Heat release capacity

These polymers are self-extinguishing in air with LOI between 24 and 65 (see Table 8). Their thermal stabilities (300-400 °C) are typical of organic polymers, but the char yields are higher ( -30%), and a low heat release capacity is observed [582]. 

As an example of incinerator use in the pesticide industry, one plant operates two incinerators to dispose of wastewater from six pesticide products [7]. They are rated at heat release capacities of 35 and 70 milhon Btu/hour and were designed to dispose of two different wastes. The first primary feed stream consists of approximately 95% organics and 5% water. The second stream consists of approximately 5% organics and 95% water. The energy generated in burning the primary stream is anticipated to vaporize all water in the secondary stream and to oxidize all the organics present. Wastes from two of the six pesticide processes use 0.55% and 4.68% of the incinerator capacity, respectively. The volume of the combined pesticide... 

The PCFC technique utilizes traditional oxygen depletion calorimetry. The specimen is first heated at a constant rate of temperature rise (typically 1-5 K/s) in a pyrolyzer. The thermal decomposition products are swept from the pyrolyzer by an inert gas. The gas stream is mixed with oxygen and enters a combustor at 900°C, where the decomposition products are completely oxidized. Oxygen concentrations and flow rates of the combustion gases are used to determine the oxygen depletion involved in the combustion process, and the heat release, as well as the heat release capacity (HRC), is determined from these measurements. 

Cone calorimetry according to the ASTM E1354138 or ISO 5660139 standards are commonly used in the laboratory to screen flammability of materials by measuring heat release characteristics of the compound.116140 This device is similar to FPA but does not have the versatility of FPA. The cone calorimeter can determine the ignitability, heat release rates, effective heat of combustion, visible smoke, and C02 and CO development of cable materials. This test has been used extensively for wire and cable material evaluation. The microscale combustion calorimeter (MCC), also known as pyrolysis combustion flow calorimeter (PCFC), was recently introduced to the industry for screening heat release characteristics of FR materials.141142 This device only requires milligram quantities of test specimen to measure the heat release capacity (maximum heat release potential). Cone calorimetry and MCC have been used in product development for flammability screening of wire and cable compounds.118... 

A probability function was proposed to screen the single wire bum flame spread using heat release capacity measured by PCFC on halogen-free FR compounds.143 Figure 26.4 shows the probability of flame spread for a single wire bum as a function of heat release capacities of wire insulation compounds. It was suggested that the probability of flame spread for an insulated wire is less than 5% when the heat release capacity is less than ca. 320J/g K. 

FIGURE 26.4 Probability for flame spread versus heat release capacity of compounds. (Cogen, J.M. et al., Correlations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen free flame retardant polyolefin compounds, Fire Mater., 2009, 33, 33-50.)... 

A micro-scale combustion calorimetric method test has been developed by Walter and Lyon, which involves pyrolysis and combustion calorimetry of the volatile products [12]. Using this technique, the heat release capacity can be obtained. The heat release capacity is a material parameter and has been used to correlate polymer structures with flammability [13]. 

This instrument measures the oxygen consumed by a sample exposed to rapid pyrolysis temperature profiles, thus measuring the heat release (HR) capacity as well as the total heat evolved from the sample. The instrument measures the inherent flammability of a polymeric material the lower the HR capacity and total heat, the less flammable the material. The PCFC results obtained from the BPC polycarbonate show a much lower heat release capacity and also a much higher char yield, compared with traditional BPA polycarbonate, thereby underscoring the effectiveness of the BPC system. 

Fig. 15) and PCFC data from the three polyarylethers show that 7 gives the highest char yields (58%) followed by 8 and 10 (Table 2). The thermal stability of the polymers is reduced with the incorporation of more aliphatic/olefinic groups, which results in a lower percentage of the char yields, which is apparent when you compare heat release capacity and char yields of polyarylethers 7 and 10. 

The PCFC total heat release data correlate well with the TG analysis char yields. Polyarylether 10 has a lower heat release capacity than polyarylether 8, but also has a lower char yield. The thermal stability of these polymers can be attributed to the BPC structure in addition, the olefin functionality in polyarylethers 7 and 10 might also give rise to its thermal resistance. Almost half the polymer weight in 7, 8, and 10 is retained this indicates some flame resistance because we would have otherwise expected complete incineration (Fig. 15). 

The burn results for polymers 15 and 19 show that the polymers are inherently flame retardant with low base flammability (Table 4). The polymer dripped but did not ignite the cotton when it was subjected to the UL-94 flame test, and with the addition of 1 wt% PTFE, it did not drip. The PCFC results show that these polymers have a high heat release capacity when compared with the BPC carbonates and aryl ethers, but it is still significantly less than that of the base commodity polymers, such as polyethylene or polystyrene (Table 5). 

Thus, addition of the nanoparticles to a regular size Mg(OH)2 led to a significant decrease of heat release capacity of filled polypropylene. 

Total heat release capacity (measured in Kcal/h). 

Fig. 1. Heat release capacity, cost, and flame resistance of commercial polymers.

From the additivity principle for polymer properties, a molar heat release capacity 4 is defined (29) with units of J/(mol K) whose functional form is equation 70 but with the thermal stability and combustion properties written as additive molar quantities H, V, E, and Y/M in place of hc, (l—pd, Ea, and Tp, respectively. If each chemical group i in the polymer adds to the component molar properties according to its mole fraction rii in the repeat unit, then in terms of molar quantities... 

Fig. 18. Average heat release rate versus heat release capacity of polymers.

Experimental heat release capacities t]c have been measured for over 200 polymers and the results are used to generate over 30 additive molar group contributions by treating the as adjustable parameters in equation 73 for poljuners with known chemical structures (29). Table 8 contains r]c for a few dozen polymers. Figure 19 compares calculated and measured heat release capacities for 50 polymers using... 

Fig. 19. Polymer heat release capacities calculated versus measured values.

The predicted heat release capacity for PET compares favorably with typical experimental values for this polymer, t]c = 326 52 kJ/(kg K) (see Table 8),... 

Table 13. Group Contributions to the Heat Release Capacity of Poly(ethylene terephthalate)...

Fig. 20. Flammability rating in UL 94 test versus heat release capacity of 50 pol)maers.

Fig. 21. Limiting oxygen index versus heat release capacity for 50 pol3rmers.

For instance, the effect of smoke reduction and flammability performance of zinc-based compounds (i.e. zinc borate and zinc hydroxystannate) in epoxy resin composites used in the aerospace and aeronautical industries have been analyzed (Formicola et al., 2011). The flammability performance of neat and loaded systems was analyzed by using micro-combustion calorimetry, while smoke generation, in terms of CO and CO2 production, was analyzed under dynamic conditions by using cone calorimetry. The experimental results have shown that the dispersion of zinc borate and zinc hydroxystannate within epoxy matrices leads to a significant variation in flame retardant properties in particular the total heat release is reduced by about 25% and 30%, respectively, and the heat release capacity by about 30% and 50%, respectively. The system containing zinc hydroxystannate shows an enhancement in all smoke reduction properties, and both compounds lead to a reduction of the CO2/CO ratio. 

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