Peak heat release rates

Peak heat release rates (PHRRs), 414 PEEK. See Poly(arylene ether ether ketone) (PEEK)... 

Thermoplastics for aircraft interiors have been evaluated by this technique (10b) in accordance with the FAA specification (peak rate of heat release of 65 kilowatts per meter squared (Kw/m 2) or less). In these tests (10b) Polyether sulfone demonstrated marginal compliance. For Polyether imide (PHI) and PEI/Polydimethyl siloxane copolymers peak heat-release rates were well below the specified value. The overall trend suggested a possible correlation of peak heat release values with aromatic carbon content in the polymers evaluated. 

Table 6 Peak heat release rate measured in the ASTM E 1354 cone calorimeter... 

Hermansson et al. carried out extensive investigations on the fire-retardant behavior of ethylene-acrylate copolymer modified with chalk and silicone elastomer.30 32 They have shown that incorporation of a silicone elastomer (at 5wt.%) and chalk filler (at 30wt.%) can greatly improve the flame-retardant properties of ethylene butyl acrylate formulations. The results show that, compared to the pure polymer, an increase in the LOI from 18 to 30, and a decrease in the peak heat release rate (PHRR) from 1300 to 330kW/m2 were observed. 

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. 

Requirements for upholstered furniture flammability exist in various states, including California, based on California Technical Bulletin 133 (CA TB 133),91 which was also made into a consensus standard by ASTM committee E05 as ASTM E 1537.92 The gas burner used as the ignition source in CA TB 133 is a square-shaped burner that applies propane gas for 80s at a flow rate of 13L/min. The test is severe enough that it can usually not be met, unless the foam contained in the upholstered furniture item is flame-retarded. The pass/fail criteria are a peak heat release rate of 80 kW and a total heat released that does not exceed 25 MJ over the first 10 min of the test. In California, moreover, all foam contained within upholstered furniture must be flame-retarded to comply with CA TB 117. Moreover, the IFC and NFPA 101 both have parallel requirements to those discussed earlier for mattresses. In other words, the 2006 editions of both the codes contain requirements that upholstered furniture items in health care occupancies as well as detention and correctional occupancies that are not sprinklered must comply with a peak heat release rate of 250kW and a total heat release of no more than 40 MJ in the first 5 min of the test, when tested to ASTM E 1537 (or CA TB 133). However, the 2007 edition of the IFC and the 2009 edition of NFPA 101 lowered these values to 80 kW and 25 MJ over 10 min. Finally, the IFC 2007 added college and university dormitories to the list and eliminated the sprinkler exception for detention occupancies. 

Subsequently, the ignition temperature and the HRC parameter can be determined and used to compare PCFC data with data from other test methods. The HRC is defined as the ratio of the heat release rate and the heating rate. The peak heat release rates determined in cone calorimeter experiments correlate well with peak HRC data from PCFC experiments. In terms of other tests, results from the LOI (ASTM D 2863) test method exhibit a reciprocal correlation with HRC values, while HRC can also be a rough indicator for UL 94 ratings. In approximate terms, it has been said that HRC results can classify materials into three ranges of material flammability, as follows ... 

FIGURE 26.2 Spearman ranking order correlation between time to peak heat release rate (TTPHRR) and single wire burn. (From Cogen, J.M. et al., Assessment of flame retardancy in polyolefin-based non-halogen FR compounds, In Proceedings of the 53rd IWCS/Focus International Wire and Cable Symposium, 2004, pp. 185-190.)... 

FIGURE 26.6 Relationship between FIGRA and THR measured in MCC (i.e., PCFC). FIGRA = PHRR/ TTPHRR, FPI = TTI/PHRR, where PHRR is peak heat release rate, TTPHRR is time to peak heat release rate, and TTI is time to ignition. (Based on Lin, T.S. et al., Correlations between microscale combustion calorimetry and conventional flammability tests for flame retardant wire and cable compounds, in Proceedings of 56th International Wire and Cable Symposium, 2007, pp. 176-185.)... 

Ethylene copolymers were compared with liquid plasticisers for use as additives to improve the flexibility of poly(vinyl chloride) (PVC) for electrical cable insulation applications. The PVCs were assessed by determining smoke generation, flammability, tensile properties and the low temperature brittle point. The ethylene copolymers gave similar peak heat release rates, but the peak smoke and the total smoke generation were lower. They also gave similar or increased strength, similar elongation and flexural modulus, and lower brittle point temperatures. 4 refs. 

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. 

The addition of glass fiber, aramid, or graphite has little effect on the peak heat release rates of epoxy and phenolic resins. ... 

Nanocomposites refer to the combination of nanosized fillers (10 m diameter) with polymers, rather than the combination of polymer matrix (filled with nanoparticles) and fiber reinforcement The most popular fillers used as fire retardants are layered silicates. Loading of 10% or less (by weight) of such fillers significantly reduces peak heat release rates and facilitates greater char production [7]. The char layer provides a shielding effect for the composites below and the creation of char also reduces the toxicity of the combustion products, as less carbon is available to form the CO and CO2. 

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]. 

CNTs improve the flame retardancy of PP [36-38]. Figure 9.2 shows the heat release rates of PP and two nanocomposites. The peak heat release rate (PHRR) of PP was reduced by 73% by the addition of 1 vol% of MWCNTs. Although all samples burned nearly completely, the two nanocomposites burned much slower than PP. Further improvement on flame retardancy was achieved by the functionalization of CNTs with intumescent flame retardant (IFR) [38]. At the same CNTs content of 1 wt%, the PHRR of PP was reduced by 68% using pristine CNTs, and by 75% using IFR-functionalized CNTs. It was suggested that CNTs... 

Table 11.10 Peak Heat Release Rate Measured in the ASTM E1354 Cone Calorimeter ... 

FIGRA index (fire growth rate index) defined as the peak heat release rate in kW during the period from ignition to flashover (excluding the contribution from the ignition source) divided by the time at which the peak occurs (kW/s) ... 

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... 

Blends made by extrusion have created difficulties and show a degradation of the molecular weight with development of colour. Processing leads to more exfoliation of platelets in the clay that causes two competing effects. A reduction of the peak heat release rate (HRR) because of the exfoliated platelets, versus degradation processes that increase the peak HRR. The dominant effect in low ash and/or low shear situations is reduction of peak HRR. The opposite is true with high ash or high shear since the peak increases. 

Studies involving carbon nanotubes have also shown decrease in the peak heat release rate with no change in the total heat release (Kashiwagi et al. 2002, 2005) with effectiveness equal to or better than exfoliated clay. The level of dispersion of the carbon nanotubes in the polymer matrix was shown to be an important variable (Kashiwagi et al. 2005). Upon combustion, the surface layer was enriched with a protective nanotube network providing a thermal and structural barrier to the combustion process. Continuity of the network was important to achieve optimum performance as very low levels of nanotube incorporation or poor dispersion did not allow a continuous surface network during the combustion process. It is noted that the incorporation of nanoclay and carbon nanotubes often results in slightly earlier... 

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