20-09-2014, 11:31 AM
HEATS OF COMBUSTION OF HIGH TEMPERATURE POLYMERS
[attachment=68222]
ABSTRACT
The heats of combustion for forty-nine commercial and developmental polymers of known
chemical structure were determined using an oxygen bomb calorimeter according to standard
methods. The experimental results were compared to thermochemical calculations of the net heat of
combustion from oxygen consumption and the gross heat of combustion from group additivity of
the heats of formation of products and reactants. The polymers examined were thermally stable,
char forming thermoplastics and thermoset resins containing a significant degree of aromaticity and
heteroatoms including– nitrogen, sulfur, phosphorus, silicon, and oxygen in linear and heterocyclic
structures. The gross and net heats of combustion calculated from polymer enthalpies of formation
and oxygen consumption thermochemistry were within 5 percent of the experimental values from
oxygen bomb calorimetry. The heat released by combustion per gram of diatomic oxygen
consumed in the present study was E = 13.10 ± 0.78 kJ/g-O2 for polymers tested (n = 48). This
value is indistinguishable from the universal value E = 13.1 kJ/g-O2 used in oxygen consumption
combustion calorimetry
INTRODUCTION
Commercial passenger aircraft cabins contain several tons of combustible plastics, thermoset
resins, and elastomers in sidewall panels, ceilings, seat parts, foamed cushions, carpets, etc. Using
full- and bench-scale fire testing the Federal Aviation Administration determined that the fire hazard
in an aircraft cabin is not only a function of the effective heat of combustion of the cabin materials
but also the rate at which this heat is released by the burning material in a fire [1]. Consequently,
FAA regulations were developed for both effective heat of combustion and heat release rate of large
area cabin materials [2,3]. In the FAA test, convected heat released during flaming combustion is
calculated from the temperature rise of an air stream flowing past a standard-sized sample of the
burning material. Bench-scale fire calorimeters have since been developed which use the oxygen
consumption principle [4] to determine the chemical heat release rate of burning materials [5-7].
The oxygen consumption principle is based on the observation that combustion of a wide range of
organic compounds [4,8] and common polymers [5,8] produces 13.1 ± 0.7 kJ of heat per gram of
diatomic oxygen consumed independent of the chemical composition of the organic material. The
gases evolved during polymer decomposition are usually unknown and do not burn to completion
in real fires. Oxygen consumption is a means of measuring heat release without detailed
knowledge of the fuel species. The oxygen consumption principle has recently been adopted by the2
FAA for measuring non-flaming heat release rate of milligram-sized research samples in a
combustion flow calorimete
DISCUSSION
Reevaluation of the constant used for calculating the heat release rates of burning polymers
based on oxygen consumption has been updated to include high performance plastics. A value of E
= 13.10 ± 0.78 kJ/g-O2 was found for the net heat of combustion per gram of diatomic oxygen
consumed from the data for all of the polymers in table 1 (n = 48). Included are the halogenated,
phosphorus-, sulfur-, and, nitrogen-containing materials. The mean E value from this study is
identical to the universal value used in oxygen consumption calorimetry, although the coefficient of
variation of 6.0 percent is somewhat higher than the 5 percent usually reported for oxygen
consumption calorimetry. Regardless, the uncertainty in E is significantly lower than the reported
15 percent uncertainty in peak heat release and mass loss rates in oxygen consumption fire
calorimetry measurements [18] and will not be a factor in the accuracy of a heat release rate test
CONCLUSIONS
The heats of combustion of 49 polymers of known chemical composition were measured and
calculated. The agreement between experimental values for the gross and net heats of combustion
and thermochemical calculations of this quantity from heats of formation and oxygen consumption
was 4.2 and 4.4 percent, respectively, for these two methods. Either method could be used to
predict a reasonably accurate value for the heat of combustion from known polymer structure
regardless of the constituent atoms. The thermochemical quantity used to calculate heat release
rates based on the measured heats of combustion now encompasses a wider polymer range. The
new average value, E = 13.10 ± 0.78 kJ/g-O2 (n = 48) for the net heat released by combustion per
unit weight of diatomic oxygen consumed was obtained in the present study of high temperature,
heteroatomic polymers. This value of E for the thermally-stable polymers is statistically
indistinguishable from the universal value E = 13.1 kJ/g-O2 used for calculating heat release rates
of burning materials from oxygen consumption calorimetry. As new high performance materials
are made modifications to the heat release constant will not be necessary for calculating the heat
release rate of these heteroatomic polymers.
[attachment=68222]
ABSTRACT
The heats of combustion for forty-nine commercial and developmental polymers of known
chemical structure were determined using an oxygen bomb calorimeter according to standard
methods. The experimental results were compared to thermochemical calculations of the net heat of
combustion from oxygen consumption and the gross heat of combustion from group additivity of
the heats of formation of products and reactants. The polymers examined were thermally stable,
char forming thermoplastics and thermoset resins containing a significant degree of aromaticity and
heteroatoms including– nitrogen, sulfur, phosphorus, silicon, and oxygen in linear and heterocyclic
structures. The gross and net heats of combustion calculated from polymer enthalpies of formation
and oxygen consumption thermochemistry were within 5 percent of the experimental values from
oxygen bomb calorimetry. The heat released by combustion per gram of diatomic oxygen
consumed in the present study was E = 13.10 ± 0.78 kJ/g-O2 for polymers tested (n = 48). This
value is indistinguishable from the universal value E = 13.1 kJ/g-O2 used in oxygen consumption
combustion calorimetry
INTRODUCTION
Commercial passenger aircraft cabins contain several tons of combustible plastics, thermoset
resins, and elastomers in sidewall panels, ceilings, seat parts, foamed cushions, carpets, etc. Using
full- and bench-scale fire testing the Federal Aviation Administration determined that the fire hazard
in an aircraft cabin is not only a function of the effective heat of combustion of the cabin materials
but also the rate at which this heat is released by the burning material in a fire [1]. Consequently,
FAA regulations were developed for both effective heat of combustion and heat release rate of large
area cabin materials [2,3]. In the FAA test, convected heat released during flaming combustion is
calculated from the temperature rise of an air stream flowing past a standard-sized sample of the
burning material. Bench-scale fire calorimeters have since been developed which use the oxygen
consumption principle [4] to determine the chemical heat release rate of burning materials [5-7].
The oxygen consumption principle is based on the observation that combustion of a wide range of
organic compounds [4,8] and common polymers [5,8] produces 13.1 ± 0.7 kJ of heat per gram of
diatomic oxygen consumed independent of the chemical composition of the organic material. The
gases evolved during polymer decomposition are usually unknown and do not burn to completion
in real fires. Oxygen consumption is a means of measuring heat release without detailed
knowledge of the fuel species. The oxygen consumption principle has recently been adopted by the2
FAA for measuring non-flaming heat release rate of milligram-sized research samples in a
combustion flow calorimete
DISCUSSION
Reevaluation of the constant used for calculating the heat release rates of burning polymers
based on oxygen consumption has been updated to include high performance plastics. A value of E
= 13.10 ± 0.78 kJ/g-O2 was found for the net heat of combustion per gram of diatomic oxygen
consumed from the data for all of the polymers in table 1 (n = 48). Included are the halogenated,
phosphorus-, sulfur-, and, nitrogen-containing materials. The mean E value from this study is
identical to the universal value used in oxygen consumption calorimetry, although the coefficient of
variation of 6.0 percent is somewhat higher than the 5 percent usually reported for oxygen
consumption calorimetry. Regardless, the uncertainty in E is significantly lower than the reported
15 percent uncertainty in peak heat release and mass loss rates in oxygen consumption fire
calorimetry measurements [18] and will not be a factor in the accuracy of a heat release rate test
CONCLUSIONS
The heats of combustion of 49 polymers of known chemical composition were measured and
calculated. The agreement between experimental values for the gross and net heats of combustion
and thermochemical calculations of this quantity from heats of formation and oxygen consumption
was 4.2 and 4.4 percent, respectively, for these two methods. Either method could be used to
predict a reasonably accurate value for the heat of combustion from known polymer structure
regardless of the constituent atoms. The thermochemical quantity used to calculate heat release
rates based on the measured heats of combustion now encompasses a wider polymer range. The
new average value, E = 13.10 ± 0.78 kJ/g-O2 (n = 48) for the net heat released by combustion per
unit weight of diatomic oxygen consumed was obtained in the present study of high temperature,
heteroatomic polymers. This value of E for the thermally-stable polymers is statistically
indistinguishable from the universal value E = 13.1 kJ/g-O2 used for calculating heat release rates
of burning materials from oxygen consumption calorimetry. As new high performance materials
are made modifications to the heat release constant will not be necessary for calculating the heat
release rate of these heteroatomic polymers.