| In recent years,high density polyethylene(HDPE)membrane materials has been widely used as an anti-seepage layer in many engineering projects,like the construction of landfill,sewage treatment plants,artificial lakes and aquaculture and so on,and the material is to be used at least about 50 years,therefore,scholars pay more attention in the life prediction of HDPE geomembrane.After been subjected to ultraviolet light,HDPE occurs molecular structure change,mechanical properties decrease by serious aging,then the service life get shortened.The prediction of service life is usually performed in laboratory conditions,but it also requires the data from actual environment to support.Thus,it is necessary to study the correlation between the aging process and the aging properties of HDPE geomembranes in different environments,before predicting the life of HDPE geomembranes.According to the market research,the geomembrane with carbon black and without carbon black was mainly used in industry.Therefore,the subject of this study is the HDPE geomembrane with carbon black and without carbon black added.The main contents are as follows:(1)Four UVB-313 fluorescent UV lamps were used as radiation source in accelerated aging test on a non-metallic aging tester.The aging process of the two kinds of membrane materials was comprehensively studied on the macroscopical level by analyzing the breaking strength retention of the two kinds of membrane materials.The surface morphology,crystallinity and degradation products(carbonyl,vinyl)contents of the aged samples were tested by scanning electron microscopy(SEM),differential scanning calorimetry(DSC)and Fourier transform infrared spectroscopy(FTIR).The photocatalytic kinetics of different HDPE films was studied.It was found that the aging mechanism of HDPE film was the same under artificial accelerated aging condition.When the carbon black was added into the film,the degradation rate of HDPE film would be slowed down,but the final two materials will achieve the same aging effect.Under laboratory conditions,carbon black can extend the length of HDPE membrane material life of up to 5 to 6 times.(2)The natural aging test was carried out in outdoor air environment by irradiating the aged samples with natural light.Based on the analysis of the surface morphology,breaking strength retention rate and carbonyl index of aged samples,it was found that under the natural conditions,the mechanism of photo-oxidation of different HDPE film materials is still the same.In the short test period,the initial stage of the photo-oxygen aging process occurs with carbon black HDPE film material,and at the beginning of the aging,carbon black has a good light shielding effect,effectively reducing the rate of photo-oxygen aging;HDPE film material with carbon black exposure in the outdoor environment for a long time,the thermal energy conversion of carbon black will cause aging of the material,resulting in the degradation of the mechanical properties of the material,which makes the degradation of the HDPE film under different test conditions deteriorated.(3)The aging properties of the same kind of materials were studied by means of macro-micro performance test,and the aging-related properties of the same kind of materials under different aging conditions were studied.The analysis of HDPE film without carbon black showed that the breaking strength retention and the carbonyl index all showed that the aging properties of HDPE film were correlated under different test conditions,but when the amount of accumulated UV radiation was same,the aging effect was not exactly the same,which did not meet the reciprocity law.Therefore,the constant p is introduced on the basis of the reciprocity law,when the product of the p-th power of the ultraviolet radiation intensity I and the aging time t is constant,the oxygen aging effect is equivalent,which is the Schwarzschild law.It was calculated that there was a good correlation between natural aging and artificial accelerated aging of HDPE film without carbon black at p = 0.79,but this result was not applicable to HDPE film with carbon black added.The recalculation of the HDPE film with carbon black shows that the p value was 1.89.Based on the above studies,it is found that carbon black does not change the aging mechanism of HDPE film under different experimental conditions,but it will change the aging process.Moreover,the aging process of the same kind of HDPE film is similar under different aging conditions,and the correlation model can be established by using Schwarzschild law to analyze the effect of carbon black on the properties of HDPE film. |
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