Effect of Carbon Nanofillers on Processes of Structural Relaxation in the Polymer Matrixes

Abstract

The effect of filler concentration and morphology on structural relaxation of polymer matrixes has been studied in this research. Several investigation techniques were used to achieve this objective. Two types of nanocomposite materials (NCMs) were made: low-density polyethylene (PE) filled multi-walled carbon nanotubes (MWCNTs) and fluoroplastic (FP) filled expanded graphite (EG). Changes in crystalline structure of composite induced by addition of different carbon components were studied by X-ray diffraction. The results of X-ray experiments showed an increase in crystallinity of the extruded composite matrix in comparison to pure PE due to the increase in MWCNTs content. This is probably because of nucleating effect of nanotubes in the polymer matrix, causing more crystallization and orientation of molecules to take place around them. Comparison of the results for extruded samples and those obtained by the sintering method indicates the effect of the cooling rate of the samples on the crystallinity matrix. It was shown that the degree of crystallinity decreases with increasing both concentration and the average particle size of EG. Measurement of the amplitude dependences of internal friction (ADIF) was carried out through the inverted torsion pendulum method, which showed that MWCNTs cause the structuring of the matrix and the relative stabilization of the segmental mobility of the molecular chains. Stress relaxation data have shown that PE became more stiff with the increase of the filler concentration up to 5 vol.% and FP relaxation time increased with the increase of EG particles average size.