160
8 Self-Reinforcement in Natural Rubber (NR): Template Crystallization
to the troubles: LTC was effectively kept off by vulcanization, and the NR vulcanizates displayed stable rubber elasticity at much wider temperature range [1, 39, 40,
84, 123–128]. Finally, it has given rise to an indispensable material in the modern
society [9]: Without NR, heavy-duty automobiles are not driven and planes are not
able to take off, nor make landing. Together with the spread of automobiles and
aircraft, technical progress of NR utilization has been phenomenal in the twentieth
century, when two issues have been most highlighted: The first is the use of carbon
black for rubber reinforcement reported by S. C. Mote (1867–1944) in 1904 [128],
and the second is the discovery of accelerating effect of aniline on sulfur curing by
G. Oenslager (1873–1956) in 1906 [128]. The two topics have enjoyed lots of scientific fundamental and developmental studies in rubber arena, followed by huge
amount of reports during the past one hundred years, and lots of rubber engineers are still concerned with reinforcement effect by compounding a nanofiller
and rationalization of sulfur vulcanization [1].
While the abundant reports on vulcanization and reinforcement have been published, crystallization of NR, particularly SIC, has not been much focused until a very
recent time. The first textbook-style comprehensive monograph on NR was published
in 1963 [28]. There, Chap. 9 authored by E. H. Andrews and A. N. Gent, was dedicated to ‘Crystallization in natural rubber.’ However, only LTC was treated in this
chapter, and SIC was scarcely mentioned. At that time, SIC was not highlighted at
all, even though it was reported as early as in 1925 by Katz (1880–1938) [54–57].
The second version of the book [29] published in 1988 contained a chapter entitled
‘Low temperature crystallization of natural rubber,’ but any chapter on SIC was not
included, i.e., the trend of disregarding SIC continued. From the modern viewpoint
that the SIC would be the most important factor in understanding mechanical performance of NR, it is highly surprising that a chapter on SIC in monograph on NR
is firstly found in the one published as late as in 2014 [73].
The basic reason of the delay of research on SIC seems to be due to the extreme
high rate of SIC. On LTC, more studies have been conducted because the rate of
LTC is slow enough to be studied by some conventional techniques. On the one
hand, experimental cognition of LTC is usually possible in months on raw NR in the
temperate zones. Note that LTC is not observed in tropical countries. On the other
hand, observation of wide-angle X-ray diffraction (WAXD) at a modern synchrotron
radiation facility is a must for the scientific analysis of SIC of NR, e.g., at SPring-8
in Hyogo, Japan [62–72]. In other words, it has been found mandatory to conduct
the time-resolved simultaneous measurements of tensile and WAXD, since the rate
of SIC of NR is so high to necessitate WAXD measurement in millisecond time
scale. In order to elucidate the details of SIC, such modern approach must have been
adopted in rubber science much earlier.
The reason of the not-so-active studies on LTC of NR is more or less obscure
compared with that of SIC. Note that LTC had been more actively researched than
SIC until the end of the twentieth century. This negative trend of LTC studies is
apparently against a few historical facts: One of the earliest investigations of X-ray
structure determination on NR was conducted by Meyer and Mark in 1928 [1, 8, 9],
and the early study of LCT on NR by Wood and Bekkedahl [27] contributed much to
8 Self-Reinforcement in Natural Rubber (NR): Template Crystallization
to the troubles: LTC was effectively kept off by vulcanization, and the NR vulcanizates displayed stable rubber elasticity at much wider temperature range [1, 39, 40,
84, 123–128]. Finally, it has given rise to an indispensable material in the modern
society [9]: Without NR, heavy-duty automobiles are not driven and planes are not
able to take off, nor make landing. Together with the spread of automobiles and
aircraft, technical progress of NR utilization has been phenomenal in the twentieth
century, when two issues have been most highlighted: The first is the use of carbon
black for rubber reinforcement reported by S. C. Mote (1867–1944) in 1904 [128],
and the second is the discovery of accelerating effect of aniline on sulfur curing by
G. Oenslager (1873–1956) in 1906 [128]. The two topics have enjoyed lots of scientific fundamental and developmental studies in rubber arena, followed by huge
amount of reports during the past one hundred years, and lots of rubber engineers are still concerned with reinforcement effect by compounding a nanofiller
and rationalization of sulfur vulcanization [1].
While the abundant reports on vulcanization and reinforcement have been published, crystallization of NR, particularly SIC, has not been much focused until a very
recent time. The first textbook-style comprehensive monograph on NR was published
in 1963 [28]. There, Chap. 9 authored by E. H. Andrews and A. N. Gent, was dedicated to ‘Crystallization in natural rubber.’ However, only LTC was treated in this
chapter, and SIC was scarcely mentioned. At that time, SIC was not highlighted at
all, even though it was reported as early as in 1925 by Katz (1880–1938) [54–57].
The second version of the book [29] published in 1988 contained a chapter entitled
‘Low temperature crystallization of natural rubber,’ but any chapter on SIC was not
included, i.e., the trend of disregarding SIC continued. From the modern viewpoint
that the SIC would be the most important factor in understanding mechanical performance of NR, it is highly surprising that a chapter on SIC in monograph on NR
is firstly found in the one published as late as in 2014 [73].
The basic reason of the delay of research on SIC seems to be due to the extreme
high rate of SIC. On LTC, more studies have been conducted because the rate of
LTC is slow enough to be studied by some conventional techniques. On the one
hand, experimental cognition of LTC is usually possible in months on raw NR in the
temperate zones. Note that LTC is not observed in tropical countries. On the other
hand, observation of wide-angle X-ray diffraction (WAXD) at a modern synchrotron
radiation facility is a must for the scientific analysis of SIC of NR, e.g., at SPring-8
in Hyogo, Japan [62–72]. In other words, it has been found mandatory to conduct
the time-resolved simultaneous measurements of tensile and WAXD, since the rate
of SIC of NR is so high to necessitate WAXD measurement in millisecond time
scale. In order to elucidate the details of SIC, such modern approach must have been
adopted in rubber science much earlier.
The reason of the not-so-active studies on LTC of NR is more or less obscure
compared with that of SIC. Note that LTC had been more actively researched than
SIC until the end of the twentieth century. This negative trend of LTC studies is
apparently against a few historical facts: One of the earliest investigations of X-ray
structure determination on NR was conducted by Meyer and Mark in 1928 [1, 8, 9],
and the early study of LCT on NR by Wood and Bekkedahl [27] contributed much to