It is clear that the increase of micro-hardness is a consequence
of the modifications of the celluloid chemical structure provoked by
exposure to light. It is anticipated that such an important increase
of the hardness reflects crosslinking reactions. Analysis at the
polymer surface by AFM nanoindentations was then performed in
order to investigate any possible densification at the surface that
could come from cross-linking reactions. Fig. 7 shows the loading/
unloading indentation curves for 50 h exposure time