The determination of the molecular distributions of graphite binder materials by gel permeation chromatography

Carbon 1968,Vol.6,pp.93-100. PergamonPress.Printed inGreat Britain

THE DETERMINATION OF THE MOLECULAR DISTRIBUTIONS OF GRAPHITE BINDER MATERIALS BY GEL PERMEATION CHROMATOGRAPHY* E. M. WEWERKA Los Alamos Scientific Laboratory,

University of California, Los Alamos, New Mexico

(Received3 JuJy 1967)

Abstract-The molecular distributions of a number of furfuryl alcohol resins, coal tar pitches, coumarone-indene resins and gilsonite resins were characterised by the new technique of gel permeation chromatography (GPC). The components of the furfuryl alcohol resins ranged in mol. wt. from about 5000 down to monomer. The lower mol. wt. species were well resolved by GPC, and the degrees of conversion to higher mol. wt. polymer could easily be noted. The GPC curves of the tetrahydrofuran-soluble fractions of a series of coal tar pitches fell between 4000 and 70 or 80. The pitch fractions all had peak maximums at about 200 and tailed on the high mol. wt. sides. The coumarone-indene GPC curves varied markedly with softening points. The molecular distributions of these polymers appeared between 5000 and 70 or 80. A dependence of the coumarone-indene molecular distributions on color index was also found. The gilsonite resin molecular distributions ranged from 5000 to 70 or 80 with the peak maximums at approximately 2000.

1. INTRODUCTION of the current

MOST

are

polymeric

resins.

many

extensively

known

about

the effect

The

binder

thermoplastic

Although

been

graphite

studied,

range

or thermosetting

of these

binders

relatively

their

molecular

distributions

or

molecular

distributions

on

of binder

the properties

is

of binder

of this

cular

characterisation,

of furfuryl alcohol.

here

from

towards

of the

this objective.

new

technique (GPC)

The

have

been

characterised

alcohol

marone-indene

resins,

binder

by GPC; coal

tar

resins and gilsonite

of gel

structures

are a step

molecular

tions of four types of resinous furfuryl

Commercial

but the results reported

chromatography

and to further

molecular

to

a wide study

distributions

on

Furfuryl alcohol resins manufactured

use

is twofold:

of graphites.

the properties of graphites. The chemical complexity of these materials defies complete mole-

permeation

study

of characterising

polymers,

the effects of binder

have

little

purpose

develop better methods

materials

furfuryl alcohol resins are usually by the acid or thermal

of these resins have

sised identification

distribu-

DUNLOP

materials

and

these

were

of acid-catalyzed

pitches,

cou-

fractionally

resins.

cally

tested

reported

reaction

the products

individual

stages of polymerisation 93

the identity

products

recently, CONLEY and METIL structures of furfuryl alcohol

*Work done under the auspices of the United States Atomic Energy Commission.

emphaof

of a series

furfuryl alcohol resins.(l)

distilled the

mainly

of the low mol. wt. species.

PETERS

some of the initial

catalysis

Past studies of the molecular

and

They chemi-

fractions.

More investigated the resins at various

by infrared

analyses.(s)

94

E. M. WEWERKA

HACHIHAMAand SHONOidentified the low mol. wt. products, and also measured the average mol. wt. of several acid-catalyzed furfuryl alcohol resins.c3) Many of the products of alumina-condensed furfuryl alcohol resins were identified by BOQUIST and his co-workers.(4) Similar information about the higher end of the mol. wt. distributions of furfury alcohol resins is lacking because of the experimental difficulties of isolating and identifying the larger molecules.

The chemical and structural complexity of coal tar pitches makes them extremely difficult to characterise. The most effective method of investigating the molecular distributions of these materials has been to study fractions, separated from the whole, according to their solubilities in various solvents or solvent combinations. Coal tar pitches are generally thought to consist mainiy of fused aromatic ring compounds of low mol. wt.(s. 6) Wool and PHILLIPS, at the Coal Tar Research Association, measured the average mol. wt. of a series of coal tar pitch fractions separated by a solvent extraction and precipitation technique.“) These authors report materials with mol. wt. as high as 5000 in some pitches. Attempts to shed light on the structures of pitches has led to many sophisticated studies. Recently, workers at the FederaI Bureau of Mines at Pittsburgh reported the application of (33 nuclear magnetic resonance and mass spectrometry techniques to this problem.@* *) A number of other analytical methods, including i.r. spectroscopy, U.V. spectroscopy, gas chromatography, nuclear magnetic resonance and elution chromatography have been used to help elucidate the structures of coal tar pitches.(lO) Here also, because of greater analytical difficulties, less is known about the structures of the higher mol. wt. fractions than those of the lighter fractions. Considerable work has also been directed towards the characterisation of the insoluble or “free carbon” fractions of coal tar pitches.ol)

Commercial coumarone-indene resins are manufactured by the thermal or catalytic polymerisation of the resin-forming constituents of coal tar distillates. The coumarone-indene resins consist mainly of polyindene with small amounts of polymeric products derived from coumarone, cyclopentadiene and styrene.“~) The molecular distributions of coumaroneindene resins have been determined by SOIvent fractionation and fractional precipitation methods as well as turbidimetric titration.(l3) In addition to the usual physical properties, coumarone-indene resins are graded according to a color index with a scale ranging in number from 0 - 5 to 15 with increasing darkness.d4) The carbon char yields of coumarone-indene resins are about 7 per cent.““’ Gilsonite resins

Gilsonite is a natural bitumen available in several grades and softening points. Structural evidence indicates that gilsonite is composed of aromatic hydrocarbon clusters linked together by aliphatic side chains.o”* 17f The carbon char yields of gilsonite resins is approximately 18 per cent.(ls) The average mol. wt. of gilsonite is reported by the manufacturer to be about 1500. Gel permeation chromatography Until recently, most of the routine methods of polymer molecular characterisation were based on a physical or chemical separation of the polymer into fractions. (Is) The average mol. wt. of the individual fractions were then determined and a block distribution of the original was constructed. Meaningful results from these methods with chemically heterogeneous polymers, such as most graphite binders, were either limited or impossible to obtain. The technique of GPC is fast, convenient, and less dependent on the chemical homogeneity of the polymer than the above mentioned methods. GPC is adequately described elsewhere, and only a brief description of it will be given here.@@

OF THE MOLECULAR

THE DETERMINATION GPC

is a type of liquid-solid

which

separates

molecules

in a series of columns polystyrene polymer

the

solvent

separated

molecules, stream

in the

different

depths

of molecular solely the

porosities.

after introduction

at

the

column

inlet, The

to

depth

determined

size restrictions.

Therefore,

emerge

first

from

followed by smaller molecules molecular

of emerging

molecules by

are

is, ideally,

molecules

measured

into

by diffusing

into the gel pores.

diffusion

of decreasing is

with crosslinked

gel network

by physical

largest

columns,

packed

to sizes

gels of known maximum

The

filter when necessary

chromatography according

a

at each

in order

elution

to remove

by the having

narrow mol. wt. distributions

mol. wt., and noting their elution volumes. average

mol.

wt. was assumed

maximum

for these materials.

propylene

and polyethylene

carbon

polymers

volume

of pure

aromatic

benzene

to chrysene,

After flowing through

the sample stream passes into

a 5 ml syphon. As the syphon dumps, a photocell activates the chart pen, leaving a record at each The

recorded

curve of An (concentration)

vs. elution

(molecular

the molecular

size)

distribution. cular mol.

size

represents

With suitable distributions

wt. distributions.

aiding

calibration can

This

communication

be

volume size

the mole-

converted

conversion,

to

while

wit-h those familiar

only

mol.

wt.

resins

this method

at any elution volume. In some instances the commercial the determined

with

motor

driven

a heating

meation sample

Chromatograph columns

meabilities

were run at room 200 Gel Per-

equipped

in series.

The

of these columns

1 per cent solutions times

per-

reaction

mixture

alcohol,

200

from

15 set

0.5

or

Sample to

1 min

were

passed

through

a microporous

wt. of

Model 302 Vapor at 37°C. alcohol

and

anhydride.) temperature,

water-

a paddle

Heating

type,

was provided

with a Variac. were

essentially

anhydride

resins.

Furfuryl

by The the

and phosalcohol,

catalyst were added to the flask and stirring commenced. (A typical

103, 250

were 8 x

mol.

thermometer,

controlled

acid catalyzed

three

in tetrahydrofuran.

varied

phoric

water and and heating

with

depending on the refractometer response for that particular material. The solvent flow rate was held constant at 1 ml per min. The sample solutions

a

conditions

maximum

and 45A. Resin samples were, by weight, injection

stirrer.

mantle

experimental

Model

by

of the mol. wt.

furfuryl

same for both the maleic distributions

resins

resins were made in a 3 necked, round bottomed condenser,

in a Waters

gilsonite

Calibration

laboratory-prepared

reflux

The molecular

with

in tetrahydrofuran

equipped

temperature

The

calibrated

average

with a Mechrolab

Pressure Osmometer The

from

materials were not known. For number average mol. wt. were

these,

cooled

Procedure

and

allows an estimate

flask

2. EXPERIMENTAL

was

of narrow mol. wt. distributions.

with mol. wt. terms, does not usually add to the curves.

ranging

in tetrahydrofuran.

region

coumarone-indene

The

with a series

which falls at the solubility

useful interpretation

of the GPC

for the hydro-

hydrocarbons

limit for these materials

a count.

for the furfuryl

was done in two parts.

higher

called

A series of polyglycols was used as

standards

index,

An, vs. elution volume is made

The

to fall at peak

alcohol resins. Column calibration

with pure solvent. A record of relative

5 ml increment,

and known average

low mol. wt. region was calibrated

refractometer

which

of a series of model compounds

refractive

the refractometer,

material

injection

balanced

by a strip chart recorder.

95

might plug the columns. The column system was calibrated

mol. wt. calibration

the

sizes. The concentration differential

DISTRIBUTIONS

contained

ml of water This mixture

500 ml of furfuryl and

approximately

there for time periods

1 g of maleic

was heated

varying

92”C,

to reflux and

held

from 30 min to

2 hr. After the desired reflux period, the mixture was cooled to 50°C and neutralised with 5 per cent sodium hydroxide solution. The phases were separated and the resin was stripped of

E. M. WEWERKA

96 residual

water

in

house vacuum The

furfuryl

measured

a

rotary

evaporator

alcohol

resin

viscosities

on a MacMichael-Fisher

at 25°C. The resins were presoaked temperature

bath

at 25°C

viscosity

measurement

viscosity

temperature

spindle order

for

because

cup was rotated

The

furfuryl

MCB

phosphoric grade.

to

high

Viscosimeter were used in

viscosity

range.

The

GPC

and

DuPont obtained

the

maleic

and

tetrahydrofuran the vapor

from

the

anhydride 86 per

pressure

the

osmometer

was were

Chemical

hydrocarbons

Baker

K

K

reagent

grade. The polyglycols

the Baker

the

cent

used in both

and the pure aromatic or

&

Company, from either

Chemical

Company.

Distilled water was used at all times. In addition, other standard

laboratory

apparatus

and chem-

alcohol

resins were

icals were used. The

commercial

furfuryl

purchased

from

pany.

coal tar pitches

The

by the Allied rone-indene Company, buted The

Chemical by

(Krueger

through

K Filter).

materials were manufacturers.

Chemical

resins were distriProducts

Company.

were dissolved a

in tetra-

fraction

removed

microporous

All the other chemicals

used

3. RESULTS

the couma-

Neville

and the insoluble

filtration

Com-

were manufactured

the Tar

coal tar pitches

Chemical

Company,

and the gilsonite

by the Crowley

hydrofuran by

the Varcum

resins

In addition, binder

the

pores in

it is desirable

volume

of the

between

to retain

with minimum

out-

gassing during carbonisation

and graphitisation.

These

towards

considerations

material

composed

point

of a distribution

sizes. The optimum depend

amount

a binder

of molecular

of each size would

on filler characteristics

and processing

used for this study was

quality,

commercial

to wet the surfaces

fill the interstices

and fill the surface-connected

the particles.

acid was Baker and Adamson

The

particles,

serves

and fabrication

variables.

Furfuryl alcohol resins

label,

standard

particles,

maximum

at 20 rpm.

alcohol

white

binder

filler

in a constant

Chemicals and materials Eastman

The

Viscosimeter

of their

coefficients.

the entire

were

1 hr prior

wires of 18 to 34 gauge to cover

sample

with

and steam heat.

as

received

from

filter and the

AND DISCUSSION

The effect of binder molecular distribution as a graphite raw material variable has not yet been determined experimentally, but in some cases it is considered to be an important one.ul)

A number

of furfuryl alcohol resins have been

investigated

with

GPC,

mercial

resins (Varcum

mental

resins.

prepared with

The

from

either

some

experimental

furfuryl

maleic

phosphoric

including

com-

resins) and some experiresins

alcohol

anhydride

by

were

catalysis

or 86 per

cent

acid. These were dark, soluble resins

with experimental

resin viscosities

of 20 centi-

poises (cp) to 7 x

100 cp. Viscosity

of the Var-

cum

resins

was 250

chromatograms 15 and

23 5000

furfuryl

The

gel permeation

of these resins appear

counts

(elution

115 ml), indicating mately

cp.

to

alcohol

volumes

between of 75 to

a mol. wt. range of approxi100.

The

results

in

species within each molecular

polymerisation several

of

chemical

size range. There-

fore, each point on the chromatogram

ordinate

represents

resulting

the total

detector

response

from all of the species emerging

at that specific

elution volume. The

continued

binders

to emphasis molecular

use

for experimental on

the

distributions.

of

Varcum

reactor

resins

graphites

characterisation

as led

of their

The extremes of batch to

batch differences of Varcum resins are shown in Fig. 1. Particularly noticeable are the monomer, dimer and trimer peaks at 22 *4,21* 3 and 20 *2 counts respectively. The main detectable differences between these resin batches are found in the intermediate and high mol. wt. regions. Resin (a) (Fig. 1) has slightly more material in the intermediate mol. wt. region and less in the higher molecular weight region than resin (b).

THE

DETERMINATION

OF THE

MOLECULAR In

Fig.

maleic

DISTRIBUTIONS

2 appear

97

a series

of experimental,

anhydride-catalyzed

resins with viscosities Here

also,

furfuryl

alcohol

of 200 cp to 198,000

the low mol.

wt. species

resolved and the degrees of conversion mol.

wt. polymer

curves illustrate resin

molecular

degrees

crosslinking

FIG. 1. Varcum resins, illustrating batch differences of resins obtained five years.

the extremes over a period

This

(b)

is probably

slightly resin

higher (a).

Varcum

All resins,

five years

ago,

shown in Fig. laboratories Varcum

some

within

the

manufactured

sensitivity

alcohol

of

resins

tool

to

of the

properties

them. small

makes for

error

the

from

GPC

distributions control

affect

resins molecular

experimental

of

However, changes

of

it an excellent

commercial

furfuryl

2c,

23

21

18

have

very

higher

These

differences

stantially

mol. (Fig.

the

origin

of the

monomer

COUNTS (ml

2a)

of conthan

the

experi-

amounts

of

such as Fig.

and

viscosities resins.

may have arisen from a sub-

have

of GPC

elaborated

of

resins

(Fig.

those of the Varcum mode of polymerisation been

the

further,

further

first

stripping

)

furfuryl alcohol resins prepared with 1 g of maleic anhydride.

from

processed

from

resins. On the

possibility

but many

and vacuum

from

resins, or the Varcum

resins similar to the experimental basis

those

Conversely,

comparable

little

than

different

may

viscosity

weight products,

that of the experimental resins

with

wt. products 1).

IT

FIG. 2. Experimental furfury alcohol

essentially anhydride.

and a lower degree

with

much

blending

resins.

Varcum

to higher

here,

about

distributions

Varcum mental

illustrated

are

resins. The experimental

version

between

resins prepared

molecular

the experimental

than

results from our

very little

of their

higher

differences

alcohol catalysis

conclusions

obtained

batches

lo6 cp have been

x

indicating

resins can be drawn from a comparison

have less monomer

of

increasing resins with

Varcum

at a

curves

with

to those made with maleic

the two extremes

as those

graphites

quality

from

that

processes

molecular

GPC

1. Experimental

fabrication the

other

fell between

such

being

of polymerisation

the

indicate

resins,

do not

of

acid

of approximately

due to resin degree

of of

of furfuryl

phosphoric Some

These

has yet taken place. The molecular

distributions identical

to higher

be noted.

Soluble

by this method,

well

of furfuryl alcohol

distributions

in the order of 7

synthesised

COUNTS (mP1

easily

of polymerisation.

viscosities

by

can

the variability

cp.

are

cannot

be

combinations

of

could produce

E. M. WEWERKA

98 TABLE

1. PROPERTIES

Soft point % CIA, ASTM D23 19T

Pitch CP-I5V CP 276-150 CP 275-260 CP 275-350

OF COAL

TAR

PITCHES CHARACTERWED

Qtinoline insolubles %, ASTM D2318T

90 63 127 178

4-o 8.8 11.5 19.1

BY GPC

Benzene insolubles@) 76, ASTLM023 17T

Coking value %, ASTM D2416T

15.7 22.0 (*’ 35.5 44.9

47 44 60 75

(a) Approximately equal to the tetrahydrofuran-insolubles. (*I Calculated from the CS,-insolubles. Varcum-like experimental

distributions resins.

from

those of the

Coal tar pitches The tetrahydrofuran-soluble fractions of a series of coal tar pitches were investigated by GPC. (The fraction of a coal tar pitch which is soluble in tetrahydrofuran is about equal to that which is soluble in benzene.)“*) Some of the physical properties of these resins appear in Table 1.

All of them tailed on the high mol. wt. side and had peak maximums in the 200 mol. wt. area. The enormous number of distinct chemical species comprising the compositions of coal tar pitches tends to detract from the accuracy or the usefulness of free comparisons between pitch molecular distributions. It is not unexpected that pitches with such similar molecular distributions of the tetrahydrofuran-soluble fractions vary so in physical properties. Undoubtedly, more important in this respect is the wide variation of the tetrahydrofuran insoluble fractions of these pitches. Coumarone-indene resins Some of the physical properties of the coumarone-indene resins which were characterised by GPC are shown in Table 2. TABLE

III

III

2,

P5

es

I

COUNTS

III

el

19

I

I

IT

I

I

2. PROPERTIES OF COUMARONE-KNDENE CHARACTERISED BY GPC

RESINS

IS

hn..f)

FIFIG.3. GPC curve of the tetrahydrofuran soluble fraction of coal tar pitch CP 275-350.

Resin

Color

Soft point “C Ring and ball

Figure 3 shows a typical member of this pitch series. The distribution covers a mol. wt. range of approximately 4000 (16 counts) down to 70 or 80 (26 counts) with the peak fraction at about 200. The molecular distributions of the tetrahydrofuran soluble &actions of the other pitches varied little from that in Fig. 3.

LX-509 R-6 R-10 R-12 R-16 R-19 R-28

I-2.5 2-2.5 1 2-2-5 2-2.5 3-5

155 min 126 min 108-117 108-117 94107 50-66

1.5-2

28-38

THE

DETERMINATION

OF THE

MOLECULAR

be useful as blending agents

with

The

wide

available

99

DISTRIBUTIONS

other

or block

potential

variety

polymerisation

binder

of molecular

polymers.

distributions

makes them useful in an investigation

of the effects

of the molecular

thermoplastic

binder

distributions

of

materials.

Gilsonite resins The 4. The GPC curves of a series of commercial coumarone-indene resins.

FIG.

These resins were found to be completely in

Figure

tetrahydrofuran.

variety

4

of coumarone-indene

distributions

illustrates resin

coal tar pitches, at 15 counts

etc.)

A small amount distribution rest appear

and Selects.

of the properties

Table

of these resins. The molecular

as determined

by GPC,

the gilsonite

resins appears

in Fig.

resins were completely

hydrofuran.

High

3 gives some

distribution, sonite

from the

Standard,

The

for one of 6. The

soluble

distinctive

feature

gil-

in tetraof

the

appear

5

of monomer

of resin LX-509

5000

The elution

materials

at about

Illllllllll

used for the

i.e. a mol. wt. of about

and 100 at 24 counts.

for the monomeric

coumarone,

molecular

Temperature,

for the coumarone-

resins is the same as that

volumes

the

resins were available in three grades:

available.

The mol. wt. calibration indene

soluble

gilsonite

manufacturer

(indene,

24.5

counts.

can be seen in the (Fig.

4c),

but the

to be monomer-free.

*I3 COUNTS (me)

FIG. 6. GPC curve of a Selects gilsonite resin.

TABLE 25

FIG.

In

23

21

I5 23 COUNTS 1rn.f) 17

17

3.

PROPERTIES

5. The molecular distributions of two coumaroneindene resins illustrating color dependence. addition

to the

expected

changes

with

softening points, a marked dependence of molecular distribution on color index was found. An illustration of this is seen in Fig. 5. The coumarone-indene resins are amenable to further chemical modification, and also may

OF GILSONITE

TERISED

I3

Resin Selects Standard High Temperature

BY

Soft Point “C Ring and ball

RESINS CHARAC-

GPC

Fixed Solubility carbon o/0 CS* %

130-150 150-175

13-15 15-18

99.7 99.5

175-200

16-20

99.5

E. M. WJZWERKA gilsonite

molecular

molecular

distributions

is

the

high

weights of the bulk of the constituents.

The peak elution volume of 17 counts represents a molecular

weight

of about

curves of the Standard resins

were

2000.

The

GPC

and High Temperature

also featureless

and similar

to the

Selects.

molecular

materials

distributions

tography

of graphites. provides

elucidating

of the

of graphite

gel permeation

distributions

binder

materials,

effects feasible.

chromatography

control

experimental

Gel permeation

the molecular

10.

chromameans of of a wide making

a

In addition,

is an excellent

tool for commercial

binder

binder

effect on the

a fast, reproducible

study of distribution quality

9.

may have an important

properties

variety

7. 8.

4. SUMMARY The

5. FRANCKH. G., BrennstofiChem. 36, 12 (1955). 6. DE RUITERE. et al., Characterization of Binders Used in The Fabrication of Graphite Bodies. WADD

as well as

11. 12. 13. 14. 15.

resins. 16.

REFERENCES DUNLOPA. P. and PETERSF. N., Ind. Eng. Chem. 34, 814 (1942). CONLEY R. T. and METIL I., J. Ap~l. Polym. Sci. 7, 37 (1963). HACHIHAMAY. and SHONOT., $hem. Abstr. 50, 11709d (1956). BOQUIST C. W. et al., Alumina Condensed Fwfuryi! Alcohol Resins. WADD Technical Report 61-72, Volume XV, Armour Research Foundation, Chicago, Illinois ( 1963).

17. 18. 19.

20.

21. 33

Technical Report 61-72, Volume XI Supplement, Union Carbide European Research Associates, Brussels, Belgium ( 1964). WOOD L. J. and PHILLIPSG., J. A#. &m. (London) 5, 326 (1955). FRIEDELR. A. and RETCOPSKY H. L., Chem. d Ind. (London), No. 11, 455 (1966). SHULTZ J. L., FRIEDEL R. A. and SHARKEY A. G., JR., Fuel 44, 55 (1965). HOOKERJ. R., Pitch Binders For Graphite: A Survey ef the Literature, U.S.A.E.C., Division of Technical Information, GA 3985, General Atomics, San Diego, California, pp. 3-10 (1963). Ref. 10, pp. 6-10. POWERS P. O., Encyl. Polym. Sci. Tech. 4, 273 (1966). Ref. 12, p. 282. KENNY J. A., Colloid Chem. 6, 966 (1946). RIESZ C. H. and SUSMANS., Proceedings oj. the Fourth Conference on Carbon, p. 611. Pergamon Press, New York (1960). YEN T. F., ERDMANJ. G. and POLLACKS. S., Anal. Chem.33, 1587 (1961). SUGIHARA J. M. and MCCULLOUGHT. F., Anal. Chem. 28, 370 (1956). Ref. 15, p. 610. FLORYP. J., Principles of Polymer Chemistry, p. 3 17. Cornell University Press, Ithaca, New York (1953). ALTGELTK. H. and MOOREJ. C., Gel permeation chromatography. In PolymerFractionation,pp. 123179. Academic Press, New York (1967). Ref. 6, p. 2. Ref. 10, p. 9.