Electrostatic Interactions: An Effective Mechanism for Rubber Adhesion and Blending

Abstract

Deryagin introduced electrostatic adhesion many years ago but it was later considered unimportant, largely due to the difficulties in making eproducible electrostatic measurements and to the lack of clear understanding about the mechanisms for insulator electrostatic charging. More recently, electric force microscopy results on latex, polymer latex blends, and nanocomposites have shown the ubiquity of domains with excess charge, in every polymer material. In some cases, excess charge was identified by analytical transmission electron microscopy as the result of excess ions (positive or negative) concentration distributed throughout the coexisting phases and interfaces. Interaction between charged domains within nanostructured rubber blends and composites prepared from aqueous dispersions may thus contribute to their stability and mechanical properties. This article shows charge distribution patterns in one natural rubber blend, together with elemental and electric potential maps for rubber latex films from two commercial sources, evidencing large differences that were not previously reported. Electrostatic adhesion effectiveness in the making of a multicomponent system is demonstrated by casting films from a natural rubber-starch-clay nanocomposite, from aqueous dispersions and without using any sort of chemical modification or compatibilizing agent. Microscopy examination of these films show parallel clay lamellae finely interspersed within polymer, which accounts for the singular macroscopic tensile behavior of this material, with modulus in the 70 MPa range together with 500% elongation.