Heat release rate organoclays

The nanodispersed nanoadditives usually show enhanced fire performance and CCA has been the most powerful tool in analyzing the flammability of the PNs. In most cases, the PNs, as seen in Figure 11.20, show a significantly reduced peak HRR in the CCA curve. More examples of this are seen in PA-6/clay nanocomposite, which shows a 63% reduction in the peak HRR at 5% loading (Figure 11.2898 in which the heat release rate as a function of time for pure PA-6 and its clay nanocomposites is shown) and in poly(ethylene-co-vinyl acetate) (EVA)/clay nanocomposite,99 which shows a reduction of the peak HRR at about 50% at 5% organoclay loading. 

Flammabihty studies using cone calorimetry at 50 kW m heat flux showed that incorporation of 5 wt% organoclay reduced peak heat release rate (PHRR) by 23-27% and total heat release (THR) values by 4—11%, depending on the clay modification. However, no simple correlation was observed between the FR efficiency and the degree of day exfoliation. The synergistic effect was observed for the combination of ammonium polyphosphate and 5 wt% amount of nanoday, which resulted in the total reduction of the PHRR of polyester resin in the range 60-70%. 

Figure 7.6 Heat release rated at heat flux 35 kW/m for various EVA (Escorene UL 00328 with 28 wt% vinyl acetate content)-based materials (a) pure EVA matrix and EVA matrix with 5 wt% Na montmorillonite (b) EVA + 3 wt% organoclays (c) EVA + 5 wt% organoclays and (d) EVA + 10 wt% organoclays.

Figure 7.8 (A) Heat release rate (HRR) of EVA-ATH compounds containing organoclay. 65 65% ATH, 35% 60-3 60% ATH, 3% organoclay, 37% EVA 58-3 58% ATH, 3% organoclay, 39% EVA. EVA Escorene UL 00328 with 28 wt% vinyl acetate content and heat flux 35 kW/m polymer plates of 100 X 100 X 3 mm within aluminum dishes. (B) Rate of smoke production (RSP) of EVA-ATH compounds containing organoclay. 65 65% ATH, 35% organoclay 60-3 60% ATH, 3% organoclay, 37% EVA 58-3 58% ATH, 3% organoclay, 39% EVA. EVA Escorene UL 00328 with 28 wt% vinyl acetate content and heat flux 35 kW/m polymer plates of 100 x 100 x 3 mm within aluminum dishes.

The great improvements in flame retardancy caused by the organoclays also opened the possibility of decreasing the level of ATH within the EVA polymer matrix. The content of ATH needed to maintain 200 kW/m as a peak heat release rate could be decreased from 65 to 45 wt% by the presence of only 5 wt% organoclays within the EVA polymer matrix. Reduction in the total amount of these fillers resulted in improved mechanical and rheological properties of the EVA-based nanocomposite. 

In addition, several studies have reported the use of conventional ATH in combination with other types of nanofillers, particularly organoclays, to improve the FR properties of polymer nanocomposites [12, 13]. Organoclays are not considered as FR despite their ability to decrease peak heat release rates of several polymers under firelike conditions... 

Beyer clearly observed a delay in thermal degradation using TGA (in air) with the addition of a small amount of organoclay to EVA-ATH composite [20]. The char of the EVA-ATH-organoclay compound formed in a cone calorimeter was rigid, with only a few small cracks, whereas the char of the EVA-ATH composite was much less rigid (reduced mechanical strength) and had many big cracks. These observations allowed the author to explain the reduction of the peak heat release rate to 100 kW/m for the nanocomposite, compared to 200 kW/m for the EVA-ATH composite [21]. 

FIGURE 7.6 Heat release rates at heat flux = 35 kW/m for various EVA-based materials A, EVA-h 5.0 phr organoclays B, EVA-t-5.0 phr pure MWCNTs C, EVA-l-2.5 phr organoclays - - 2.5 phr pure MWCNTs. EVA, Escorene UL-00328 with 28 wt% vinyl acetate content organoclay, Nanofll 15. (From Ref. 59, copyright 2002, John Wiley Sons, Ltd., with permission.)... 

The data for nanocomposites polymer/organoclay on the basis of polyamide-6 (PA-6), polyamide-12 (PA-12), polystyrene (PS) and polypropylene (PP), which are listed in table 11.1, were used for the relationships structure-flame-resistance characteristics. The maximum rate of heat release measured with the use of a cone calorimeter according to the standards ASTM 1354-92 and ISO/DIS 13927 [2], the values of which are also listed in Table 11.1, was used as flame-resistance characteristic of the indicated nanomaterials. 

For further calculations as the first approximation 6 =1 was accepted, that corresponds to perfect adhesion by Kemer [4], In Fig. 11.1, the dependence of heat release maximum rate on the sum of nanofiller (organoclay) and interfacial regions relative volume contents is adduced, calculated according to the Eqs. (3) and (4) for intercalated and exfoliated organoclay, respectively. As one can see, all data correspond to one curve, which extrapolates to d 1450 kw/m at ((p +(pp=0, that is, for unfilled polymer. This value corresponds to the indicated parameter mean value for the four matrix pol5miers, mentioned above. The sole essential deviation from the obtained curve is the data for nanocomposite on the basis of PP. This deviation can be due to the condition b= for all considered nanocomposites. The value b can be estimated more precisely with the aid of the following percolation relationship [4] ... 

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