Dielectric spectroscopy of recycled polylactide

Abstract

Abstract: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 10 7 Hz over the temperature interval from 0ºC to 140ºC. 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 were 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.J.D. Badia, L. Monreal, V. Sáenz de Juano-Arbona, A. Ribes-Greus, Dielectric spectroscopy of recycled polylactide, Polymer Degradation and Stability, Volume 107, September 2014, Pages 21-27, ISSN 0141-3910, http://dx

Long-term properties and end-of-life of polymers from renewable resources

“…In addition, Differential Scanning Calorimetry (DSC) can be used to determine the main thermal properties and the balance between crystalline and mobile and rigid amorphous fractions [179], [180]. As well, Dielectric Thermal Analysis (DETA) and Dynamic-Mechanical Thermal Analysis (DMTA) is of great importance to test the segmental rearrangements and dynamic fragility of polymers [181]- [184], which modifications are not perceptible by other macroscopic techniques.…”

“…This could be the case of polymers used for packaging, which need gas transmission experiments [185]- [187]. As well, those used in electrical or insulating applications may rely on dielectric characterisation [181]. Moreover, for those which serve in contact with food or in aggressive environments, the ecotoxicity should be assessed [188]- [190].…”

“…The mechanical recycling of PLA has been approached in lab-scale studies by means of multiple injection [183], [275]- [277] and extrusion [278]- [281] steps, and the recyclates characterized in terms of structural and morphological analysis rheological, thermal and mechanical properties, release of low molecular weight compounds (LMWC) [282], and application-driven techniques such as mass-transport [221] or dielectric properties [181]. A review devoted to the mechanical recycling of PLA [261] showed that, in general terms, reprocessing of PLA was responsible for a decrease in molecular weight, modification of thermal properties and crystallization kinetics, dynamic fragility or permeation performance, among other parameters [261].…”

Dielectric Properties of 3D Printed Polylactic Acid

“…To investigate the main relaxation process in detail, Figure 3 depicts the frequency-dependent dielectric constant (a) and the dielectric loss (b) for temperatures above the glass transition ranging from 340 K to 410 K. The lines are fits using only a Havriliak-Negami function [19] to describe the orientational relaxation process. This model originates from the Debye function describing the dielectric properties of a relaxation for noninteracting dipoles.…”

“…The mechanical properties of PLA are already described in detail in [12][13][14] as well as the references therein. However, for applications as a component in an electrical measurement setup or even as a functional material itself in an electronic device [15], the electric and dielectric properties of PLA [16][17][18][19][20] in the "as-printed" state are rarely investigated.…”