Page 667 - Handbook of Thermal Analysis of Construction Materials

Section 2.0 - Paints 635

for documentation of artists’ techniques. DSC provided the means to
characterize the paint media at the microscopic level. Furthermore, DSC,
[5]
TG, and TMA were used by Wingard to study hypalon paint coatings for
the solid rocket booster of the space shuttle.
DTMA has even been used in the evaluation of deacidification
treatment, as well as the effects of environmental conditions, and the
preventive conservation treatment of painting canvases. [6][7] From the
results of both studies, it was concluded that DTMA is a suitable technique
for the evaluation of the effect of treatment.
Dielectric thermal analysis (DEA) is another thermoanalytical
technique that has been used to characterize paints. The technique mea-
sured the electrical characteristics (capacitance and conductance) of a
material as a function of time, temperature, and frequency. Odlyha, et al., [8]
used DEA to study variations in the relative humidity in canvas paintings.
The study showed that DEA allowed an assessment of the effects of water
vapor on samples of primed canvas. It was concluded that the ability to
quantify the degree of water binding within works of art in a non-invasive
manner assisted optimization of conservation treatment such as
rehumidification of surface paint layers to remove surface deformations
and, where necessary, to allow adhesion of flaked paint fragments. Thermal
stress analysis is another promising technique used by Perera and co-
[9]
workers to study the cure of stoving paints. The technique allows,
amongst other things, measurement of the glass transition temperature of a
coating.
The final properties of a paint, leveling characteristics and durabil-
ity, depend on the cure conditions. Uncured coatings present unsatisfactory
resistance to water and chemical reagents and insufficient hardness. Over-
cured coatings can be hard yet fragile and present signs of thermal
degradation such as a decrease of adhesion, gloss and change in color. To
solve this problem, it is necessary to know the mechanism of film formation
or factors affecting it. Hence, techniques capable of evaluating cure
characteristics are essential. This can be achieved by using a combination
of thermoanalytical techniques. For example, DSC, DMA, TG, and TMA
can be used to study the reaction kinetics and determine a number of basic
coating characteristics sensitive to the degree of curing.
The use of combined thermoanalytical techniques for materials
characterization has increased in the last few years. For example, differen-
tial scanning calorimetry and thermally stimulated current (TSC) have also
been used to study polyurethane and mono- and bilayer paints. [10] TSC
(considered a relaxation technique) is based on the degree of chain and