Char yield

Properties. Results for the operation using subbituminous coal from the Wyodad mine near Gillette, Wyoming, are shown in Table 13. Char yields decreased with increasing temperature, and oil yields increased. The Fischer assay laboratory method closely approximated the yields and product assays that were obtained with the TOSCOAL process. 

Polypyromehitimide films based on cyclotriphosphazene and bisaspartimide-derived diamines have shown thermal stabiUties up to 800°C and char yields of 56—68% in N2 and 24% in air (29). High strength fine- and heat-resistant imide resins containing cyclotriphosphazene and... 

Silicone foam thus formed has an open ceU stmcture and is a relatively poor insulating material. Cell size can be controlled by the selection of fillers, which serve as bubble nucleating sites. The addition of quartz as a filler gready improves the flame retardancy of the foam char yields of >65% can be achieved. Because of its excellent dammabiUty characteristics, siUcone foam is used in building and constmction fire-stop systems and as pipe insulation in power plants. Typical physical properties of siUcone foam are Hsted in Table 10. 

Table 14 LOI Values, Char Yields, and Thermal Stability (in Air)...

A series of phosphorus- and bromine-containing FRs were synthesized and studied to understand their role, especially their combined effects. Thus, monocar-danyl phosphoric acid, its bromo derivatives and their formaldehyde condensates and crosslinked products [28,188] were prepared and their properties compared with analogous products made from phenol [28,189]. Table 14 gives the LOI values, char yields (Cy at 600°C), and thermal stability at 50% (T6o) decomposition. 

The lower thermal stability of cardanol-formaldehyde resin and their derivatives were expected because of the presence of the libile side chain in the system. Although phenolics are superior in their properties, their bromo derivatives exhibit very low char yields. Oxidation of the char by a decomposition product is suspected. Evaluation of the LOI data with char yields individually for phosphorus and bromine suggests a positive interac-... 

Epoxy Phenolic-Epoxy (wt/wt) PHRR (KW/m2) Char Yield (%) Toxicity" (xl0 3)... 

Novolac hydroxyl groups reacted with cyanogen bromide under basic conditions to produce cyanate ester resins (Fig. 7.41).105,106 Cyanate esters can thermally crosslink to form void-free networks, wherein at least some triazine rings form. The resultant networks possess high s, high char yields at 900°C, and high decomposition temperatures.105... 

Novolac resins containing cardanol moieties have also been converted to cyanate ester resins.107 The thermal stability and char yields, however, were reduced when cardanol was incorporated into the networks. 

The beneficial effects are demonstrated of heterogeneous secondary pyrolysis reactions on the liquid products of PU pyrolysis. Pyrolysis volatiles are passed through a packed bed of carbonaceous solids that promote the secondary reactions. Activated carbon and reaction injection moulded PU (RIM) char were found to be suitable bed materials. The long-term object was to develop marketable solid products by pyrolysis of wastes, so obtaining high char yields. In addition to affecting the liquid products, RIM char also increased the total char... 

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]. 

Figure 4. Total char yield (solid line) and polymer char yield (dashed line) of complexes pyrolyzed to 800°C vs weight % copper in the complex.

The synthesis of block polymers of diacetylene-silarylene and diacetylene-carboranylenesiloxane polymers (99a-e) (Fig. 61) by the polycondensation reaction of 1,4-dilithiobutadiyne with l,4-bis(dimethylchlorosilyl) benzene and/or l,7-bis(tetramethylchlorodisiloxane)-m-carborane have been reported by Sundar and Keller.129 These polymers are a hybrid between the carboranylenesiloxane and silarylene-siloxane polymers and have high char yields (up to 85%) at 1000°C in N2 and in air, reflecting the thermal stabilizing effects of the carborane and aromatic units in the polymeric backbone. 

Thermosets or highly crosslinked polymers give high char yields. Similarly, many high performance polymers, e.g., PEEK, PES, polyethe-rimide (PEI), not only have high LOI values but also tend to decompose to a char. 

Carbonaceous char barriers may be formed by the normal mode of polymer burning, and besides representing a reduction in the amount of material burned, the char may act as a fire barrier. The relationship of char yield, structure, and flame resistance was quantified by Van Krevelen (5) some years ago. For polymers with low char-forming tendencies, such as polyolefins, one approach to obtain adequate char is to add a char-forming additive. Such additives generally bear a resemblance to intumescent coating ingredients (6, 7). 

Studies at the International Tin Research Institute showed that 2.5% zinc stannate strongly enhanced the flame retardant action of ATH in ethylene-acrylic rubber, and enhanced the char yield (34) (Fig. 5). 

The increase in char yield, the decrease in exothermicity, and the delay of the peak oxidative-pyrolysis rate by the zinc... 

Table VI. Residual Char Yields and Extents of Elemental Volatilisation from Brominated Polyester Resin Samples during Combustion in Air... 

A DuPont 910 differential scanning calorimeter (DSC) and a DuPont 951 thermogravimetric analyzer (TGA) connected to a DuPont 1090 thermal analyzer 3ftre used to study the transition data, thermal stability, and char yield, respectively, for all the polymers. The DSC was run under a nitrogen stream at a flow rate of 80 c.c./min. and at a heating rate of 20°C/min.. 

As shown in Figure 1, the onset of decomposition temperature was in this order polybenzoxazole ) 2,4-DIF-PMTAI> 2,4-DIF-PMI. The char yield of these polymers followed the same sequence. It showed that the introduction of more fused heterocyclic rings into the backbone of the polymers enhanced the thermal stability and flame resistance of polymeric materials. 

Additives 10% IDT (°C) Residue of the pure additive at 900°C, (%) Char Yield % 700° 800° 900° 900°C after Correction Oxygen Index... 

The char yield after correction for the inorganic additive. 

The char yield of 900°C, after correcting for the additives to give a corrected char yield, was calculated on the basis of the following equation ... 

Char Yield of PMI Char Yield Contributed with Additives "from Additives Char Yield = —— ——... 

The char yield contributed by the additives alone was evaluated by measuring the residue obtained from the pure additives by TGA. 

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