Influence of ultraviolet absorbers on the ultraviolet-irradiation behaviour of rigid poly vinyl chloride

The effects of ultraviolet absorbers (UVAs) on the UV-irradiation behaviours of rigid PVC were studied through Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. In addition, the absorption behaviours of these UVAs in non-polar and polar solvents were characterised and the solution photolysis experiments of these UVAs in ethanol were investigated in the absence and presence of a free radical initiator during the UV irradiation. The results showed that the protection efficiency to photo-degradation of PVC was in the following order: 2,4,6-tri(2-hydroxy-4-butoxylphenyl)-1,3,5-triazine (U3)?>?2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methyl phenol (U2)?>?2-hydroxy-4-n-octoxy-benzophenone (U1). This protection efficiency was related to the chemical structures of the UVAs, especially the intermolecular hydrogen bond (IMHB). In a polar solution, such as dimethyl sulfoxide, the absorption corresponding to the IMHB of U3 was intact, while that of U1 disappeared. The free radical initiator weakened the intensity of the absorption, accelerating the destruction of the IMHB.