Effect of Weathering on Dynamic Mechanical Properties of the Multilayer Polyamide//Ethylene Vinyl Alcohol Copolymer//Polyamide//Polyethylene Film

Commercial co-extruded multilayer film of 25 micron thickness was tested for use as an airborne module. The module in a form of a cylindrical balloon rotates at high altitudes in order to convert wind energy to electrical energy. The film consists of low-density polyethylene, ethylene vinyl alcohol copolymer, two layers of polyamide 6 (PA6//EVOH//PA6//LDPE) and tie layers between them. The asymmetric film was aged in a weathering chamber at room temperature, with either the PA6 surface or the LDPE surface directly exposed to the xenon-arc light. The exposure of 1000 hours to a rainy and a sunny cycle ruined the film; therefore, the film was exposed to shorter sunny cycles only, for 3, 6, 16, 44, and 67 hours. The effect of solar radiation on tensile properties was tested in the machining and transverse directions by means of tensile testing at room temperature and dynamic mechanical analysis (DMA) at temperatures ranging from 83 to 373 K. In order to get a better insight into structural changes, the Fourier transform infrared spectroscopy (FTIR) analysis is performed. Water vapour sorption and the melting temperature range of the unexposed film were determined by means of thermogravimetric analysis (TGA) and optical microscopy, respectively. The tensile tests indicate a high anisotropy of the coextruded film. After irradiation, there is an increase in crystallinity degree. Kinetics of crystallization and hence the mechanical properties depend on the exposed surface