Peel strength improvement of silicone rubber film by plasma pretreatment followed by graft copolymerization

Here we discuss the improvement in the peel strength of silicone rubber film by O2 plasma pretreatment followed by grafting with hydrophilic monomers: acrylamide (AAm) and acrylic acid (AA). The peroxides concentration after O2 plasma treatment was determined by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method. ESCA analysis was carried out to confirm the existence of AAm. The peroxides concentration and hence the peel strength increased with increasing plasma treatment power and time, reached a maximum value, and then decreased with further increasing plasma treatment power and time. Peel strength of the silicone film with 3M-600 tape was observed to increase with grafting time; however, it was found to decrease with overgrafting. The maximum peel strength of 384.4 g/cm was found for the 20 W, 10 min plasma treated, AAm grafted film with maximum peroxides concentration of 4.86 x 10-9 mol/cm2 and also with maximum nitrogen-to-carbon ratio (N/C) of 0.247. Hydrolysis experiments show that -NH2 provides higher contribution to adhesion than -COOH does and the grafting degree of AA is lower than that of AAm. The relationship between the degree of grafting and peel strength can be well explained by the mechanical interlocking theory of adhesion.