Pressure sensitive adhesives (PSAs) are viscoelasticelastomeric materials that adhere to a substrate under the application of light contact pressure and short contact time. The adhesive performances of a PSA are usually defined by three properties: tack, shear resistance, and peel strength. Tack is the ability of an adhesive to form a bond of measurable strength instantaneously. The shear resistance is the adeptness of the PSA of holding under the application of a shear stress. Peel strength is an index of the resistance to bond separation.All these properties can qualitatively be correlated to the linear viscoelastic spectrum of PSA. In many cases, selected frequency intervals can be isolated within the linear viscoelastic spectrum (obtained by oscillatory shear testing and time-temperature superposition), representing 'windows' associated to the in-service performances of the adhesive. Indeed, fine tuning of viscoelastic properties allows PSA manufacturers to tailor individual products in order to meet the user's requirements in different applications. 1 Water-based PSAs display, in general, inferior performance when compared to their solvent-based countertype, and show anomalous properties. Their film can retain a structure as an effect of original particle morphology. Furthermore, these systems contain significant amounts of microgels, permeated by uncrosslinked chains, producing micronetworks after film formation. Tobing et al. 2,3 recently demonstrated the correlation of the performances of this class of PSA with relevant molecular and structural parameters, such as the entanglement molecular weight, the crosslink molecular weight, the microgel amount, and the glass transition temperature. This same class of PSA will be examined in this work, with specific emphasis on its viscoelastic characterisation.In particular, we will consider the relevant viscoelastic phenomena selectively associated with the peeling process. In this connection, it is well established that, since in the early stage of the debonding a cavitation process occurs, the flow of the peeling front between the backing material and the tape is governed by the formation of fibrils (Fig. 1). Such a mechanism enables the PSA to deform significantly, thus providing relevant energy dissipation.The pioneering works by Zosel 4 showed that typically, during the debonding process, the elongation of fibrils reaches more than 10 times the original film thickness. Christensen and Flint 5 proposed criteria for the rheological modelling of PSA peeling, based on the knowledge of the linear viscoelastic spectrum. The validation of these criteria was obtained in peel tests, where the deformation of the adhesive was quantified under the assumption of uni-axial elongation.In this paper, we present a systematic characterisation of the stress-strain uni-axial elongational behaviour of
