Page 683 - Handbook of Thermal Analysis of Construction Materials

Section 3.0 - Coatings 651

reported that the study serves to illustrate the sensitivity of DEA measure-
ments.
Schultz and co-workers [35] investigated the real-time kinetics of film
formation of a floor polish polymer latex coating using DEA. They also used
DSC and TMA. From the results of the study, it was reported that the drying
DEA curves of latex film under study showed that at ambient temperature,
the drying mechanism varied as a function of humidity. As the humidity
increased, water evaporation slowed down and drying times increased. At a
very high humidity, a rupture of the film was observed, which was attributed
to internal stresses. They concluded that coalescence plays an important role
in the film formation mechanism. The TMA and DSC results showed a long-
drying time for the film as well as an increase in the T (>65°C). The second
g
T was attributed to film phase separation. Evidence of a considerable
g
amount of residual stress remaining in the film after two months was also
reported. It was finally concluded that DEA can be used to measure the effect
of variables on film formation.
Another useful thermoanalytical technique to characterize coat-
ings and paints is TMA. For example, the thermomechanical effects of
indentation of thin polymethyl (methamethacrylate) coatings attached to a
steel substrate were investigated by Jayachandran. [36] He reported that it
was informative to examine the stress field developed under the indenter to
forecast potential sites and modes of failure during indentation as well as
their dependence on loading conditions such as rate and friction. Moreover,
TMA was used by Pindera, et al., [37] to analyze functionally graded thermal
barrier coatings.
Acrylic coatings have been used for asphalt-based roof applica-
tions. Thermoanalytical techniques can be used for characterizing this type
of coating. A study carried out by Antrim, et al., [38] reported that the acrylic
coating prolonged the life of the asphaltic roofing material using low- and
steep-slope roofing. Furthermore, the degradation mechanism of the as-
phalt is not only due to changes in the maltene/asphaltene ratio, but is more
complex and of secondary dimension. It was mentioned that T is an
g
important indicator of the tolerance for movement of a membrane or coating
formulated with elastomeric coatings. However, it was not clear which
thermoanalytical technique was used to measure T . It is, therefore, as-
g
sumed that DSC, TMA, DMA, or DEA may have been used.
Thermoanalytical techniques combined with the IR and SEM would have
provided a greater amount of information on the degradation process of
asphalt.