Outdoor Ageing of an Ethylene-Propylene Copolymer: A Positron Annihilation Study

G. Consolatia, F. Quassoa, R. Gallob and F. Severinic aDipartimento di Fisica and INFM, Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 Milano, Italy bDipartimento di Chimica Industriale e Ingegneria dei Materiali, Universitá di Messina, Salita Sperone, 98166 S. Agata di Messina, Italy cDipartimento di Chimica, Materiali e Ingegneria Chimica "G. Natta", Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 Milano, Italy

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Received: 20 09 2004;

An investigation on the environmental degradation of an ethylene-propylene copolymer was carried out through positron annihilation lifetime spectroscopy, density and differential scanning calorimetry measurements. Polymer sheets were exposed to sunlight up to 11000 hours. Density and melting enthalpy increase with ageing, while ortho-positronium intensity decreases; ortho-positronium lifetime does not show significant variations up to 4400 hours. At higher exposures it starts to decrease. Outdoor ageing produces an increased crystallinity of the copolymer; also a degradation occurs with formation of carbonyl groups. The corresponding Ps inhibition is the main reason for the decrease in ortho-positronium intensity, the other one being the reduced amount of the amorphous phase available. The lifetime decrease observed at the highest exposures can be interpreted in terms of a shrinking of the nanoholes trapping positronium.

DOI: 10.12693/APhysPolA.107.805 PACS numbers:61.41.+e, 78.70.Bj, 81.05.Lg