On The Photo-Oxidation Of PVC-Coated Membrane Material

With the development of PVC-coated membrane materials, its applications in the construction and other related engineering fields are attracting more and more attention. To understand its photo-oxidation ageing performances are very important and necessary to both users and manufacturers. The present project studies the effect of accelerated weathering tests on PVC-coated membrane materials. Because the material are rapid aged under strengthened simulated experimental conditions in accelerated weathering tests, in which UV radiation intensity plays the dominant role, there is a need to investigate the effects of UV intensity on the photo-oxidation of the material to evaluate the conditions in the simulated experiments.The ageing performance of PVC-coated membrane material was first analyzed under a strong UV intensity (with 8 UVB-313 fluorescent lamps). It was found that photo-oxidation occurred mainly in the PVC coating on the surface of the material. As results, the PVC film used for coating was studied alone. The study has shown that the PVC film containing no antioxidant was aged very fast, but it was slowly when the film containing antioxidant. Therefore, there is a great impact on the photo-oxidation of PVC with different antioxidant formulas.The study of the effects of UV intensity on the photo-oxidation of PVC coating shows that the photo-oxidation mechanism of the material does not change under the different UV intensities, but the photo-oxidation reaction rate is out of the proportion to UV intensity. Therefore, the simple reciprocity law (the materials' photo-oxidation effects are equivalent to the cumulative UV radiation energy is the same) does not apply to PVC's life prediction model. On the other hand, the Schwarzschild's law is valid when introducing a constant p on the basis of the reciprocity law. That is, when the product of UV intensity and the p-th power of the ageing time is the same, the photo-oxidation effects of the PVC coating are equivalent. It was found that, when p=0.7, the correlation between the ageing time and the UV intensities is good. The equations of ageing degree, ageing time and the number of lamps, indicating the intensity of UV radiation, are developed. They are:Yellowness index increment =7.5+ 0.21Nt^0.7 Breaking strength retention=120.23 - 0.26Nt^0.7Elongation retention=105.57 - 0.38Nt^0.7 Where, N is the number of lamps and t is the ageing time in hours. Thus, the ageing time of the samples reaching a certain ageing degree under different UV intensities can be calculated.