Investigation of mechanical recycling effect on electromagnetic properties of polylactic acid (PLA) – nanoclay nanocomposites: Towards a valorization of recycled PLA nanocomposites

Virgin and recycled poly(lactic acid) (PLA) based nanocomposite materials were obtained and subjected to microstructural, thermal and mechanical analysis in view of fabricating efficient microwave absorbers. PLA was first exposed to artificial accelerated aging, next was mechanically recycled through grinding followed by reprocessing using melt extrusion and compression molding, resulting in recycled PLA samples (rPLA). Addition of organically modified montmorillonite (OMMT) as nanoclay was performed in a second melt extrusion process in order to obtain virgin and recycled PLA-OMMT nanocomposites. The impact of recycling process and presence of OMMT nanoclay in the host PLA matrix has been studied by FTIR, TGA and DSC, while the mechanical performance has been investigated by micro-hardness test. The dielectric properties were measured in the 26–40 GHz frequency range using a Vector Network Analyzer to assess the performance of virgin and recycled PLA and OMMT-PLA material as microwave absorbers. The FTIR results show that the recycling process generated more C = O groups in the polymer. These polar groups tend to orient themselves in the direction of the applied field and increase the dielectric constant (ε'). Measured electromagnetic absorption index revealed that rPLA-4OMMT with a thickness of 400 µm is able to absorb 20.3% on average of the spectrum with a peak of 36%, while 200 µm-thick films of rPLA-4 wt.% OMMT has a mean absorption index of 14.5%. The overall results show that mechanically recycled polymer can replace virgin polymer in this kind of applications.