138
8 Self-Reinforcement in Natural Rubber (NR): Template Crystallization
Chloroprene rubber (CR), another crystallizable rubber, displays its maximum at
−10 °C [34].
Nucleation is due to the density fluctuation, or molecularly speaking, due to the
statistical fluctuation of the micro-Brownian segmental movement hence density
[1, 11, 14, 26, 35, 36]. Consequently, the statistical analyses are indispensable in
considering crystallization behaviors, which is one of the reasons of difficulty in
practical applications. This problem remains unsolved over the century. Recently, a
paper entitled ‘Observations of the birth of crystals’ claims [37]:
The development of rational approaches for the design and control of crystal growth, requires
an understanding of nucleation---the initial stage of crystallization, in which the building
blocks begin to form clusters known as nuclei.
Namely, the paper claims that having an accurate understanding of nucleation is
mandatory for the design and control of crystallization. However, the paper continues:
Unfortunately, there are two main hurdles: First, the nuclei are typically too small to be
visualized in 3D space. Second, such nuclei are, by definition, unstable and therefore form
only transiently.
Here, ‘by definition’ means per the nature of fluctuation, which has to be treated as
a stochastic process. Nucleation still remains to be understood simply as ‘a transient
random process,’ and the details are not well elucidated yet. This situation is estimated
due to the ‘two main hurdles’ as mentioned above.
In the utilization of plastics, which are usually much more crystallizable than
rubbers, annexation of an appropriate nucleating agent is a common technique to
control the crystallization before serving to the consumers. By this heterogeneous
crystallization technique, nucleating agent promotes the crystallization not toward
the single crystal formation, but toward formation of crystallites all at once to result
in the formation of randomly oriented many small sphere crystallites. This shows a
specific morphology of plastics for general use; many small crystallites are dispersed
randomly in an amorphous glassy matrix, which afford much superior toughness of
the plastics.
For the practical applications of rubber, the progress of LTC is simply detrimental
to the rubber users, and hence, how to avoid LTC of rubber has been studied for
long [1, 7, 28, 29, 38–42]. Notwithstanding these extensive efforts, vulcanization,
or more generally cross-linking reactions of rubber, has been found to be the solely
effective and uniquely practical method so far. This simple fact again confirms the
significance of Goodyear’s invention of vulcanization. For example, raw NR is stored
in a temperature-controlled room at 70 °C until the feed to the manufacturing process
of many rubber goods, in order to arrest the possibility of LTC during the storage in
the temperate or subarctic zones. Otherwise, at each operation time, the frozen NR
block has to be warmed enough to melt the crystallites just before dumping into a
mechanical mixer. On such a problem of NR processing, Fig. 8.2 may give some
insights [41, 42].
8 Self-Reinforcement in Natural Rubber (NR): Template Crystallization
Chloroprene rubber (CR), another crystallizable rubber, displays its maximum at
−10 °C [34].
Nucleation is due to the density fluctuation, or molecularly speaking, due to the
statistical fluctuation of the micro-Brownian segmental movement hence density
[1, 11, 14, 26, 35, 36]. Consequently, the statistical analyses are indispensable in
considering crystallization behaviors, which is one of the reasons of difficulty in
practical applications. This problem remains unsolved over the century. Recently, a
paper entitled ‘Observations of the birth of crystals’ claims [37]:
The development of rational approaches for the design and control of crystal growth, requires
an understanding of nucleation---the initial stage of crystallization, in which the building
blocks begin to form clusters known as nuclei.
Namely, the paper claims that having an accurate understanding of nucleation is
mandatory for the design and control of crystallization. However, the paper continues:
Unfortunately, there are two main hurdles: First, the nuclei are typically too small to be
visualized in 3D space. Second, such nuclei are, by definition, unstable and therefore form
only transiently.
Here, ‘by definition’ means per the nature of fluctuation, which has to be treated as
a stochastic process. Nucleation still remains to be understood simply as ‘a transient
random process,’ and the details are not well elucidated yet. This situation is estimated
due to the ‘two main hurdles’ as mentioned above.
In the utilization of plastics, which are usually much more crystallizable than
rubbers, annexation of an appropriate nucleating agent is a common technique to
control the crystallization before serving to the consumers. By this heterogeneous
crystallization technique, nucleating agent promotes the crystallization not toward
the single crystal formation, but toward formation of crystallites all at once to result
in the formation of randomly oriented many small sphere crystallites. This shows a
specific morphology of plastics for general use; many small crystallites are dispersed
randomly in an amorphous glassy matrix, which afford much superior toughness of
the plastics.
For the practical applications of rubber, the progress of LTC is simply detrimental
to the rubber users, and hence, how to avoid LTC of rubber has been studied for
long [1, 7, 28, 29, 38–42]. Notwithstanding these extensive efforts, vulcanization,
or more generally cross-linking reactions of rubber, has been found to be the solely
effective and uniquely practical method so far. This simple fact again confirms the
significance of Goodyear’s invention of vulcanization. For example, raw NR is stored
in a temperature-controlled room at 70 °C until the feed to the manufacturing process
of many rubber goods, in order to arrest the possibility of LTC during the storage in
the temperate or subarctic zones. Otherwise, at each operation time, the frozen NR
block has to be warmed enough to melt the crystallites just before dumping into a
mechanical mixer. On such a problem of NR processing, Fig. 8.2 may give some
insights [41, 42].