Figure 3: Molecular weight and polydispersion for all exposure times.
The reduction in the mass produced with increasing exposure times of 336
and 575 h was 6% and 13%, respectively. There was no stability trend,
suggesting that longer exposure times would imply smaller molecular
masses [19-21]. The profile of the curves obtained suggests the
occurrence of oxygen diffusion and the attenuation of UV radiation on
the surface region of the investigated PS, as a consequence of
heterogeneous degradation and lack of mass uniformity [22, 23].
The gel percentages for all conditions are shown in Table 4. No
significant increase was found in the degree of crosslinking after UV
irradiation as compared to the as-received PS. A maximum of 1% increase
at an irradiated dose of 575 h was observed when compared to the
non-irradiated material [24, 25].
Table 4. Degree of cross-linking of PS, before and after UV radiation.