ESTIMATION OF DEGRADATION OF PVC-U SUBJECTED TO PHOTOOXIDATING ACCELERATED AGEING

The fourteen various compositions of PVC-U blends containing a filler (occluded calcium carbonate), two types of pigments [titanium white or the mixture of iron(II) and (III) oxides] and different one-pack stabilizing systems [S1-S7 where S1-S3 are lead based stabilizers while S4-S7 calcium zinc stabilizers] (Table 1 and 2) were prepared. Ageing resistance of PVC-U to UV radiation was investigated by accelerated ageing in a Suntest CPS+ chamber. The thickness of degraded surface layer (WWZ) was measured using PVC-U cross-section by optical microscopy (Fig. 2 and 3). The aged samples were then etched with methylene chloride and cyclohexanone mixture and visual observation of the sorption was done. It has been found that the course and degree of degradation of PVC-U depend mainly on the type of stabilizing system used and the type of accompanying pigment.