The National Academies Press

Currently Skimming:

Pages 52-67

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.

From page 52... ... CONDENSED PHASE COMBUSTION C H E M I S T R Y LEO A WALL Naltonal Bureau of Standards In this article we shall endeavor to survey the pyrolj^ic processes occumng in polymeric melts on the assumption that our comprehension of these processes are highly important if not cntical for control of igmtion and burning of matenals. Read the entire page →
From page 53... ... ABSTRACTS AND REVIEWS 205 TABLE 1 Yield of monomer m the pyrolysis of some organic polymers m a vacuum (In per cent of total volatibzed) Read the entire page →
From page 54... ... 206 F f f i E R E S E A R C H T A B L E 2 Activation energies of thennal degradation of some organic polymers m a vacuum (Rcf. Read the entire page →
From page 55... ... ABSTRACTS AND R E V I E W S 207 In this rare case, it is seen that Z is a constant. Also, since we have restricted termination to disproportionation, we have already assumed that Z « P „ , where P„ is the number average degree of polymerization. Read the entire page →
From page 56... ... 208 R E S E A K C H T A B L E 3 Zip lengths for polymer depolymenzation at 1%/niin rates Polymer Zip lengths Methyl methacrylate ~10» a-methyl styrene ~10' Styrene ~ 5 Tetrafluoroethylene ~ 3 low thermal stability. For the polymethyl methacrylate a variety of rates and activation energies (30-52 kcal/mole) Read the entire page →
From page 57... ... T A B L E 4 ^ Absolute rate constants (at 25°C) , activation energies, and PZ factors for propagation and termination in radical polymerization (Ref 7) Read the entire page →
From page 58... ... 210 F I B E B E S E A B C H T A B L E 5 Standard enthalpies of polymerization (hquid-crystal) Read the entire page →
From page 59... ... ABSTRACTS AND R E V I E W S 211 and certam volatile products. There are m mam two types of decompositions. Read the entire page →
From page 60... ... 212 F I R E R E S E A R C H T A B L E 7 Pnncipal products from pyrolysis of polymers (Ref 2) Polymer Structural umt Pnncipal volatile products Cellulose VmyUdene chlonde Vmyl chlonde Vinyl acetate Chloroprene Acrylonitnle p-Xylene Benzyl Phenyl CHjOH I C - 0 / H \ -- C -- H HC -- O -- \ H H / C -- C 0 0 H H -- C H j C C l r -- C H , -- C H C l -- O O C -- C H , I -- C H , -- C H -- H - C H r - C = C -- C H r Cl H H C N Levoglucosan, CO, CO.; HjO -CH, i<( ^ C H , - C H , . Read the entire page →
From page 61... ... ABSTRACTS AND R E V I E W S 213 faster oxygen-induced rate of initial weight loss to depend upon the 0 4 power of the oxygen pressure One would, by postulating a chain reaction and oxidative imtiation, anticipate an 0 5-power dependence The oxidation of hydrocarbons at low pressure when measured by oxygen consumption normally has a first-power dependence upon oxygen pressure The physical deterioration of polymers by oxidative aging processes"'" has long been of concern to the polymer field. Dependmg on the polymer and conditions, most polymers oxidize slowly at ambient temperatures and antioxidants are incorporated in polymeric articles Oxidative aging will, m general, be expected to enhance the ignition probabihty and combustibihty of polymers Studies of pyrolytic decomposition are normally earned out on highly punfied materials and, thus, data such as listed m Tables 1 and 2 are not hkely to be always characteristic of aged materials T A B L E 8 Thermodynamic quantities* Read the entire page →
From page 62... ... 214 F I B E R E S E A R C H Burning of Polymers Fnedman'5 has pointed out that plastics burn with several times the intensity of cellulose and that the heat of combustion per gram (or cc) for polyethylene is greater than that for cellulose by over a factor of 2 Also, cellulose absorbs water and tends to char while polyethylene is lyophobic and burns without char production These variations in behavior and properties suggest that a comparison of enthalpies of combustion and approximate reaction temperatures may be helpful. Read the entire page →
From page 63... ... ABSTRACTS AND R E V I E W S 215 T A B L E 9 Comparison of enthalpies (kcals) of combustion-t3rpe reactions A H „ kcal ~Reaction T, °C Carbon as (carbon as Reaction Graphite Gas graphite) Read the entire page →
From page 64... ... 216 TIRE R E S E A R C H T A B L E 10 Estimated heats of gasification for some polymers at ~25°C L (cal/g) Polymer (g/mole) Read the entire page →
From page 65... ... ABSTRACTS AND R E V I E W S 217 composition For polyvinyhdene fluonde, one estimates an exothermic heat of approximately 20-30 kcal/64 g. A C T I V A T I O N E N E R G I E S F R O M R E G R E S S I O N R A T E S An extensive study of the burning of polymers has been earned out by Blazowski, Cole, and McAlevy " An expenmental arrangement was used which permitted measurements to be made of the length of polymer rod consumed per time mterval and the surface temperature of the burmng polymer From such measurements, determination of activation energy for polymer consumption under burmng conditions were made. Read the entire page →
From page 66... ... 218 F I R E R E S E A R C H where p and A are density and burning area, respectively By assuming a constant active weight Wa at the measured surface temperature as the source of volatile fuel, we can equate dl/dt=Kla, where la is the active thiclcness for the pyrolyzmg skm. It is interestmg to note that, with available data,"'"-' one finds that h values of 1-2X10-=' mm for polymethylmethacrylate, and 1-2X10"' for polyethylene, and are relatively constant with regression rate. Read the entire page →
From page 67... ... ABSTRACTS AND R E V I E W S 219 example, the variety of substances in textiles, garments, composite structures, and building materials. References I S L MADORSKT Thermal Degradation of Orgamc Polymers, Interscience, 1964 2. Read the entire page →

From page 52...

... CONDENSED PHASE COMBUSTION C H E M I S T R Y LEO A WALL Naltonal Bureau of Standards In this article we shall endeavor to survey the pyrolj^ic processes occumng in polymeric melts on the assumption that our comprehension of these processes are highly important if not cntical for control of igmtion and burning of matenals.