Self-extinguishing polymers

TABLE 26.6 Average requirements for fire-retardant elements to render common polymers self-extinguishing (Lyons, 1970)... 

In Reference 142, PET was used in blends with HIPS and modified MMT clay. The use of PET was justified since this polymer self-extinguishes under fire. In addition to study the flame-retardant properties of the HIPS-clay and HIPS-PET-clay systems, mechanical and rheological properties were measured to provide explanations on the... 

By means of compounding, tailor-made engineering plastics parts are manufactured to satisfy every conceivable application. The warping problem, which existed in the past for the production of large area parts, e.g. for car body parts and bumpers, can be overcome by selected reinforcement/filler systems. Simultaneously the heat distortion temperature could be raised from about 150 °C for pure PBT homopolymer to approximately 210 °C for reinforced polymer. Self-extinguishing behavior was imparted by incorporation of flame retardant synergistic systems. Further, in the last thirty years, many commercial products have been developed by blending PBT with other polymers in the melt. Moreover, a variety of additives, fillers or reinforcements, which have been mentioned previously in this Chapter, may be added to the PBT blends. 

Polymeric vinylidene chloride generally produced by free radical polymerization of CH2 = CCl2. Homopolymers and copolymers are used. A thermoplastic used in moulding, coatings and fibres. The polymers have high thermal stability and low permeability to gases, and are self extinguishing. 

Pentaerythritol is used in self-extinguishing, non dripping, flame-retardant compositions with a variety of polymers, including olefins, vinyl acetate and alcohols, methyl methacrylate, and urethanes. Phosphoms compounds are added to the formulation of these materials. When exposed to fire, a thick foam is produced, forming a fire-resistant barrier (see Elame retardants) (84—86). 

Poly(vinyl chloride). PVC is a hard, brittle polymer that is self-extinguishing. In order to make PVC useful and more pHable, plasticizers (qv) are added. More often than not the plasticizers are flammable and make the formulation less flame resistant. Flammability increases as the plasticizer is increased and the relative amount of chlorine decreased, as shown in Table 7. The flame resistance of the poly(vinyl chloride) can be increased by the addition of an inorganic flame-retardant synergist. 

Blends of ABS with polycarbonates have been available for several years (e.g. Bayblend by Bayer and Cycoloy by Borg-Wamer). In many respects these polymers have properties intermediate to the parent plastics materials with heat distortion temperatures up to 130°C. They also show good impact strength, particularly at low temperatures. Self-extinguishing and flame retarding grades have been made available. The materials thus provide possible alternatives to modified poly(phenylene oxides) of the Noryl type described in Chapter 21. (See also sections 16.16 and 20.8.)... 

Polar substituents such as chlorine increase the interchain forces and hinder free rotation of the polymer chain. Hence polydichlorostyrenes have softening points above 100°C. One polydichlorostyrene has been marketed commercially as Styramic HT. Such polymers are essentially self-extinguishing, have heat distortion temperatures of about 120°C and a specific gravity of about 1.40. 

The chlorine present results in a self-extinguishing polymer. It also leads to a polymer which has a high rate of decomposition at the temperatures required for processing. 

Vinylidene chloride-vinyl chloride polymers are also self-extinguishing and possess very good resistance to a wide range of chemicals, including acids and alkalis. They are dissolved by some cyclic ethers and ketones. 

The self-extinguishing characteristics of the chlorine-containing resins are improved by incorporation of antimony oxide but this approach is not possible where translucent sheet is required. As an alternative to chlorine-based systems a number of bromine-containing resins have been prepared and, whilst claimed to be more effective, are not currently widely used. It is probably true to say that fire-retarding additives are used more commonly than polymers containing halogen groupings. 

The FR characteristics of PCP and Anorin-38 were improved substantially by introducing bromine. When five bronine atoms were introduced by controlled bromi-nation, the resin (the product obtained was still fluid in nature and could be crosslinked by hexamine to get hard partially brominated PCP-PBPCP) showed excellent FR characteristics exhibiting self-extinguishing property and UL 94 V-0 grade when blended with polyethylene, NR, etc. There was excellent compatibility with polyolefins as well as with other polymers such as cellulose, polyurethane, etc. Table 13 shows the FR properties of NR-PBPCP. 

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]. 

Polyvinyl chloride is considered to be a self-extinguishing polymer - in other words, it does not support combustion well. Why does it exhibit this behavior ... 

Fire Resistant Elastomers. The poly(aryloxyphosphazene) elastomers offer excellent fire resistance without incorporating halogen in the polymer or as an additive. These polymers are self-extinguishing in air and generate only moderate non-corrosive smoke and a minimum of toxic combustion products upon combustion (50-53). The poly(aryloxyphosphazene) elastomers (APN ) have excellent potential for applications such as... 

Due to the chlorine content, the fire resistance is inherently better than for hydrocarbon polymers. Rigid PVC is self-extinguishing but releases chlorine during combustion. Oxygen indices are about 45 but can decrease with some plasticizers. 

The above flame retardants, HMPN and TMP, along with another commercially available alkyl phosphate, triethyl phosphate (TEP), were systematically characterized by Xu et al. To quantify the flammability of the electrolytes so that the effectiveness of these flame retardants could be compared on a more reliable basis, these authors modified a standard test UL 94 HB, intended for solid polymer samples, and measured the self-extinguishing time (SET) instead of the universally used flame propagation rate. Compared with the UL 94 HB, this new quantity is more appropriate for the evaluation of the electrolytes of low flammability, since the electrolytes that are determined to be retarded or nonflammable by this method all showed zero flame propa-... 

Cyovin Self-extinguishing ABS graft polymer blends BorgWarner... 

The low burning result and the self-extinguishing characteristic obtained were not surprising. I say this in hindsight, for the inherent flammability of polyurethane foam, in general, is almost entirely a function of the chemical composition of the solid polymer and one route used to produce flame retardant polyurethane foams has been to alter the structure of the ure-... 

Polyphenylene sulphide (PPS) (e.g. Ryton ) is a highly crystalline polymer with a melting point of 290 °C. It combines good mechanical properties with very high thermal and chemical resistance it is, moreover, self-extinguishing. It is, i.a., used as protective coating on metal surfaces. 

Polyimide (PI) caps all other polymers in its temperature range of use (-200 to 260 °C in air short-time even up to 500 °C). Because of its high price, it is used in special cases only, such as space vehicles, nuclear reactors and some electronic parts. Newer developments, related to polyimide, are the polyether imides (e.g. Ultem ), polyester imides and polyamide imides (e.g. Torlon ), all with very good mechanical, thermal and electrical properties and self-extinguishing. 

Whereas UL 94 delivers only a classification based on a pass-and-fail system, LOI can be used to rank and compare the flammability behavior of different materials. In Figure 15.2 the increasing LOI values are presented for different polymers as an example POM = poly(oxymethylene), PEO = poly(ethyl oxide), PMMA = poly(methyl methacrylate), PE = polyethylene), PP, ABS, PS, PET = polyethylene terephthalate), PVA = poly(vinyl alcohol), PBT, PA = poly(amide), PC, PPO = poly(phenylene oxide), PSU, PEEK = poly(ether ether ketone), PAEK = poly(aryl ether ketone), PES, PBI = poly(benzimidazole), PEI = poly(ether imide), PVC = poly(vinyl chloride), PBO = poly(aryl ether benzoxazole), PTFE. The higher the LOI, the better is the intrinsic flame retardancy. Apart from rigid PVC, nearly all commodity and technical polymers are flammable. Only a few high-performance polymers are self-extinguishing. Table 15.1 shows an example of how the LOI is used in the development of flame-retarded materials. The flame retardant red phosphorus (Pred) increases... 

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