Influence of Nanofillers Concentration on Physical and Mechanical Characteristics of Their Polymer Composites

The influence of the concentration of nanofillers (multi-wall carbon nanotubes and pyrogenic silica A-300) on the structural, electrophysical, and mechanical characteristics of polymer composites was studied by transmission electron microscopy, X-ray diffraction, conductivity, stretching, and compression. The high-pressure polyethylene (PE), isostatic polypropylene (PP), and polytetrafluoroethylene (PTFE) were selected as polymer matrices. PE and PP compositions with multi-walled carbon nanotubes (MWCNT) were obtained by mixing in a melt or hot pressing polymer powders with MWCNTs planted on their surface from pre-homogenized stable dispersions. The composition of PTFE with MWCNTs was obtained, by mixing its stable dispersion with PTFE aqueous suspension. It is shown, that the introduction of a small concentration of nanofillers in polymer matrices changes the structural characteristics of composites, namely the degree of crystallinity and the size of X-ray coherent scattering blocks (XRCSB). The dependence of electrical conductivity on MWCNTs concentration is percolation. The critical concentration at which a continuous volumetric current grid is formed depends on the degree of homogeneity of the MWCNTs distribution in the matrix and can be a parameter that characterizes it. The strength characteristics of the studied composites are non-monotonically dependent on the filler concentration but linearly depend on the size of the coherent X-ray scattering blocks. These dependencies have two sections the inflection point for which corresponds to the critical concentration of the percolation transition. This confirms the theoretical calculations of various approximations that quantitatively the response of the matrix is proportional to the surface area of the interface.