PITCH AS A UV STABILIZER FOR POLYMERS

Pitches are excellent absorbers of ultraviolet (UV) radiation and gene rally have screening capabilities superior to those of carbon black. O ne such pitch (Aerocarb 70) was mixed with linear low density polyethy lene at concentrations of 0, 0.5, 1.0, and 2.5%, and compared with pol ymer filled with carbon black at the same concentrations. The samples were subjected to accelerated weathering tests for up to 43 days. As e xpected, the samples containing neither pitch nor carbon black suffere d great losses in molecular weight and mechanical properties after UV exposure. Similarly exposed carbon black filled specimens showed negli gible changes in these properties. Specimens blended with Aerocarb 70 showed slight reductions in molecular weight and large decreases in th eir tensile properties with the same UV exposure. The reasons for thes e phenomena are discussed.