Skip @ Oct 15 2005 01:11 wrote:As I recall, carbon black is effective in ABS and polyolefins as a UV "stabilizer", while TiO2 (Rutile) is preferred in rigid PVC--as a UV "reflector". I'm thinking of extruded pipe, siding, profile products.
As to UV absorbers,they function well in clear polymer products, but in an opaque product UV degradation is strictly a surface phenomenon and only that UV absorber on the surface offers protection. If the UV- discolored and degraded surface is shaved away,material with original color and physicals are seen
below the surface. This is why capstock coextrusion with additive-rich material is done.
Surface, smurf-us! Tell the folks at a famous maker of curbside containers that it's just a surface thing. We had to replace (at cost) all the contaniers for NYC collection program, back in the day, and everyone of them were "protected" by CB from UV. LOL. The sun beat down, the temperature in the part rose, the free-radical cats and dogs were set loose...micro-crazing. The micro-cracks in the "surface" caused the parts to fail upon minor impact. Garbage collectors are not gentle w/ the empties, but no matter...the mode of failure was in adequate UV protection.
Just be cautious w/ a dependence on CB as an UVI.
Cap stocks work on the principle that the capping polymer are robust toward UV or that they have been properly stabilized against UVA, UVB, and IR radiation. And yes UV degradation is a surface phenomenone. Not many customers care to scrap off the caulky or yellowed polymer layer off their siding, lawn furnature, etc. to enjoy the prestine original color/strength of the article.
MTC - I stand by my original statements about carbon black as a UV inhibitor. It can work, but testing in the end application/environment is recommended.