The Effect of Particle Structure and Formulation On the Protection of Photosensitive Molecules

Photosensitivity to ultraviolet (UV) radiation impacts many industrial products, including cosmetics, pharmaceuticals, automotive coatings, clothing, paints, and dyes. Novel methods of protecting photosensitive materials continue to be in constant demand as product photodegradation continues to be a problem. The addition of UV protective species to a formulation is a common method for UV protection. Encapsulation in a polymer matrix has also been shown to protect photosensitive molecules. A combination of the two methods is investigated as a means to provide substantial protection to a molecule sensitive to UV radiation.

Two types of core-shell polymeric microparticles were created, one with a solid core and the other whose core is a suspension of uniform polymer particles. The photosensitive molecule beta-carotene was added to the core of all particles, and UV absorbers and an antioxidant were added to various compartments. The shell thickness of the particles was also varied. Particles were exposed to UV radiation for predetermined amounts of time before the amount of undegraded beta-carotene was determined via Ultraviolet / Visible Spectrophotometry. Extent of degradation was analyzed using degradation curves and rate constants fit from the curves.

Encapsulation in uniform particles offers protection to beta carotene, and the extent of protection increases with the addition of UV absorbers or antioxidants. Both core-shell particle geometries offer additional protection without the addition of UV protectants, although the core consisting of many particles protects better than the solid core. In most cases UV protection increased as protectants were added to the formulation and as concentration of protectant was increased. Proximity of the protectant molecule to beta-carotene was shown to be a significant factor by comparing degradation of the uniform particles and the core-shell particles.