dispersion of nanofiller in a monomer, which can polymerize. This method gives
many possibilities for synthesis and modification (matrix or filler). In the third
method (melt blending/mixing), the polymer is processed using extruders, very
often a twin-screw extruder. This method, based on polymer processing (in a bulk
state) is widely available, but good dispersion of the nanofiller in the polymer
matrix is sometimes difficult to achieve [40].
Rubber nanocomposites can be based on many rubber matrices, for example
(clay reinforcement): natural rubber [41] or synthetic rubber materials such as
styrene-butadiene rubber [42], nitrile-rubber [43], EPDM [44] or polyurethane
[45, 46].
Nanoparticles, compared with traditional fillers, provide more reinforcement
due to the higher interfacial area. Introduction of these particles into the rubber
matrix improves many of its properties, in particular tensile strength, thermal
stability, elasticity, processability or barrier improvement. The final properties of
nanocomposites are determined by the filler-filler and polymer-filler interactions.
Therefore, it is very important to have knowledge of the characteristics of nonlinear
viscoelastic behavior for rubber reinforced systems, especially an analysis of the
low strain dynamic mechanical properties (Payne effect).
The next sections present the influence of 3D nanofillers in rubber
nanocomposites on the nonlinear viscoelastic behavior of these systems.
3.1 Polyhedral Oligomeric Silsesquioxane Rubber
Nanocomposites
Poly(dimethylsiloxane) (PDMS) is one of the most popular inorganic elastomers
and can be modified with many nanofillers. Pan et al. used silanol-terminated
PDMS and modified this matrix with mono-POSS and tetra-POSS cages which
were physically blended into the matrix. The authors prepared another type of
PDMS which had vinyl terminal groups that are also able to react with the central
siloxane core by hydrosilylation. The idea was to obtain larger POSS-based fillers
than silica particles typically used to reinforce elastomers (Fig. 8).
Figure 9 gives the dynamic mechanical analysis results showing that the POSS
containing composites possess higher storage modulus with increasing POSS
content in the low strain modulus amplitude. This behavior is characteristic for
the Payne effect. Percolation of the filler particles is part of the filler network
interpretation of the Payne effect. The authors expected a dramatic increase in the
described effect at loadings of about 15 % wt of the nanofiller. Figure 9a suggests
that the percolation threshold is at 10 % wt or more with the addition of POSS. This
level of percolation threshold may result from a larger effective filler volume
fraction in these systems. Useful information about the filler-networking behavior
comes from the loss tangent vs. strain amplitude observed in the Fig. 9b. The
maximum of the loss tangent is visible in the 10 % wt POSS-containing
68
M. Strankowski
many possibilities for synthesis and modification (matrix or filler). In the third
method (melt blending/mixing), the polymer is processed using extruders, very
often a twin-screw extruder. This method, based on polymer processing (in a bulk
state) is widely available, but good dispersion of the nanofiller in the polymer
matrix is sometimes difficult to achieve [40].
Rubber nanocomposites can be based on many rubber matrices, for example
(clay reinforcement): natural rubber [41] or synthetic rubber materials such as
styrene-butadiene rubber [42], nitrile-rubber [43], EPDM [44] or polyurethane
[45, 46].
Nanoparticles, compared with traditional fillers, provide more reinforcement
due to the higher interfacial area. Introduction of these particles into the rubber
matrix improves many of its properties, in particular tensile strength, thermal
stability, elasticity, processability or barrier improvement. The final properties of
nanocomposites are determined by the filler-filler and polymer-filler interactions.
Therefore, it is very important to have knowledge of the characteristics of nonlinear
viscoelastic behavior for rubber reinforced systems, especially an analysis of the
low strain dynamic mechanical properties (Payne effect).
The next sections present the influence of 3D nanofillers in rubber
nanocomposites on the nonlinear viscoelastic behavior of these systems.
3.1 Polyhedral Oligomeric Silsesquioxane Rubber
Nanocomposites
Poly(dimethylsiloxane) (PDMS) is one of the most popular inorganic elastomers
and can be modified with many nanofillers. Pan et al. used silanol-terminated
PDMS and modified this matrix with mono-POSS and tetra-POSS cages which
were physically blended into the matrix. The authors prepared another type of
PDMS which had vinyl terminal groups that are also able to react with the central
siloxane core by hydrosilylation. The idea was to obtain larger POSS-based fillers
than silica particles typically used to reinforce elastomers (Fig. 8).
Figure 9 gives the dynamic mechanical analysis results showing that the POSS
containing composites possess higher storage modulus with increasing POSS
content in the low strain modulus amplitude. This behavior is characteristic for
the Payne effect. Percolation of the filler particles is part of the filler network
interpretation of the Payne effect. The authors expected a dramatic increase in the
described effect at loadings of about 15 % wt of the nanofiller. Figure 9a suggests
that the percolation threshold is at 10 % wt or more with the addition of POSS. This
level of percolation threshold may result from a larger effective filler volume
fraction in these systems. Useful information about the filler-networking behavior
comes from the loss tangent vs. strain amplitude observed in the Fig. 9b. The
maximum of the loss tangent is visible in the 10 % wt POSS-containing
68
M. Strankowski