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Radost Ivanova, Rumiana Kotsilkova
Rheological study of poly(lactic) acid nanocomposites with carbon nanotubes and graphene additives as a tool for materials characterization for 3D printing application
Appl. Rheol. 28:5 (2018) 54014 (10 pages)
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In the last decades, one of the most critical issues concerning the control on the processing, structure and properties of
nanocomposites is related to the dispersion of nanofiller in the polymer matrix and internal interactions resulting in percolation.
In this study, we investigate the rheological behavior in oscillatory and steady shear flow of poly(lactic) acid based
nanocomposites incorporating 0 - 12 wt% graphene nanoplates (GNP) and multi-walled carbon natotubes (OH-MWCNT). The
effect of the filler contents and aspect ratio on the viscosity and viscoelastic response is evaluated. Three rheological techniques
are used for estimation of rheological percolation threshold. Due to different aspect ratio and state of dispersion of
GNP and MWCNTs the percolation threshold differs significantly for both compositions φ ≤ 1.5 wt% for MWCNT/PLA
and φp ≤ 5 wt% for GNP/PLA. The larger the aspect ratio of nanofiller, the lower is the rheological percolation threshold. The visualized
structure by TEM analysis confirms the rheological predictions for both type composites. The index of flow was estimated
by the power law slope of the flow curves and a better dispersion was assumed for MWCNTs in comparison with GNPs
due to the surface modification. Based on the rheological percolation threshold and the flow index, nanocomposites were
classified in three groups: Newtonian, percolated composites and elastic solids. Both characteristics are used to select the
printing parameters for the three groups of nanocomposites, suitable for fused deposition modeling (FDM).
► Cite this publication as follows:
Ivanova R, Kotsilkova R: Rheological study of poly(lactic) acid nanocomposites with carbon nanotubes and graphene additives as a tool for materials characterization for 3D printing application, Appl. Rheol. 28 (2018) 54014.
Evgeni Ivanov, Hristiana Velichkova, Rumiana Kotsilkova, Silvia Bistarelli, Antonino Cataldo, Federico Micciulla, Stefano Bellucci
Rheological behavior of graphene/epoxy nanodispersions
Appl. Rheol. 27:2 (2017) 24469 (9 pages)
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Graphene/polymer nanocomposites are the latest trends in materials science in the recent years, but the technology of their
preparation plays a crucial role in obtaining reliable materials with repeatable and enhanced properties. Up to now, there are
many unresolved problems in controlling the dispersion of the graphene filler and the corresponding influence on the properties
of the final nanocomposite materials. In the present study, we apply rheological methods for controlling the quality of
the graphene dispersion. We prepare and characterize epoxy/graphene nanodispersions with graphene contents varying from
0.05 to 1 wt% and explore the effect of different mixing regimes on the dynamic moduli and viscosity, thus assessing the
degree of the dispersion. The rheological percolation threshold and relaxation time spectra are determined, in order to evaluate
the internal structure of the nanodispersions. The relaxation spectrum is highly efficient to probe the effects of interfaces and
interconnections on the relaxation dynamics of molecules in nanodispersions. Rheological results combined with transmission
electron microscopy (TEM) observations confirm that the low frequency dynamic viscosity and moduli strongly increase, with
increasing the degree of dispersion due to the exfoliation of graphene sheets. The rheological percolation threshold was found
at very low concentration depending from the processing conditions. The weight of the relaxation spectra is strongly shifted
to higher values, compared to the neat epoxy resin and this effect is much stronger around and above the rheological percolation
threshold.
► Cite this publication as follows:
Ivanov E, Velichkova H, Kotsilkova R, Bistarelli S, Cataldo A, Micciulla F, Bellucci S: Rheological behavior of graphene/epoxy nanodispersions, Appl. Rheol. 27 (2017) 24469.
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