2.4 Reinforcing Nanofiller
23
It is quite regrettable that a mountain of data of mechanical (tensile) test results, having
been accumulated on rubber products, are useless due to the insufficiency of experimental
conditions for the scientific studies, in particular.
Regrettably, this advice has to be repeated still now. Accumulation of tensile curves
simply makes sense for rubber business, not much of value for science without any
other information, e.g., structural information on the dispersion of CB in rubber
matrix, which is exactly aimed in the studies discussed in the present book.
2.4.3 Particulate Silica
Among silica particles for rubber, the diameter of a few grades is even smaller than
that of CB (see Fig. 2.2), and silica constitutes a representative nanofiller for rubber
reinforcement together with CB. In general, its features include better tear strength,
lower heat buildup, and better tack in shaping the rubber compounds, to name a few
in comparison with CB. On the market, two types of particulate silica are available;
one is fumed silica, and the other is precipitated silica (wet silica is in use, too). A
few grades of the former are very fine and smaller than the latter. Yet, the cheaper
precipitated silica is preferred in the rubber industry [5, 8, 10–12, 37–39, 54–56].
Due to the presence of silanol group on the surface of the precipitated silica,
interaction between silica and rubber is relatively smaller than that between CB and
rubber. In other words, the silica-to-silica interaction is stronger than the CB-to-CB
interaction due to hydrogen bonding by silanol groups, which results in relatively
more aggregation of silica particles in the rubber matrix than CB. In the processing
of rubber, this aggregation causes difficulty in mixing, which has been more or less
overcome by using silane coupling agents [57–60]. They carry two functional groups,
one reactive to the silanol group on silica surface and the other reactive to rubber
molecule.
The other way to realize a good silica dispersion in rubber is in situ silica generation using the sol–gel reaction technique, which has been developed in glass
manufacturing [12, 56, 60–69]. The in situ produced silica particles in rubber matrix
show characteristic reinforcing behaviors, and Chap. 6 is devoted to this silica, too.
Industrialization of this method to obtain in situ silica/rubber compounds is the next
subject to be developed.
2.4.4 Non-spherical Rubber Reinforcing Materials
Rubber is an amorphous material, and hence, it is reasonable that the most properties of rubber goods are isotropic. Accordingly, fillers of isotropic sphere shape are
favorable for rubber. However, when we consider that the unavoidable aggregation
of nanofillers (we are not using the single CB particle but the primary aggregate of
23
It is quite regrettable that a mountain of data of mechanical (tensile) test results, having
been accumulated on rubber products, are useless due to the insufficiency of experimental
conditions for the scientific studies, in particular.
Regrettably, this advice has to be repeated still now. Accumulation of tensile curves
simply makes sense for rubber business, not much of value for science without any
other information, e.g., structural information on the dispersion of CB in rubber
matrix, which is exactly aimed in the studies discussed in the present book.
2.4.3 Particulate Silica
Among silica particles for rubber, the diameter of a few grades is even smaller than
that of CB (see Fig. 2.2), and silica constitutes a representative nanofiller for rubber
reinforcement together with CB. In general, its features include better tear strength,
lower heat buildup, and better tack in shaping the rubber compounds, to name a few
in comparison with CB. On the market, two types of particulate silica are available;
one is fumed silica, and the other is precipitated silica (wet silica is in use, too). A
few grades of the former are very fine and smaller than the latter. Yet, the cheaper
precipitated silica is preferred in the rubber industry [5, 8, 10–12, 37–39, 54–56].
Due to the presence of silanol group on the surface of the precipitated silica,
interaction between silica and rubber is relatively smaller than that between CB and
rubber. In other words, the silica-to-silica interaction is stronger than the CB-to-CB
interaction due to hydrogen bonding by silanol groups, which results in relatively
more aggregation of silica particles in the rubber matrix than CB. In the processing
of rubber, this aggregation causes difficulty in mixing, which has been more or less
overcome by using silane coupling agents [57–60]. They carry two functional groups,
one reactive to the silanol group on silica surface and the other reactive to rubber
molecule.
The other way to realize a good silica dispersion in rubber is in situ silica generation using the sol–gel reaction technique, which has been developed in glass
manufacturing [12, 56, 60–69]. The in situ produced silica particles in rubber matrix
show characteristic reinforcing behaviors, and Chap. 6 is devoted to this silica, too.
Industrialization of this method to obtain in situ silica/rubber compounds is the next
subject to be developed.
2.4.4 Non-spherical Rubber Reinforcing Materials
Rubber is an amorphous material, and hence, it is reasonable that the most properties of rubber goods are isotropic. Accordingly, fillers of isotropic sphere shape are
favorable for rubber. However, when we consider that the unavoidable aggregation
of nanofillers (we are not using the single CB particle but the primary aggregate of