Structure property relations in pressure sensitive adhesives : A review

Considerable progress has been made in the adhesion science of soft polymers, which is a good base to study the influence of molecular and structural parameters on the adhesion performance of pressure sensitive adhesives, characterized by tack, peel strength and shear resistance. High tack and peel strength are connected with a particular mechanical behaviour: cavitation and fibrillation. A crucial parameter for tack and peel strength is the molecular mass between entanglements; a large entanglement length is advantageous for contact formation and for the formation and growth of fibrils during bond separation. Experience has been accumulated concerning the influence of crosslinks. A very loose and imperfect network structure with a large fraction of uncrosslinked material, found just above the gel point, gives rise to high tack and peel strength as well as good shear resistance. Inhomogeneous deformations are also observed in shear tests, leading to a catastrophic failure within the adhesive.