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Results of the Thermal Protective Performance Test

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Results of the Thermal Protective Performance Test

Author: Date :2019-05-30 Views: order
Results of thermal analysis by measuring TPP ratings of fabrics and assemblies are shown in Table 3. The data are presented in tolerance time and in TPP ratings. The maximum and minimum of TPP ratings from measurements are also represented to give an idea about the accuracy of our apparatus.
Generally, results of measurements of single layer fabrics show close values.But the best performance of all is exhibited by the fabric 2. It is the thickest and the only fabric containing PBI fibers, although the heaviest fabric is fabric 3,which has the second highest TPP rating.One of the reasons of lower TPP rating of this fabric may be the construction of the fabric, because it has a compact structure(twill) and this may increase heat transfer by conduction. Fabric 1 has the same weave fabric 2 and is heavier than this fabric but has a lower TPP rating. The cause of this may be its thickness and its fiber type is different and the fiber type used (is thinner than fabric 2).
From this table, it is obvious that adding a layer, even with a low area mass and low thickness to the outer layer fabric is very useful for thermal performance. As the maximum TPP rating in single layer
samples is 11.5, the maximum value for two layer fabrics increases to 15.2 as in table. So this is an indicator of why protective clothing must be produced from multi-layer fabrics and not with single fabrics of high area mass; because air trapped in the fabric layers is a good insulator.
In the test, the three-layer assemblies have greater thickness; and are heavier and bulky. Therefore it permits to obtain higher TPP ratings. The maximum TPP value is observed from again PBI/paramid sample and is 34.8 cal cm-2. In NFPA 1971 standard, the TPP rating required for a multi-layer fabric consisting of an outer layer, a thermal layer and a moisture layer is 35.0 cal cm-2. Consequently, it seems that the TPP rating of 34.8 cal cm-2 without moisture barrier is almost sufficient for insulation.
Burning Behaviors of Fabrics Among fabrics, PBI /p-aramid 40/60 suffers the least hazard at the end of the TPP test. It does not ignite but becomes black in color. Generally char and ash do not form and the fabric is flexible at the end of the tests. Even if the fabric is exposed to flame and heat for a long time, it does not ignite. The fabric glows with flame but there is no afterglow when flame is removed. When glowing occurs in the test, the fabric forms a brittle char. However in the case of TPP tests of single layer fabrics there is usually no glowing. The fabric glows with odor and colorless smoke [18].
The black color of Nomex Delta A /paramid 60/40 fabrics becomes yellowy at exposure area. The fabric does not shrink by heat. There is a char after exposure. If the flame and heat are applied for a long time, the fabric forms brittle chars. There is white smoke with a bad odor for all aramid fabrics. The reason for this is thought as the nitrogen in their structures.
The exposure areas of fabrics are also yellowy. This may be due to the degradation of pigments of dyestuffs with elevated temperatures. Of all, the highest shrinkage by flame and heat is seen in Nomex III. After the tests, the fabric forms bright and thick chars. The char is brittle, but due to its thickness it does not break easily. In the tests, there is a liquid on the back surface of the fabric when exposure time is long.
Nomex Delta T /P140 forms char quickly. Generally after almost all tests a brittle char is formed. There is shrinkage by heat and flame and there is no color change.


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