Polymer flammability

The control of polymer flammability, which has enjoyed considerable success in the last forty years, had its beginnings in antiquity with the first early attempts to reduce the flammability of natural cellulosic materials such as cotton and wood (1-3). Some of these early developments are summarized in Table I. Perhaps the... 

Oxygen index method of evaluating relative polymer flammability. 

Thermal analysis, in the form of TG, has been employed extensively in the area of polymer flammability to characterize polymer degradation. 

Reduction of polymer flammability is of broad interest for applications ranging from plastics to textiles. For polyesters, given their inherent instability towards water at elevated temperatures, and the high temperatures of manufacture, many classes of flame-retardant (FR) agents, including most halogen-containing materials, are impractical. Phosphate esters, capable of incorporation into the polymer backbone, were pioneered by Hoechst AG, and continue to be the materials of choice [84, 85],... 

Gilman JW, Davis RD, Shields JR et al. (2004) Development of high-throughput methods for polymer flammability property characterization. International SAMPE Symposium and Exhibition 460-469... 

In an attempt to look for alternatives to the use of halogenated fire retardants, which function in the gas phase, an approach has been pursued which controls the polymer flammability by modifying the condensed phase chemistry. Silica gel combined with potassium carbonate have been reported to be an effective fire retardant for a wide variety of common polymers, such as polypropylene, nylon, poly(methylmethacrylate), poly(vinyl alcohol), cellulose, and to a lesser extent, polystyrene and styrene-acrylonitrile.49 The cone calorimeter data shown in Table 8.5 indicate that the PHHR is reduced by up to 68% without significantly increasing the smoke or carbon monoxide levels during the combustion. 

For more than a decade, numerous research studies have been carried out on the flame-retardant properties conferred by nanoparticles and mainly by organo-modified layered silicates (OMLS). Earlier work at Cornell University and National Institute of Standards and Technology in the United States showed that nanocomposites containing OMLS reduced polymer flammability and enhanced the formation of carbonaceous residue (char).14 Owing to a strong increase in polymer viscosity, impairing processability, and also due to the breakdown of ultimate mechanical properties, the acceptable rate of incorporation for nanoparticles to improve flame retardancy is generally restricted to less than 10 wt %. 

Lyon, R., Walters, R., and Stoliarov, S., A thermal analysis method for measuring polymer flammability. Journal ofASTM International 2006, 3, 1-18. 

Lyon, R. and Janssens, M., Polymer flammability. In Encyclopedia of Polymer Science Engineering (On-line Edition), John Wiley Sons New York, 2005. 

Levchick SV. Introduction to flame retardancy and polymer flammability. In Flame Retardant Polymer Nanocomposites. Morgan AB, Wilkie CA, Eds. John Wiley Sons Hoboken, NJ, 2007 chap. 1, pp. 1-29. 

Walters RN, Lyon RE. Molar group contributions to polymer flammability. J. Appl. Polym. Sci. 2003 87 548-563. 

Case Study 2. High Throughput Polymer Flammability Characterization Using... 

Molar Chemical Group Contributions Used to Predict Polymer Flammability... 

CASE STUDY 2. HIGH THROUGHPUT POLYMER FLAMMABILITY CHARACTERIZATION USING GRADIENT HEAT FLUX ENVIRONMENTS AND RAPID CONE CALORIMETRY ... 

Source Lyon, R.R. and Janssens, M.L. Polymer flammability, Office of Aviation Research Washington,... 

FIGURE 26.5 Relationships between LOI and HRC for pure polymers and FR compounds. (From 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.) The LOI-HRC relationship for pure polymers is obtained from the literature. (From Lyon, R.E. and Janssens, M.L., Polymer flammability, Final Report DOT/FAA/AR-05/14 May, 2005.)... 

Lyon, R.E., A molecular basis for polymer flammability, Proceedings of Flame Retardant 2008, London, England, 2008. 

Fenimore and Jones (12) report die first of their investigations into the modes of inhibiting polymer flammability. They show that chlorine substituted in polyethylene inhibits by affecting the pyrolysis of the condensed phase, but the pair of reactants, antimony plus a little chlorine, poisons the flame. Bromine is more effective than chlorine because it also poisons the flame. They speculate that halogen seems necessary to vaporize Sb from Sb203. 

Although the term "polymer flammability" is widely used, it has no intrinsic scientific meaning it depends on the physical state of the product in which it appears and on the... 

Thus, the theory opens up new possiblilities for determining more details about polymer flammability by using data obtained from other independent experiments. 

T o demonstrate more clearly the effect of structural factors on polymer flammability, we considered the relationship between the limiting oxygen index and the specific... 

The nature and number of the terminal groups, the type of bonds, the presence of aromatic cycles and carbonate groups in the unsaturated ester molecule, as well as other structural features affect polymer flammability. The slope of the straight lines increases from methacrylate to acrylate polymers. Thus, for polymers of alkylene glycol dimethacrylates it is 2,82x 10 kJ/kg, for polymers with carbonate bonds 2.86 X 10 -2.9 X 10 kJ/kg for acrylic polymers it is somewhat higher, 3.27 x 10 kJ per kg. Linear polymers, e.g. PMMA, PE, etc. have a smaller slope corresponding to... 

Thus, considering the combustion heat and the oxygen consumption for the combustion it is possible to study the influence of certain structural features on polymer flammability. 

This chapter reviews the basic principles of polymer flammability, the relationship of polymer flammability to polymer structure, and the general approaches to flame retardation. In addition, examples illustrating the concepts of polymer flammability and flame retardation are presented. 

This section deals briefly with the basics of polymer flammability and the approaches to flame retardation. A familiarity with both of these subjects is essential for designing polymeric materials of desired flammability properties. 

Table I. Effect of Structure on Polymer Flammability Properties... 

Polymer flammability continues to be an important field of research even though it is reasonably well understood at present. Current efforts will contribute to the design of safer polymeric materials of the future. 

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