EFFECT OF UV LIGHT ON THERMOPLASTICS


THE MECHANISM OF DEGRADATION FOR MOST PLASTICS, FOR EXAMPLE, POLY-OLEFINS, IS PHOTOCHEMICAL IN NATURE, AND THE ENERGY FROM THE NEAR ULTRAVIOLET (UV) RANGE OF ELECTROMAGNETIC RADIATION (290-400 NANO-METERS) IS THE INITIATING FACTOR.

ABSORPTION OF UV LIGHT BY THE PLASTIC PROVIDES ADEQUATE ENERGY TO BREAK KEY MOLECULAR BONDS, NAMELY C=C, C-H, AND C=O, NEAR THE SURFACE OF THE EXPOSED PLASTIC.

THE RESULTANT FREE RADICALS THEN REACT WITH OXYGEN TO FORM PEROXY RADICALS, WHICH ATTACK OTHER POLYMER MOLECULES, OR EVEN POINTS IN THE SAME POLYMER CHAIN. HYDROPEROXIDES AND MORE FREE RADICALS ARE FORMED, ESTABLISHING A CHAIN REACTION.

THE DURATION OF THE REACTION IS A FUNCTION OF THE POLYMER CHAIN LENGTH. IN THE CASE OF PVC, THE ABSORBED UV LIGHT APPEARS TO ENHANCE POLYMER DECOMPOSITION BECAUSE OF THE FORMATION OF HYDROCHLORIC ACID (HCL), WHICH CAUSES FURTHER POLYMER BREAKDOWN.

HERE AGAIN, A SELF-PERPETUATING CHAIN REACTION IS INITIATED.

BOTH THIS MECHANISM FOR PVC DEGRADATION AND THE ONE DESCRIBED FOR POLYOLEFINS CAN RESULT IN SERIOUS DETERIORATION OF PHYSICAL, CHEMICAL, AND ELECTRICAL PROPERTIES. THEREFORE, PLASTICS FOR USE IN PRODUCTS EXPOSED TO UV LIGHT MUST BE STABILIZED BY THE ADDITION OF SUITABLE UV INHIBITOR ADDITIVES.

PLASCO RECOMMENDS THE USE OF CARBON BLACK PIGMENTS TO IMPART UV RESISTANCE TO MOST THERMOPLASTICS. THERE ARE NATURAL TINT UV CONCENTRATES AVAILABLE ALSO. UV RESISTANCE CAN BE FORMULATED INTO YOUR COLOR CONCENTRATES OR CUSTOM COMPOUNDED MATERIALS IF NEEDED. CONTACT ME AT 831-464-1111 FOR MORE DETAILED INFORMATION.