【作者】 杨旭东；

【导师】 丁辛；

【作者基本信息】 东华大学 ， 纺织工程， 2005， 博士

【摘要】 随着土工合成材料在工程领域的广泛应用,对其老化问题的研究,特别是如何准确预测土工合成材料的使用寿命,显得日趋重要。本课题以长江口深水航道治理工程中大量使用的聚丙烯土工织物为研究对象,围绕其使用寿命预测这一问题展开研究工作。 本文对聚丙烯土工织物在不同产外使用环境下的老化行为进行了研究。在上海某地方建立了户外曝晒场,进行了一年的大气自然老化试验,定期对试样的断裂强力进行测试,并对老化过程中各环境因素,包括紫外辐射、温度和降雨量进行了监测。结果表明,在户外曝晒的环境条件下,紫外辐射对聚丙烯土工织物老化起决定性作用,而且紫外辐射能对聚丙烯土工织物的老化有累积效应,即聚丙烯土工织物的强力下降与所接受的累积紫外辐射能呈线性关系。对于温度和降雨量等其他环境因素,所完成的实验并没有明确的迹象表明这些因素影响到紫外辐射所起的作用。同期在曝晒场采取不同的掩埋深度对聚丙烯土工织物进行沙土掩埋试验。试验结果表明,土壤中的温湿度、含氧量、微生物和化学物质等对聚丙烯土工织物老化没有显著影响。在横沙码头2m深的水域进行的水下老化试验结果表明,在无紫外辐射的作用下,水和水下微生物、化学物质等对聚丙烯土工织物老化不产生显著影响。通过以上三种不同的户外老化试验可以看出,光氧老化是聚丙烯土工织物强力下降的主要因素,其他环境因素的影响较小。因此,探索紫外辐射对聚丙烯光氧老化所起的作用,就有可能对其使用寿命有较准确的把握。 在此基础上,采取人工加速老化和大气自然老化试验,对不同老化过程中聚丙烯长丝试样的断裂强力、特性粘度(粘均分子量)、熔点和结晶度进行了测定。结果表明,在两种老化条件下,聚丙烯长丝的熔点随着老化时间的增加而降低,其下降趋势与断裂强力相一致,更多还原

【Abstract】 The use of polypropylene (PP) geotextiles has expanded to such an extent that nowadays they are almost certain to be include in any construction work. But geotextiles may be expected to survive a number of environmentally related challenges with regards to durability. As a result, extensive researches have been done on the ageing process of PP material to evaluate its long-term service performances. The objective of this study is to develop a long-term lifetime prediction model for PP geotextiles used in the channel project at Yangtze River.The long-term performances of PP geotextiles under three outdoor environments were evaluated. During one year of outdoor weathering tests under atmospheric conditions in Shanghai, the geotextiles were sampled and the tensile strength of the samples measured. In addition, the environmental factors, such as UV irradiation, ambient temperature and rainfall, were recorded to study the influence of these factors on the ageing of the samples. It shows that under the weathering conditions outdoors in Shanghai, UV irradiation plays an important role on the ageing of PP geotextiles. A linear relationship can be built between the reduction of tensile strength of samples and the cumulated UV irradiation. Other environmental factors, such as ambient temperature and rainfall, have no significant effects on the linear relationship. At the same period of the outdoor tests under atmospheric conditions, PP geotextiles were buried under a layer of local soil with different thicknesses to evaluate the long-term performance of the samples under the condition. The tensile strength of samples show that theenvironmental factors inside the soil such as temperature, humidity, content of oxygen, microorganisms and chemicals, etc will give no noticeable effects on the ageing of the geotextiles. The long-term performance of PP geotextiles 2-meter under water was also examined in water area of Hengsha Dock, the site of the project. The tensile strength of samples shows that water, microorganisms and chemicals under water have no notable influence on the ageing of the geotextiles. The results of the three weathering tests mentioned show that the reduction of tensile strength is mainly due to the photo-oxidation of PP geotextiles, therefore, further study should focus on the photo-oxidation process of PP materials.Both accelerated weathering tests (with fluorescent lamps) and outdoor weathering tests were then conducted to study the relationship between the macro-property (tensile strength) and micro-structure of PP filaments, which were used to weave the geotextiles. Tensile strength, intrinsic viscosity (viscosity average molecular weight), melting point and degree of crystallization of the filaments under both weathering conditions were then measured. Results show that, under both weathering conditions, the reduction of melting point and the degree of crystallization of PP filaments are not consistent with the reduction of tensile strength of the corresponding samples. However, a linear correlation can be developed between the reduction of tensile strength and the reduction of intrinsic viscosity of the filaments samples under both weathering conditions. It shows that, during photo-oxidation of PP filaments, the reduction of tensile strength can be characterized by the reduction of intrinsic viscosity of the corresponding samples. It means that a relationship can be built between the macro-property and the micro-structure of PP filaments during photo-oxidation.Influence of the intensity of UV irradiation on the photo-oxidation of PP filaments is then investigated. Three intensities of UV irradiationwere provided in accelerated weathering tests. One year of outdoor weathering tests were also conducted. The intrinsic viscosity of the filaments samples under different weathering conditions was then measured. In addition, FTIR spectrometry was used to analyze the corresponding samples. The FTIR results show clearly that the samples under accelerated weathering tests and outdoor weathering tests degrade with the same degradation mechanism of hydroperoxides, when the intensity of UV irradiation in the accelerated weathering tests is lower than 162.58 W/m2. But when the intensity of UV irradiation in the accelerated weathering test is 325.25 W/m2, the degradation mechanism of hydroperoxide will be different with that in the outdoor weathering tests. The study shows the possibility, by choosing a suitable UV irradiation intensity in accelerated tests, that the same kinetics of main oxidation route during photo-oxidation of the filament samples could be followed under both accelerated and outdoor weathering tests. It is actually the basic requirement if the weathering performance of PP filament outdoors is to be evaluated by means of accelerated tests.On the condition that the same kinetics of main oxidation route is followed, the weathering performance of PP filaments under atmospheric conditions is predicted by means of the "energy equivalent" principle. Based on the smallest residuals of variances of the testing data, a best-fit curve is obtained to show the relationship between the tensile strength of PP filaments under outdoor weathering tests and the accelerated ones with a low intensity of UV irradiation. The corresponding equation of the curve can be used to estimate the residual tensile strength of the PP filaments after certain period of outdoor service.The photo-oxidation of PP filaments under different loads is investigated finally. Results show that the greater the mechanical stress on the PP samples is, the more quickly the tensile strength of the samplereduces. Safe stress of the PP filaments in the present study is 10% of the tensile strength. It means that the influence of stress on the ageing of PP geotextiles can be ignored if the maximum load of the PP geotextiles is lower than the safe stress.It is aware that the present study focuses on the PP geotextiles used in the channel project at Yangtze River and the weathering conditions are the atmospheric conditions in Shanghai. Different PP materials under different weathering conditions may give different weathering performances and different lifetime prediction equations. However, the long-term service performance of PP geotextiles can still be evaluated by the present method if the local weather records can be obtained.更多还原