136
8 Self-Reinforcement in Natural Rubber (NR): Template Crystallization
point. Contribution of the trapped entanglement to rubber elasticity is still under
active debates. Roughly speaking, the affine network and phantom network theories
are the two developments from the classical rubber elasticity theory [16], and pro
or con to the role of trapped entanglements may be the watershed between the two.
Though this debate is theoretically important and urgent, it is not highlighted in the
present book. Relevant original papers by us [17–23] and advanced textbooks are to
be studied [16, 24, 25].
8.1.2 Nucleation and Low-Temperature Crystallization of NR
Initiation of LTC of NR is due to nucleation and is considered to be a homogeneous
crystallization. LTC is not due to the addition of any foreign materials. Polymer
crystallization in general is started either by annexing a specific foreign body (called
nucleating agent) or by nucleation (namely homogeneous crystallization). The former
is designated as heterogeneous crystallization. There have been observed lots of
difference between LTC and SIC already. Yet, many researchers have been discussed
SIC of NR on the basis of the nucleation theory, since SIC is not due to any nucleating
agents. For example, L. Mandelkern, who has worked on polymer crystallization for
long, wrote in his book [26] at Chap. 12 in Volume One:
…the crystallization rate constant of natural rubber increases by six to nine orders of magnitude with extension ratio at constant temperature... The change in rate can be attributed in
part to the changing crystallization mechanism with deformation.
Here, he mentioned the possibility of a different crystallization mechanism other
than nucleation. On second thought, however, he wrote:
However, the main contributor is the substantial increase that occurs in the undercooling
with extension at constant temperature.
In addition, again however, he mentioned the difficulty associated with this
explanation:
In order to resolve the problem, reliable values of the equilibrium melting temperature as
a function of the extension ratio are needed. The discussion in Ch. 7 (Vol. 1) showed how
difficult it is to reliably establish this quantity.
In conclusion, Mandelkern seems to have adhered to the nucleation theory on
SIC of NR, even though he has mentioned possibility of a different crystallization
mechanism. And, he has had many followers so far, which may not be unusual if one
takes his great contribution of many years to polymer crystallization into account.
Thus, the attachment to nucleation has continued even after disclosure of number
of publications on SIC of NR, investigated by the time-resolved techniques using
the synchrotron radiation sources for the measurements. Before shifting to the new
crystallization mechanism of SIC without any nuclei in the next section, LTC of NR is
explained in this subsection which is well within the nucleation theory [1, 14, 26–31].
8 Self-Reinforcement in Natural Rubber (NR): Template Crystallization
point. Contribution of the trapped entanglement to rubber elasticity is still under
active debates. Roughly speaking, the affine network and phantom network theories
are the two developments from the classical rubber elasticity theory [16], and pro
or con to the role of trapped entanglements may be the watershed between the two.
Though this debate is theoretically important and urgent, it is not highlighted in the
present book. Relevant original papers by us [17–23] and advanced textbooks are to
be studied [16, 24, 25].
8.1.2 Nucleation and Low-Temperature Crystallization of NR
Initiation of LTC of NR is due to nucleation and is considered to be a homogeneous
crystallization. LTC is not due to the addition of any foreign materials. Polymer
crystallization in general is started either by annexing a specific foreign body (called
nucleating agent) or by nucleation (namely homogeneous crystallization). The former
is designated as heterogeneous crystallization. There have been observed lots of
difference between LTC and SIC already. Yet, many researchers have been discussed
SIC of NR on the basis of the nucleation theory, since SIC is not due to any nucleating
agents. For example, L. Mandelkern, who has worked on polymer crystallization for
long, wrote in his book [26] at Chap. 12 in Volume One:
…the crystallization rate constant of natural rubber increases by six to nine orders of magnitude with extension ratio at constant temperature... The change in rate can be attributed in
part to the changing crystallization mechanism with deformation.
Here, he mentioned the possibility of a different crystallization mechanism other
than nucleation. On second thought, however, he wrote:
However, the main contributor is the substantial increase that occurs in the undercooling
with extension at constant temperature.
In addition, again however, he mentioned the difficulty associated with this
explanation:
In order to resolve the problem, reliable values of the equilibrium melting temperature as
a function of the extension ratio are needed. The discussion in Ch. 7 (Vol. 1) showed how
difficult it is to reliably establish this quantity.
In conclusion, Mandelkern seems to have adhered to the nucleation theory on
SIC of NR, even though he has mentioned possibility of a different crystallization
mechanism. And, he has had many followers so far, which may not be unusual if one
takes his great contribution of many years to polymer crystallization into account.
Thus, the attachment to nucleation has continued even after disclosure of number
of publications on SIC of NR, investigated by the time-resolved techniques using
the synchrotron radiation sources for the measurements. Before shifting to the new
crystallization mechanism of SIC without any nuclei in the next section, LTC of NR is
explained in this subsection which is well within the nucleation theory [1, 14, 26–31].