Molar Group Contributions - Walters

Molar Group Contributions to Polymer Flammability

Richard N. Walters,1 Richard E. Lyon2

1Galaxy Scientific Corporation, 3120 Fire Road, Egg Harbor Township, New Jersey 082342Fire Safety Section AAR-440, Airport and Aircraft Safety Research and Development, William J. Hughes TechnicalCenter, Federal Aviation Administration, Atlantic City International Airport, New Jersey 08405

Received 8 March 2002; accepted 26 April 2002

ABSTRACT: The specific heat-release rate is the molecu-lar-level fire response of a burning polymer. The FederalAviation Administration obtains the specific heat-releaserate of milligram samples by analyzing the oxygen con-sumed by the complete combustion of the pyrolysis gasesduring a linear heating program. Dividing the specific heat-release rate (W/g) by the rate of the temperature rise (K/s)of a sample during a test gives a material fire parameter withthe units (J/g K) and significance of the heat (release) capac-ity. The heat-release capacity appears to be a true materialproperty that is rooted in the chemical structure of the

polymer and is calculable from additive molar group con-tributions. Hundreds of polymers of known chemical com-positions have been tested to date, providing over 40 differ-ent empirical molar group contributions to the heat-releasecapacity. Measured and calculated heat-release capacitiesfor over 80 polymers agree to within 15%, suggesting anew capability for predicting flammability from the polymerchemical structure. 2002 Wiley Periodicals, Inc. J Appl PolymSci 87: 548563, 2003

Key words: plastics; calculations; thermal properties

INTRODUCTION

The additivity of molar group contributions to the phys-ical and chemical properties of polymers is the basis ofan empirical methodology for relating the chemicalstructure to the polymer properties.13 The early work inthis area4 focused on calculating the heats of combustionfrom the individual atoms comprising small molecules.However, performing calculations for large (polymer)molecules based on the interactions of the individualatoms can be very difficult.2 A simpler approach tocorrelating the polymer chemical structure to the prop-erties is to group the atomic contributions into charac-teristic structural elements (e.g., OCH3), determine thevalue of the group contribution to the property of inter-est parametrically, and add these group contributionsaccording to their molar fractions in the polymer repeatunit. This method has been used to relate the chemicalstructures of polymers to their thermal, chemical, optical,and mechanical properties with excellent results.13 Ofparticular interest in this context is the ability to predictthe thermal stability parameters of polymers (pyrolysisactivation energy, thermal decomposition temperature,and char/fuel fraction) from additive molar group con-tributions.1

A prerequisite for any structureproperty correla-tion is the ability to identify and reproducibly measurethe intrinsic property of interest. In the area of poly-

mer flammability, no single material property hasbeen correlated with fire performance, nor does anytest measure fire performance unambiguously be-cause the burning rate, ignitability, flammability, andheat-release rate are not intrinsic properties. Rather,they are extrinsic quantities resulting from the reac-tion of a macroscopic polymer sample to severe ther-mal exposure. Because the sample size in a flamma-bility or fire test is orders of magnitude larger than thechemical process zone,57 heat and mass transfer dom-inate the fire response. Therefore, an intrinsic materialproperty for use by scientists in designing fire-resis-tant polymers is not obtainable from standard fire orflammability tests.

Recently, a material fire parameter with the unitsand significance of the heat-release capacity57 hasbeen identified that appears to be a good predictor ofthe fire response and flammability of polymers. Aquantitative laboratory pyrolysiscombustion methodfor directly measuring the heat-release capacity hasbeen reported.810 This article provides empirical mo-lar group contributions to the heat-release capacitythat allow its calculation from the polymer chemicalstructure. The relationship between the measured (orcalculated) heat-release capacity of a polymer and itsfire behavior or flammability is described.

THEORY

The solid-state thermochemistry of flaming combus-tion57 reveals a material fire parameter that has theunits of the heat (release) capacity (J/g K):

Correspondence to: R. N. Walters ([email protected]).

Journal of Applied Polymer Science, Vol. 87, 548563 (2003) 2002 Wiley Periodicals, Inc.

c hc

01 EaeRTp

2 (1)

The heat-release capacity (c) is a combination of thethermal stability and combustion properties, each ofwhich is known to be calculable from additive molargroup contributions.1 The component material prop-erties are the heat of complete combustion of the py-rolysis gases [hc

0 (J/g)], the weight fraction of the solidresidue after pyrolysis or burning [ (g/g)], the globalactivation energy for the single-step mass-loss processor pyrolysis [Ea (J/mol)], and the temperature at thepeak mass-loss rate [Tp (K)] in a linear heating pro-gram at a constant rate [ (K/s)]. The constants in eq.(1) are the natural number (e) and the gas constant (R).Equation (1) shows the heat-release capacity to be aparticular function of the thermal stability and com-bustion properties, each of which is known to be cal-culable from additive molar group contributions.1

Consequently, c itself is a material property andshould be calculable from the same (or similar) molargroups as the component properties as long as thereare no interactions between the chemical structuralunits. Along with this assumption of group additivity,there is the postulate that for a polymer repeat unit ofmolar mass M, there is a molar heat-release capacity[ (J/mol K)] whose functional form is eq. (1) butwhich has thermal stability and combustion propertieswritten as the molar quantities H, V, E, and Y/M inplace of hc

0, (1 ), Ea, and Tp, respectively. If eachchemical group i in the polymer adds to the compo-nent molar properties according to its molar fraction niin the repeat unit,

HVE

eRY/M2

i

niHi i

niVi i

niEieR

i

niYi/Mi 2 (2)

where Hi, Vi, Ei, Yi, and Mi are the molar heat ofcombustion, molar fraction of fuel, molar activationenergy, molar thermal decomposition function,1 andmolar mass of component i, respectively. Expandingthe summations in eq. (2) and retaining only the non-interacting terms for which i j k (i.e., neglectingterms containing products and quotients with mixedindices), we have the following:

i

niHiViEi

eRYi/Mi2

i

nii (3)

Equation (3) shows that there is a molar group contri-bution to the heat-release capacity i that adds ac-cording to its molar fraction in the repeat unit of thepolymer. If Ni and Mi are the number of moles and themolar mass, respectively, of group i in the polymerwith the repeat unit molar mass M

ni Ni

i

Niand M

i

niMi i

Nii

NiMi

then the heat-release capacity on a mass basis is

c

M

i

nii

i

niMi

i

Nii

i

NiMi(4)

Equations (2)(4) provide the physical basis for anadditive heat-release capacity function, but the valuesof the molar contributions of chemical groups must bederived empirically (i.e., experimentally). To this end,the heat-release capacities of more than 200 polymerswith known chemical structures have been measuredwith the measurement technique described later, andthese experimental values have been used to generateover 40 group contributions.11,12

Figure 1 Schematic diagram of the pyrolysiscombustion flow calorimeter.

MOLAR GROUP CONTRIBUTIONS 549

EXPERIMENTAL

Materials

Polymer samples were unfilled, natural, or virgin-grade resins obtained from Aldrich (Milwaukee, WI)and Polysciences, Inc. (Warrington, PA), and researchuniversities or directly from the manufacturers. Theoxygen and nitrogen gases used for calibration andtesting, obtained from Matheson Gas Products(Bridgeport, NJ), were dry and greater than 99.99%pure.

Methods

A pyrolysiscombustion flow calorimeter810 wasused for all experiments (see Fig. 1). In this device, apyrolysis probe (Pyroprobe 2000, CDS Analytical, Ox-ford, PA) is used to thermally decompose milligram-size samples in flowing nitrogen at a controlled heat-ing rate. The samples are heated at a constant rate(typically 4.3 K/s) from a starting temperature that isseveral degrees below the onset degradation temper-ature of the polymer to a maximum temperature of1200 K (930C). The 930C final temperature ensuresthe complete thermal degradation of organic polymersso that the total capacity for heat release is measuredduring the test and eq. (1) applies. Flowing nitrogensweeps the volatile decomposition products from theconstant-temperature (heated) pyrolysis chamber, andoxygen is added to obtain a nominal composition of4:1 N2/O2 before a 900C furnace is entered for 60 s toeffect complete nonflaming combustion. The combus-tion products (carbon dioxide, water, and possiblyacid gases) are then removed from the gas stream with

Ascarite and Drierite scrubbers. The mass flow rateand oxygen consumption of the scrubbed combustionstream are measured with a mass flowmeter and zir-conia oxygen analyzer (Panametrics model 350,Waltham, MA), respectively.

The specific heat-release rate (Qc) in the pyrolysiscombustion flow calorimeter is determined from oxygenconsumption measurements with the assumption that13.1 kJ of heat is released per gram of diatomic oxygenconsumed by combustion.1316 Because Qc is equal to thefractional mass-loss rate multiplied by the heat of com-plete combustion of the pyrolysis products,

Qct E

m0O2t

hc,v0 tm0

dmtdt (5)

where E 13.1 0.6 kJ/g of O2, O2 is the instan-taneous mass consumption rate of oxygen, m0 is theinitial sample mass, hc,v

0 is the instantaneous heat ofcomplete combustion of the volatile pyrolysis prod-ucts, and dm/dt is the instantaneous mass-loss (fuel-generation) rate of the sample during the test. Theadvantage of synchronized oxygen consumption cal-orimetry for determining the specific heat-release rateis the ease and speed of the method in comparisonwith the simultaneous measurement of the mass-lossrate of the solid and the heat of combustion of thepyrolysis gases.17 At Tp, the specific heat-release ratehas an analytical form:57,18

Qcmax

Em0

O2max

hc,v0 t

m0dmtdt

max

hc01Ea

eRTp2

(6)

Figure 2 Specific heat-release rates for several polymers measured with the microscale calorimeter.

550 WALTERS AND LYON

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nSt

ate

[NA

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204

21.9

2025

9.24

Poly

(dic

hlor

oeth

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ethe

r)R

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Uni

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ity

(MW

9350

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C14H

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165.

257

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254

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cyan

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[470

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231

614

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poly

cyan

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eA

roC

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Che

mic

als

[115

6-51

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C17H

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228

317

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Poly

(hex

amet

hyle

nese

baca

mid

e)N

ylon

6/10

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es[9

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16H

30O

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287

835

.70

282.

43

Poly

(eth

eret

her

keto

ne)

(PE

EK

)45

0F,V

ictr

exU

SA[2

9658

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19H

12O

315

512

.446

.528

8.3

Poly

(silo

xyte

traa

lkyl

biph

enyl

ene

oxid

e)(P

SA)

Gen

eral

Ele

ctri

c[N

A]

C18H

18Si

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119

15.7

60.1

294.

42

Poly

(eth

erke

tone

keto

ne)

(PE

KK

)G

040

(vir

gin

flak

e),

Dup

ont

[749

70-2

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C20H

12O

396

8.7

60.7

300.

31

Tet

ram

ethy

lbi

sphe

nol

Fpo

lycy

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Aro

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iba

Spec

ialt

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ical

[101

657-

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19H

18O

2N

228

017

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.430

6.36


TA

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Tot

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benz

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anes

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34

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amet

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ned

odec

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dia

mid

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6/12

,Po

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es[2

6098

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270

730

.80

310.

48

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phen

olC

,po

lycy

anur

ate

BPC

CE

,Cib

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Che

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[NA

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l 224

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tic

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465

726

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934

0.42

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poly

carb

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hem

ical

[NA

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528

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(am

ide

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AI)

TO

RL

ON

4203

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Am

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[429

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233

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poly

cyan

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[309

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312

29.

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ldri

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6023

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22H

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225

6.6

51.9

382.

33


TA

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EI

Con

tinu

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Mat

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tre

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eca

paci

ty(J

/g

K)

Tot

alhe

atre

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e(k

J/g)

Cha

r(%

)M

W(g

/m

ol)

Hex

afluo

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nol

Apo

lycy

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ate

Aro

Cy

F-10

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Che

mic

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[327

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322.

355

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phen

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U-3

66,C

iba

Spec

ialt

yC

hem

ical

s[1

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C26H

24O

2N

223

922

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6.49

Poly

(phe

nyl

sulf

one)

Rad

elR

5200

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[258

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C24H

16SO

415

311

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phen

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poly

aryl

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BPC

PA,U

MA

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78.8

438.

44

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sulf

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[251

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The rate-independent heat-release capacity is obtainedfrom eq. (6) by the division of the maximum specificheat-release rate by the constant sample heating rate[ (K/s)]:

c Qc

max

Em0

O2max

hc01 Ea

eRTp2 (7)

The quantities measured in the test are the initial samplemass and Qc (W/g). The time integration of the specificheat-release rate gives the total heat released by thecomplete combustion of the pyrolysis gases per unit ofthe initial sample mass [hc

0 (J/g)]. c (J/g K) is calculatedfrom the peak specific heat-release rate and the linearheating rate of the sample according to eq. (7). Weighingthe sample after the test allows for the calculation of (g/g) and the average heat of complete combustion perunit mass of volatiles.

RESULTS

Pyrolysiscombustion flow calorimeter data for the spe-cific heat-release rates of polyethylene (PE), polypro-pylene (PP), polystyrene (PS), an acrylonitrilebuta-dienestyrene terpolymer (ABS), poly(methyl methacry-late) (PMMA), poly(ethylene terephthalate) (PET),poly(ether ether ketone) (PEEK), and polybenz-imidazole (PBI) are shown in Figure 2, having beenhorizontally shifted for clarity. Dividing the maximumspecific heat-release rate (W/g) measured during the test(peak height in Fig. 2) by the constant sample heatingrate ( 4.3 K/s in these tests) gives the heat-releasecapacity of the polymer (J/g K) for materials that ther-mally decompose in a single step. Materials exhibitingmultiple heat-release peaks are beyond the scope of thisreport and will be addressed in the future.

The measured heat-release capacities for more than100 polymers with known chemical structures areshown in Table I. These data have been used to gen-erate the group contributions shown in Table II. Themolar group contributions were obtained by i beingtreated as adjustable parameters in the linear systemof equations for polymers with known chemical struc-tures and measured c values. The optimization cal-culation continued until the sum of the squares of therelative error between the measured c value and thevalue calculated from group contributions was a min-imum. The calculation converged rapidly to theunique i values listed in Table II, which were inde-pendent of initial estimates.

Figure 3 is a plot of the calculated and measuredheat-release capacities for over 80 polymers for whichoptimized i values were determined. The correlationcoefficient between the measured and predicted heat-release capacities is r 0.96, and the average relativeerror is 15%.

TA

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tinu

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eria

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ure

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tre

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ty(J

/g

K)

Tot

alhe

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/m

ol)

Poly

(eth

erim

ide)

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I)U

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ric

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benz

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hyd

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NA

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ey[1

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11.7

6369

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[790

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700.

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t.


Calculation of the Heat-Release Capacity

The following example illustrates the calculation ofthe heat-release capacity from molar group contribu-

tions for a diglycidyl ether of bisphenol A (BPA ep-oxy) cured by anionic ring-opening polymerization.This polymer has the following repeat unit chemicalstructure:

TABLE IIStructural Groups and Their Molar Contribution to the Heat Release Capacity

Structural groupContribution(kJ/mol K) Structural group

Contribution(kJ/mol K) Structural group

Contribution(kJ/mol K)

118a OH 8.1 OOH 19.8

77.0 {NH}

7.6 OBr 22.0

69.5 OCH2OOO 4.18O

OCO22.0

30.6 {CF2}

1.8 23.2a

29.5 0.1 25.5

28.8 8.8 OCl 34.7

28.3 OSO 10.9a 36.4a

26.6 OOO 11.6O

OOOCOOOPendant: 39.5

Backbone: 13.7

22.5 13.8 }ON{

43.0a

19.0 ONH2 13.9a

O

OOOCOOO 49.0

18.7 OCF3 14.8POSiOP

53.5a

16.7 OC'N 17.6 66.7

15.1 18.9a 74.5

9.7 19.2 76.7

a Molar group contribution derived from a single polymer.


The polymer repeat unit consists of six basic chemicalgroups, and the heat-release capacity is calculatedfrom the associated Ni, Mi, and i values for thesegroups, which are listed in Table III.

The molar heat-release capacity is obtained by thesumming of the group contributions according to theirmolar fraction in the repeat unit and division by themolar mass of the repeat unit to give the heat-releasecapacity on a mass basis (J/g K).

c

M

i

nii

i

niMi

i

Nii

i

NiMi

204.5 kJ/mol K340 g/mol

601 J/g K

The predicted value of 601 J/g K compares reasonably wellwith the measured value of 657 J/g K for this polymer.

Heat-Release Capacity and Fire Hazard

The primary indicator of the fire hazard of a materialis the heat-release rate in forced flaming combustion.19

Figure 4 is a plot of the average flaming heat-releaserate of samples (10 cm 10 cm 0.64 cm, 80 g) ofpure polymer measured in a fire calorimeter at anexternal heat flux qext 50 kW/m

2) according to stan-dard methods2022 versus the measured heat-releasecapacity. Proportionality is observed between the av-erage flaming heat-release rate of kilogram-size sam-ples and the heat-release capacity of milligram-sizesamples of the same polymer with a slope of 1.0 (kg/s)/m2/K, which is in general agreement with predic-tions for steady burning at this external heat flux.57

Figure 3 Calculated and measured heat-release capacities for 80 pure polymers.

TABLE IIIGroup Contributions Used in the Calculation of the Heat Release Capacity of Bisphenol A Epoxy

Chemical group (i) N Mi (g/mol)

(kJ/mol K)NiMi

(g/mol)Ni

(kJ/mol K)

C

1 12 28.3 12 28.3

CH

CH22 13 26.6 26 53.2

4 14 16.7 56 66.8

CH3 2 15 22.5 30 45.0

2 76 28.8 152 57.6

OOO 4 16 11.6 64 46.4Total 340 204.5


Consequently, c is a reasonable predictor of the firehazard with an empirical correlation (e.g., Fig. 4) orphysically based calculations.57

Heat-Release Capacity and Flammability

Flammability is taken here to mean the tendency of athin sample of a material ignited by a small flame tocontinue burning in the absence of external radiantheat after the removal of the ignition source. Self-extinguishing behavior in these tests implies a certainresistance to ignition and/or flame propagation, andstandard methods have been developed to measurethis characteristic. These flame tests are widely used torank the burning propensity of combustible solids, butthey do not yield any material property information.Two common flammability test methods are the Un-derwriters Laboratories UL 94 test for upward vertical(V) and horizontal burning (HB)23 and the criticaloxygen concentration for flame extinguishment or lim-iting oxygen index (LOI) in downward burning.24

In flammability tests, the flame heat flux at thesample tip must provide all of the heat energy tocontinue the burning process after the removal of theBunsen burner (UL 94) or methane diffusion flame(LOI) used to cause ignition. If the heat flux from thesample surface flame is constant (UL 94 test) or in-creases in a known way with oxygen concentration(LOI), the criterion for self-extinguishing behavior inthese tests can be formulated in terms of a criticalheat-release capacity if it is assumed that a minimumheat-release rate of about 100 kW/m2 25 is needed tosustain flaming combustion. Such an analysis for theUL 94 test6 indicates that polymers with c valueslower than about 300 J/g K should self-extinguishbecause they do not release heat at a high enough rateto overcome heat losses and so the flame cannot prop-agate. Therefore, for pure polymers with c 300 J/gK, self-extinguishing behavior in the UL 94 vertical

test (a V rating) is expected. Figure 5 contains UL 94data26 and measured heat-release capacities for sev-eral pure polymers. A transition from a self-propagat-ing (HB) flame behavior to a self-extinguishing (V-0)flame behavior occurs in the vicinity of c 300 J/g K,as predicted from the critical heat-release-rate crite-rion.

The criterion for self-extinguishing behavior in theLOI test must take into account the fact that an in-crease in the oxygen concentration of the flowing gasstream in the test chamber increases the temperature(radiant heat flux) of the sample diffusion flame and,therefore, the amount of thermal energy deposited inthe polymer. Because the heat-release rate of the sam-ple increases with the flame heat flux, which in turnincreases with oxygen concentration, an inverse rela-tionship between c and the limiting oxygen concen-tration is expected and observed, as shown in the LOIdata1,27,28 plotted versus c in Figure 6.

Figure 5 UL-94 ratings versus the measured heat-releasecapacities of pure polymers.

Figure 4 Average flaming heat-release rate (HRR) versusthe heat-release capacity for several polymers. Figure 6 LOI versus the measured heat-release capacity.


Comparing Figures 5 and 6 shows that self-extin-guishing behavior in the UL 94 vertical test occurs at alower heat-release capacity (c 300 100 J/g K)than in the LOI test (c 550 100 J/g K) underam-bient conditions (298 K, LOI 21% O2). The reason forthis is that the upward burning UL 94 test is moresevere than the downward burning LOI test becauseof convective and radiative preheating of the sampleby its flame and so requires more material fire resis-tance (lower heat-release capacity) for self-extinguish-ing behavior under ambient conditions.

CONCLUSIONS

The heat-release capacity is a physically based mate-rial property that is a good predictor of the fire behav-ior and flammability of pure polymers. The heat-re-lease capacity is simply calculated for pure polymersfrom their chemical structures with additive molargroup contributions that have been determined em-pirically with a high level of confidence (15%). Theproposed methodology for predicting the fire behav-ior and flammability of polymers from their chemicalstructures allows for the molecular-level design ofultra-fire-resistant polymers without the expense ofsynthesizing and testing new materials.

The authors are indebted to Stanislav I. Stoliarov of theUniversity of Massachusetts (Amherst, MA) for performingthe optimization calculations for the molar group contribu-tions to the heat-release capacity. Certain commercial equip-ment, instruments, materials, or companies are identified inthis report to adequately specify the experimental proce-dure. This in no way implies endorsement or recommenda-tion by the Federal Aviation Administration.

References

1. Van Krevelen, D. W. Properties of Polymers, 3rd ed.; Elsevier:Amsterdam, 1990.

2. Bicerano, J. Prediction of Polymer Properties, 2nd ed.; MarcelDekker: New York, 1996.

3. Coleman, M. M.; Graf, J. F.; Painter, P. C. Specific Interactionsand the Miscibility of Polymer Blends; Technomic: Lancaster,PA, 1991.

4. Bensen, S. W. Thermochemical Kinetics, Methods for the Esti-mation of Thermochemical Data and Rate Parameters; Wiley:New York, 1968.

5. Lyon, R. E. In Fire Retardancy of Polymeric Materials; Wilkie,C. A.; Grand, A. F., Eds.; Marcel Dekker: New York, 2000.

6. Lyon, R. E.; Walters, R. N. Proceedings of the Fire and Materials2001 Conference, San Francisco, CA; Interscience Communica-tions Limited: London, England, 2001, pp 285300.

7. Lyon, R. E. Fire Mater 2000, 24, 179.8. Walters, R. N.; Lyon, R. E. Proc Int SAMPE Symp Exhibition

1997, 42, 1335.9. Walters, R. N.; Lyon, R. E. NISTIR 5904, Beall, K., ed.; National

Institute of Standards and Technology, Annual Conference onFire Research: Book of Abstracts, October 2831, 1996, Gaith-ersburg, MD, 1996, pp 8990.

10. Lyon, R. E.; Walters, R. N. U.S. Pat. 5,981,290 (1999).11. Walters, R. N.; Lyon, R. E. PMSE Prepr 2000, 83, 86.12. Walters, R. N.; Lyon, R. E. The 2000 Conference on Flame

Retardancy of Polymeric Materials; Business CommunicationsCorporation: Norwalk, CT, 2000.

13. Thornton, W. Philos Mag J Sci 1971, 33, 196.14. Hugget, C. Fire and Materials, 1980, 61.15. Janssens, M.; Parker, W. J. In Heat Release in Fires; Babrauskas,

V.; Grayson, S. J., Eds.; Elsevier Applied Science: London, 1992;Chapter 3, p 31.

16. Walters, R. N.; Hackett, S. M.; Lyon, R. E. Fire Mater 2000, 24,245.

17. Inguilizian, T. V. M.S. Thesis, University of Massachusetts, 1999.18. Lyon, R. E. Polym Degrad Stab 1998, 61, 201.19. Babrauskas, V.; Peacock, R. D. Fire Safety J 1992, 18, 255.20. Hirschler, M. M. In Heat Release in Fires; Babrauskas, V.;

Grayson, S., Eds.; Elsevier Applied Science: New York, 1992;p 207.

21. Scudamore, M. J.; Briggs, P. J.; Prager, F. H. Fire Mater 1991, 15,65.

22. Lyon, R. E.; Gandhi, S.; Walters, R. N. Proceedings of the Societyfor the Advancement of Materials and Process Engineering(SAMPE) 44th International Symposium and Exhibition;SAMPE: Covina, CA, 1999.

23. Standard for Tests for Flammability of Plastic Materials for Partsin Devices and Appliances, Underwriters Laboratory: UL 94, 4thed.; Underwriters Laboratories: Research Triangle Park, NC,1991.

24. Standard Test Method for Measuring the Minimum OxygenConcentration to Support Candle-Like Combustion of Plastics;ASTM D2863; American Society for Testing and Materials: Phil-adelphia, PA, 1991.

25. Tewarson, A. SFPE Handbook of Fire Protection Engineering,2nd ed.; Society of Fire Protection Engineers: Boston, MA, 1995;Section 3, p 53.

26. Plastics Digest, Ranked Properties Reference Indexes; D.A.T.A.Business Publishing: Englewood, CO, 1996, 17(1), 773.

27. Cullis, C. F.; Hirschler, M. M. The Combustion of OrganicPolymers; Oxford University Press: Oxford, 1981.

28. Hilado, C. J. Flammability Handbook for Plastics, 5th ed.; Tech-nomic: Lancaster, PA, 1998.


Documents

Molar Group Contributions - Walters