  The modelling of the adherence energy during peeling of Pressure Sensitive
Adhesives (PSA) has received much attention since the 1950's, uncovering
several factors that aim at explaining their high adherence on most substrates,
such as the softness and strong viscoelastic behaviour of the adhesive, the low
thickness of the adhesive layer and its confinement by a rigid backing. The
more recent investigation of adhesives by probe-tack methods also revealed the
importance of cavitation and stringing mechanisms during debonding, underlining
the influence of large deformations and of the related non-linear response of
the material, which also intervenes during peeling. Although a global modelling
of the complex coupling of all these ingredients remains a formidable issue, we
report here some key experiments and modelling arguments that should constitute
an important step forward. We first measure a non-trivial dependence of the
adherence energy on the loading geometry, namely through the influence of the
peeling angle, which is found to be separable from the peeling velocity
dependence. This is the first time to our knowledge that such adherence energy
dependence on the peeling angle is systematically investigated and
unambiguously demonstrated. Secondly, we reveal an independent strong influence
of the large strain rheology of the adhesives on the adherence energy. We
complete both measurements with a microscopic investigation of the debonding
region. We discuss existing modellings in light of these measurements and of
recent soft material mechanics arguments, to show that the adherence energy
during peeling of PSA should not be associated to the propagation of an
interfacial stress singularity. The relevant deformation mechanisms are
actually located over the whole adhesive thickness, and the adherence energy
during peeling of PSA should rather be associated to the energy loss by viscous
friction and by rate-dependent elastic hysteresis.
