Heat release rate curves nanocomposites

FIGURE 12.7 Heat release rate curves for ABS and its nanocomposites with different MWNTs and MWNT-PDSPB content. (From Ma, H. et al., Adv. Fund. Mater., 18, 414, 2008. With permission.)... 

The heat release rate curves shown in Fig. 4A are consistent with the characteristic burning patterns of intermediate thick, non-charring samples (II). The PHRR values for PE-ZCHS-5 and PE-ZCHS-10 nanocomposites are reduced by 27 and 25% relative to the pure PE respectively. For smectite clay/polymer nanocomposites, reduction in PHRR has been shown to be correlated with nanodispersion of the additive in the polymer matrix (72). With HDS and related layered metal hydroxide additives, we have also only found PHRR reduction in the case of PVE with CHDS, a system with some... 

Figure 11.5 Heat release rate curves for PP and PP/Ceo nanocomposites at a heat flux of 35 kW/m. Reprinted with permission from Ref. [17]. 2008 lOP Publishing Ltd.

FIGURE 10.10 Heat release rate curves of PU nanocomposites on PET knitted fabrics at 35 kW/m incorporation of nanoadditives in the second stage of sample preparation. (From Ref. 30, copyright 2002, John Wiley Sons Ltd., with permission.)... 

FIGURE 10.14 Heat release rate curves of St-BA and St-BA/GO nanocomposites. (From Ref. 41, copyright 2004, Elsevier, with pamission.) (See insert for color representation of figure.)... 

The effects of the concentration of MWNTs in PP on the heat release rate curves of the nanocomposites are shown in Figure 10.25. The results show two distinct characteristics brought on by the addition of MWNTs first, there is a shortened ignition delay time with the PP-MWNT(0.5%), followed by an increase in ignition delay time with an increase in the concentration of MWNT second, there is a gradual increase in peak heat release rate above about 1% by mass of MWNT. A similar trend was observed for PMMA-SWNT nanocomposites (less obvious for PMMA-SWNT, due to a lower concentration of SWNT, as shown in Figure 10.20). The lowest heat release rate curve for PP-MWNT is achieved with about 1% by mass of MWNT compared to about 0.5% by mass of SWNT. The increase in peak heat release rate with concentration of MWNT above 1% appears to be due to an increase in thermal conductivity of the nanocomposite. ... 

Figure 2.15 Heat release rate curves for PMMA and PMMA-LDH nanocomposite prepared by suspension polymerization with different LDH loadings. Reproduced with permission from reference 142.

A typical heat release rate curve for a neat epoxy system and the respective layered silicate nanocomposite, is shown in Fig. 2.12. Both peak and average heat release rate, as well as mass loss rates, are all significantly improved through the incorporation of the nanopartieles. In addition, no increase in specific extinction area (soot), CO yields or heat of combustion is noticeable. However, the mechanism of improved flame retardation is still not clear and no general agreement exists as to whether the intercalated or exfoliated structure leads to a better outcome. The reduced mass loss rate occurs only after the sample surface is partially covered with char. The major benefits of the use of layered silicates as a flame retardation additive is that the filler is more environmentally-friendly compared to the commonly used flame retardants and often improves other properties of the material at the same time. However, whilst the layered silicate strategy is not sufficient to meet the strict requirements for most of its application in the electrical and transportation industry, the use of layered silicates for improved flammability performance may allow the removal of a significant portion of conventional flame retardants. 

The impact of the nanocomposite technology on polymers is huge, reflected in enhanced properties of the resulting PNs, such as enhanced mechanical, barrier, solvent-resistant, and ablation properties.12 The effect of nanocomposite technology on the thermal and fire performance of the polymers is primarily observed in two important parameters of the polymers (1) the onset temperature (7( ,nsct) in the thermogravimetric analysis (TGA) curve—representative of the thermal stability of the polymer, and (2) the peak heat release rate (peak HRR) in cone calorimetric analysis (CCA)—a reflection of the combustion behavior (the flammability) of the polymer. The Tonset will be increased and the peak HRR will be reduced for a variety of polymers when nanoscale dispersion of the nanoadditive is achieved in the polymer matrix. 

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. 

Cone calorimetry was used to measure the effectiveness of the additives on reducing the flammability of PE the parameters available include the heat release rate and especially its peak value, the peak heat release rate (PHRR) and time to peak heat release rate (tPHHR) total heat release (THR) time to ignition (tig) average mass loss rate (AMLR) and average specific extinction area (ASEA), a measure of smoke formation. A decrease in the PHRR, THR, AMLR, and ASEA are desired along with an increase in tig and tPHRR. The heat release rate (HRR) curves as a function of time for pure PE and its nanocomposites are shown in Figure 4A and cone data are summarized in Table II. 

Figure 3.8 The heat release rate (HRR) curves of the pure HIPS and HIPS/OMT nanocomposites. Reproduced from [42] with permission.

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. 

In order to predict the behavior of flame-retarded materials they are investigated using a cone calorimeter. A typical value found for the heat release rate of polyethylene is about 2200 kWm". Figure 23 shows the development of the heat release rate of the LDH polyethylene nanocomposites found by Costa. The curves indicate a dramatic reduction of the peak heat release rate (PHRR) and at the same time an inaease in the time of burning as the curves get flat and... 

FIGURE 8.8 Rate of heat release curves of PU-nanocomposite coatings on PET knitted fabrics at 35kW/m2. (From Devaux, E. et al., Fire Mater., 26, 149, 2002. With permission.)... 

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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