Transdermal Excipients Effect on Adhesion Strenght of a Pressure Sensitive Adhesive

Different amounts of two skin permeation enhancers, oleic acid (OA) and propylene glycol (PG), were mixed thoroughly with solution of an acrylic copolymer pressure sensitive adhesive (PSA). Films with different adhesive layer thicknesses (30 and 60 μ) were prepared by casting of the mixed solutions with a film applicator on PET 80 μ films followed by drying of solvents. The results of peel test were explained on the basis of changing of entanglement molecular weight (Me) of the copolymer and its miscibility with the enhancers. PG concentration had no significant effect on the peel strength. This is related to a constant amount of Me, resulting from hydrogen bonding between PG and the copolymer. The presence of OA decreased the peel strength, specially when concentration exceeded 5(w/w%). This decrease can be related to the formation of a weaker surface layer in addition to the diminution of the adhesive effective thickness. A two fold increase in the thickness had no effect on the peel strength of OA samples. This shows that at least one half of the thickness of 60 μ samples is ineffective in viscoelastic energy dissipations in the copolymer. Cohesive failure for 30 μ samples occurred, when OA concentration exceeded 15 (w/w%). However, this failure was observed above 10 (w/w%) for 60 μ samples, because the applied force is not transferred through the ineffective thickness to the backing layer.