聚酯镀铝膜的湿热老化机理

Hydrothermal Aging Mechanism of Aluminized Polyethylene Terephthalate Films

针对聚酯(PET)镀铝膜在湿热条件下表面腐蚀脱落的现象及其随老化时间的变化规律,分别从物理老化和化学老化角度研究了PET本体膜在湿热条件下的玻璃化转变、熔融行为、特征基团以及相对分子质量的变化。结果表明,PET本体膜物理老化显著,玻璃化转变温度在不同湿热条件下随老化时间出现不同程度的上升;而化学老化,即相对分子质量和特征基团(酯基)的变化并不明显。湿度是影响镀铝层腐蚀脱落的主要原因,而与温度相关的PET本体膜自身老化无关。扫描电镜结果显示,镀铝层腐蚀首先发生在缺陷部位,并形成腐蚀坑。通过光谱分析检测聚酯镀铝膜水热老化后铝离子浓度的变化,进一步证实铝层脱落的主要原因是铝在水热的作用下发生腐蚀。

Glass transition temperature （Tg）, melting behaviors, characteristic group and viscosity-average molecular weight of polyethylene terephthalate （PET） films were studied in terms of physical aging and chemical aging based on phenomena and variation with time of exfoliation of aluminum layer of PET aluminized films under hydrothermal condition. Resuks show that Tg increases under different hydrotherrnal conditions meaning obvious physical aging of PET films. However, chemical aging, namely the changes of characteristic group and viscosity- average molecular weight are unconspicuous. Relative humidity plays the dominant role in exfoliation of aluminum layer and the exfoliation of aluminum layer has nothing to do with the aging of PET films which is related to temperature. SEM images indicate that corrosion of aluminum layer occurs from defect and subsequently pittings of corrosion develop. It has been proven further that the main reason of exfoliation of aluminum layer is the corrosion of aluminum under hydrothermal condition by detecting concentration of aluminum ion after hydrothermal aging of PET aluminized films using spectroscopic analysis.