Mechanooptical investigations of polyimide films exposed to electrons, mechanical loads, and temperatures

Abstract

Joint effect of high-energy electrons, mechanical loads, and temperature on polyimide films of thicknesses in the range 30–130 µm is investigated. The films were preliminary irradiated by electrons in air using an ÉLU-6 linear accelerator with energy of 2 MeV and doses D = 1, 5, 10, 20, 30, 40, and 100 MGy and then subjected to uniaxial mechanical tension at temperatures (T) from 293 to 593 K. It is established that at T = 293–450 K and D = 20–40 MGy, the mechanical load causes almost the same deformations (ε_{l max}) of nonirradiated and irradiated samples; at T = 450–550 K, deformations of films sharply increase, and the character of their dependence changes. The ε_{l max} value of the initial sample increases almost linearly with temperature by a factor of 10, whereas the character of changing ε_{l max}(T) of the irradiated films is more complex, and its value increases approximately by a factor of 4. For T > 500 K, the deformation reaches limiting values. Irradiation increases the intensity of IR-spectra by 2–6 times and essentially increases the widths of absorption bands at 720, 1380, and 1775 cm⁻¹, which is caused by the formation of hydrogen bonds and cycles with nitrogen as well as by the formation of nitrogen oxides. External loading applied to film rupture causes an increase in the EPR signal amplitude from 3·10³ to 5·10³, which is connected with an increased concentration of radicals =N-H and-NH ₂. The electron irradiation of the polyimide films with their subsequent mechanical loading causes the spectrum lines to displace from 3475.0 to 3512.5 cm⁻¹ with simultaneous reduction of the signal amplitude from 6·10³ to 4·10³.