146
8 Self-Reinforcement in Natural Rubber (NR): Template Crystallization
The fully stretched chains have acted as nucleus of crystallites.
Namely, the review author intuited the extended network chain being the nucleus
to explain our result in accordance with the nucleation theory, without recognizing
that it is simply an extended rubber chain as described in Sect. 8.2.1, which is much
different from the nucleus that has not been identified well in general [37]. In other
words, they totally disregarded to consider a new mechanism by adhering to the
traditional nucleation theory. Our not suggesting the above scenario explicitly then in
the paper [64] could be one of the reasons of this situation. Unfortunately, our explicit
disclosing of it was delayed to 2017 [39, 40]. However, the fact that nucleation has
been enjoying an overwhelming acceptance among major polymer crystallographers,
as we have shown already for the cases of Mandelkern [26] and Bassett [35], is a
more important factor than our delay in disclosing the template mechanism for SIC
different from the nucleation. The trend for nucleation has been so popular that
the nucleation theory has negated even the logically rational interpretation of SIC
behaviors of NR vulcanizates for long.
Because there have been no proposals of materializing nucleus for SIC up to
now, one opinion that claims organic acids with a long alkyl group, for example,
stearic acid, has been widely assumed to be a possible nucleating agent for SIC
of NR vulcanizates. NR contains such non-rubber components as organic acids,
which are by-products from the biosynthesis of NR. Additionally, stearic acid is
always compounded as an activator of vulcanization. Certainly, stearic acid and
other acids carrying a long alkyl chain do accelerate LTC, that is, they are acting as
a nucleating agent for LTC. However, IR without any such acids did undergo SIC
was confirmed [66, 67]: While NR contains stearic acid and a few other organic
acids as a natural origin, IR does not. Since the manufacturing process of IR does
exclude such possibility, here the vulcanization system without stearic acid was used.
Accordingly, SIC of NR and IR is a process that does not necessitate the presence of
such acids for SIC, while they are the effective agents for LTC of them.
Further, the uniaxial stretching rate determines the time of the fully extended network chains as shown in Fig. 8.4. The strain rate is dependent on the mechanical
constructions, and the rate is usually of 100 cm/s at most for the sample of l or 2 cm
length. On the other hand, the crystallization rate in SIC of NR vulcanizates is estimated so high that Fig. 8.4 did not allow us to estimate the SIC rates experimentally.
The rates so far estimated were within the range between 20 and 200 ms (the time
needed for the degree of crystallization to reach the half of its maximum values)
[31, 75, 76]. For LTC, it is between hours and years, as shown in Fig. 8.1. For the
quantitative study on SIC, a new method equivalent to P-jump has to be developed.
For a time being, the rate of stretching is determining the template formation, which
is assumed to influence not much to the template crystallization.
In this connection, the time necessary to the onset strain (see Fig. 8.4, the curves
at the left-hand side) was apparently defined as an ‘induction time’ [77]. However,
the needed time is for the extension of the vulcanizate specimen to a certain length
at which some randomly coiled network chains of a certain length are fully extended
by the uniaxial tensile deformation. This cannot be an induction time. The name
8 Self-Reinforcement in Natural Rubber (NR): Template Crystallization
The fully stretched chains have acted as nucleus of crystallites.
Namely, the review author intuited the extended network chain being the nucleus
to explain our result in accordance with the nucleation theory, without recognizing
that it is simply an extended rubber chain as described in Sect. 8.2.1, which is much
different from the nucleus that has not been identified well in general [37]. In other
words, they totally disregarded to consider a new mechanism by adhering to the
traditional nucleation theory. Our not suggesting the above scenario explicitly then in
the paper [64] could be one of the reasons of this situation. Unfortunately, our explicit
disclosing of it was delayed to 2017 [39, 40]. However, the fact that nucleation has
been enjoying an overwhelming acceptance among major polymer crystallographers,
as we have shown already for the cases of Mandelkern [26] and Bassett [35], is a
more important factor than our delay in disclosing the template mechanism for SIC
different from the nucleation. The trend for nucleation has been so popular that
the nucleation theory has negated even the logically rational interpretation of SIC
behaviors of NR vulcanizates for long.
Because there have been no proposals of materializing nucleus for SIC up to
now, one opinion that claims organic acids with a long alkyl group, for example,
stearic acid, has been widely assumed to be a possible nucleating agent for SIC
of NR vulcanizates. NR contains such non-rubber components as organic acids,
which are by-products from the biosynthesis of NR. Additionally, stearic acid is
always compounded as an activator of vulcanization. Certainly, stearic acid and
other acids carrying a long alkyl chain do accelerate LTC, that is, they are acting as
a nucleating agent for LTC. However, IR without any such acids did undergo SIC
was confirmed [66, 67]: While NR contains stearic acid and a few other organic
acids as a natural origin, IR does not. Since the manufacturing process of IR does
exclude such possibility, here the vulcanization system without stearic acid was used.
Accordingly, SIC of NR and IR is a process that does not necessitate the presence of
such acids for SIC, while they are the effective agents for LTC of them.
Further, the uniaxial stretching rate determines the time of the fully extended network chains as shown in Fig. 8.4. The strain rate is dependent on the mechanical
constructions, and the rate is usually of 100 cm/s at most for the sample of l or 2 cm
length. On the other hand, the crystallization rate in SIC of NR vulcanizates is estimated so high that Fig. 8.4 did not allow us to estimate the SIC rates experimentally.
The rates so far estimated were within the range between 20 and 200 ms (the time
needed for the degree of crystallization to reach the half of its maximum values)
[31, 75, 76]. For LTC, it is between hours and years, as shown in Fig. 8.1. For the
quantitative study on SIC, a new method equivalent to P-jump has to be developed.
For a time being, the rate of stretching is determining the template formation, which
is assumed to influence not much to the template crystallization.
In this connection, the time necessary to the onset strain (see Fig. 8.4, the curves
at the left-hand side) was apparently defined as an ‘induction time’ [77]. However,
the needed time is for the extension of the vulcanizate specimen to a certain length
at which some randomly coiled network chains of a certain length are fully extended
by the uniaxial tensile deformation. This cannot be an induction time. The name