2.5 Reinforcing Factors of Particulate Nanofiller
25
an agglomerate in rubber matrix. The possible structure of these aggregates and
the ultimate of them, i.e., the agglomerate has been actively discussed, and the
clustering is expressed as ‘structuring of filler,’ among rubber engineers.
Many studies have discussed rubber reinforcement at either of the two sides so
far. At an early stage, experimental evidences of the bound rubber were accumulated.
Additionally, the rubber layer encircling filler surface makes it easier for the filler
to be dispersed homogeneously, and hence, bound rubber is reasonably assumed to
be an important factor for reinforcement. On the other hand, studies on the structure of aggregates and/or agglomerate have failed to propose a reasonable model.
Aggregation of nanoparticles by the van der Waals force is fundamentally a random
process. Moreover, aggregation (and agglomeration, too) may be accompanied by
degradation or not, depending on the conditions of mechanical mixing with rubber.
Consequently, the difficulty of structure estimation has resulted in a favorable trend
to the bound rubber supporters. Some of the structuring side researchers thought of
the filler network structure as the ultimate agglomerate of filler, but experimental
evidence of the filler network structure has not been presented. The final conclusive
study has been brought over to the twenty-first century.
The present book highlights the studies showing the image of the ultimate
agglomerate of nanofillers, i.e., the network structure of nanofiller by threedimensional transmission electron microscopy (3D-TEM) and elucidating the relationship between the two, i.e., bound rubber and nanofiller network structure. This
section gives preparative descriptions on these studies described in Parts 2 and 3.
Furthermore, the third factor of rubber reinforcement, ‘hydrodynamic volume
effect’ is also included in this section and in the next section. A. R. Payne introduced
three factors, ‘Hydrodynamic, Strong Links, and Structure,’ at Chap. 3 of the book
edited by Kraus [5]. Here, ‘Strong Links’ is equivalent to bound rubber, and ‘Structure’ to structuring of filler, respectively. The three have been mentioned on many
occasions and lively discussed for long, and the debate continues to this century. But
on ‘Hydrodynamic,’ even the theoretical settlement has not been conclusive yet from
the viewpoint of rubber reinforcement. We hope two subsections, 2.5.4 and 2.6.4,
give some insight into this factor, which may hopefully stimulate the start of final
conclusive study on the hydrodynamic volume effect.
2.5.2 Bound Rubber
J. H. Fielding used the words ‘bound rubber’ for the first time [77]. It was experimentally quantified as a weight of rubber component in the rubber/filler compound which
was insoluble to good solvents of rubber (cyclohexane, tetrahydrofuran, toluene,
etc.). In the case of CB/rubber compounds, ‘carbon gel’ or ‘filler gel’ was once
used [78], but bound rubber is now most commonly utilized for the insoluble rubber
layer encircling the filler surface. Later, the mobility of rubber molecules in the layer
was subjected to the broad-line nuclear magnetic resonance (NMR) measurements,
25
an agglomerate in rubber matrix. The possible structure of these aggregates and
the ultimate of them, i.e., the agglomerate has been actively discussed, and the
clustering is expressed as ‘structuring of filler,’ among rubber engineers.
Many studies have discussed rubber reinforcement at either of the two sides so
far. At an early stage, experimental evidences of the bound rubber were accumulated.
Additionally, the rubber layer encircling filler surface makes it easier for the filler
to be dispersed homogeneously, and hence, bound rubber is reasonably assumed to
be an important factor for reinforcement. On the other hand, studies on the structure of aggregates and/or agglomerate have failed to propose a reasonable model.
Aggregation of nanoparticles by the van der Waals force is fundamentally a random
process. Moreover, aggregation (and agglomeration, too) may be accompanied by
degradation or not, depending on the conditions of mechanical mixing with rubber.
Consequently, the difficulty of structure estimation has resulted in a favorable trend
to the bound rubber supporters. Some of the structuring side researchers thought of
the filler network structure as the ultimate agglomerate of filler, but experimental
evidence of the filler network structure has not been presented. The final conclusive
study has been brought over to the twenty-first century.
The present book highlights the studies showing the image of the ultimate
agglomerate of nanofillers, i.e., the network structure of nanofiller by threedimensional transmission electron microscopy (3D-TEM) and elucidating the relationship between the two, i.e., bound rubber and nanofiller network structure. This
section gives preparative descriptions on these studies described in Parts 2 and 3.
Furthermore, the third factor of rubber reinforcement, ‘hydrodynamic volume
effect’ is also included in this section and in the next section. A. R. Payne introduced
three factors, ‘Hydrodynamic, Strong Links, and Structure,’ at Chap. 3 of the book
edited by Kraus [5]. Here, ‘Strong Links’ is equivalent to bound rubber, and ‘Structure’ to structuring of filler, respectively. The three have been mentioned on many
occasions and lively discussed for long, and the debate continues to this century. But
on ‘Hydrodynamic,’ even the theoretical settlement has not been conclusive yet from
the viewpoint of rubber reinforcement. We hope two subsections, 2.5.4 and 2.6.4,
give some insight into this factor, which may hopefully stimulate the start of final
conclusive study on the hydrodynamic volume effect.
2.5.2 Bound Rubber
J. H. Fielding used the words ‘bound rubber’ for the first time [77]. It was experimentally quantified as a weight of rubber component in the rubber/filler compound which
was insoluble to good solvents of rubber (cyclohexane, tetrahydrofuran, toluene,
etc.). In the case of CB/rubber compounds, ‘carbon gel’ or ‘filler gel’ was once
used [78], but bound rubber is now most commonly utilized for the insoluble rubber
layer encircling the filler surface. Later, the mobility of rubber molecules in the layer
was subjected to the broad-line nuclear magnetic resonance (NMR) measurements,