Linear viscoelasticity is usually applicable only for small deformations.
Nonlinear viscoelasticity is when the function is not separable. It usually happens
when the deformations are large or if the material changes its properties under
deformations (http://en.wikipedia.org/wiki/Viscoelasticity).
This chapter focuses on the non-linear viscoelastic behavior of rubber composites and nanocomposites. Here, we have discussed about the effect of individual
fillers (mineral fillers, nanotubes, carbon nanofillers, fibrous nanofillers, biofillers,
special structured fillers viz. nanorods, nanowires, nanoflowers etc.) on the linear/
nonlinear viscoelastic behavior of rubber composites. Moreover, as this chapter is
more concerned on the non-linear viscoelastic behavior, we have also discussed the
effect of hybrid fillers on the nonlinear viscoelastic behavior of rubber composites
in more detail.
2 Different Types of Nanofillers and Its Effect
on Viscoelasticity Behavior of Rubber Nanocomposites
2.1 Mineral Fillers
Fillers are defined as additives in solid form that differ from the polymer/rubber
matrix with respect to their composition and structure. A mineral filler is defined as
a finely pulverized inert mineral or rock that is included in a manufactured product
(e.g. paper, rubber, and plastics) to impart certain useful properties, such as
hardness, smoothness, or strength etc (http://www.mindat.org/glossary/
mineral_filler). Mineral particulate fillers are used in rubber/polymer composites
to reduce the cost of the final product and to add some mineral property with the
host (rubber/polymer) matrix, that is, to improve the properties of the matrix [19–
22]. Common mineral fillers include asbestos, kaolin, talc, mica, wollastonite, and
calcium carbonate etc (http://www.mindat.org/glossary/mineral_filler) [19].
The characteristics which determine the properties filler that will impart to a
composite are particle shape, particle size, surface area, and particle-matrix compatibility (Fig. 1). Particle-matrix compatibility relates to the ability of the polymer
to coat and adhere to the filler. The shape of most mineral filler particles can be a
sphere, cube, block, plate, needle, or fiber whereas some filler also contain a
mixture of shapes. Mineral particles resembling plates, needles, and fibers are
further characterized by their aspect ratio (http://www.rtvanderbilt.com/
fillersintroweb.pdf). In rubber/polymer composites, applied stress is transferred
from the rubber/polymer matrix to the strong and stiff mineral. It seems reasonable
that this stress transfer will be better affected if the mineral particles are smaller,
because greater surface is thereby exposed for a given mineral concentration.
Moreover, if these particles have a high aspect ratio (are needle-like, fibrous or
platy in shape), they will better intercept the stress propagation through the matrix
(Fig. 2) (http://www.rtvanderbilt.com/fillersintroweb.pdf).
Effect of Hybrid Fillers on the Non-Linear Viscoelasticity of Rubber. . .
137
Nonlinear viscoelasticity is when the function is not separable. It usually happens
when the deformations are large or if the material changes its properties under
deformations (http://en.wikipedia.org/wiki/Viscoelasticity).
This chapter focuses on the non-linear viscoelastic behavior of rubber composites and nanocomposites. Here, we have discussed about the effect of individual
fillers (mineral fillers, nanotubes, carbon nanofillers, fibrous nanofillers, biofillers,
special structured fillers viz. nanorods, nanowires, nanoflowers etc.) on the linear/
nonlinear viscoelastic behavior of rubber composites. Moreover, as this chapter is
more concerned on the non-linear viscoelastic behavior, we have also discussed the
effect of hybrid fillers on the nonlinear viscoelastic behavior of rubber composites
in more detail.
2 Different Types of Nanofillers and Its Effect
on Viscoelasticity Behavior of Rubber Nanocomposites
2.1 Mineral Fillers
Fillers are defined as additives in solid form that differ from the polymer/rubber
matrix with respect to their composition and structure. A mineral filler is defined as
a finely pulverized inert mineral or rock that is included in a manufactured product
(e.g. paper, rubber, and plastics) to impart certain useful properties, such as
hardness, smoothness, or strength etc (http://www.mindat.org/glossary/
mineral_filler). Mineral particulate fillers are used in rubber/polymer composites
to reduce the cost of the final product and to add some mineral property with the
host (rubber/polymer) matrix, that is, to improve the properties of the matrix [19–
22]. Common mineral fillers include asbestos, kaolin, talc, mica, wollastonite, and
calcium carbonate etc (http://www.mindat.org/glossary/mineral_filler) [19].
The characteristics which determine the properties filler that will impart to a
composite are particle shape, particle size, surface area, and particle-matrix compatibility (Fig. 1). Particle-matrix compatibility relates to the ability of the polymer
to coat and adhere to the filler. The shape of most mineral filler particles can be a
sphere, cube, block, plate, needle, or fiber whereas some filler also contain a
mixture of shapes. Mineral particles resembling plates, needles, and fibers are
further characterized by their aspect ratio (http://www.rtvanderbilt.com/
fillersintroweb.pdf). In rubber/polymer composites, applied stress is transferred
from the rubber/polymer matrix to the strong and stiff mineral. It seems reasonable
that this stress transfer will be better affected if the mineral particles are smaller,
because greater surface is thereby exposed for a given mineral concentration.
Moreover, if these particles have a high aspect ratio (are needle-like, fibrous or
platy in shape), they will better intercept the stress propagation through the matrix
(Fig. 2) (http://www.rtvanderbilt.com/fillersintroweb.pdf).
Effect of Hybrid Fillers on the Non-Linear Viscoelasticity of Rubber. . .
137