|
A unique device for
measuring the complex moduli of materials was designed
and applied to the study on the change of the network
density during isothermal cure of coatings. The
device is composed of a rigid pendulum with a sharp
knife edge as a axis of oscillation and non-contact
displacement metering system. From the decay of
oscillation, specimen's rheological properties such
as elastic modulus were calculated. The change of
the Elastic modulus in a temperatures range between
110°C and 160°C showed a common formula
of E'r=E'r∞(1-exp(-k(t-td))),
where E'r is relative elastic
modulus, t is time, and E'r∞,
k, td are constants. This
result corresponded with the 1st orderreaction rate.
The temperature dependence of the rate constant
k showed the apparent activation energy Ea=54.5
kJ/mol, and the delay time td
showed Ea=94.1 kJ/mol. Functional groups
to be crosslinked are supposed to be very limited
to move because of being attached to infinite network.
This seemed to be the reason why the change of modulus
followed 1st order reaction formula, and why Ea
value calculated from the rate constant differed
from that corresponding to the delay time.
@
@
|
