Study On Photo-Oxidation Of Pvc-Coated Membrane Material Under Different Light

With the development of PVC-coated membrane materials, it’s widely used in many fields. It is becoming more and more important to study its photo-oxidation aging performance and life prediction. Generally, accelerated weathering test is the main method to investigate material’s aging performance. As each light source’s spectrum and UV radiation intensity are different, it’s necessary to study PVC-coated membrane materials’aging performance under different light sources. Therefore, our major work is to study PVC-coated membrane materials’ aging performance under different light sources through accelerated weathering test.Two types of lamp were used as light source in the experiment, and they were UVB313lamp and UVA340lamp. To compare the aging performance under different UV radiation intensity, two UV radiation intensities (1lamp test and4lamps test) were respectively operated under each type of lamp. So both the aging performance under different light sources and aging performance under different UV radiation intensities were studied.Result shows that the photo-oxidation mechanism of the material does not change under different light sources, as well as under different UV radiation intensities. But when the cumulative UV radiation energy is equal, the aging performance is different both under different light sources and under different UV radiation intensity. That is to say, the photo-oxidation reaction rate is out of the proportion to UV radiation intensity. Therefore, the simple reciprocity law (the materials’photo-oxidation effects are equivalent to the cumulative UV radiation energy) does not apply to PVC’s life prediction model. On the other hand, after introducing a constant p in reciprocity law, Schwarzschild’s law is valid. Its new form is:Ipt=constant. That is, when the product of the p-th power of UV intensity and the ageing time is the same, the photo-oxidation effects of the PVC coating are equivalent. It was found that, when p=1.112, the correlation is good in UVB313lamp test, and when p=1.228, the correlation is good in UVA340lamp test. The equations of ageing degree, ageing time and UV radiation intensity are obtained under different type lamps, and they are:UVB313test: Tensile strength retention=100e-0.000152I1.112t Elongation retention100e-000215I1.112t Yellowness index increment=0.14579I1.112tUVA340test: Tensile strength retention100e-0000369345I1.448t Elongation retention100e-0000435964I1.228Yellowness index increment=0.04102I1.228t Where,I is UV radiation intensity and t is the ageing time in hours.Using the original Schwarzschild’s law, the aging correlation between UVB313lamp test and UVA340lamp test can’t be established. Taking lamp’s spectrum into condition, another coefficient a is introduced in Schwarzschild’s law. Here a is the ratio of effective UV radiation energy and total UV radiant energy, and it depends on lamp type. The new Schwarzschild’s law form is:(αI)pt=constant. When UVA340lamp’s a=0.258343, UVB313lamp’s a=0.765019, andp=1.18, according to the new Schwarzschild’s law, the correlation equations between different light sources are established, and they are: Tensile strength retention=100e-0.00201(αI)"81Elongation retention=100-0.20076(αI)1.18T Yellowness index increment=0.19898(αI)1.18tWhere,I is UV radiation intensity and t is the ageing time in hours. Thus, the ageing time of the samples reaching a certain ageing degree under different light sources can be calculated through these equations.