Volumen II - SAM

The LOI test (ASTM D 2863) was carried out on identical panels to those employed for evaluating the
resistance to Salt Spray Chamber and 100% Relative Humidity Cabinet; in these tests, panels size was 150 x
30 x 2 mm. The gas flow rate in the column was 3.2 cm.s -1 . TFT tests (ASTM D 3806) were done on steel
panels of 610 x 100 x 2 mm prepared in analogous way to those employed for the LOI determinations. For
each sample, the three highest values, expressed in cm of fire-spreading that exceeded the corresponding to
the bare steel panel considered as reference (distance due to flame reflection, 6 cm), were determined during
the test development. The average values were calculated for each sample. Before beginning testing, the
panels under study remained at laboratory conditions during 10 days after the application of the last coat.
Then, the panels were heated at 45-48°C for 24 hours for eliminating the remaining solvent.
3. RESULTS AND DISCUSSION
Micaceous iron oxide particle diameter, PVC and film permeability. The photo-microscopic analysis allowed
the determination of the micaceous iron oxide particle diameter on each one of the elaborated samples and
then the calculation of the mean diameter. Generally, a lower mean diameter was associated with a broad
size distribution which improved the packaging density of pigment particles in the coating film, Table 3.
A fast decrease of particle size during the first hour of dispersion time and a slight reduction during the
subsequent hours were observed. Values included in Table 3 show that coatings formulated with PVC 45%
required a shorter time than those formulated with PVC 50 and 55% for attaining a similar micaceous iron
oxide particle diameter. Coatings with lower PVC displayed a reduced permeability for a similar particle
size; this could be attributed to the higher easiness of particles to dispose in a plane parallel to the substrate
during film drying when pigment concentration is lower.
Thermal analysis of flame retardant pigments. TGA of zinc borate (Argon atmosphere at 10°C/min) shows
the highest thermal stability at the beginning (approximately up to 150°C) which means that the hydrating
water is not released in this stage. On the other hand, the presence of interstitial water into the crystal was not
observed. The residual fraction of weight at 800°C was approximately 76%.
The nature of the reaction of zinc borate with the increase of temperature was determined by DTA (Argon
atmosphere at 10°C/min). Experimental curve shows endothermic peaks at 173 and 195°C. The DTA curve
of trihydrated alumina indicates three regions of endothermic activity; the first appeared at approximately
242°C, the second from 250 to 350°C with a maximum endothermic peak at 311°C and another at 538°C.
These results were confirmed by TGA which also shows a residual fraction in weight of 64.5% at 800°C.
It is important to mention that both flame retardant pigments have low water solubility and consequently
they remain into the films on service. Besides, they do not release toxic gases when heated.
Dry film tests. Statistical interpretation. Results corresponding to Salt Spray Chamber, 100% Relative
Humidity Cabinet, LOI and TFT are shown in Table 4. For the statistical treatment of results, variables
studied are the principal effects. The simultaneous analysis of all principal effects is shown in Table 5.
Considering only the corrosion and blistering resistance, the best behavior (highest average values) was
observed with the sample formulated with PVC 55% and with the fire retardant pigment of volumetric
composition VIII. The variable Dp does not seem to exhibit a significant action (similar average values). To
carry out the statistical interpretation, the following considerations were carried out:
-Degree of rusting. The scale from 1 to 10 included in ASTM D 610 Standard was kept.
-Degree of blistering. Size quantitative value defined in ASTM D 714 Standard and the numeric values
assigned arbitrarily to the frequency were averaged; the last quoted values were: without blisters, 10.0; F
(few) 7.5; M (medium), 5.0; MD (medium dense), 2.5 and D (dense), 0.0.
-Rusting and blistering resistance. The degree of rusting and the degree of blistering were averaged.
-LOI index. The scale from 0 to 10, in which 0 corresponds to 0% oxygen and 10 to 60% oxygen, was
defined; intermediate values have a direct proportionality.
-Flame-spreading in the TFT. In this case the proportionality is inverse (as flame front distance increases, the
performance diminishes); for this reason, a scale with extreme values of 0 and 10, corresponding to 55 and 0
centimeters respectively, was selected.
-Fire tests performance. It corresponds to LOI and TFT average values.
-Total efficiency. This index interprets simultaneously corrosion resistance, blistering resistance, minimum
oxygen level for keeping combustion as candle and ability for controlling the flame-spreading; this
efficiency was calculated as average of results attained in the four tests carried on dry films.
Concerning fire tests, the coating with PVC 55% and pigmentation VIII displayed also the best efficiency. In
these experiments, other pigment compositions exhibited an excellent reply as well: average values higher
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