Paper AS-ThP4
A Quantitative Model Relating Interphase Chemistry and Adhesive Fracture in Steel Cord-Rubber Composites

Thursday, October 18, 2007, 5:30 pm, Room 4C

In steel cord-rubber adhesion testing high rubber coverage, or cohesive fracture in the rubber, is generally accepted as a necessary condition for good adhesive bonding. On the microscopic level the transition from high rubber coverage to exposed wire is a transition from fracture in the rubber to separation in the sulfide layer in the adhesive interphase. This sulfide layer is a mixture of copper(I)- and zinc sulfides. Multivariate statistical analysis of Auger depth profiles of the interphase produced chemical depth profiles from which the composition of the interfacial sulfide (percent zinc sulfide and copper(I)sulfide) can be measured. For a variety of compounds, cures, and aging conditions the rubber coverage was a function of the percent zinc sulfide, with rubber coverage dropping abruptly as the percent zinc sulfide increased from 60 to 80%; specifically the a rubber coverage of one-half the initial value appeared to correspond to a percent zinc sulfide of 75%. A mechanism has been proposed wherein the loss of adhesion was attributed to the one or both of (i) overgrowth of the bonding copper sulfide by the non-bonding zinc sulfide in the interphase, (ii) embrittlement of the sulfide by increased content of zinc sulfide.