Dielectric spectroscopy of recycled polylactide

The effects of multiple mechanical recycling on amorphous polylactide (PLA) were simulated by means of five successive injection-grinding cycles. The influence of the induced thermo-mechanical degradation on the dielectric properties of PLA was analysed. The relaxation spectra were studied in terms of the complex dielectric permittivity (ε′ and ε″) and the dielectric loss tangent, tg(δ) in the frequency range from 10−2 to 107 Hz over the temperature interval from 0 °C to 140 °C. It was possible to distinguish two relaxations zones, one at low temperatures and high frequencies (β relaxation) and another at higher temperatures and lower frequencies (α relaxation). The individual relaxations were characterised using the Havriliak-Negami model and the effect of conductivity at high temperatures was subtracted. The thermal activation of the β relaxations was explained on an Arrhenius model basis while the α relaxation was modelled using Vogel-Fulcher-Tammann-Hesse (VFTH) equations. The study of the segmental dynamics showed a decrease in the fragility parameters, connected with the decrease of molar mass, along with an increase in the free volume, the higher the number of reprocessing cycles were applied, particularly up to the second reprocessing step.