Influence of Nanofillers Concentration on Physical …
691
to a composition with a concentration of 5% wt. is almost seven orders of magnitude
for PE–MWCNTs (Fig. 4a) and nine orders for PP–MWCNTs (b), PTFE–MWCNTs
(c). Of course, to create a continuous conductive grid in the polymer matrix, the size
of the filler (the length of the MWCNTs agglomerates) and its distribution in the
matrix are of great importance.
Approximating the experimental curves (Fig. 4) and given the linear dependence
of the lgσ ~ lg(θ –θ F ), percolation parameters for the three systems were determined.
The percolation threshold for the PE–MWCNTs system was (0.45 ± 0.02) % vol.
In this case, the value of electrical conductivity is ≈1.1 × 10
3 (m·cm)
−1 , and the
critical index is t ~ 1.8, corresponding to the three-dimensional system. The calculation of critical indices for the system PP–MWCNTs gives the following values:
θ F = 0.345% vol., t = 1.83. Deterioration of the homogeneity of the distribution of
MWCNTs (curves 2, 1 Fig. 4b) corresponds to an increase in the critical concentration (percolation threshold) in the range of 0.345% vol., 0.92% vol., 1.28% vol.
For the PTFE–MWCNTs system (Fig. 4c), we also observe a shift of the percolation
threshold to the region of lower values from θ F = 6.68% vol. for initial MWCNTs
to θ F = 3.89% vol. (t = 1.64) for MWCNTs pre-deaglomerated in a rotary hydrodynamic homogenizer (RHDH) using the simultaneous action of the shear deformation
and a cavitation mixing. Therefore, the value of the critical MWCNTs concentration
can be used as a parameter to determine the degree of the homogeneity of filled
polymer systems.
Analysis of the results on the electrical conductivity of the obtained systems indicates a significant role of the polymer particle size in the formation of the conductive
clusters. This is due to the MWCNTs distribution in the polymer matrix provided
that the polymer particles have a much larger size than MWCNTs agglomerates [7].
Due to mechanical mixing, the filler covers the surface of the polymer particles, and
during hot pressing, this structure changes little and the filler remains at the boundary
of the polymer particles. Therefore, a cluster conductive structure with a concentration of MWCNTs above the average and a system of cells with a lower concentration
of MWCNTs or their absence can be formed. In this case, the PE–MWCNTs system
has a sufficiently low percolation threshold and a relatively low influence of the
MWCNTs agglomerate size on the percolation properties of the systems [7].
3.3 The Mechanical Characteristics of the Nanocomposites
The tests of tensile (Fig. 5) and compression (Fig. 6) showed that the introduction
of MWCNTs changes the mechanical characteristics of the considered composite
systems. The dependence of elongation relative to tension stress (Fig. 5) for the
PE–MWCNTs system can be divided into four regions. The region with positive
curvature in the range up to 5% of deformation is used for composites. It may
be due to the presence of pores (nanoscale), which works as elastic deformation
elements [27], the elastic, plastic regions and fracture of the samples. Thus, the
introduction of nanotubes in the polymer matrix leads to a change in the limit of
the tensile strength (increase), modulus of elasticity (120–213 MPa), the conditional
691
to a composition with a concentration of 5% wt. is almost seven orders of magnitude
for PE–MWCNTs (Fig. 4a) and nine orders for PP–MWCNTs (b), PTFE–MWCNTs
(c). Of course, to create a continuous conductive grid in the polymer matrix, the size
of the filler (the length of the MWCNTs agglomerates) and its distribution in the
matrix are of great importance.
Approximating the experimental curves (Fig. 4) and given the linear dependence
of the lgσ ~ lg(θ –θ F ), percolation parameters for the three systems were determined.
The percolation threshold for the PE–MWCNTs system was (0.45 ± 0.02) % vol.
In this case, the value of electrical conductivity is ≈1.1 × 10
3 (m·cm)
−1 , and the
critical index is t ~ 1.8, corresponding to the three-dimensional system. The calculation of critical indices for the system PP–MWCNTs gives the following values:
θ F = 0.345% vol., t = 1.83. Deterioration of the homogeneity of the distribution of
MWCNTs (curves 2, 1 Fig. 4b) corresponds to an increase in the critical concentration (percolation threshold) in the range of 0.345% vol., 0.92% vol., 1.28% vol.
For the PTFE–MWCNTs system (Fig. 4c), we also observe a shift of the percolation
threshold to the region of lower values from θ F = 6.68% vol. for initial MWCNTs
to θ F = 3.89% vol. (t = 1.64) for MWCNTs pre-deaglomerated in a rotary hydrodynamic homogenizer (RHDH) using the simultaneous action of the shear deformation
and a cavitation mixing. Therefore, the value of the critical MWCNTs concentration
can be used as a parameter to determine the degree of the homogeneity of filled
polymer systems.
Analysis of the results on the electrical conductivity of the obtained systems indicates a significant role of the polymer particle size in the formation of the conductive
clusters. This is due to the MWCNTs distribution in the polymer matrix provided
that the polymer particles have a much larger size than MWCNTs agglomerates [7].
Due to mechanical mixing, the filler covers the surface of the polymer particles, and
during hot pressing, this structure changes little and the filler remains at the boundary
of the polymer particles. Therefore, a cluster conductive structure with a concentration of MWCNTs above the average and a system of cells with a lower concentration
of MWCNTs or their absence can be formed. In this case, the PE–MWCNTs system
has a sufficiently low percolation threshold and a relatively low influence of the
MWCNTs agglomerate size on the percolation properties of the systems [7].
3.3 The Mechanical Characteristics of the Nanocomposites
The tests of tensile (Fig. 5) and compression (Fig. 6) showed that the introduction
of MWCNTs changes the mechanical characteristics of the considered composite
systems. The dependence of elongation relative to tension stress (Fig. 5) for the
PE–MWCNTs system can be divided into four regions. The region with positive
curvature in the range up to 5% of deformation is used for composites. It may
be due to the presence of pores (nanoscale), which works as elastic deformation
elements [27], the elastic, plastic regions and fracture of the samples. Thus, the
introduction of nanotubes in the polymer matrix leads to a change in the limit of
the tensile strength (increase), modulus of elasticity (120–213 MPa), the conditional