Info

Pet Decomposition Polymer
Figure 11.2. The ASTM E 2058 Fire Propagation Apparatus [31].

polymers was the development of a polymer melt pool fire [32]. The observation was consistent with the polymer melt flow characteristics of the polymers (Tgl and Tm values of PP, PC, PET, and sheet molding compound (SMC) in Table 11.2). See the nomenclature list at the end of this chapter for abbreviations used in the discussion.

11.5. POLYMER VAPORIZATION/DECOMPOSITION

On heat exposure, a thermoplastic or an elastomer undergoes softening, melting, flow of polymer melt, and vaporization (or decomposition), whereas a thermoset vaporizes or decomposes. As the polymer vaporizes/decomposes, a combustible vapor-air mixture is generated that ignites and the polymer starts burning. The vaporization/decomposition characteristic of a polymer is governed by its thermal stability characterized by its vaporization/decomposition temperature, Tv(Td).

The factors that govern Tgl and Tm, namely the chain rigidity and strong interchain forces also govern Tv(Td) [4]. The Tv(Td) values for the polymers from various minivan parts are included in Table 11.2, where data are taken from Ref. [30] and in Table 11.3 for generic polymers, where data are taken from Ref. [33]. The Tv(Td) values are in the range of 240-572°C in Table 11.2 for polymers from the minivan parts and in the range of 270-789°C in Table 11.3 for generic polymers, suggesting significant differences in the thermal stability of the polymers. Thermal stability is one of the major parameters affecting the fire behavior of polymers.

For sustaining combustion in polymer fires, Tv(Td) values as well as AHg values need to be satisfied by the external/internal heat source. The AHg value combines all the energy requirements associated with the softening, melting, and vaporizing/decomposition of a polymer. Its value can be obtained [23]: (1) by quantifying each of its components in Eqs. (11.3) and (11.4), such as by the differential scanning calorimetry (DSC), and (2) by the direct quantification technique using some of the standard flammability test apparatuses, such as the ASTM E2058 [31].

For the direct quantification of the AHg values in ASTM E2058 [31], polymer samples (100 mm2 or 100 mm in diameter and 25 mm thick) are exposed to external heat flux in a co-flowing air with oxygen concentration reduced to below 10% to maintain nonflaming combustion condition [21-23]. By measuring the release rate of polymer vapors under the nonflaming steady-state combustion condition, the AHg value of a polymer is calculated from Eq. (11.1). In the calculations, q£ is the applied external heat flux, qf is zero, and q^ is the external heat flux value where release rate of polymer vapors is zero. Table 11.4 lists AHg and values for selected polymers determined in this fashion in the ASTM E2058 apparatus [21-23].

Was this article helpful?

0 0
Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook


Post a comment