(133a) 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, clothing, paints, and dyes. Novel methods to protect photosensitive materials are in constant demand as the severity of product photodegradation continues to be realized. 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 singly and in combination. Particles were exposed to UV radiation for predetermined amounts of time before the amount of beta-carotene left intact was determined via Ultraviolet / Visible Spectrophotometry. Extent of degradation was analyzed using degradation curves and rate constants fit from the curves, and compared to that of uniform particles of similar formulation.

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 even without the addition of UV protectants, although the core consisting of many particles protects better than the solid core. UV protection increased as protectants were added to the formulation. Proximity of the protectant molecule to beta-carotene was shown to be a significant factor by comparing degradation when a protectant is present in various compartments.