NUREG/CR-2868

SAND82-0485

RV

Printed August 1982

Aging Effects on Fire-Retardant

Additives in Organic Materials for

Nuclear Plant Applications

Roger L. Clough

This report documents part of the Qualification Testing Evaluation (OTE)

Program being conducted by Sandia National Laboratories

Prepared by

Sandia National Laboratories

Albuquerque, New Mexico 87185 and &vermore, California 94550

for the United States Department of Energy

under Contract DE-ACO4-76DP00789

oI

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U. S, NU 'LEAR REGULATORY COMMISSION

SF 2900-Q(6-82)
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NUREG/CR-2868

SAND82-0485

RV

Printed August 1982

Aging Effects on Fire-Retardant Additives in

Organic Materials for Nuclear Plant Applications

Roger L. Clough

Sandia National Laboratories

Albuquerque, New Mexico 87185

operated by

Sandia National Laboratories

for the

U. S. Department of Energy

Prepared for

Electrical Engineering Branch

Division of Engineering Technology

Office of Water Reactor Safety Research

U. S. Nuclear Regulatory Commission

Washington, DC 20555

Under Interagency Agreement DOE 40-550-75

NRC FIN No. A-1051

i-ii
,.
ABSTRACT

Inhibiting fire is a major concern of nuclear safety. One

of the most widely used commercial fire-retardant additives

incorporated into cable insulation and other organic materials

to reduce their flammability has been the halocarbon (usually a

chlorinated hydrocarbon),typically in combination with antimony

oxide. Such materials may be installed for the design lifetime

of a nuclear plant; this report describes an investigation of

the long-term aging behavior of these fire-retardant additives

in polymeric materials.

Extensive aging experiments on fire-retarded formulations

of ethylene propylene r,'-er (EPR) and of chlorosulfonated polyethylene (CSPE) have been carried out, with chemical analysis of

halogen and antimony content performed as a function of aging

time and conditions. Oxygen index flammability measurements were

also performed on selected samples. Significant fire-retardant

losses (both chlorine (Cl) and antimony (Sb)) were found to occur

in certain of the fire-retardant materials but not in others, depending on the molecular structure of the particular halogencontaining component. The Cl:Sb loss ratios indicate that a

chemical reaction takes place under the aging conditions to

form the volatile compound, antimony trichloride (SbC1 3 ). The

EPR formulations showed a modestly increased flammability with

fire-retardant loss on aging. CSPE materials exhibited a

significant decrease in flammability on aging despite the

loss of flame retardants. This appears to be correlated

with the loss of flammable, volatile components from the

formulation.

Using the activation energy of 34 kcal/mol derived from

Arrhenius treatment of the antimony loss data for the EPR

formulation having the most rapid loss rate, it is predicted

that fire-retardant loss should become appreciable for this

material only at substantially elevated temperatures or exceedingly long times. The data indicate that the loss of

halogen- and antimony-based fire retardants appears to be

insignificant under ambient conditions expected for nuclear

plants.

iii
ACKN4OWL1EDGMEMNTS

The author wishes to acknowledge the assistance of C. A. Quintana#

who carried out the aging experiments, of R. W. Bild, who performed the

neutron activation analysis, and of E. A. Salazar, who was responsible

for the polymer formulation.

iv
CONTENTS

INTRODUCTION ........................ . . . . . . . . . . . . .

EXPERIMENTAL .. . ....... o .......... o ... ...* ...... .. .. ......... 3

RESULTS AND DISCUSSION ..................................... 7

Fire-Retardant Loss from EPR ...... .............. ...... 7

Mechanistic Implications ... ........ ....................... 7

Loss Rates ....... ................... . .... ............. 12

Formulation Differences . .......... ....... . ........... 15

Radiation-Thermal Aging ........ ................. .. ...... 16

EPR Flammability Measurements ............................. 17

Fire-Retardant Loss from CSPE ................... o......... 19

CSPE Flammability Measurements .............. o............. 22

CONCLUSIONS ... ............... ... ..... ..... ............. . 24

REFERENCES ..... . . .. . . . .. . ............. ............ 25

V
LIST OF TABLES

Table Page

I EPR Base Formulations ............................. ........ 3

II Fire-Retardant Components Used ............................ 4

III Chlorosulfonated Polyethylene Formulation ................. 5

IV Experimentally Determined Times for Loss of

25% of Initial Antimony Content (EPR-V) ................... 14

V Extrapolated Times for Loss of 25% of Initial

Antimony Content (EPR-V) . .......... ........... - 14

VI Oxygen Index Data on Aged Samples of FireRetarded EPR Formulation EPR-V ....................... 18

VII Total Weight Loss from HYP-II Aged at 110 0C ......... 21

VIII Oxygen Index Data on Samples of Chlorosulfonated

Polyethylene Aged at II0°C ............................... 23

IX TGA Data Showing Integrated Weight Loss to 425 0 C

for HYP-II Samples Preaged at 1100C .................... 23

vi
LIST OF FIGURES

Figure Page

1 Antimony content (weight percent) as determined by

atomic absorption spectroscopy on fire-retarded EPR

(formulation EPR-V) as a function of thermal aging ....... 8

2 Chlorine content (weight percent) as determined by

silver coulometry on fire-retarded EPR (formulation

EPR-V) as a function of thermal aging .................... 9

3 Antimony content (weight percent) as determined by

14 MeV neutron activation analysis for fire-retarded

EPR (formulation EPR-V) as a function of thermal aging... 10

4 Chlorine content (weight percent) as determined by

14 MeV neutron activation analysis for fire-retarded

EPR (formulation EPR-V) as a function of thermal

aging .................................................... 11

5 Arrhenius plot for 25% antimony loss rate [-log

(.25/time in months)] from EPR-V as a function of

inverse temperature ............................... 13

6 Arrhenius plot for 25% chlorine loss rate [-log

(.25/time in months)] from EPR-V as a function of

inverse temperature ............... ....... ............... 13

7 Antimony content (weight percent) as determined by

atomic absorption spectroscopy on fire-retarded EPR

(EPR-V) as a function of thermal aging with simultaneous

y-irradiation at 5 krad/hr ............................... 16

8 Chlorine content (weight percent) as determined by

silver coulometry on fire-retarded EPR (EPR-V) as a

function of thermal aging with simultaneous y-irradiation

at 5 krad/hr ............................................. 17

9 Chlorine content (weight percent) as determined by

silver coulometry on HYP-II as a function of thermal

aging .................................................... 19

10 Antimony content (weight percent) as determined by

atomic absorption spectroscopy on HYP-II as a function

of thermal aging ......................................... 20

11 Chlorine content (weight percent) as determined by

silver coulometry on HYP-I as a function of thermal

aging ............................................. 21

vii

INTRODUCTION

Fire protection is a major concern in nuclear safety.

Awareness in this area was much heightened following the fire

in the nuclear plant at Brown's Ferry in March of 1975.1-3

The NRC issued a Regulatory Guide on Fire Protection in June

of 1976,4 and has been funding research in the area of fire

testing,:5 including an extensive series of cable tray fire

tests performed by Klamerus at Sandia. 6

Flammable materials in nuclear plants include a variety

of organic polymers used in various applications, most notably

as cable insulation materials. The flammability of organic

polymers, many of which consist chiefly of carbon and hydrogen,

is a problem of general concern to the polymer industry. Consequently, much work has been done on the study of polymer

combustion properties. Reduction of the flammability of

organic materials is achieved by the incorporation of fireretardant additives into the polymer formulations. One of

the most widely used types of fire-retardant additive has

been the halogenated hyqrocarbon, usually in combination with

antimony oxide (Sb20 3 ). This halogen-antimony combination

has been employed in conjunction with many different generic

polymer types, and is used today in a variety of applications

including (along with cable insulation materials) a host of

commercial products made with rubbers, plastics, paints and

textiles.

The halogenated hydrocarbon (the halogen is usually

chlorine, but may be bromine) by itself can have a fireretardant effect,:? while antimony oxide alone acts essentially as an inert filler and has little effect on the flammability properties of polymer materials. 1 0- 1 2 In combination,

the two additives work in a synergistic fashion. This is

believed to occur by reaction under the high temperatures

of the fire environment to give a volatile antimony halide.

The overall chemical reaction is outlined in equations 1

and 2.7,8

Chlorinated hydrocarbon -- HC1 (1)

HC1 + Sb 2 0 3 - SbCl 3 (2)

The antimony halide and/or its secondary breakdown products

apparently serve as efficient free radical scavengers in the

flame region above the burning material. 7 ,8, 1 0 , 1 3 The fireretardant effect of these two additives has been seen in a

variety of small-scale flammability tests which reflect the

susceptibility of materials t? combustion in the environment

of a small ignition source.",

I
Some types of polymers are intrinsically less flammable

than others. For example, polymers containing chlorine substituents along the chain backbone such as polyvinyl chloride

(PVC), chlorosulfonated polyethylene (Hypalon)8*, and chloroprene (neoprene), have inherently reduced flammability. 1 0

Depending on the degree of flame retardancy desired, these

materials may be used either with or without added antimony

oxide. 1 4 , 1 5 The three chlorinated materials named above are

used extensively as cable jacketing materials in the nuclear

industry. Non-chlorinated polymer types can be fire retarded

by inclusion of Sb 20 3 along with a low molecular weight

halogenated-hydrocarbon in the formulation.

Materials used in nuclear plant applications are

expected to last for the design lifetime (typically 40 years).

Recently there has been increased concern over qualifying

critical components with respect to their ability to function

after ambient aging. Because of this concern, extensive NRCfunded research has been carried out on orga'nic polymers to

investigate the effects of ._ing on their mechanical properties. 1 6

The results have shown that dramatic differences can exist between

aged and unaged materials, indicating that aging must be a major

consideration in qualification testing with respect to mechanical

and electrical performance.

Because of the concern for understanding the performance

of aged materials, the question was raised of the long-term

aging behavior of cable insulation materials with respect to

potential loss of the fire-retardant additives and resulting

loss of flammability-inhibiting properties. A literature

search failed to bring to light any study on fire-retardant

aging of halogen or halogen-antimony flame-retarded materials,

despite the fact that this retardant system has had widespread

use during the past several decades. 7

This report describes the results of an extensive series of

fire-retardant aging experiments on formulations of two material

types of importance in present-day nuclear plant applications.

One of these, Hypalons, is a chlorinated material; the other,

ethylene-propylene rubber (EPR) is a nonchlnrinated material.

*Hypalon is a registered trademark of E. I. duPont de Nemours

and Company.

2
EXPERIMENTAL

Samples made from two different EPR types (mable I) were

used in the aging experiments. One of these (A) is typical of

formulations currently used in certain cable material.17,18

The other (W) is similar to formulations used for certain structural applications. Five different variations with respect to

fire-retardant additives were prepared. Four of these contained

antimony oxide (Sb 2 03 ) in combination with one of three different

commercial halogenated-hydrocarbon flame-retarding agents. The

halogenated-hydrocarbon additives are representative of compounds used as flame-retardant additives in recent years. 8 ,9, 1 9

One formulation prepared for the aging studies (EPR III) was

intended as a control sample and not a realistic flame-retardant

system; it contained only Sb 2 03 in the absence of any chlorinated

compound. The five flame retardant EPR formulations are summarized

in Table II.

TABLE I

EPR BASE FORMULATIONS

EPR A (parts) EPR B (parts)

Nordel 2722

Low Density PE

Zinc Oxide

Paraffin Wax

Litharge

Zn Salt (ZMB)

Aminox

Treated Calcined Clay

Vinyl Silane

SRF Black

Di*-cup R

(90)

(20)

(5)

(5)

(5)

(2)

(1)

(60)

(1)

(2)

(3)

Vistalon 4608

Zinc Oxide

Stearic Acid

•AF Black

SRF Black

MT Black

Sunpar 2280

Ethyl Tellurac

MBT

Sulfur

(100)

(5)

(1)

(50)

(50)

(50)

(40)

(0.5)

(1.0)

(1.5)

3
Table II

FIRE RETARDANT COMPONENTS USED

'DESIGNATION BASE COMPOUND* FIRE RETARDANTS (parts)

a 0c

EPR A (33)

CI J C CI I a(3

a ci

Sb,0 (10)

EPR1 A 120(

a~ €!

Sb:oa (10)

EPE III ASb20 8 (10)

EPR IV B cI 1 l1 (20)

ci ci

SbROg (10)

EPR V B XJC--'CXe--n CX8 (20)

X - H, Cl

Id - 70%, by weight,

of the cpd.]

Sb,01 (10)

*Refers to base formulations in Table I.

4
A chlorosulfonated polyethylene (Hypalons) formulation,

similar to that used in cable material applications 1 8 (shown

in Table III), was used in the aging experiments. Two hypalon

variations were studied, namely with and without added Sb 2 03

(HYP-I = no added Sb 2 03; HYP-II = 7 parts added Sb 2 0 3 ).

Samples of the compression-molded polymers were prepared by

Burke Rubber Corporation; specimens having dimensions of 15.2

cm x .6 cm x .2 cm (6" x .22" x .07") were utilized in the

aging experiments.

Thermal aging of polymer samples was carried out in chambers

which were placed inside ovens. The chambers had carefully

controlled air flow (giving the equivalent of two changes of

atmosphere per hour) and temperature control to within + 1C.

TABLE III

CHLOROSULFONATED POLYETHYLENE FORMULATION*

HYP I (parts)

Hypalon 40 (100)

LGB Clay (75)

Philblack A (15)

NBC (2)

Kenaflex A (10)

Sunolite 240 (2)

Sundex 790 (30)

Litharge Paste (20)

MBT (Captex) (1)

Tetrone A (2)

*HYP II is identical to HYP I except that

it contains an additional 7 parts Sb2 03

5
The wet chemical analysis for antimony (Sb) and chlorine

(Cl) was carried out by Spang Microanalytical Laboratories of

Eagle Harbor, Michigan. Chlorine was determined using a

standard silver coulometric technique. 2 0 , 2 1 Antimony was

determined using atomic absorption spectroscopy. 2 2 Wet

chemical analytical data given throughout this report represent

the average of at least two different determinations. The

mean error in the data given for Cl is approximately + 0.15

absolute percent in the case of the EPR samples. In the case

of the Hypalon samples, it ranged from + 0.2 to + 0.5 absolute

percent. The mean error for the antimoiiy determTnations was

approximately + 0.07 absolute percent in both materials.

Neutron activation analysis for Cl and Sb was performed

on intact polymer specimens using 14 MeV neutrons. 2 3 The

activation reactions used were: 3 7 C1 (fn,p) 3 7 S and

1 2 3 Sb (fn, 2n) 1 2 2 Sb. The activation reaction generally

used for Sb analysis t 1 2 1 Sb(fn, 2n) 1 2 0 Sb) was impractical

with these polymer samples due to interference by other

elements in the formulation including silicon and chlorine.

Reference standards were established with NaCl-Sb2 03 - benzoin

oxime mixtures. Activated samples were counted on a Ge(Li)

detector coupled to a 4096-channel multichannel analyzer. The

precision of the analysis for both Cl and Sb was on the order

of + 10% relative.

Oxygen index flammability measurements were carried out

by US Testing Corporation of Los Angeles, California, according

to the ASTM standard. 2 4

6
RESULTS AND DISCUSSION

Fire-Retardant Loss From EPR Formulations

Of the EPR formulations studied, four of the five (EPR

numbers I through IV) did not show appreciable changes in fireretardant content after either 6 months at 1200C or 8 months at

l10"C. In contrast to this are the results obtained with the

formulation designated as EPR-V. Initial scoping experiments

revealed significant fire-retardant losses in this material, and

extensive aging tests were undertaken at a series of different

temperatures. The temperature range (120"C-80*C) was chosen to

include the lowest temperatures (based on the scoping experiments) expected to be practical for use in thermal aging

experiments on a reasonable timescale. This experimental

design was chosen to provide the optimum data to allow for

extrapolation of the results on the most rapidly changing

formulation examined (i.e., EPR-V) to lower temperature

conditions which would be typical of ambient environments

of interest.

Aging at 80'C gave rise to no measurable changes in the

fire-retardant content during the timescale of the experiment

(two years). Figs. 1 and 2 present the data for antimony

content (as derived by atomic absorption) and for chlorine

content (as derived by coulometry) as a function of aging

time at the temperaturess 120*, 110, 100* and 90"C. In

order to provide independent verification of the aginginduced disappearance of thesE elements from the polymer

matrix, a portion of the samples were analyzed by the neutro.On

activation technique. This data is presented in Figs. 3 and

4. The trends seen with the two techniques are in agreement;

significant losses of both chlorine and antimony are clearly

seen.

Mechanistic Implications

Chlorine loss can conceivably occur by two mechanisms:

1) simple migration and evaporation of the chlorinated hydrocarbon out of the polymer matrix, and 2) degradation involving

dehydrochlorination. Antimony oxide has a volatilization

temperature of 1550*C, 2 5 so that any significant antimony loss

at low temperatures must be preceled by chemical reaction to

yield a more volatile species.

7
Two antimony species, SbOCI and SbCl 3 , have been discussed

in the past as playing key roles in the synergistic Oire retardancy of the antimony oxide - halocarbon combination. 2 6 , 2 7

Evidence that the principle species in the vapor phase in

the flame environment was SbCl 3 has been previously obtained

by mass spectrometry. 7 However, it had been thought that HC1

reacted with Sb 2 0 3 to generate SbOC1, and that the production

of SbC1 3 depended upon a series of endothermic disproportionation reactions of SbOCl which have been shown by differential

thermal analysis to take place only at very high temperatures. 7 ' 2 8

The fact that the antimony oxide - halocarbon combination makes

such a good flame-retardant agent had been discussed in terms

of the fact that the decomposition temperature of SbOCl matched

3.0 ,, , ....

2.0

p1.0

0 1200 C

A 1108C

a 100 0 C

goo C

0.0

0 2 4 8 a 10 12 14 14 18 20 22 24

AGING TIME (MONTHS)

Figure 1. Antimony content (weight percent) as determined by

atomic absorption spectroscopy on fire-retarded EPR

(formulation EPR-V) as a function of thermal aging.

8
very well with the decomposition temperatures of typical

polymeric materials with which it is used1 (the so-called "right place at the right time" theory of flame retardancy).

Recently, a laser pyrolysis - mass spectrometry study has

demonstrated that, in fact, when either the pyrolysis products

of a PVC formulation or HCl from a cylinder were passed over

unheated Sb 2 0 3 , evidence coul be obtained for the introduction

of SbCl 3 into the gas phase. These results indicated that

SbC1 3 production was possible by reaction of HC1 with Sb 2 03

without involving the high temperature disproportionation

reactions of intermediate SbOCl. Subsequent mass spectral

studies in which mixtures containing Sb 2 0 3 and polyvinylidene

chloride were pyrolyzed together similarly revealed SbCl 3

volatilization at temperatures around 170*C, and also revealed

Sb 4 06 volatilization at temperatures around 300*C. 3I The

species Sb 4 was also detected, and its appearance was closely

correlated to the appearance of SbC1 3 and of Sb 4 0 6 .

I.-

2

tu

0

0

_j

10 12 14

AGING TIME (MONTHS)

Figure 2. Chlorine content (weight percent) as determined by

silver coulometry on fire-retarded EPR (formulation

EPR-V) as a function of thermal aging.

9
From the data on the loss rates at the various aging

temperatures and time periods obtained by us (Figs. I and 2),

it can be calculated that the average molar ratio for the loss

of these two elements is approximately 3:1 Cl:Sb. (There is

a fair amount of experimental scatter in the data, along with

indications of somewhat higher Cl:Sb ratios at the lowest

temperature of 90*C). The data are consistent with a picture

of the aging-induced antimony volatilization proceeding

through the same chemical reactions (Eqs. 1 and 2) by which

Z2.0

0

4 

o

0.0 0 2 - 4 6 8 10

Figure 3.

AGING TIME (MONTHS)

Antimony content (weight percent) as determined by

14 MeV neutron activation analysis for fire-retarded

EPR (formulation EPR-V) as a function of thermal aging.

10
the two additives are believed to react in the fire environment to produce the flame-retarding effect. The stoichiometry

indicates that the principle species through which the antimony

volatilized from the polymer on aging is SbC1 3 (which has a

boiling point of 283*C).25 The antimony loss found in this

work is consistent with the recent mass spectral evidence

that SbCl 3 can be generated at low temperatures. Moreover,

it demonstrates that very significant amounts of antimony volatilization (indeed, apparently total antimony loss) can

occur from Sb 2 03 -halocarbon fire-retarded polymer formulations

at temperatures far below those required for thermal degradation and volatilization of the polymer itself. A large part

of the chlorine lost on aging apparently involves decomposition of the chlorinated hydrocarbon, with evolution of HCl

(which then reacts with the Sb 2 0 3 ).

4.0

ZU

3.0

0

o 2.0-

2 4 6 8 10 12

AGING TIME (MONTHS)

Figure 4. Chlorine content (weight percent) as determined by

14 MeV neutron activation analysis for fire-retardel

EPR (formulation EPR-V) as a function of thermal

aging.

11
Loss Rates

Figure 5 shows a plot of the log of the time required for

disappearance of 25% of the antimony initially present, as a

function of inverse aging temperature. The antimony loss is

seen to exhibit linear Arrhenius behavior over this temperature

range. Similar plots for 12.5% loss and for 50% loss also

exhibit relatively linear Arrhenius behavior. The chlorine

data covers a more limited range of relative total loss, and

also has a larger relative error. Arrhenius plots exhibit more

scatter, but also appear reasonably linear; Figure 6 is a plot

of the log of the time required for disappearance of 25% of the

initial chlorine content as a function of inverse temperature.

From the data in Figures 5 and 6, it is possible to

estimate an apparent activation energy (Ea) for loss of the

two fire-retardant components. The antimony loss gives an

Ea of 34 + 3 kcal/mole; chlorine loss has an Ea of about

31 + 4 kcal/mole. The activation energies obtained for

chlorine and antimony are very similar, and may in fact be

the same within experimental error. The halogen-bearing

component used in this formulation (EPR-V, Table I) is a

chlorinated paraffin wax. The Ea values are similar to

the apparent activation energies reported by Madorsky 3 2

for the thermal dehydrochlorination of three different polyvinyl chloride specimens (26, 30 and 32 kcal/mol) obtained

at higher temperatures (235-260*C).

Using the activation energy calculated for antimony

loss, it is possible to extrapolate the loss rate to lower

temperatures. The accuracy of such extrapolation depends,

of course, on the overall process retaining linear Arrhenius

behavior at the lower temperatures. Table IV presents data

for the observed time for loss of 25% of the initial antimony

content, while Table V shows calculated values of time for

loss of 25% of initial antimony content at lower temperatures.

The extrapolated data indicate that for EPR formulation V,

antimony loss in sufficient amount to cause an appreciable

effect on flammability properties during timescales of

practical importance would only occur for material applications at significantly elevated temperatures (i.e., above

70°C).

The temperature of an operating high voltage cable will

be below 50*C, and in most cases will fall in the range of

30-40OC; 3 3 low and medium voltage cables generate less heat

than the high voltage cables. The ambient temperature of

12
I-.

0

0j

2.8 2.7 2.6 2.5

Il/T (x 103)

Figure 5. Arrhenius plot for 25% antimony loss rate [-log (.25/time in months)) from EPR-V as a function of

inverse temperature.

4

03 0

_j

2.6

1/T (x103)

Figure 6. Arrhenius plot for 25% chlorine loss rate [-log (.25/time in months)] from EPR-V as a function of

inverse temperature.

13
TABLE IV

EXPERIMENTALLY DETERMINED TIMES FOR LOSS OF 25%

OF INITIAL ANTIMONY CONTENT

(EPR-V)

TEMP.

120*C

1106C

1000C

900C

TIME

2 wk

1.4 mo

4.8 mo

21 mO

TABLF V

EXTRAPOLATED TIMES FOR LOSS OF 25%

OF INITIAL ANTIMONY CONTENT

(EPR-V)

TEMP.

800C

700C

60*C

50 0C

400C

300C

TIME

7 yr

28 yr

120 yr

600 yr

3 x 103 yr

2 x 104 yr

14
- nuclear plant may contribute to raising the absolute

_emperature of the cable somewhat, depending on specific

plant location. It appears that even for the material

(EPR-V) which has the most rapid loss rate of the formulations tested, the fire-retardant loss should not be significant in the temperature range and timescale important for

nuclear plants.

The data would, however, indicate the volatilization

of fractional percentages of antimony at temperatures near

ambient. The generation of antimony trichloride (SbCl 3 ) in

applications having large quantities of fire-retardant materials in confined areas could have significant implisations,

since SbC1 3 has both corrosive and toxic properties.

Formulation nifferences

The EPR formulations examined showed major differences in

fire-retardant aging characteristics; only one formulation

showed appreciable loss of fire-retardant additives under the

thermal aging conditions studied. A major factor behind the

differences between the EPR formulations examined is most

likely the ease with which the particular halogenated hydrocarbon can break down to yield HCl (or HBr), which serves as

the first step leading to the eventual loss of SbC1 3 (or

SbBr 3 ).

Of the three halocarbon fire-retardant additives examined

in this study (see Table II), the partially chlorinated paraffin used in EPR-V stands alone as being able to readily undergo

an intramolecular dehydrohalogenation. (The bromine substituents i-nthe halocarbon of EPR-II have no adjacent hydrogen

substituent. The loss of adjacent H and Cl atoms from the

halocarbon of EPR-I and EPR-IV would result in the formation

of a double bond connecting two bridgehead positions - a

situation of extremely unfavorable geometry [Bredt's rule). 3 5 )

It has been pointed out before 9 that thermal degradation of

halogenated flame-retardant additives during polymer processing

can be a concern and that substantial differences exist in

the thermal stability of various halogenated flame retardants

at polyolefin processing temperatures (which can typically

fall in the approximate range of 235*C - 250 C). 9 Other

differences in individual formulations could conceivably

play a contributing role in determining rates of fire-retardant

loss on aging.

15
Radiation-Thermal Aging

For. the majority of cable insulation in a nuclear plant,

probably only thermal aging will be important. Some of the

cable, however, which is in the containment area may experience

a significant amount of radiation. Figs. 7 and 8 show data

for samples of EPR-V aged at 100' and at ll0*C under conditions

of simultaneous y-irradiation at approximately 5 krad/hr.

Comparison with Figs. 1 and 2 leads to the conclusion that

the added radiation did not appreciably affect the fire

retardant loss rate. Other irradiation experiments were

performed on EPR-I at 110C and 1000C, using a dose rate

of approximately 5 krad/hr to a total dose of about 30 Mrad.

As with the oven-aging experiments, no measurable change in

chlorine-or antimony content was detected. These results

would tend to indicate that unlike aging-induced changes in

tensile properties, where radiation exerts a predominant

influence, the radiation aging of EPR with respect to the

loss of fire-retardant additives is relatively less significant compared with-the effects of thermal aging.

DOSE (Mrad)

t2.0

2

0

1

0

X

1.

4 8

AGING TIME (MONTHS)

Figure 7. Antimony content (weight percent) as determined by

atomic absorption spectroscopy on fire-retarded EPR

(EPR-V) as a function of thermal aging with simultaneous

y-irradiation at 5 krad/hr.

16
This conclusion is consistent with a related observation

reported previously. A value for the radiation yield of HC1

loss from y-irradiated PVC near room temperature was determined as G(-HC1) = 13.36 A similar radiation yield for the

chlorinated hydrocarbon in EPR-V would lead to the expectation that only a small fraction of the total chlorine present

would be lost after exposure to the radiation doses used in

this study. By way of contrast, radiation effects show up

strongly in terms of tensile property changes because only

very small changes in chain scission or crosslinking are

needed to produce noticeable macroscopic effects.

EPR Flammability Measurements

Material flammability can be discussed in terms of two

general testing categories. The most commonly used type of

combustion test evaluates flammability in the presence of

a small-scale ignition source, and gives information on the

propensity of materials to ignite and burn under low-level

fire-initiating conditions (as was the case with the Brown's

DOSE (Mrad)

10 20 6.0 1

5.0-

I 4.0

z

,J

0

,U 3.0-

0

S2.0

Figure 8.

AGING TIME (MONTHS)

Chlorine content (weight percent) as determined by

silver coulometry on fire-retarded EPR (EPR-V) as a

function of thermal aging with simultaneous y-irradiation

at 5 krad/hr.

17
Ferry fire, which was set off by a candle used by an employee).1, 3

There are numerous ASTM tests designed to fulfill this function.

Such small-scale combustion results are strongly dependent on

fire-retardant additives. 8 , 9 A second type of fire test focuses

on material flammability characteristics in the environment

of an already existing, large-scale fire. 3 7

For the purposes of this study, we employed one of the

most widely used of the small-scale ASTM flammability tests,

the Limiting Oxygen Index Method, 2 4 for testing of selected

samples from the aging experiments for comparison with the

fire retardant loss data. The limiting oxygen index is

defined as the minimum concentration of oxygen, in volume

percent of a mixture of nitrogen and oxygen, that will

support combustion.

(02)

LOI

(02) + (N2 )

Data from Oxygen Index Flammability Tests performed on

several aged EPR samples having substantial fire retardant loss

are given in Table VI. Changes in oxygen index are not large;

the aged samples exhibit moderately increased flammability.

TABLE VI

OXYGEN INDEX DATA ON AGED SAMPLES OF

FIRE RETARDED EPR FORMULATION EPR-V

AGING CONDITION OXYGEN INDEX

Unaged 28.0

12 months at 100*C 27.0

8 months at 110*C 26.5

4 months at 120*C 26.0

18
a

Fire-Retardant Loss From Chlorosulfonated Polyethylene

The second polymer type included in this work was chlorosulfonated polyethylene (Hypalons). The formulation studied is

characteristic of that used in cable jacketing material. 1 8

Hypalon contains chlorine substituents distributed along the

backbone of the polymer chain. Chlorination in the range of

35% is typical. 3 8 (Chlorosulphonyl groups initially present

in low concentration in the resin react during curing as a

part of the crosslinking process.)

Figs. 9 and 10 present data for chlorine and antimony content

as determined by coulometry and atomic absorption, respectively,

for HYP-II as a function of aging. Significant losses of both

elements are found. Fig. 11 presents data for chlorine content

(determined by coulometry) for CSPE formulation HYP-I which

contains no Sb 2 0 3 . Again, significant aging-induced chlorine

loss is seen.

15

U * 12O0C

e 5. ..

6 8 10

AGING TIME (MONTHS)

Figure 9. Chlorine content (weight percent) as determined by

silver coulometry on HYP-II as a function of thermal

aging.

19
Interestingly, the curves for antimony and chlorine loss

exhibit a level phase or even an upward trend during the early

stages. This behavior can be explained in terms of the loss

of other volatile components from the formulations: Table VII

shows weight loss for HYP-II as a function of aging time at

1100C.

Arrhenius treatment of the data is complicated by the rapid

loss of volatile components proceeding simultaneously with

the fire-retardant loss (the two processes could be expected to

have different activation energies). A straightforward

treatment of the data does not appear to yield suitably linear

Arrhenius behavior, so that activation energies for the fireretardant loss were not obtained. However, the chlorine and

antimony losses are of the same general magnitude as those

observed with the EPR-V over this temperature range. The

fact that the hypalon formulations lose antimony and chlorine

on aging must result from the fact that chlorosulfonated

polyethylene, with its random distribution of chlorine substituents along the polymer backbone, can readily undergo

intramolecular dehydrochlorination (as was the case with

the chlorinated additive used in EPR-V).

i $ i I i i

~*12o0c

2.0 ei 120C

* iorc

z

w

I0

z

0

4

0.0I

0 2 4 6 8 10 12

AGING TIME (MONTHS)

Figure 10. Antimony content (weight percent) as determined by

atomic absorption spectroscopy on HYP-II as a function

of thermal aging.

20
z10

0

z

U 0

2 120T

0•

I0 I I I f

0 2 4 6 8 10 12

AGING TIME (MONTHS)

Figure 11. Chlorine content (weight percent) as determined by

silver coulometry on HYP-I as a function of thermal

aging.

TABLE VII

TOTAL WEIGHT LOSS FROM HYP - II

AGED AT 1100 C

AGING TIME

2 wk

4 wk

8 wk

12 wk

% WEIGHT LOSS

2.4%

4.3%

5.4%

6.5%

21
Chlorosulfonated Polyethylene Flammability Measurements

Oxygen index measurements indicated very large changes between

aged and unaged CSPE samples, with the material becoming less

flammable after aging. The effect is seen with both HYP-I

and with HYP-II (see Table VIII). This decreased flammability

results despite the loss of both chlorine and antimony on aging.

The principle explanation for this observation most likely

results from the loss of low molecular weight organic components

from the formulation. These low molecular weight additives

are relatively volatile and are nonchlorinated, and hence

should be substantially more flammable than the highly chlorinated

base polymer resin. Thermogravimetric analysis confirms a progressive decrease in the amount of weight loss during the

early stages of the thermolysis of the CSPE samples, as a

function of the extent of aging: Integrated weight loss data

for samples heated from ambient to 425*C at 10/min is tabulated

in Table IX. Even assuming that a part of the species

volatilized in the TGA experiment represents chlorine and

antimony, the TGA differences between aged and unaged samples

are substantially larger than can be accounted for by the

differences in Cl and Sb content of the samples. The TGA

analysis is probably a good indication of the relative amounts

of volatile components released from these samples under

combustion-initiating conditions of small-scale flammability

tests.

Large changes in the flammability of chlorinated polymers

as a function of additives has been noted before. For example

plasticized PVC has much reduced flame retardancy compared

with the unplasticized material. 1 5 Apparently, in the case

under consideration in the present study, the effect of the

loss of chlorine and antimony on the oxygen index value is

overridden by the effect of the loss of volatile organic

additives.

22
TABLE VIII

OXYGEN INDEX DATA ON

SAMPLES OF CHLOROSULFONATED POLYETHYLENE

AGED AT 110*C

FORMULATION

HYP-I

AGING TIME

Unaged

4 mo

8 mo

OXYGEN INDEX

35

46

46

39

43

HYP-II Unaged

4 mo

8 mo 50

TABLE IX

TGA* DATA SHOWING INTEGRATED WEIGHT LOSS

TO 4250C FOR Uiz - II SAMPLES

PREAGED AT 1100 C

PREAGING TIME % VOLATILIZED

ON HEATING TO 4250C

Unaged

2 mo

4 mo

8 mo

25%

22.4%

16.5%

15.1%

*TGA performed at 10*C/min heating

rate in air.

23
CONCLUSIONS

Polymers containing halocarbon or halocarbon-antimony oxide

based fire retardants can lose appreciable amounts of both

halogen and antimony through volatilization during thermal aging.

This is seen to hold where the halogen is contained in a low

molecular weight additive in the formulation (as with EPR)

as well as for the case where the halogen is a part of the base

polymer resin (as with hypalon). Fire-retardant loss appears to

be strongly dependent upon the molecular structure of the halocarbon in terms of its ability to undergo intramolecular loss of

HCl. The HCl generated can react readily with Sb 2 03 to produce

the volatile SbCl 3 .

Oxygen index flammability tests indicated modest increases

in flammability of ETR with fire-retardant loss on aging. Hypalon

formulations actually became markedly less flammable on aging;

this behavior appeared % be associated with the loss of flammable, volatile additives from the polymer on aging.

Using the loss-rate data on the EPR formulation which

lost fire retardants most rapidly, Arrhenius extrapolation

indicated that the fire-retardant loss from this formulation

should be important only at very significantly elevated

temperatures; for example, loss of 25% of the initial antimony

content should require some 120 years at 60*C and some 3,000

years at 40*C. The hypalon aging data was not amenable to

an Arrhenius treatment, though fire-retardant loss rates

under the accelerated laboratory conditions employed in this

study were on the same order as those of the EPR formulation

mentioned above.

The data generated-in this work indicate that the loss of

antimony-halocarbon fire retardants due to aging under the ambient conditions expected in nuclear plants should not be significant over the timescales of interest. There is nothing in

the results that would be inconsistent with a supposition that

the specification and testing of flammability and fire-retardant

properties in terms of the unaged polymer materials is appropriate

for indicating behavior throughout an estimated 4G year nuclear

plant lifetime.

24
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26
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27
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