Flow Criterion for Elastomer Tack

Abstract In order to form a tack bond, the first step is to establish molecular contact between the two sample surfaces. This requires viscous flow of material near the surfaces under the contacting pressure. The tack of specimens with model surface roughness has been performed using a T-peel geometry. A simple flow parameter has been found that uniquely correlates with the relative tack of NR samples of varying molecular weights. For various contacting pressures and molecular weights, a single mastercurve was found in which relative tack is a linearly increasing function of the cumulative creep compression strain of the material. For instance, consider two samples of NR, one with a high molecular weight (I) and the other with a lower molecular weight (II). For a given contacting pressure, Sample II will exhibit a greater value of relative tack. However, if a different contacting pressure is selected for each sample such that both exhibit the same extent of flow, (i.e., possess equal cumulative creep compression strains) during tack bond formation, then relative tack is identical for both samples. That is, difference in the tack strength of NR samples of various molecular weights can be completely explained on the basis of differences in viscous flow behavior without consideration of molecular interdiffusion rates.