Peak heat release

The Ohio State University (OSU) calorimeter (12) differs from the Cone calorimeter ia that it is a tme adiabatic instmment which measures heat released dufing burning of polymers by measurement of the temperature of the exhaust gases. This test has been adopted by the Federal Aeronautics Administration (FAA) to test total and peak heat release of materials used ia the iateriors of commercial aircraft. The other principal heat release test ia use is the Factory Mutual flammabiHty apparatus (13,14). Unlike the Cone or OSU calorimeters this test allows the measurement of flame spread as weU as heat release and smoke. A unique feature is that it uses oxygen concentrations higher than ambient to simulate back radiation from the flames of a large-scale fire. 

Flammability. PhenoHcs have inherently low flammabiHty and relatively low smoke generation. For this reason they are widely used in mass transit, tiinnel-building, and mining. Fiber glass-reinforced phenoHc composites are capable of attaining the 1990 U.S. Federal Aviation Administration (FAA) regulations for total heat release and peak heat release for aircraft interior facings (1,70). 

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. 

In that way, the viscoelastic behavior of a PP-based intumescent formulation including polyurethane (PU) as carbon source in association with APP has been evaluated.30 The use of PU/APP mixture in PP brings a decrease in the peak heat release from 1700 kW/m2, in the case of the virgin matrix, to 300kW/m2, in the case of the intumescent formulation. 

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. ... 

PHR peak heat release PMDI polymeric methylene diphenylene diiso-... 

To moderate the previous problem, a longitudinally fired zone in a reheat furnace can be fired with a combination of small and large burners designed to permit paralleling them. The small burners will have their peak heat release closer to the burner wall whereas the large burners will have a peak heat release farther from the burner wall. With such a combination, the zone temperature profile will be much flatter, regardless of the firing rate. 

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 ... 

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