Practical Approaches to the Light Stabilization of Polypropylene Multifilaments

Abstract

The stabilization of polypropylene against the effects of ultraviolet light has been the subject of considerable research. Stabilizing polypropylene multifilament yarns is understandably more difficult than stabilizing monofilaments or molded articles. Due to the small diameters of fiber (< 50 microns), conventional uv screeners (such as the benzophenones and benzotriazoles) offer little protection from ultraviolet light. Peroxide decomposers of the dialkylthiodipropionate variety have been found to be virtually ineffective in increasing fiber lifetimes, whereas certain phosphites are quite useful. Supporting laboratory data have shown that at low temperatures phosphites decompose hydroperoxides more rapidly and more efficiently than the dialkylthiodipropionates. Nickel stabilizers appear to be considerably more effective for multifilaments than the uv screeners. Our findings indicate that the Ni compounds function as quenchers of electronically excited carbonyl groups which arise from the photolysis of carbonyl impurities in the polymer. Combinations of the various types of stabilizers can lead to increased fiber lifetimes.