LOI and UL-94 Tests

Wilkie used a UL-94 test to study whether any synergy exists between aromatic phosphate flame retardants and PS nanocomposite formation, the results of which are shown in Table 8.12. At 30% ArP content, various V ratings are obtained that improve as the clay content increases. 

TABLE 8.13 Properties of Brominated Flame Retardant PBT-Organoclay Nanocomposites  

Example Composite Silicate (%) Additive % Added Exfoliation UL-94 

Dispersibility good good good — poor poor 

The generally accepted mechanism that has been suggested to explain the reduction in flammability for polymer-organoclay nanocomposites containing 

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Table 10.9 Effect of a mineral flller/melamine combination with PP on LOI and UL 94 tests...

There is a reasonably good correlation between LOI and UL-94 test ratings. Thus it will usually be found that a flame-retarded polypropylene of LOI 28-30 will also meet UL-94 V-0 at 3.2 mm whilst a LOI of 30-32 is a... 

TABLE 6.6 Fire Retardant Performance of EVA-APP/PA6 Containing OMMT, OLDH, and NPSi According to LOI and UL-94 Tests... 

In general, roughly LOI values of up to 27% signify flammability 33 higher LOI values signify self-extinguishing behavior in the UL 94 test (Table 15.2). However, there is no clear correlation between LOI and UL 94, and some extremes down to 22% and up to 47% (Figure 15.2, Table 15.2)... 

Higher irradiation levels give better reproducibility, more clearly defined ignition, and shorter measurement times, but correspond to more developed fires. Thus particularly for flame-retarded polymers, a smaller irradiation level often corresponds better to the fire protection goals addressed. Cone calorimeter results for the HRR at small irradiances correspond to flammability tests such as LOI and UL 94, if a reasonable set of materials are compared and the behavior is not dominated by dripping effects. Thus different considerations govern the choice of external heat flux.76 77... 

Chiang and co-workers [50] studied the flame retardance of phenolic resin-silica nanocomposites. The char yields of the polymer were observed to increase when the tetraethoxysilane content of the polymer was increased. LOI and UL-94 [13] tests revealed that the hybrid possessed excellent flame resistance. 

With few exceptions, nanocomposites do not self-extinguish until most of the fuel has been burnt. That is, they burn slowly but completely. Therefore, polymer/clay nanocomposites are unable to meet the fire safety standard of UL-94 and LOI tests when used alone. Improvements on LOI or UL-94 tests can be observed in some systems that combine clay and conventional flame retardants. In this section, the issue will be discussed briefly. 

In spite of the encouraging results obtained in polymer/LDH flame retardant nanocomposites, the use of LDHs alone is insufficient for ensuring adequate fire resistance to meet the required standards, such as LOI values and UL-94 test ratings, especially at low LDH concentrations. The combination of LDH with conventional flame retardants is an effective way to avoid this limitation. By this means, it is possible to reach the flame retardancy required by the market with a halogen-free, nontoxic flame retardant system and improved mechanical properties. There are also many issues concerning the synergy between LDH and conventional flame retardants. 

Intumescence of polyethylene (PE) and PP has been reviewed using as intumescent agents zeolites [36], melamine phosphate and pentaerythritol [37]. Ammonium polyphosphate-pentaerythritol [38], zinc borate and ammonium polyphosphate [39], and APP [40], limiting oxygen index (LOI) [36, 37], cone calorimetry [36] and the UL 94 test [25, 36, 37] have all been used in these studies. 

Schafer et al. have compared DPPA (5,10-dihydrophenophosphazine 10-oxide) and DOPO incorporated into DGEBA-based epo)q resins. Contrarily to DOPO, DPPA contains both phosphorus and nitrogen without any direct covalent N-P bond. DOPO is slightly more efficient than DPPA VO in the UL-94 test could be achieved for a lower phosphorus content and a higher LOI was also obtained for DOPO at a similar phosphorus content. 

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