dependence. The effect of filler morphology, namely, its fineness related to surface
area and/or particle size and distribution; and its structure related to its aggregate
irregularity of shapes and their distribution, has been investigated and reviewed
[1]. In addition, the importance of surface characteristics in the dynamic properties
of the filled rubbers has also been emphasized in the literature [2].
It is well known that a thin layer of rubber, which is at the surface of nano-fillers,
e.g. silica or carbon black, is immobilized by chain adsorption. The estimated
thickness of the immobilized layer, the rubber-filler interface, is in the range of
two diameters of the monomer unit. Filler aggregates, which are covered by the
interface, can be considered as multifunctional physical crosslinks. Traditionally,
the physical rubber-filler network is characterized by the content of the apparent
“bound” rubber [3], which is determined as the amount of unvulcanized rubber still
adhering to the dispersed filler aggregates after extraction. Since the amount of
bound rubber is related to the surface area and the surface activity of the fillers, this
phenomenon provides indirect proof of a multicontact chain adsorption at the filler
surface. The formation and the strength of the physical network influence nonlinear
viscoelastic behavior of filled rubbers. Carbon black-filled rubbers show a typical
nonlinear viscoelastic behavior [4]. At strains of about 1 %, a significant decrease of
storage modulus occurs from the zero-strain value G
0
0 to a high amplitude plateau
value G
0
1 connected with the appearance of a loss modulus G
00 maximum [4]. This
effect was described by Payne in the 1960s [5, 6], who interpreted this behavior as
the result of breakage and reforming of physical bonds between the filler aggregates. These bonds were assumed to build filler agglomerates of different size and,
above a certain threshold, an elastic filler-filler network within the rubber matrix.
For a typical rubber compound, roughly half of the energy dissipation during cyclic
deformation can be ascribed to the agglomerated filler, the rest coming from chain
ends and internal friction. Empirical relations have been derived which relate the
propensity of carbon black to agglomerate with the heat buildup of the rubber
compound. Minimizing this hysteresis can be a major criterion in developing a
rubber compound.
The nonlinear viscoelastic behavior of filled vulcanizates is somewhat different
from that of filled compounds, since the chemical crosslink network of the rubber
matrix is formed and, the physical rubber-filler networks and filler-filler networks
are enhanced during curing at a relatively high temperature [7]. Speaking from a
broad sense, filled vulcanizates can be viewed as a “double network” structure in
which the nanoparticles supplement the inherent viscoelasticity of crosslink rubbers
with additional physical network junctions.
In practice, the energy loss in filled vulcanizates during dynamic strain is of great
importance, as for example, in vibration mounts and automotive tires where it
affects the service performance of these products with regard to heat generation
and fatigue life for the former, and rolling resistance, traction and skid resistance for
the latter [2]. In fact, with regard to tire applications, it has been well established
that repeated straining of the filled vulcanizates due to rotation and braking can be
approximated as a process of constant energy input involving different
162
Y. Chen and C. Xu
area and/or particle size and distribution; and its structure related to its aggregate
irregularity of shapes and their distribution, has been investigated and reviewed
[1]. In addition, the importance of surface characteristics in the dynamic properties
of the filled rubbers has also been emphasized in the literature [2].
It is well known that a thin layer of rubber, which is at the surface of nano-fillers,
e.g. silica or carbon black, is immobilized by chain adsorption. The estimated
thickness of the immobilized layer, the rubber-filler interface, is in the range of
two diameters of the monomer unit. Filler aggregates, which are covered by the
interface, can be considered as multifunctional physical crosslinks. Traditionally,
the physical rubber-filler network is characterized by the content of the apparent
“bound” rubber [3], which is determined as the amount of unvulcanized rubber still
adhering to the dispersed filler aggregates after extraction. Since the amount of
bound rubber is related to the surface area and the surface activity of the fillers, this
phenomenon provides indirect proof of a multicontact chain adsorption at the filler
surface. The formation and the strength of the physical network influence nonlinear
viscoelastic behavior of filled rubbers. Carbon black-filled rubbers show a typical
nonlinear viscoelastic behavior [4]. At strains of about 1 %, a significant decrease of
storage modulus occurs from the zero-strain value G
0
0 to a high amplitude plateau
value G
0
1 connected with the appearance of a loss modulus G
00 maximum [4]. This
effect was described by Payne in the 1960s [5, 6], who interpreted this behavior as
the result of breakage and reforming of physical bonds between the filler aggregates. These bonds were assumed to build filler agglomerates of different size and,
above a certain threshold, an elastic filler-filler network within the rubber matrix.
For a typical rubber compound, roughly half of the energy dissipation during cyclic
deformation can be ascribed to the agglomerated filler, the rest coming from chain
ends and internal friction. Empirical relations have been derived which relate the
propensity of carbon black to agglomerate with the heat buildup of the rubber
compound. Minimizing this hysteresis can be a major criterion in developing a
rubber compound.
The nonlinear viscoelastic behavior of filled vulcanizates is somewhat different
from that of filled compounds, since the chemical crosslink network of the rubber
matrix is formed and, the physical rubber-filler networks and filler-filler networks
are enhanced during curing at a relatively high temperature [7]. Speaking from a
broad sense, filled vulcanizates can be viewed as a “double network” structure in
which the nanoparticles supplement the inherent viscoelasticity of crosslink rubbers
with additional physical network junctions.
In practice, the energy loss in filled vulcanizates during dynamic strain is of great
importance, as for example, in vibration mounts and automotive tires where it
affects the service performance of these products with regard to heat generation
and fatigue life for the former, and rolling resistance, traction and skid resistance for
the latter [2]. In fact, with regard to tire applications, it has been well established
that repeated straining of the filled vulcanizates due to rotation and braking can be
approximated as a process of constant energy input involving different
162
Y. Chen and C. Xu