Study of charge relaxations after thermal aging in poly (methyl methacrylate)

Effects of thermal aging on physico–chemical and electrical properties of polymethyl methacrylate (PMMA) are reported in this paper. PMMA samples are submitted to successive heat–cooling cycles (Tmin=20 ∘C and Tmax=90 ∘C) in the ambient air, each cycle lasts 12h. Different techniques are thus employed to investigate structural modifications, dielectric relaxations and conduction processes. These are the Fourier Transform Infrared (FTIR) spectroscopy, thermal step method (TSM), thermally stimulated depolarization currents (TSDC), dielectric spectroscopy (DS) and current–voltage technique. Results are discussed and a relationship between structural modifications and charge relaxations was emphasized. We demonstrated that thermal aging favors oxidation phenomenon. Three distinguishable charge relaxations (β, α and ρ) have been highlighted by TSDC.