result concerns in fact the evolution of the hysteresis between the
loading/unloading indentation curves with the exposure duration.
One can obviously see an important decrease of the hysteresis for
the irradiated sample. This behaviour is consistent with an increase
of the elastic properties of the polymer or a decrease of the plastic
properties. The variations of these properties (hardness, Young’s
modulus, hysteresis) have two possible explanations: cross-linking
of the polymeric matrix and/or loss of plasticizer. In the first part of
this article, it has been shown that a loss of camphor resulting from
evaporation/migration occurred during exposure. The loss of plasticizer
is expected to be temperature dependent. For that reason we
completed the experiments by submitting the samples to thermooxidation
experiments (without light exposure) at two different
temperatures, 60 and 100 C. The obtained results are given in
Table 2. The camphor amount in the celluloid samples was calculated
from a calibration curve between the IR characteristic band of
camphor at 1730 cm1 and the weight percent of camphor.