176
9 Reinforcement in the Twenty-First Century
in its latex [44, 45]. Hence, raw NR is obtained by coagulating the NR latex. NR
latex has its own wide applications [46]: Thin NR films prepared from NR latex
are popular among a lot of thin rubber products for medical, cosmetic, and everyday
usages, e.g., rubber tubes, rubber balloons, condoms, and rubber bands. Furthermore,
NR latex contains various non-rubber components dispersed in water, other than
rubber particles. Some of them may be potentially of use for a specific function, and
lots of application-oriented researches are continuing [47]. Such applications of NR
latex are still under active investigation now, and their utilization is expected to keep
expanding.
Not only NR latex but also some synthetic rubber emulsions are already in use,
since the first synthetic rubber, SBR, that was mass produced in Germany and USA
during the World War II, has been synthesized by emulsion polymerization technique
to give SBR in the emulsion form. Thus, often it is called SBR latex interchangeably.
Because the emulsion is synthetic, various modifications are easier than on NR latex.
Taking advantages of synthetic chemistry, design of microspheres, i.e., dispersed
particles in water, is conducted for highly functional soft materials. For example, the
control of the components including their size is possible, and the product is to be
designed for a specific purpose such as a carrier of the drug for pathological diagnosis.
NR latex and emulsions or even suspensions of synthetic rubbers are colloidal soft
materials of much value, and their development becomes more and more important
in this century.
In the polymer arena, polymer gels are also one of the soft materials and now under
active investigations [48–50]. Polymer gels are a cross-linked material, but are in use
at the swollen state by a solvent. Apparently, very similar to rubber vulcanizates, but
the absence or presence of solvent is much decisive for their properties and utilization.
Multifaceted developmental researches are anticipated. When water is the solvent,
the gel is called hydrophilic gels. Some of them are on the market under the name
of a highly water absorbable resin. More sophisticated applications are surely under
developmental research all over the world.
In non-rubber areas, as liquid-state materials, liquid crystals are to be mentioned.
Liquid crystalline elastomers have been studied long, and they are still under active
investigations now [51, 52]. Further, biomaterials are another promising soft materials, since all the biomaterials are elastic except bones and teeth. Reinforcement
mechanism in naturally produced elastic tissues such as musculature and skin tissue
are worth to be studied more.
From the viewpoint of SD, reuse and recycle of various devices and relevant
materials are socially urgent issue as well as the longer lifetime of the devices. At
an initial stage of the product design, that is, at the material design stage, we have
to take reuse and/or recycle into account. On this occasion, it is notable that NR is
not recyclable even though the trees producing NR are renewable. NR molecule is
a hydrocarbon (not hydrophilic), and chemically cross-linked, hence not amenable
to more or less general recycling techniques of polymeric materials [53, 54]. Thus,
recycling of employed tires is still a big problem to be solved in this century [55].
One more comment on tires is related to the global warming by the discharged
gas, CO 2 : The life cycle of tires is of five stages, i.e., raw material, manufacturing,
9 Reinforcement in the Twenty-First Century
in its latex [44, 45]. Hence, raw NR is obtained by coagulating the NR latex. NR
latex has its own wide applications [46]: Thin NR films prepared from NR latex
are popular among a lot of thin rubber products for medical, cosmetic, and everyday
usages, e.g., rubber tubes, rubber balloons, condoms, and rubber bands. Furthermore,
NR latex contains various non-rubber components dispersed in water, other than
rubber particles. Some of them may be potentially of use for a specific function, and
lots of application-oriented researches are continuing [47]. Such applications of NR
latex are still under active investigation now, and their utilization is expected to keep
expanding.
Not only NR latex but also some synthetic rubber emulsions are already in use,
since the first synthetic rubber, SBR, that was mass produced in Germany and USA
during the World War II, has been synthesized by emulsion polymerization technique
to give SBR in the emulsion form. Thus, often it is called SBR latex interchangeably.
Because the emulsion is synthetic, various modifications are easier than on NR latex.
Taking advantages of synthetic chemistry, design of microspheres, i.e., dispersed
particles in water, is conducted for highly functional soft materials. For example, the
control of the components including their size is possible, and the product is to be
designed for a specific purpose such as a carrier of the drug for pathological diagnosis.
NR latex and emulsions or even suspensions of synthetic rubbers are colloidal soft
materials of much value, and their development becomes more and more important
in this century.
In the polymer arena, polymer gels are also one of the soft materials and now under
active investigations [48–50]. Polymer gels are a cross-linked material, but are in use
at the swollen state by a solvent. Apparently, very similar to rubber vulcanizates, but
the absence or presence of solvent is much decisive for their properties and utilization.
Multifaceted developmental researches are anticipated. When water is the solvent,
the gel is called hydrophilic gels. Some of them are on the market under the name
of a highly water absorbable resin. More sophisticated applications are surely under
developmental research all over the world.
In non-rubber areas, as liquid-state materials, liquid crystals are to be mentioned.
Liquid crystalline elastomers have been studied long, and they are still under active
investigations now [51, 52]. Further, biomaterials are another promising soft materials, since all the biomaterials are elastic except bones and teeth. Reinforcement
mechanism in naturally produced elastic tissues such as musculature and skin tissue
are worth to be studied more.
From the viewpoint of SD, reuse and recycle of various devices and relevant
materials are socially urgent issue as well as the longer lifetime of the devices. At
an initial stage of the product design, that is, at the material design stage, we have
to take reuse and/or recycle into account. On this occasion, it is notable that NR is
not recyclable even though the trees producing NR are renewable. NR molecule is
a hydrocarbon (not hydrophilic), and chemically cross-linked, hence not amenable
to more or less general recycling techniques of polymeric materials [53, 54]. Thus,
recycling of employed tires is still a big problem to be solved in this century [55].
One more comment on tires is related to the global warming by the discharged
gas, CO 2 : The life cycle of tires is of five stages, i.e., raw material, manufacturing,