Natural rubber-based pressure-sensitive adhesive films

Pressure-sensitive adhesive (PSA) films were prepared from natural rubber using ultraviolet (UV) light-mediated crosslinking of the rubber molecules. Effects of the UV irradiation time, the amounts of the crosslinking agent (1,6-hexanediol diacrylate; HDDA), and the photoinitiator (2-hydroxy-2-methylpropiophenone; Irgacure1173) on the properties of PSA films are reported. Adhesive performance (tack and peel), crosslink density, and mechanical properties (tensile strength, elongation at break, and moduli) of the films depended on the specifics of preparation. UV irradiation simultaneously promoted crosslinking within the rubber matrix and degradation of the surface molecules via photooxidation. HDDA and Irgacure1173 accelerated these processes due to their carbonyl groups facilitating the conversion of molecular oxygen to highly reactive singlet oxygen. The chain degradation reduced molecular weight, enhanced wettability, and improved adhesion, although excessive degradation weakened cohesion. Films with an optimal balance of properties were produced using 120 min UV irradiation time, and equal concentrations (2 phr each) of HDDA and Irgacure1173. With this combination, both the adhesive strength and the cohesive strength were maximized. Thus, the PSA film properties could be tuned by adjusting the preparation conditions, potentially expanding their envelope of applications.