LOI Test

Gardziella, L.A. Pilato and A. Knop, Phenolic Resins, 2nd Edition, Springer- 

Fisher, Chemistry of Natural and Synthetic Rubbers, Reinhold Publishing 

Principles of Polymer Chemistry, Cornell University Press, Ithaca, NY, 

Billmeyer, Textbook of Polymer Science, 3rd Edition, Wiley, New York, 

Senturia and N.F. Sheppard, Advances in Polymer Science, Ed., K. Dusek, 

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Limited oxygen index (LOI) test, 10 175 13 380, 384, 385. See also Limiting oxygen index (LOI)... 

Relative to carbon/carbon composites, the hybrid composites have a reduced thermal stability in air due to the resin content of the matrix. The flammabilities of the hybrid composites, as measured by the limiting oxygen index (LOI) test (63) are given in Figure 36. Pure carbon/carbon composites are not inflammable in... 

The LOI value for self-extinguishing behavior is often taken as 27, not 21 (which is the volume % concentration of oxygen in air), to correct for a lack of convective heating in the LOI test. 

The problem with all such tests, however, is their interpretation and comparison. Physical form can influence the test (for instance the sample may readily deform out of the flame region), and some tests are more demanding than others. The LOI test has a flaw in that the sample is burning from the top down, and the heat flow into the polymer below the flame is necessarily limited. The data in Table 4.6 also clearly show that the range of measured values can vary dramatically depending on the exact sample form, test protocol and sample chemistry. 

As a resnlt of this and further studies by thermogravimetric analysis (TGA), solid-state NMR and electron probe microanalysis, Dabrowski and co-workers [27] conclude that melamine polyphosphate is an efficient flame retardant additive in polyamide-6,6 (glass fibre reinforced or not). The glass fibres are shown to strongly inflnence the fire performance of the intumescent FR material. A reactivity between the additive and the glass fibre and the formation of alumino-phosphates was demonstrated. These species might be responsible for the improvement of the FR behaviour particularly in the conditions of the LOI test. 

The fire reaction of filled polyisocyanurate-PU foams has been analysed by use of DIN 4102-2 [22] and LOI tests. The results of the DIN 4102-2 test are reported in Table 7.1. Only the foams filled with EG containing at least 15 wt% of filler, can be classified as B2 materials. Pentane blown foams filled with 25 % of APP and MC cannot be rated as B2. 

The LOI test showed that the LOI increases with increasing filler content. In particular while the presence of MC does not significantly change the LOI, the presence of APP and EG leads to an increase of about 25% and 35%, respectively, using 25% of the filler. 

EG leads to formation of a char layer characterised by the presence of worms resulting from its expansion. It was found that the higher the filler content the lower the compression strength. The presence of APP or MC results in worsening of thermal conductivity while the presence of EG leads to an increase in thermal conductivity. Cone calorimetry and the LOI test were used to study the fire behaviour. The best... 

Figure 12.3 Relation between char content in TGA and char on burning (from LOI test) from the study of Ehdon et al. °...

The LOI values and UL 94 classification of polymers are interrelated as shown in Figure 11.14. The LOI values for V-0 polymers are >35, whereas the LOI values are <30 for polymers classified as V-1, V-2, and HB. As intended, the LOI test is applicable to polymers with small surface areas such as in small parts of metallic devices and appliances exposed to small ignition sources, similar to UL 94 test. 

LOI testing shows a significant increa.se in value compared with pure PVC and PVC with antimony oxide, but the best indices are given by a combination of zinc sulphide and antimony oxide. 

A value HRRb 100 kW/m has been observed for the LOI test. This value is somewhat higher than the critical heat release rate for incipient burning/extinction of horizontal slabs (HRRb 70 kW/m see Table 6) and upward burning of vertical strips (HRRb 50 kW/m ) because heat transfer from the flame is less efficient in downward burning, and so a higher HRR is necessary for sustained ignition in the LOI test. 

With regard to flammability as measured in the LOI test (25) (see section on The Limiting Oxygen Index Test), if Equation 52 applies and Aflame= LOI, then equation 74 gives the criterion for flame extinction... 

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