Molecular basis for the mullins effect

Abstract A molecular theory for the softening of filled rubbers which is caused by prestressing is presented. It is based upon the assumption that the centers of the filler particles are displaced in an affine manner during deformation of the rubber. Those network chains which are fastened at both ends to filler particles will break when the filler particles have separated enough to stretch the chains to near full elongation. The loss of these chains causes a prestressed rubber to exhibit a much lower modulus than did the original rubber. Equations are derived to describe this phenomena and are tested by comparing with data for black filled synthetic rubber. Good agreement is found if the filler surface area per chain attachment is taken as 44 A. 2 and if the strength of the chain is 2 × 10 −4 dynes. It is shown that the chains break loose from the filler particle rather than breaking at C C bonds along the chain. The theory appears to offer a convenient tool for systematic studies of rubber–filler interactions.