative to their effect on filler network formation. Further discussion of these parameters is beyond the subject of the present paper. However, some guidance to these important topics is given in a handbook that was recently published.