R. Zhang et al., Characterization of photodegradation of a polyurethane coating by positronannihilation spectroscopy: correlation with cross-link density, PROG ORG C, 42(3-4), 2001, pp. 244-252
Photodegradation of a polyurethane coating by Xe arc-lamp irradiation as a
function of time is studied by positron annihilation spectroscopy. Doppler
broadening energy spectra (DBES) of annihilation irradiation is measured as
a function of incident positron energy (0-30 keV). A significant decrease
in the S-defect parameter from DBES is observed as a function of irradiatio
n time. This is interpreted as a loss of free-volume and holes during the p
hotodegradation process. The cross-link density in the same system is measu
red by a solvent (methylene chloride) swelling method and is found to incre
ase as a function of irradiation time. A direct correlation between the inc
rease in cross-link density and the decrease in the S-defect parameter from
the DBES data is observed. These results are used to discuss the photodegr
adation process in terms of chemical and physical changes due to UV-irradia
tion in protective polymeric systems. (C) 2001 Elsevier Science B.V. All ri
ghts reserved.