Peak heat release rate char formation

Cone calorimetry measurement has demonstrated that such a modification drastically reduces the peak heat release rate and facilitates the char formation. This serves as a physical barrier for the heat flux through the polymer surface [75]. 

The major approach now for EVA compounds, especially those designed for cable jackets, is the introduction of nano-clays to the mix. As little as a 3% loading of a nanofiller produces a marked effect on heat release. 5% of nanofiller reduces the peak heat release rate by almost 50% as well as shifting that peak towards longer time-lapse. The flame retardant properties are due to the formation of a char layer that acts as a Arm insulating layer and dramatically reduces the emission of volatiles towards the flame front. The silicate layers not only play the active role in char... 

Figure 7.9 (A) Char formation of nano-LDPE after cone testing heat flux 35 kW/m and (B) Peak heat release rates of LDPE and nano-LDPE heat flux 35 kW/m. ...

Curves of heat release rate (HRR) versus time for intumescent EVA-based formulations (Figure 6.11) exhibit two peaks assigned to the development of intumescence. The first corresponds to formation of a protective layer, and the second corresponds to its destruction or failure. It clearly appears that when a nanocomposite is included in the formulation (in the matrix, in the carbonization agent, or in both), the first peak heat release rate (PHRR) is reduced (from about 340 kW/m to 200 kW/m ). However, the second peak decreases only when EVAnano is used, suggesting the formation of a stronger char. Work is in progress to explain these phenomena. 

One invariably finds that nanocomposites have a much lower peak heat release rate (PHRR) than the virgin polymer. The peak heat release rate for polystyrene and the three nanocomposites are also shown graphically in Fig. 5.16. P16-3 means that the nanocompoite was formed using 3% of P16 clay with polystyrene. The peak heat release rate falls as the amount of clay was increased. The suggested mechanism by which clay nanocomposites function involves the formation of a char that serves as a barrier to both mass and energy transport. It is reasonable that as the fraction of clay increases, the amount of char that can be formed increases and the rate at which heat is released is decreased. There has... 

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