because bigger deformations need more torque but polymer chains flow more easily
thus shear modulus (G) decreases in higher strains. S of NR/reclaimed rubber
blends is lower than two polymers (i.e. natural rubber and reclaimed rubber),
while authors predicted that the torque of blends is between the torque of two
polymers. This behavior can be attributed to nonhomogeneity of phases in blends. It
seems that friction of polymer chains in a completely homogenized and compatible
blend is more than non homogenized one.
They studied the elastic modulus (G
0 ) and loss modulus (G
00 ) of compounds.
They observed that the G
0 changes with strain can be divided to three different
zones: linear viscoelastic in low strains, non-linear viscoelastic in medium strains
and linear viscoelastic in high strains. In low strains, G
0 of reclaimed rubber is
higher than natural rubber due to the fillers left in reclaimed rubber. But non-linear
viscoelastic behavior of reclaimed rubber begins in lower strains than NR. This can
be attributed to the beginning of the filler-filler and rubber-filler networks breakdown in these strains. In medium strains, elastic modulus (G
0 ) decreases due to
rubber-filler and filler-filler networks breakdown and disentanglement of polymer
chains. The rate of G
0 drop in this non-linear viscoelastic zone in reclaimed rubber
is less than NR due to filler presence in reclaimed rubber and its elastic nature. In
high strains, G
0 of compounds is the same but linear viscoelastic behavior (i.e. the
plateau) of reclaimed rubber begins in higher strains than NR. In other words,
non-linear viscoelastic zone in reclaimed rubber is longer than NR, begins in lower
strains and finishes in higher strains.
The elastic modulus of NR/reclaimed rubber blends is lower than NR and
reclaimed rubber which is due to non-homogeneity and non-uniform dispersion
of filler in these blends. The G
0 of blends has similar trend to their major phase
(i.e. NR or reclaimed rubber).
Three zones indicated in G
0 , can also be detected in the graph of loss modulus
(G
00 ) versus strain. In low strain, the first linear viscoelastic zone, G
00 of reclaimed is
lower than NR due to its filler content. In higher strains, G
00 of NR compounds
decreases due to disentanglement of polymer chains whereas, reclaimed rubber has
different behavior. In medium strains, loss modulus of reclaimed rubber increases
due to energy dissipation for rubber-filler and filler-filler networks breakdown and
then decreases due to rubber chains disentanglement.
In high strains, moving of polymer chains is completely laminar and all compounds have linear viscoelastic behavior, thus G
00 has no significant change. Final
G
00 of reclaimed rubber is lower than NR which is due the fillers left in reclaimed
rubber. Loss modulus G
00 of NR/reclaimed rubber blends has similar trend to the
major phase of blend (i.e. NR or reclaimed rubber). It is indicated that the increase
of loss modulus in non-linear viscoelastic zone can be detected in NR/reclaimed
rubber 25/150 blend while this behavior cannot be observed in NR/reclaimed
rubber 75/50 blend. In high strains linear viscoelastic zone, nonhomogeneity of
phases and non-uniform dispersion of filler cause lower loss modulus of
NR/reclaimed rubber blends than NR and reclaimed rubber. In addition, in the
first low strain linear viscoelastic zone, G
00 of NR/reclaimed rubber blends has no
significant difference with reclaimed rubber. It seems filler amount, homogeneity of
104
A.B. Nair et al.
thus shear modulus (G) decreases in higher strains. S of NR/reclaimed rubber
blends is lower than two polymers (i.e. natural rubber and reclaimed rubber),
while authors predicted that the torque of blends is between the torque of two
polymers. This behavior can be attributed to nonhomogeneity of phases in blends. It
seems that friction of polymer chains in a completely homogenized and compatible
blend is more than non homogenized one.
They studied the elastic modulus (G
0 ) and loss modulus (G
00 ) of compounds.
They observed that the G
0 changes with strain can be divided to three different
zones: linear viscoelastic in low strains, non-linear viscoelastic in medium strains
and linear viscoelastic in high strains. In low strains, G
0 of reclaimed rubber is
higher than natural rubber due to the fillers left in reclaimed rubber. But non-linear
viscoelastic behavior of reclaimed rubber begins in lower strains than NR. This can
be attributed to the beginning of the filler-filler and rubber-filler networks breakdown in these strains. In medium strains, elastic modulus (G
0 ) decreases due to
rubber-filler and filler-filler networks breakdown and disentanglement of polymer
chains. The rate of G
0 drop in this non-linear viscoelastic zone in reclaimed rubber
is less than NR due to filler presence in reclaimed rubber and its elastic nature. In
high strains, G
0 of compounds is the same but linear viscoelastic behavior (i.e. the
plateau) of reclaimed rubber begins in higher strains than NR. In other words,
non-linear viscoelastic zone in reclaimed rubber is longer than NR, begins in lower
strains and finishes in higher strains.
The elastic modulus of NR/reclaimed rubber blends is lower than NR and
reclaimed rubber which is due to non-homogeneity and non-uniform dispersion
of filler in these blends. The G
0 of blends has similar trend to their major phase
(i.e. NR or reclaimed rubber).
Three zones indicated in G
0 , can also be detected in the graph of loss modulus
(G
00 ) versus strain. In low strain, the first linear viscoelastic zone, G
00 of reclaimed is
lower than NR due to its filler content. In higher strains, G
00 of NR compounds
decreases due to disentanglement of polymer chains whereas, reclaimed rubber has
different behavior. In medium strains, loss modulus of reclaimed rubber increases
due to energy dissipation for rubber-filler and filler-filler networks breakdown and
then decreases due to rubber chains disentanglement.
In high strains, moving of polymer chains is completely laminar and all compounds have linear viscoelastic behavior, thus G
00 has no significant change. Final
G
00 of reclaimed rubber is lower than NR which is due the fillers left in reclaimed
rubber. Loss modulus G
00 of NR/reclaimed rubber blends has similar trend to the
major phase of blend (i.e. NR or reclaimed rubber). It is indicated that the increase
of loss modulus in non-linear viscoelastic zone can be detected in NR/reclaimed
rubber 25/150 blend while this behavior cannot be observed in NR/reclaimed
rubber 75/50 blend. In high strains linear viscoelastic zone, nonhomogeneity of
phases and non-uniform dispersion of filler cause lower loss modulus of
NR/reclaimed rubber blends than NR and reclaimed rubber. In addition, in the
first low strain linear viscoelastic zone, G
00 of NR/reclaimed rubber blends has no
significant difference with reclaimed rubber. It seems filler amount, homogeneity of
104
A.B. Nair et al.