110
6 Particulate Silica Reinforcement of Rubber
products, yet it results in a higher price without exception. Still, it is evident that we
have much room to improve for the practical utilization of silica. We have to take
a simple fact into account: CB has a history of more than one hundred years now,
during which extraordinary efforts have successfully been dedicated to developing
CB. In the case of silica, one possibility might be to establish a completely different
rubber processing method from that of the CB compounds.
When having this ambitious purpose in mind, we were impressed by a paper
of Mark et al. [31]. They described the synthesis of particulate silica by the sol–gel
reaction, conducted in polydimethylsiloxane, a silicone elastomer. It was suggesting a
revolutionary method of mixing filler into rubber, i.e., in situ preparation of particulate
silica in rubber matrix, divorcing from the traditional and conventional mechanical
mixing of particulate silica into rubber. Tentatively, we assumed that its extension to
diene rubbers could be the first step toward a soft process for rubber compounding
in general [6, 22, 32–34], different from the traditional hard process which totally
depended on the mechanical mixing by consuming much energy. Thus, our first letter
paper on in situ synthesis of particulate silica in styrene-butadiene rubber (SBR)
matrix was published in 1994 [35], and the effect of silane coupling agent (TESPT)
on in situ generated silica was also confirmed in 1998 [21]. The following studies on
silica generated in situ are to be described in the next section.
6.2 Rubber Reinforcement by In Situ Silica
6.2.1 Silica Particle Generated at Place in the Cross-Linked
Diene Rubber
The technical significance of preparation of particulate silica at place has been elucidated through quite a number of publications on in situ silica, particularly in the
rubber field, including papers mainly from our group [6, 21, 22, 32–62]. Figure 6.2
shows the sol–gel reaction to produce silica from tetraethoxysilane (TEOS) as a starting material, which is often conducted at room temperature [63–65]. If the reaction
is catalyzed by an acid (e.g., hydrochloric acid), the product can be spun to a fiber
form or spread to a film form. On the other hand, particulate silica is produced by a
basic catalyst such as ammonia or organic amines.
After trials, we have chosen n-butylamine as the catalyst for particulate silica
synthesis in the diene rubber vulcanizates. It is estimated to penetrate deep into
the vulcanizate which has been swollen by TEOS, to result in the formation of
in situ silica inside the vulcanizate [21, 22, 32–38]. Figure 6.3 shows the process of
preparation (Method A): Conventionally processed rubber vulcanizate is subject to
swelling by TEOS, and to the swollen vulcanizate n-butylamine (catalyst) is added
to conduct the sol–gel reaction. It is noted that the preparation of the vulcanizates is
by a conventional method inclusive of mechanical mixing of all the ingredients into
rubber except filler.
6 Particulate Silica Reinforcement of Rubber
products, yet it results in a higher price without exception. Still, it is evident that we
have much room to improve for the practical utilization of silica. We have to take
a simple fact into account: CB has a history of more than one hundred years now,
during which extraordinary efforts have successfully been dedicated to developing
CB. In the case of silica, one possibility might be to establish a completely different
rubber processing method from that of the CB compounds.
When having this ambitious purpose in mind, we were impressed by a paper
of Mark et al. [31]. They described the synthesis of particulate silica by the sol–gel
reaction, conducted in polydimethylsiloxane, a silicone elastomer. It was suggesting a
revolutionary method of mixing filler into rubber, i.e., in situ preparation of particulate
silica in rubber matrix, divorcing from the traditional and conventional mechanical
mixing of particulate silica into rubber. Tentatively, we assumed that its extension to
diene rubbers could be the first step toward a soft process for rubber compounding
in general [6, 22, 32–34], different from the traditional hard process which totally
depended on the mechanical mixing by consuming much energy. Thus, our first letter
paper on in situ synthesis of particulate silica in styrene-butadiene rubber (SBR)
matrix was published in 1994 [35], and the effect of silane coupling agent (TESPT)
on in situ generated silica was also confirmed in 1998 [21]. The following studies on
silica generated in situ are to be described in the next section.
6.2 Rubber Reinforcement by In Situ Silica
6.2.1 Silica Particle Generated at Place in the Cross-Linked
Diene Rubber
The technical significance of preparation of particulate silica at place has been elucidated through quite a number of publications on in situ silica, particularly in the
rubber field, including papers mainly from our group [6, 21, 22, 32–62]. Figure 6.2
shows the sol–gel reaction to produce silica from tetraethoxysilane (TEOS) as a starting material, which is often conducted at room temperature [63–65]. If the reaction
is catalyzed by an acid (e.g., hydrochloric acid), the product can be spun to a fiber
form or spread to a film form. On the other hand, particulate silica is produced by a
basic catalyst such as ammonia or organic amines.
After trials, we have chosen n-butylamine as the catalyst for particulate silica
synthesis in the diene rubber vulcanizates. It is estimated to penetrate deep into
the vulcanizate which has been swollen by TEOS, to result in the formation of
in situ silica inside the vulcanizate [21, 22, 32–38]. Figure 6.3 shows the process of
preparation (Method A): Conventionally processed rubber vulcanizate is subject to
swelling by TEOS, and to the swollen vulcanizate n-butylamine (catalyst) is added
to conduct the sol–gel reaction. It is noted that the preparation of the vulcanizates is
by a conventional method inclusive of mechanical mixing of all the ingredients into
rubber except filler.