Carbon Black for UV Protection

Many polymers are unsuitable for outdoor use on their own because of rapid degradation through the action of visible light and especially UV light. In particular, in combination with ozone and other aggressive environmental chemicals, those components of the sunlight can cause an increased physical and chemical degradation rate. Carbon black absorbs both visible and UV radiation converting it to heat and thus makes an excellent stabilizer. In many cases, stabilities spanning decades can be obtained, making the polymers suitable for outdoor applications.

The main carbon black properties affecting UV stabilization are particle size, aggregate size, and surface chemistry. UV stabilization by carbon black in polymers depends on its ability to absorb and to backscatter light. While the absorption increases with smaller primary particles and aggregates, the backscattering decreases. This explains why UV stabilization tends to level off for primaries smaller than 20-25 nm with the accompanying small primary aggregates. Surface chemistry is also important, with oxygenated groups promoting the effectiveness. This is mainly through their action as radical scavengers, but they may also function as chromophores. As with pigmentation, only low addition levels are required and the effects plateau at about 3% loading. Typical end markets for carbon black used as a UV stabilizer are the wire and cable jacket markets, automotive plastic parts, plastic films for agricultural and industrial use, and plastic tubes and coatings in industrial applications.

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