Decomposition products, polymer flammability

Substances applied to or incorporated in a combustible material (e.g. organic polymers, nylon, vinyl and rubber, etc.) to reduce flammability. Act by retarding ignition, control/douse burning, reduce smoke evolution. Slow down or interrupt the self-sustained combustion cycle when the heat-flux is limited. Flame retardants (FRs) improve the combustion behaviour and alter the combustion process (cool, shield, dilute, react) so that decomposition products will differ from nonflame retarded articles. FRs are usually divided into three classes ... 

The TGA apparatus becomes very hot and caution should be exercised while using it. In order to safely handle volatile materials or polymer decomposition products which may be irritating and harmful, it is suggested that a gas bubbler be constructed to scrub the gaseous effluent from the instrument (Fig. 15.5). Care must be taken to prevent excessive gas pressure from building up if the system is being operated under vacuum or with gases, both inert and flammable. Consult the instrument operations manual for any special safety instructions. 

The burning behavior of a polymer cannot, therefore, be regarded as an intrinsic property of the material. Rather do the major variables in the case of a fire — flammability, propagation of the fire, production of heat, smoke and toxic or conosive decomposition products — depend on all the factors mentioned above. 

Some of the important factors to consider in the development of alternative physical blowing agents are solubility, permeability, boiling point, vapor pressure, flammability, toxicity, VOC, ODP, GWP, availability, and cost. Similarly, the key important factors to be considered in the selection of CBAs for a given polymer are decomposition temperature, gas yield, rate of gas release, environmentally acceptable decomposition products, toxicity, and dispersability in the polymer matrix. 

The presence of pyrophosphoric and metaphosphoric acid on the surface of the polymer promotes char formation via a dehydrating effect which reduces the amount of flammable gaseous decomposition products. In addition, hypo- or metaphosphoric acid readily polymerizes ... 

Il-polyacrylate (compared with BPA-polyacrylate) is mainly due to the low mass loss rate and the lesser amount of fuels generated. While, in the case of BPC Il-polyacrylate, release of less flammable decomposition products is another important factor for its low flammability. So, compared with some other commercial polymers, Chakon II-and BPC Il-polyacrylates are more heat and flame resistant, and BPC Il-polyacrylate has an especially low flammability. 

Degradation of polymers at higher temperatures results in a variety of different products poly(oxy-l,4-phenyleneoxy-l,4-phelylenecarbonyl-l,4-phenylene) or poly ether ether ketone (PEEK) is an aromatic polyketone with low flammability and excellent mechanical properties [19]. Although a wealth of literature is available on the thermal decomposition products of PEEK and relevant kinetic parameters, there have not been many investigations about the mechanistic aspects of PEEK degradation. Patel et al. [20] propose decomposition mechanisms based on prior literature. Table 6.3 summarizes Patel s reports of volatile products identified at different temperatures. 

The decomposition of MH starts at about 300 °C, the associated endotherm is about 1450 Jg and 30.8% H2O is released during the decomposition of As expected, the water release decreases the temperature and dilutes oxygen and flammable gases near the flame. Also, the product, MgO, acts as a barrier to minimize any further combustion and decomposition of the flammable polymer. 

The retarding effect of metal compounds on the flaming combustion of polymers must be primarily attributed to the decrease of the yield of flammable volatile pyrolysis products. There are two alternative paths 1) catalysis of the formation of non-combustible products (COj, HjO) 2) inhibition of polymer decomposition at the high temperatures developed during steady-state combustion (high-temperature stabilization)... 

Mancozeb is a grayish-yellow powder with a musty odor, which is practically insoluble in water as well as most organic solvents. It is a polymer of maneb combined with zinc. While it is relatively stable and noncorrosive under normal, dry storage conditions, it is decomposed at high temperatures by moisture and by acid. Mancozeb may produce flammable products upon decomposition. It is also unstable in acidic conditions. 

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