It has been shown how preferential molecular orientation
within the molten phase of a rubber specimen can be extracted
from X-ray data. Though quite simple the method appears very
sensitive. It is our experience that anisotropy effects due to an absolute
change of 0.01 in elongation can be detected. Assuming that
the average length of molten chains is not affected by SIC, the local
elongation of the molten fraction may be evaluated. During
stretching and after crystallization onset, a mechanism of “strain
regulation” of the molten fraction has been confirmed. The limitation
of the elongation of the molten fraction elongation close to
lO could be one of the protective effects of SIC against tearing. The
stress upturn obtained during this part of the mechanical cycle is
tentatively explained by some crystallite networking. During recovery
the elongation of the molten fraction decreases rapidly till a
value close to the macroscopic elongation at melting. It then remains
close to this value by a “strain regulation” process mirror of
the one observed during stretching. Similarly the stress amplitude
decreases rapidly to values that can be accounted for by the
contribution of the sole molten fraction. This sharp drop is attributed
to a disintegration of the crystallite network.
The possibility of accessing the elongation of the molten fraction
in real-time experiments opens interesting perspectives in particular
in the case of filled materials; the contribution of the filler to
the scattering is easily subtracted and more penetrating radiations
can be used in the case of highly absorbing materials. Strain