Civil Engineering Reference
In-Depth Information
Taylor
[19]
concluded from the thermal analysis study, that the
understanding of the mechanism of intumescent coatings increased, and
that it was possible to optimize the mixing ratios in terms of minimizing
weight loss. Furthermore, the results proved that the melamine was present
not only as a blowing agent (spumific), but also as a contributor to the
chemical composition of the char.
3.2
Silicone Coatings
Modulated temperature differential scanning calorimetry (MDSC),
a modification to the linear temperature DSC, was used by Meyer and co-
workers
[20]
to demonstrate the advantage of MDSC over DSC when analyz-
ing coatings. Two batches of product (one manufactured in the pilot plant
and one in the lab) were heated at 2°C/min (linear temperature ramp) and
a modulation of 1°C amplitude with a period of one minute. The DSC traces
showed that the change in
C
p
at
T
g
is
obscured by kinetic events. The traces
from the amplitude of the temperature difference between the sample and
the reference showed clearly the difference between the two batches and
T
g
can easily be assigned. However, it was concluded that the MDSC offers a
tremendous advantage over the DSC mode for determining the
T
g
of two
batches of coatings. In addition to the increased sensitivity, MDSC allows
separation of the kinetic and non-kinetic (
C
p
) components.
Cross-link density in silicone release coatings has important con-
sequences on both the release as well as adhesion performance of pressure-
sensitive adhesive constructions. The degree of recrystallization of silicone
release coatings with different cross-link densities has been determined by
Chang
[21]
using DSC and DMA. The recrystallization peak was obtained
from DSC and DMA, and it was found that as the cross-link density of the
release coating increased, the recrystallization peak of the silicone dimin-
ished sharply, indicative of the increasing constraints imposed by the high
cross-link density which reduces the recrystallizability of the silicone.
Also, an increase in the T
g
of silicone together with lower recrystallization
and melting temperatures was observed.
The temperature dependence of the tan
curve for the silicone
materials obtained by DMA from -150° to 0°C displayed in Fig. 10 for
samples A-C shows that Sample A (under-cured) has a major transition at
about -123°C with a shoulder at -116°C. Chang
[21]
assigned them to the
T
g
and recrystallization respectively. Sample B (medium-cured) shows peaks
at -123°C, -116°C and -96°C. He reported that the three peaks suggested a
δ
