Page 673 - Handbook of Thermal Analysis of Construction Materials

Section 3.0 - Coatings 641

respectively, and on a dry paint sample with fillers ratio of 1:1:2. A sample
mass of 50 mg pure substance and <20 mg for mixtures or dry coating
material were heated from 20° to 600°C at 5°C/min under a flow rate of 200
mL/min of air or nitrogen depending on the experiment.
The phenomena observed represented decompostions of the pure
substance or self-cross-linking reactions. Both binary and ternary mixtures
were considered to detect interaction between the components and identify
thermal aspects of the chemical reaction involved in the complex phenom-
enon of intumescence. The test performed on both mixtures shows a
combination of these effects and interactions between components in every
binary mixture, including the effect of the ”blowing agent” (melamine).
The overall intumescence reaction can be seen from the thermal point of
view in the ternary mixture. DSC has an interesting potential as a tool for
studying thermally active coating systems, such as the intumescent
systems studied, which perform by means of chemical reactions occurring
inside the coating film when a change in temperature occurs.
Fire retardant intumescent coatings are being frequently used to
protect buildings containing structural steel from the effects of exposure to
high temperatures caused by fire. The strength of structures decreases,
especially those made of concrete and steel, with increasing temperatures
of the fire, reaching a critical point at approximately 550°C. Below this
temperature and without the benefit of an intumescent coating, a steel beam
reaches its critical point in 17 minutes. [15] However, with the insulating
effect of an intumescent coating, such time can be extended to approxi-
mately 70 minutes and up to 2 hours by using the appropriate coating
thickness. [16] Therefore, it is important to study the thermal stability of
coating materials for this type of application.
Simultaneous thermal analysis (STA) (TG/DTA) is a useful tool to
study intumescent coatings because it provides information on both the
thermal stability and the reaction type occurring with temperature in a
single experiment. For example, Trehan and Kad [15] studied cellulose and
ammonium polyphosphate intumescent coatings. They used the technique
to elucidate the mechanism of the development of intumescent chars during
the heating of an intumescent coating system based on ammonium
polyphosphate (APP) as the acid source and cellulose as the carbonic source
with a blowing agent. The completed coating was obtained by mixing APP,
cellulose, chlorinated paraffin, and TiO at different ratios by weight. The
2
thermal behavior of pure APP and cellulose was studied first.
Figure 6 shows the TG/DTA curves for pure APP and pure
cellulose. Trehan and Kad [15] reported that the TG/DTA curves for APP