Mechanistical studies on the electron-induced degradation of polymers: polyethylene, polytetrafluoroethylene, and polystyrene

Abstract

Mechanisms of the electron-induced degradation of three polymers utilized in aerospace applications (polyethylene (PE), polytetrafluoroethylene (PTFE), and polystyrene (PS)) were examined over a temperature range of 10 K to 300 K at ultra high vacuum conditions (∼10(-11) Torr). These processes simulate the interaction of secondary electrons generated in the track of galactic cosmic ray particles in the near-Earth space environment with polymer material. The chemical alterations at the macromolecular level were monitored on-line and in situ by Fourier-transform infrared spectroscopy and mass spectrometry. These data yielded important information on the temperature dependent kinetics on the formation of, for instance, trans-vinylene groups (-CH=CH-) in PE, benzene (C(6)H(6)) production in PS, fluorinated trans-vinylene (-CF=CF-) and terminal vinyl (-CF=CF(2)) groups in PTFE together with molecular hydrogen release in PE and PS. Additional data on the radiation-induced development of unsaturated, conjugated bonds were collected via UV-vis spectroscopy. Temperature dependent G-values for trans-vinylene formation (G(-CH=CH-) ≈ 25-2.5 × 10(-4) units (100 eV)(-1) from 10-300 K) and molecular hydrogen evolution (G(H(2)) ≈ 8-80 × 10(-5) molecules (100 eV)(-1) from 10-300 K) for irradiated PE were calculated to quantify the degree of polymer degradation following electron irradiation. These values are typically two to three orders of magnitude less than G-values previously published for the irradiation of polymers with energetic particles of higher mass.