88
5 Reinforcing Mechanism of Rubber by Nanofiller
of them are possibly chemically connected even to the surface of the furnace CB by
the mechanochemical reactions during the mixing stage of CB into rubber [4, 15, 18,
21]. This possibility remains to be unsolved, and hence, some quantitative studies
are still to be done. Above all, the bound rubber is easy to observe it experimentally,
namely by checking of the insoluble rubber fraction on the surface of CB. Hence, it
is not surprising that lots of experimental results on bound rubber have been reported
until now.
Kraus claimed that the importance of filler particle size was free from mistakes,
but he pointed out, too, that it was not the only factor but some interactions were
to be considered for the rubber reinforcement by filler [19, 20]. This opinion was
exactly in accordance with that of the three authors of Ref. [8] (see Sect. 5.2). In
fact, Kraus arranged Bueche’s network structure theory [18] to be placed at the
beginning of his book [9]. However, much more notable is Chap. 3 [10], in which
Payne disclosed three factors for explaining Payne effect. His excellent comments
have been conveniently and effectively used for interpreting rubber reinforcement
in general; (1) Hydrodynamic volume effect, (2) bound rubber, and (3) structuring
of filler. Quite a number of papers on rubber reinforcement adopted Payne’s three
factors for explaining reinforcement by fillers (see Sects. 2.4 and 2.5). Under these
trends, studies on bound rubber have particularly been conducted actively, which is
due to experimental feasibility to quantifying the bound rubber amount. However, it
seems to have been few studies exceeding those by Fujimoto’s model [26, 27] or no
publications have negated his model so far.
The third factor, structuring of filler, has failed to advance much due to the empirical difficulty. Specifically, the experimental evidence of the network structure of
filler, which is assumed to be the ultimate form of the structuring or aggregation of
nanofillers, has not been offered in the twentieth century. Needless to say, there have
been disclosed lots of assumptions on the filler networks, still solid evidence has not
been given (see Sects. 3.2.1 and 4.3.1. See also readable Chap. 3 by Hess in Ref.
[9]). For one more example, Ishikawa et al. proposed a morphology of CB-loaded
NR vulcanizates based on their anti-abrasion properties [28], which is in accordance
with the CB network structure at least qualitatively.
5.4 Toward Nanofiller Networking in Rubber Matrix
(Early in the Twenty-First Century)
How to model the filler network structure had been actively researched for a few
decades until the beginning of the twenty-first century. One of the most notable studies has been carried out by Krüppel et al. [29, 30]. They presented a semi-theoretical
treatment of the filler gelation process, on the basis of the scaling concept by de
Gennes [31] and the fractal theory by Mandelbrot [32]. Namely, they proposed a
5 Reinforcing Mechanism of Rubber by Nanofiller
of them are possibly chemically connected even to the surface of the furnace CB by
the mechanochemical reactions during the mixing stage of CB into rubber [4, 15, 18,
21]. This possibility remains to be unsolved, and hence, some quantitative studies
are still to be done. Above all, the bound rubber is easy to observe it experimentally,
namely by checking of the insoluble rubber fraction on the surface of CB. Hence, it
is not surprising that lots of experimental results on bound rubber have been reported
until now.
Kraus claimed that the importance of filler particle size was free from mistakes,
but he pointed out, too, that it was not the only factor but some interactions were
to be considered for the rubber reinforcement by filler [19, 20]. This opinion was
exactly in accordance with that of the three authors of Ref. [8] (see Sect. 5.2). In
fact, Kraus arranged Bueche’s network structure theory [18] to be placed at the
beginning of his book [9]. However, much more notable is Chap. 3 [10], in which
Payne disclosed three factors for explaining Payne effect. His excellent comments
have been conveniently and effectively used for interpreting rubber reinforcement
in general; (1) Hydrodynamic volume effect, (2) bound rubber, and (3) structuring
of filler. Quite a number of papers on rubber reinforcement adopted Payne’s three
factors for explaining reinforcement by fillers (see Sects. 2.4 and 2.5). Under these
trends, studies on bound rubber have particularly been conducted actively, which is
due to experimental feasibility to quantifying the bound rubber amount. However, it
seems to have been few studies exceeding those by Fujimoto’s model [26, 27] or no
publications have negated his model so far.
The third factor, structuring of filler, has failed to advance much due to the empirical difficulty. Specifically, the experimental evidence of the network structure of
filler, which is assumed to be the ultimate form of the structuring or aggregation of
nanofillers, has not been offered in the twentieth century. Needless to say, there have
been disclosed lots of assumptions on the filler networks, still solid evidence has not
been given (see Sects. 3.2.1 and 4.3.1. See also readable Chap. 3 by Hess in Ref.
[9]). For one more example, Ishikawa et al. proposed a morphology of CB-loaded
NR vulcanizates based on their anti-abrasion properties [28], which is in accordance
with the CB network structure at least qualitatively.
5.4 Toward Nanofiller Networking in Rubber Matrix
(Early in the Twenty-First Century)
How to model the filler network structure had been actively researched for a few
decades until the beginning of the twenty-first century. One of the most notable studies has been carried out by Krüppel et al. [29, 30]. They presented a semi-theoretical
treatment of the filler gelation process, on the basis of the scaling concept by de
Gennes [31] and the fractal theory by Mandelbrot [32]. Namely, they proposed a