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 (Т) from 293 to 593 K. It is established that at Т = 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 Т = 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 (Т) of the irradiated films is more complex, and its value increases approximately by a factor of 4. For Т > 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 3·10 3 to 5·10 3 , 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 6·10 3 to 4·10 3 .

Effects of Electron Irradiation and Temperature on Mechanical Properties of Polyimide Film

“…The tensile properties of PI are hardly affected by electron irradiation, and the formation of crosslinking results in a change in glass transition temperature observed in irradiated polyimides [ 23 , 24 ]. Under the joint effect of 2 MeV electron irradiation and high temperature at 373 K, mechanical tests showed an increase in plasticity, and long-term hardening was observed [ 25 ]. The effects of low temperature and mechanical loading were seldom investigated.…”