在役埋地聚乙烯给水管道自然老化行为研究

Study on natural aging behavior of buried polyethylene water supply pipeline in service

研究了埋地聚乙烯(PE)给水管道在我国台州地区实际服役7~12年过程中的自然老化行为,采用红外光谱仪(FTIR)、差示扫描量热仪(DSC)、扫描电子显微镜(SEM)等分析了管材在服役过程中不饱和基团含量、断链和支化程度、羰基指数、羟基指数等微观结构的变化趋势,考察了不同服役时间管材热稳定性、分子量、氧化诱导时间(OIT)、表面形貌、屈服强度和拉伸模量的变化规律。结果表明,埋地PE给水管道服役过程中,在抗氧化剂保护下,管材在最初服役7年内处于物理老化阶段,微观结构和宏观性能基本不变;服役7年后管材开始进入化学老化阶段,不饱和基团和断链特征峰含量逐渐增多,交联反应提高了管材的热稳定性和力学性能;服役至9年时,氧化程度急剧增加,自动氧化反应加剧,氧化产物酯羰基含量增多,断链成为主要反应,热稳定性和力学性能快速降低,管材表面形成明显的龟裂形貌;在管材服役过程中氧化产物主要为酯类物质,水分子会不断渗入管材内部;通过对氧化诱导时间曲线进行非线性拟合,计算出在服役状态下抗氧化剂耗尽时间为24.08年。

This paper reported a study on the natural aging behavior of buried polyethylene(PE)water supply pipelines in service of 7~12 years in Taizhou,China.The variations of unsaturated groups,chain scission and branching,carbonyl index,hydroxyl index of the PE pipelines in service and the thermal stability,molecular weight,oxidation induction time,microscopic morphology,yield strength and tensile modulus of the pipes with different service times were investigated using infrared spectrometer,differential scanning calorimeter,and scanning electron microscope,etc.The results indicated that during the service of buried PE water supply pipelines,the pipes were in the physical aging stage within the first 7 years in service under the protection of antioxidants,and their microstructure and mechanical properties were basically unchanged.After servicing for 7 years,the pipes entered the chemical aging stage,and the content of unsaturated groups and characteristic peaks of chain scission increased gradually.The thermal stability and mechanical properties of the pipes were improved due to a crosslinking reaction.After servicing for 9 years,the degree of oxidation increased sharply,the auto-oxidation reaction was enhanced,the content of the carbonyl increased,the chain scission became the main reaction,the thermal stability and mechanical properties decreased rapidly,and a great number of cracks formed on the surface of the pipes.By nonlinear fitting the antioxidant depletion time curve,the depletion time of antioxidant in the pipes was calculated to be 24.08 years in the service state.