NBS TECHNICAL NOTE

national tsun

Library, E«01 Mnv

JUL 3 1969 485

An Evaluation of Certain Methods

For the Chemical Analysis of

Styrene-Butadiene Rubber

^T 0F c

0t

<5 *.

\

if)

J?

Vau o* *

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards ' was established by an act of Congress March 3, 1901. Today,

in addition to serving as the Nation's central measurement laboratory, the Bureau is a principal

focal point in the Federal Government for assuring maximum application of the physical and

engineering sciences to the advancement of technology in industry and commerce. To this end

the Bureau conducts research and provides central national services in four broad program

areas. These are: (1) basic measurements and standards, (2) materials measurements and

standards, (3) technological measurements and standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials Research, the

Institute for Applied Technology, the Center for Radiation Research, the Center for Computer

Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and

uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of an Office of Measurement Services and the following technical

divisions:Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic and Molecular Physics—Radio Physics -—Radio Engineering -—Time and Frequency -—Astrophysics -—Cryogenics.-

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to im- proved methods of measurement standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; develops,

produces, and distributes standard reference materials; relates the physical and chemical properties of materials to their behavior and their interaction with their environments; and provides

advisory and research services to other Government agencies. The Institute consists of an Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations in the development of technological

standards, and test methodologies; and provides advisory and research services for Federal, state, and local government agencies. The Institute consists of the following technical divisions and

offices: Engineering Standards—Weights and Measures — Invention and Innovation — Vehicle Systems Research—Product Evaluation—Building Research—Instrument Shops—Measurement Engineering—Electronic Technology—Technical Analysis.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement, and application of radiation tjo the solution of Bureau mission problems and the problems of other agencies and institutions. The Center consists of the following divisions: Reactor Radiation—Linac Radiation—Nuclear Radiation—Applied Radiation. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and

provides technical services designed to aid Government agencies in the selection, acquisition, and effective use of automatic data processing equipment; and serves as the principal focus

for the development of Federal standards for automatic data processing equipment, techniques,

and computer languages. The Center consists of the following offices and divisions: Information Processing Standards—Computer Information — Computer Services — Sys- tems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader aspects of the National Measure- ment System, and provides appropriate services to ensure that the NBS staff has optimum accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data—Clearinghouse for Federal Scientific and Technical

Information : ' —Office of Technical Information and Publications—Library—Office of Public Information—Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

" Located at Boulder. Colorado 80302.

' Located at 6285 Port Royal Road. Springfield. Virginia 22151.
UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

NBS TECHNICAL NOTE 485

ISSUED JULY 1969

Nat. Bur. Stand. (U.S.), Tech. Note 485, 27 pages (July 1969)

CODEN: NBTNA

An Evaluation of Certain Methods for the Chemical

Analysis of Styrene-Butadiene Rubber

Edwin J. Parks

Product Evaluation Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

and

Frederic J. Linnig

Maritime Administration

Washington, D.C. 20001

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, Government Printing Office

Washington, D.C, 20402 - Price 35 cents

Contents

Page

1. Introduction 2

2. Samples 3

3. Organic Acid and Soap in SA Rubber 3

3.1 Methods Evaluated 3

3.1.1 ASTM ethanol- toluene azeo trope (ETA)

extraction procedure (ASTM D 1416,

Sections 30-40) . 3

3.1.2 I sopropanol -toluene azeotrope (ITA)

extraction procedure 3

3.1.3 A complete -solution (CS) procedure 4

3.2 Detection of Systematic Errors 4

3.3 Results and Discussion 4

3.4 Conclusions 5

4. Organic Acid and Soap in AC Rubber 5

4.1 Methods Evaluated 5

4.1.1 Aqueous ETA extraction procedure (ASTM

D 1416, Sections 30-40) 5

4.1.2 Acetic acid -ETA extraction procedure .... 5

4.1.3 Aqueous ITA extraction procedure 5

4.1.4 A complete -solution procedure 6

4.2 Systematic Errors 6

4.3 Results and Discussion 6

4.4 Conclusions 8

5. Stabilizers and Bound Styrene by ITA Extraction

Procedure 8

5.1 Methods 8

in
Page

5.1.1 Stabilizers 8

5.1.2 Bound Styrene 9

5.2 Results and Discussion 9

5.2.1 Stabilizer . „ 9

5.2.2 Bound Styrene 10

5.3 Conclusions 10

6. Thymol Blue as Indicator for Soap and Organic

Acid in Aqueous ITA Extract 10

6.1 Methods 10

6.2 Results and Discussion 11

6.3 Conclusions 11

7. Analytical Techniques for Organic Acid in Fluids . 11

7.1 Latex 11

7.1.1 Method 11

7.1.2 Discussion 11

7.2 SA Serums and Washes 12

7.2.1 Method 12

7.2.2 Discussion 13

7.3 AC Serums and Washes 13

7.3.1 Method 13

7.3.2 Discussion 13

8

.

Summary Ik

9. References 15

10. Tables 16-

2k

IV
An Evaluation of Certain Methods for the Chemical

Analysis of Styrene -Butadiene Rubber

E. J. Parks and F. J. Linnig

Abstract

The applicability of available methods for

the analysis of unvulcanized styrene -butadiene

rubber (SBR, formerly GR-S) for organic acid and

soap is influenced by the type of coagulation

(alum or salt-acid), the type of acid present

(fatty acid, rosin acid, or mixed acids), and

the presence of carbon black or oil. No single

method is universally applicable for the analysis

of organic acid and soap, but reasonably unbiased

results can be attained by proper selection of

the available procedures.

The complete -solution procedure for alumcoagulated (AC) SBR has given reasonably good

results for organic acid in samples containing

mixed acids, while the extraction procedure using

aqueous is opropanol- toluene azeotrope (ITA) gives

good results for AC samples containing fatty acid

only.

The complete-solution procedure for SBR

coagulated with salt and acid gives less biased

results for organic acid and soap than the aqueous

ITA extraction procedure, but the latter should

be used for all SBR containing carbon black and

for estimating oil in oil-rubber masterbatches.

Both complete -solution procedures and the ITA

extraction procedure can be adapted for the determination of stabilizer and bound styrene. The

present ASTM extraction procedure using ethanoltoluene azeotrope is less satisfactory than the

other procedures.

Key words: Bound styrene; carbon black; chemical

analysis; latexes; oil; organic acid;

serums; soap; stabilizer; styrene

butadiene rubber (SBR); washes.
1. Introduction

A knowledge of the chemical constituents of styrene

butadiene rubber (SBR, formerly GR-S) is useful in

maintaining uniformity of production. Some of the constituents of principal interest are organic acid, soap, bound

styrene , and stabilizer.

The nature of some of the constituents depends on the

method of coagulation used in preparing the rubber. One

method uses salt (sodium chloride) and acid (sulfuric acid)

to produce salt-acid (SA) coagulated rubber. A second uses

"alum" (aluminum sulfate) as coagulant for alum-coagulated

(AC) rubber. Sodium or potassium soap is used in the polymerization process. The SA rubber contains organic acid

derived from partial neutralization of the soap. It should

also contain a relatively small amount of unreacted soap.

Alum -coagulated rubber, however, presumably contains, as

aluminum soap, free and bound organic acid, and perhaps

some unreacted sodium or potassium soap. Materials balance

studies involving the comparison of the amount of organic

acid in the soap that goes into making AC rubber and that

found on analysis by the present ASTM procedure (1)-*-

employing aqueous ethanol- toluene azeotrope (ETA) indicate

that this procedure gives low results. Since a similar ASTM

method using anhydrous ETA to extract sodium soap and organic

acid from SA rubber (1) gives much more consistent materials

balance figures, the difficulty encountered in the analysis

of AC rubber is probably due to the presence in the rubber

of aluminum soap that is not readily extracted. Anhydrous

ETA is even less effective than aqueous ETA for extracting

AC rubber. The water present in the latter solvent aids

in the hydrolysis of the aluminum soap and thus in the

subsequent extraction of the organic acid.

Three other methods besides the ASTM procedure using

aqueous ETA have been suggested for the analysis of AC

rubber. The ASTM procedure involving the use of anhydrous

ETA for the analysis of soap and organic acid in SA rubber,

although much less biased than the method for AC rubber, is

not completely satisfactory either. Consequently, two other

methods for SA rubber have been suggested.

This paper deals largely with a comparison and evaluation

of these seven methods. The ASTM methods for stabilizer

and bound styrene are free of detectable systematic errors

The italic numbers in brackets refer to the list of

references appended to this paper.
but require separate specimens. It would be convenient to

run these tests on the same specimens used for the organic

acid and soap determinations. Methods evaluated here that

were useful for organic acid and soap have therefore also

been adapted for the determination of stabilizer and bound

styrene and checked for systematic errors by comparison with

the ASTM procedures. Several new methods of analysis

necessary for the evaluations have been developed and are

also presented, along with improvements for two of the

suggested procedures.

2. Samples

For the purpose of evaluating the systematic errors in

methods for soap and organic acid in AC rubbers, pairs of

samples of SA and AC rubber were coagulated from the same

latex. The SA samples are also used for evaluating methods

for SA rubber relative to an unbiased complete -solution (CS)

procedure for this type of rubber (2).

Two sets of samples were specially prepared by each of

three different collaborating plant laboratories. A complete

set consisted of an AC and an SA sample prepared from a

single latex, the latex itself, and the respective serums

and washes. These samples are described in Table 1. The

preparation of the two sets of samples GG-1 and GG-2 was

repeated, because of conflicting results obtained by the CS

procedure for AC rubber, using new latexes and producing

samples GG-1 N and GG-2 N. In addition, Phillips Petroleum

prepared a sample containing carbon black (designated 6608P)

and a solution polymer (Solprene 1205), both containing soap,

that were used in comparing the performance of indicators.

3. Organic Acid and Soap in SA Rubber

3.1 Methods Evaluated

3.1.1 ASTM ethanol- toluene azeotrope (ETA) extraction

procedure (ASTM D 1416, Sections 30-40) (1).

Six grams of thinly sheeted sample is extracted with

two 100-ml portions of solvent and the combined extracts

made up to 250 ml. One-hundred ml aliquots are titrated

for soap and organic acid, respectively, using m-cresol

purple as indicator in both titrations.

3.1.2 Isopropanol-toluene azeotrope (ITA) extraction

procedure (3).

ITA containing 8 percent by volume of H2O is used in

place of anhydrous ETA in the ASTM procedure.
3.1.3 A complete -solution (CS) procedure (2).

Five grams of sample is dissolved in 5:1 tolueneabsolute ethanol, the solution is made up to 250 ml, and

aliquots are used for the determination of organic acid and

soap.

3.2 Detection of Systematic Errors

The CS procedure for SA samples has been evaluated and

found free of detectable systematic error (4). Method 3,

therefore, is the standard against which methods 1 and 2

are evaluated.

3.3 Results and Discussion

The CS procedure eliminates the difficulty of incomplete

extraction inherent in the extraction procedures, but cannot

be used for the analysis of SBR containing carbon black that

gives a colorimetrically untitratable opaque solution.

Extracts of SBR containing carbon black, on the other hand,

can be titrated colorimetrically. The estimation of oil in

oil -rubber masterbatches similarly requires an extraction

procedure.

The results of the analysis by the three methods of the

eight SA samples are given in Table 2. Each value represents

at least two but usually four to six determinations. The

results for organic acid tend to run low for the extraction

procedures and on these samples may be low by as much as

0.3 percent for the ITA procedure and 0.23 percent for the

ETA procedure. Of the samples containing large amounts of

soap (over 1 percent) the extraction procedures give quite

low results for this constituent. Somewhat better results

are obtained on samples containing the usual amount of soap,

- 0.75 percent. One (PP-2 SA) is low in soap content by

0.16 percent by the ITA procedure, and one (F-l SA) low by

0.20 percent by the ETA procedure. Table 3 shows that for

both tests most of the differences are statistically

significant and that the biases are approximately the same

for the ITA and ETA methods.

Since the systematic errors in the ETA procedure are as

great as those in the ITA procedure and since, as demonstrated

below, the ITA procedure will have to be used for some AC

samples, it would simplify matters to eliminate the ETA

procedure from further consideration. In Table k, which

covers more completely the usual range of soap concentrations,

a further comparison is made of a number of samples analyzed

by the CS and ITA procedures. Each value in Table 4

represents at least two determinations. The extraction
procedure in this series of tests gives results that are low

by as much as 0.14 - 0.16 percent. The differences for the

last three samples are all statistically significant.

3.4 Conclusions

The CS procedure is the most reliable method for organic

acid and soap in SA rubber and should be used for all samples

except those containing carbon black or oil. The ITA

procedure should be used in these latter cases. Since the

ITA and ETA procedures are equivalent for SA rubbers, and

since ITA is preferred over ETA for AC rubbers, ETA should

be omitted from further consideration.

4. Organic Acid and Soap in AC Rubber

4.1 Methods Evaluated

4.1.1 Aqueous ETA extraction procedure (ASTM D 1416,

Sections 30-40 (1).

This is the same as Method 1 for organic acid and soap

in SA rubber, except that 5 percent by volume of water has

been added to the ETA to hydrolyze the aluminum soap.

4.1.2 Acetic acid-ETA extraction procedure (5).

This procedure, modified slightly in the present

application, involves extraction with ETA containing 5 percent by volume of glacial acetic acid to convert the

aluminum and sodium soaps to organic acid. The rubber is

washed with ETA and the washings added to the extract. The

acetic acid is then removed by extraction with water after

the addition of n-hexane to the extract. After partial

evaporation of the organic solvent, isopropanol is added

and the titration made with 0.05 N aqueous sodium hydroxide,

using phenolphthalein as indicator. The modifications

involve washing the extracted rubber with ETA instead of

n-hexane, which dissolves the rubber, testing the last water

wash for acidity with litmus, and using isopropanol instead

of methanol to reduce the size of the blank.

4.1.3 Aqueous ITA extraction procedure.

ITA containing 8 percent by volume of water (3) is

substituted in the present method for ETA in the ASTM

procedure (1) instead of being used in the manner originally

described (3).
4.1.4 A complete-solution procedure (6).

The rubber is dissolved in toluene, the aluminum ion is

complexed with 8-hydroxyquinoline, and 95 percent ethanol is

added before titration of the organic acid with alcoholic

sodium hydroxide, using m-cresol purple as indicator and

employing a colorimeter to follow the course of the titration.

4.2 Systematic Errors

The organic acid content of AC samples, including that

which may be present as soap, must be determined indirectly

as follows:

4.2.1 By comparing the organic acid content of the latex

before coagulation with that in the rubber, serum, and wash

water after coagulation, including that present as soap.

When rubber is coagulated from latex, the liquid portion or

serum which remains may contain a trace of soap or organic

acid. Another trace of soap or organic acid may be lost

from the rubber to the water with which it is washed. Usually

the organic acid in washes and serums amounts to less than

0.1 percent of the rubber, but for a strict accounting of all

of the soap and organic acid originally in the latex, these

traces must be determined and added to that in the rubber.

This grand total will be referred to as total organic acid.

4.2.2 By comparing the total organic acid content of the

AC sample with that of an SA sample coagulated from the

same latex. For this purpose, the organic acid and soap

contents of the SA sample are determined by the CS procedure

for this type of rubber (2), which is known to be unbiased

(4). Subtracting the organic acid found in the AC washes

and serums from the total organic acid content of the SA

sample should give the true organic acid content of the AC

rubber. For comparison, the organic acid and soap contents

of the AC sample would be determined as directed by each of

the methods under question.

4.3 Results and Discussion

All of the results present in Tables 5 and 6 represent

averages of at least two but usually three to six determinations.

The results of tests for total organic acid in samples

from all three plant laboratories are presented in Table 5.

Values for the CS procedures for AC and SA rubber, the

aqueous ITA extraction procedure, and the ASTM ETA extraction

procedures (1) are given along with values for the organic

acid contents of the latexes. The latexes, washes and serums
of these samples were analyzed by methods given later in

this paper.

It was found that some of the AC samples contained

traces to appreciable amounts of titratable base (if

calculated as organic acid, up to 16 percent of the organic

acid present) , which was assumed in the calculations for

total organic acid in the ITA and ETA analyses to be sodium

soap. As will be seen from the data, the extraction methods

generally give low values, presumably because of incomplete

extraction.

A comparison is made of the total organic acid content

of each AC sample, including serum and washes, with that of

the corresponding SA sample analyzed by the CS procedure.

In most cases the organic acid content of the latex is

somewhat higher than the total organic acid in the rubber,

serum, and washes determined by the CS procedure on the SA

sample. This fact suggests that something may be lost in

accounting for the organic acid in the serum and washes.

Since this is possible for AC and SA rubbers alike, a

comparison of the total organic acid content of the AC rubber

with that of the SA rubber seems to be more valid than the

same comparison of the AC rubber with the latex. In any

event, the difference between the two comparisons is not

excessive.

It will be noted in Table 5 that none of the methods

gives consistently good results on all of the AC samples,

with the ETA extraction method coming out a poor third.

Overall, the ITA extraction procedure gives better

results (0.18 percent low on the average) than the CS

procedure (0.51 percent high on the average) for the AC

samples containing fatty acid alone. It should be noted

that the CS procedure gives very good results for samples

F-l AC and F-2 AC and high results on GG-1 AC and GG-2 AC

and the repeated samples GG-1 N AC and GG-2 N AC.

If it is assumed that these samples are typical of

production containing fatty acid only, 95 percent confidence

intervals can be calculated for the average systematic error

of both methods. These confidence intervals do not overlap.

The one for the ITA procedure just includes zero difference

at the lower end of the interval, and the one for the CS

procedure is, of course, on the other side of zero and does

not include zero. On this basis, it is reasonable to infer

that results obtained with the use of the ITA procedure will

have smaller systematic errors than with the CS procedure.
Further evidence was obtained supporting the use of the

ITA procedure for AC samples containing fatty acid only. Of

these samples, one, GG-2 AC giving high, and one, F-2 AC

giving satisfactory results by the CS procedure, were analyzed

by the acetic acid-ETA extraction procedure (5). Both samples

gave results about 0.3 percent low by this method, values

which were comparable to those obtained with the ITA extraction

procedure. Since the method employing acetic acid should

completely convert the aluminum soap to organic acid and

provide good results, these data lend support to the use of

the ITA method for AC samples containing fatty acid only.

The acetic acid method is, of course, too time consuming

and cumbersome to be considered for routine use.

On the other hand, very poor results are obtained by

the ITA procedure on the two samples containing mixed acids.

The CS procedure fares better on these samples, giving

results only 0.52 percent low in comparison to those 1.55

percent low for the ITA procedure. These former results are,

however, erratic. The comparison of the results is more

readily seen in Table 6.

4.4 Conclusions

A considerable portion of SBR contains rosin acid.

Further work on samples containing rosin or mixed acids is

needed to verify whether the difference in behavior is

actually due to the type of acid present. Until this

research is done, the two methods (CS and aqueous ITA)

should be used on the samples for which they are better

suited. Again, the ITA procedure must be used for estimating

oil in oil -rubber masterbatches and for analyzing samples

containing carbon black.

5. Stabilizers and Bound Styrene by ITA

Extraction Procedure

5.1 Methods

5.1.1 Stabilizers

2 3 4 Samples containing PBNA, BLE, or Stalite may be

analyzed for stabilizer content by ultraviolet absorption

measurements as in the ASTM extraction procedure (ASTM D

2

3Phenyl-beta-naphthylamine

.Reaction product of acetone and diphenylamine

Mixed alkylated diphenylamines
1416, Sections 49-54, Method B (1)) by diluting a 2 ml

aliquot of the aqueous ITA extract to 100 ml with 85:15

methylcyclohexane-isopropanol spectrograde solvent mixture.

The reference solutions for calibration are made by dissolving 0.03 g of stabilizer in 100 ml of aqueous ITA and

taking three 2 ml aliquots, which are diluted to 100 ml with

the same spectrograde solvent mixture. This mixture has a

transmittance of 98.5 percent or better at 288 and 309 mn,

where the measurements are made. As implied in the ASTM

procedure, nonspectrograde solvents should be satisfactory

if the transmittance of the mixture is greater than 90 percent.

5.1.2 Bound Styrene

Alum -coagulated and SA samples may be analyzed for

bound styrene content by a modification of the ASTM procedure

(ASTM D 1416, Sections 25-29 (1)). A small piece of the

extracted 6 g sample suitable for use in the ASTM procedure

is pressed between sheets of aluminum foil about 2.5 inches

on a side in a laboratory press. The aluminum sheets are

pulled apart with a clean continuous pull, and the rubber

adhering to one sheet of the foil is dampened with a little

isopropanol to facilitate removal as a thin film. The thin

film (about 0.004 to 0.01 inch in thickness) is then extracted

for 15 min with 60 ml of aqueous ITA for the SA samples or

anhydrous ITA containing 1 percent of concentrated hydrochloric

acid for the AC samples. The small specimens are then treated

according to the ASTM procedure and the bound styrene content

determined from the refractive index.

5.2 Results and Discussion

5.2.1 Stabilizer

The results of analyses for stabilizers in AC and SA

rubbers by the ITA method are presented in Table 7, along with

values obtained by the ASTM complete -solution procedure (ASTM

D 1416, Sections 42-48, Method A (1)). The latter should

give unbiased results, since in this procedure the whole

sample is dissolved and an adequate correction is made for

the absorption of the rubber itself. Each value represents

an average of at least six measurements on each of two or

three different specimens. Unbiased results are obtained by

the extraction procedure for PBNA, somewhat low results for

Stalite, and quite low results for BLE. The reason for the

difference between the stabilizer contents of SA and AC

samples coagulated from the same latex is not clear.
5.2.2 Bound S tyrene

The results of the bound s tyrene analyses are given in

Table 7 , along with values obtained using the two 1-hour

extraction periods with the small untreated specimens as

required by the ASTM procedure (1) , which is known to give

unbiased results (7). Each value represents an average of

at least six determinations on each of two or three specimens.

The present method may be considered satisfactory. This

procedure affords some saving of time in comparison with the

ASTM procedure and avoids duplication of extracting equipment.

The extra extraction on the small sheets of rubber that

is recommended in this procedure is necessary to give unbiased

results, presumably because of occlusion of materials in the

6 g samples. For example, without this additional treatment,

values obtained on one AC sample were low by as much as

0.82 percent, with differences between specimens from a

single sample as great as 0.29 percent. Salt-acid coagulated

samples can run 0.50 percent low with similarly poor precision.

Of course, this method cannot be used with carbon black

masterbatches.

5.3 Conclusions

The ITA extraction procedure for stabilizers is unbiased

for PBNA, approximately unbiased for Stalite, and poor for

BLE. For bound styrene determinations, the ITA procedure is

quite satisfactory. It should be noted that the CS procedure

for SA samples has also been adapted for the unbiased determination of any of the three stabilizers and bound styrene on

a single specimen.

6. Thymol Blue as Indicator for Soap and Organic

Acid in Aqueous ITA Extract

6.1 Methods

The indicator is prepared by dissolving 0.06 g of thymol

blue in 6.45 ml of 0.02 N aqueous sodium hydroxide and

diluting to 50 ml with dis tilled water. The color changes

are from yellow to pink on titrating for soap with hydrochloric acid and from yellow to purple on titrating for organic

acid with sodium hydroxide.

It is suggested that of the 250 ml of aqueous ITA extract,

a 100 ml aliquot be used for organic acid, a 2 ml aliquot for

stabilizer and the remaining 148 ml for soap, instead of the

100 ml used in the ASTM procedure. Ten drops of the indicator

should be used for each 100 ml of solution.

10
6.2 Results and Discussion

Table 8 gives results obtained by using both thymol

blue and m-cresol purple on 100 ml aliquots of the same

aqueous ITA extract for both soap and organic acid. The

samples were chosen so as to cover the usual range of soap

and organic acid contents. It is apparent that essentially

the same results are obtained in both tests for both

indicators. Occasional high results for soap with m-cresol

purple are attributed to the difficulty of detecting the endpoint in this titration. Note the consequent poor precision

in these cases. Thymol blue gives a satisfactory color

change even in the presence of BLE, the most highly colored

of the materials likely to be encountered in these extracts.

6.3 Conclusions

Thymol blue gives a more readily discernible end-point

for soap titrated in aqueous ITA than does m-cresol purple,

used in the comparison study. It is equally good for the

titration of organic acid in this solvent.

7. Analytical Techniques for Organic Acid in Fluids

Methods have been devised for the determination of

organic acid in latex, serums, and washes.

7.1 Latex

7.1.1 Method

A sample containing about two grams of solids is

evaporated nearly to dryness at room temperature and to

constant weight under vacuum at 120°C, and dissolved in

100 ml of 5:1 toluene -absolute ethanol. This solution is

first titrated with 0.1 N alcoholic hydrochloric acid to the

first permanent pink coloration, using m-cresol purple as

indicator, then back titrated to the first permanent purple

coloration with 0.1 N alcoholic sodium hydroxide. The

organic acid content of the solids is calculated from the

number of milliequivalents of sodium hydroxide consumed

between the pink and purple end-points, with a correction

for the appropriate blank.

7.1.2 Discussion

The titration of organic acid in a 5:1 toluene -ethanol

solution of dried latex should give unbiased results when

m-cresol purple is used as the indicator in the titration

with sodium hydroxide (4). However, if organic acid is

determined by first titrating the solution with hydrochloric

acid to convert soap to organic acid, and then back titrating

11
with sodium hydroxide, using m-cresol purple in both cases,

different results are obtained in the two directions, depending

on whether excess base or acid is present in the latex.

Since hydrochloric acid neutralizes excess base as well as

converting soap to organic acid, it is necessary to determine

organic acid solely by means of the back titration with

sodium hydroxide. In the studies for systematic errors in

the soap titration using m-cresol purple in 5:1 toluene

ethanol solutions of SBR T2 , k) , the larger quantities of

soap present in latex were not studied. Consequently, using

a previously published plan (4) , a study has been made of

the systematic errors in the titration of these larger

quantities of a fatty acid soap approximating sodium stearate

in composition to determine the correctness of the starting

point in the back titration with sodium hydroxide.

Selected known amounts of soap of known composition

covering the range in question equivalent to 0.0 - 7 percent

of the dried latex were dissolved in 5:1 toluene -absolute

ethanol and titrated with alcoholic hydrochloric acid. The

data were analyzed statistically. Table 9 gives the slope of

the regression line as ml of hydrochloric acid per gram of

soap (ml/g) and the intercept as ml of hydrochloric acid.

These are compared respectively with the titre of the soap

determined from its composition and with the experimental

blank. Relative and constant type errors are assumed to be

absent from the analysis if the resulting differences are

insignificant in relation to the standard error of the slope

and intercept, assuming that the calculated slope and

experimental blank were determined with sufficient precision

to be without error. In this case there is no evidence of

either relative or constant type errors and the end-point in

this titration should be a valid starting point for the back

titration with sodium hydroxide.

7.2 SA Serums and Washes

7.2.1 Method

Approximately 100 g of serum or wash, weighed to the

nearest 0.1 g, is acidified with 0.1 N hydrochloric acid.

A 20 ml excess of the acid is then added to convert the soap

completely to organic acid. The sample is extracted three

times with 100 ml portions of ether. The combined ether

extracts are washed free of mineral acid with at least three

50 ml water washes and evaporated to dryness on a steam bath.

The residue is taken up in 100 ml of 5:1 toluene -absolute

ethanol and titrated with 0.1 N alcoholic sodium hydroxide,

using m-cresol purple as indicator. Organic acid in the total

serum or wash is calculated as a proportion of the weight of

the dried rubber obtained on coagulation plus the organic acid

obtained from the serum and wash.

12
7.2.2 Discussion

Additional extractions with ether beyond the three

indicated earlier did not yield additional organic acid;

extraction using the indicated method is therefore complete.

Since m-cresol purple gives good results in this solvent (4)

,

the overall method should be unbiased. It has been shown

that the absence of a pink color in the presence of m-cresol

purple at the beginning of the titration verifies that free

mineral acid had been removed from the ether by the water

washes (2).

7.3 AC Serums and Washes

7.3.1 Method

A 100 g sample of serum or wash is weighed to the

nearest 0.1 g in a 250 ml beaker, and the water is removed

by evaporating the solution at the boiling point until 20 - 30 ml remain. It is then dried at about 50°C. The residue

is taken up in 125 ml of toluene, and the aluminum is

complexed with 8-hydroxyquinoline , using the same amount as

in the CS procedure for alum -coagulated SBR. After adding

30 ml of 95 percent ethanol, the sample is titrated with

0.1 N sodium hydroxide according to that procedure but using

0.02 ml increments of base over the middle course of the

titration to avoid over titrating the end-point. Organic

acid in the total serum or wash is calculated as a proportion

of the weight of the dried rubber obtained on coagulation

plus the organic acid obtained from the serum and wash.

7.3.2 Discussion

A study similar to that made with sodium stearate has

been made with an aluminum soap of known composition. The

weighed samples covering the small concentrations encountered

in the analysis of serums and washes (0 - 2.5 mg) were dissolved in toluene and treated and analyzed for organic acid

in the manner described for AC serums and washes. A similar

study was made covering the concentration range involved in

the analysis of the AC rubber (as much as 130 mg). The results

of the statistical analysis of these data are given in

Table 9. There is no evidence of either relative or constant

type errors in the method as applied to either range.

Since only quite small quantities of organic acid are

found in the analysis of serums and washes, large positive

errors such as those observed earlier with the rubber itself

are not encountered. Furthermore, a green color is produced

when aluminum soap is treated with 8-hydroxyquinoline. In

the analysis of the serums and washes, this color developed

13
only when detectable amounts of organic acid could be titrated.

Alum itself does not react to give this color with 8 -hydroxy

quinoline in the solvent used here. Thus the green color

indicates the presence of aluminum soap and the titration

should give the amount of organic acid present in the soap.

Any unbound organic acid must also be accounted for at the

same time.

The fact that large errors, either negative or positive,

can occur when the method is applied to rubber itself, as

shown in Table 5, suggests the presence of interfering

conditions or substances not present in the aluminum soap

used in the study of systematic error.

8 . Summary

Organic acid and soap determined by the completesolution procedure for styrene -butadiene rubber (SBR) coagulated

with salt and acid exhibit smaller systematic errors than

when the aqueous ITA extraction procedure is used. However,

the aqueous ITA extraction procedure should be used for all

SBR containing carbon black and for estimating oil in oilrubber masterbatches.

The complete-solution procedure for alum-coagulated (AC)

SBR has given reasonably good results for organic acid in

samples containing mixed acids, while the extraction procedure

using aqueous isopropanol- toluene azeotrope (ITA) gives good

results for AC samples containing fatty acid only.

Both of the complete -solution procedures and the ITA

extraction procedure can be adapted for the determination of

stabilizer (except that BLE is low by 0.4 percent for the

ITA procedure) and bound styrene as part of a continuous

series of analyses. Overall, the present ASTM extraction

procedure using ethanol- toluene azeotrope is less satisfactory

than the other procedures.

Some additional work on the ITA procedure may be desirable

to see if more complete extraction can be obtained. Further

work is needed on additional samples containing mixed acids

or rosin acid alone to determine whether the presence of the

latter causes the peculiar results observed here in the

analysis of AC samples.

14
The authors are indebted to the Firestone Synthetic

Rubber and Latex Company, Goodrich-Gulf Chemicals, Inc., and

the Phillips Petroleum Company Copolymer Plant for their

cooperation in preparing the samples used in the work on SBR,

and to the Witco Chemical Company for providing sodium and

aluminum soaps of known composition used in the designed

experiments. The assistance of John Mandel and Mary N. Steel

of the National Bureau of Standards in performing the

statistical analyses is gratefully acknowledged.

9. References

1. ASTM Committee D-ll on Rubber and Rubber-Like Materials,

ASTM Designation D 1416-62a T.

2. F. J. Linnig, J. M. Peterson, D. M. Edwards, and W. L.

Acherman, "Chemical Analysis of GR-S by Complete Solution

Procedures," Analytical Chemistry 25, 1511-1517 (1953).

Rubber Chem. and Technol. 27_, 796 TT954).

3. J. L. Hutson, General Tire and Rubber Co. , Chemical

Division, Odessa, Texas, "Method for Testing AlumCoagulated Polymers," presented to ASTM Committee D-ll,

Subcommittee XIII, Task Group 2, Jan. 30, 1964.

'4. F. J. Linnig, John Mandel, J. M. Peterson, "A Plan for

Studying the Accuracy and Precision of an Analytical

Procedure," Analytical Chemistry 26 , 1102-1110 (1954).

5. P. H. Rowe, Goodrich-Gulf Chemicals, Inc., Institute,

West Virginia.

6. F. J. Linnig, "Chemical Analysis of Alum -Coagulated SBR,"

Rubber Age , 90 440-444 (1961)

7. Aurelia Arnold, Irving Madorsky, and L. A. Wood, "Measurement of Refractive Index of Elastomers," Analytical

Chemistry 23 , 1656-1659 (1951). Rubber Chem. and Technol.

25, 693 (1952).

15
a o

Pi o

0)

X

d •H cd o -P p p 0) CO

co ,d

J

<D P

$M

d T) •H >. d

PL, CO cfl o

<p

d

r-l

H o - i co a cd •H O ^ -H

T3

g

O <D o ,d

O r-l Sm o p a

QJ

O

PL, o w -

•h

d

cfl P

ad B cd o H

PM

O Pm o d <

+J00

E^

m co

CN CO J- CO JCM -CTCM -*

CO

CO

r-lI

CO

cd

(p. <D O N

•H

QJ i-l H cd p

00

d

cdbOuo

tpo -

<D

>>

coa)

r-iDB

cd CO

o) <u p p

•H -H

<s < i-Kl r-l 3 w a cd 525 cd m i-j pq p pq p

Pm PQ PM co pm co

TJ T3 o u

T3 cd cd •H ~ O - — _ .- >> d

cd

p

H

p CO ~

>, cd o p Pn p: - »-_•-•_

cd

"~

Pn

<c <: o

IT)• • o

in ~ u u o u < < s z <! <C o u H CM < <j i-l CM 1 1 i i o o

-Ii CM1 r-l CM o o o o Pm Pm 1 I o o Pm PM f* Pn » ., ^ <<w w <

<< 00 00 CO i

00 00 S3 Z r-l CM i-l i-l I-l CM

i-l CM 1 1 1 1 1 1 1 1 o o o o Pm Pm PH P«H o o o o Pm Pm

<Dd

•He

cd

r-l>>d

0) ,d&

•H co T3 0)d

T3 rH d e

cd cd

,-i QJ >, d d o CD <D p -d d QJ a

•rl

O •H

g Cd T3

cd H'H'd

>> o a) ,d p p p cd ,d O r-J ft? >>

cd tj ^ d O r-l 1 5-i cd

00. ^ TJ i d <D -I o X

>>-H •H d

+J

B

<D

O

jC cd i a cuu a) 1 p1 •H < r-l 2 W cd PQ h" p

PL) PQ CO

H|

16
Table 2. Analysis of rubbers for organic

acid and soap

Sample

F-l SA

F-2 SA

GG-1 SA

GG-2 SA

GG-1N SA

GG-2N SA

PP-1 SA

PP-2 SA

Complete -solution

Organic acid Soap

%

4.98

4.80

5.05

3.73

3.70

3.71

5.40

6.25

%

0.56

0.00

0.07

1.54

1.47

1.38

1.02

0.62

ITA Extraction

Organic acid Soap

% %

4.84 0.50

4.51 0.00

4.90 0.07

3.73 0.93

3.72 1.52

3.60 1.11

5.37 0.73

6.29 0.46

ETA Extraction

Organic acid Soap

% %

4.83 0.36

4.57 0.00

4.89 0.07

3.60 0.32

3.74 1.50

3.63 1.30

5.33 0.75

6.14 0.48

17
Table 3. Comparison of differences with standard

error of difference s±/

Organic Acid Soap

CS-ITN CS-ETA

0.138 0.156

0.042 0.035

0.290 0.233

0.044 0.040

0.143 0.153

0.044 0.040

0.000 0.127

0.038 0.035

-0.023 -0.037

0.044 0.040

0.105 0.077

0.045 0.040

0.035 0.078

0.038 0.030

-0.044 0.106

0.039 0.032

Sample

F-l SA

F-2 SA

GG-1 SA

GG-2 SA

GG-1N SA

GG-2N SA

PP-1 SA

PP-2 SA

1/ Upper value for each sample is the difference; the lower

value is the standard error computed by the following

general formula:

a diff

2 2 where a and aTM were estimated as pooled variances from all

the setH of replicate values for each method, and n-^ and n£

are the number of replicates for methods A and B, respectively,

for the sample considered.

18

CS-ITA CS-ETA

0.058 0.198

0.028 0.026

0.000 0.000

0.028 0.028

-0.007 0.000

0.028 0.028

0.611 1.218

0.026 0.026

-0.050 -0.030

0.028 0.028

0.277 0.083

0.028 0.028

0.290 0.273

0.026 0.023

0.161 0.136

0.026 0.024
Table 4. Comparison of complete-solution and

ITA extraction procedures for soap

in SA samples

Sample

F-2 SA

GG-1 SA

Solprene 1205

F-l SA

PP-2 SA

Soap

Completesolution

%

ITA

extraction

%

0.00 0.00

0.07 0.07

0.44 0.30

0.56 0.50

0.62 0.46

19
Table 5. Analysis of rubbers, serums, washes,

and latexes

Sample

F-l SA

F-l AC

F-2 SA

F-2 ACGG-1 SA

GG-1 AC

GG-2 SA

GG-2 AC

GG-1N SA

GG-1N AC

GG-2N SA

GG-2N AC

PP-1 SA

PP-1 AC

PP-2 SA

PP-2 AC

1/

Latex

Organic acid

%

5.70

Total organic

1/

2/

5.27

5.38

5.16

5.17

6.62

6.61

acid in rubber, wash, and serumComplete -solution " ITA ~~ ETA

5.52

5.70

4.85

4.85

5.11

5.88

5.16

6.22

5.06

5.66

5.06

5.51

6.52

5.66

6.87

6.69

% %

5.32 5.18

5.33 4.96

4.56 4.62

4.49 3.85

4.98 4.97

4.92 4.45

4.59 3.90

4.80 4.38

5.13 5.13

5.14 4.94

4.68 4.90

5.03 4.97

6.20 6.21

4.66 3.89

6.72 6.61

5.63 3.95

Data for each procedure usually include the traces of organic acid

recovered from washes and serums added to that found in rubber, as well as organic acid as soap. The only exceptions are samples GG-1

SA, GG-1 AC, GG-2 SA, and GG-2 AC. Samples GG-1 SA and GG-1 AC

were not washed, and the washes of samples GG-2 SA and GG-2 AC were

inadvertantly discarded. The serums of GG-1 AC and GG-2 AC were

not tested. Since in practice the quantities involved are small,

their absence should not vitiate the comparisons.

2/— Latex not available.

20
Table 6. Comparison of complete -solution

and ITA extraction procedures for

AC sample si/

Sample

F-l AC

F-2 AC

GG-1 AC

GG-2 AC

GG-1N AC

GG-2N AC

PP-1 AC

PP-2 AC

— Values given are the percent of organic acid over

and below the total organic acid determined by CS

analysis of the respective SA rubbers, serums, and

washes. (See Table 5)

Complete -solution ITA extraction

% %

+0.18 -0.19

0.00 -0.36

+0.77 -0.19

+1.06 -0.36

+0.60 +0.08

+0.45 -0.03

-0.86 -1.86

-0.18 -1.24

21
Table 7. Comparison of methods of analysis for

stabilizers and bound styrene

Type of

stabilizer

Stabil izer Bound

ITA

%

2/

s tyrene—

Sample ITA

%

ASTMi/

%

ASTM

%

F-l SA PBNA 1.21 1.22 24.5 24.6

F-l AC PBNA 1.22 1.24 24.6 25.6

F-2 SA BLE 1.01 1.30 3.0 2.9

F-2 AC BLE .96 1.40 2.9 2.9

GG-1N SA PBNA 1.54 1.54 23.5 23.3

GG-1N AC PBNA 1.26 1.24 23.5 23.3

GG-2N SA Stalite 1.22 1.29 44.2 44.2

GG-2N AC Stalite 1.26 1.38 43.9 44.0

j^ASTM D 1416, Sections 42-48, Method A(l).

—Samples extracted according to appropriate procedures

given in this paper and in ASTM D 1416, Sections 25-29 (1).

22
Table 8. Comparison of thymol blue and meta -cresol

purple for the titration of soap and organic

acid in aqueous ITA

Sample

GG-1 SA

GG-2 SA

F-2 SA

6608 P

Solprene 1205

PP-2 SA

PP-1 SA

Soap Organic acid

TB

%

MCP

t

TB

%

MCP

%

0.04 0.10 - -

.05 .05 - -

- - 3.72 3.67

- - 4.61 4.51

.15 .22 - -

.15 .13 - -

.30 .31 - -

.29 .29 - -

.50 .51 5.40 5.39

.71 .74 6.31 6.27

23
Table 9. Study of systematic errors of titrations

(Relative and constant- type errors)

Aluminum Stearate

Titration Range

Calculated slope

Slope m from st

regression study

Standard error of

estimate of m

Solvent blank

Intercept b_ from

regression study

Standard error of b

Sodium Stearate Serums and Washes

33.46 ml/g

33.47 ml/g

0.22 ml/g

0.022 ml

-0.012 ml

-0.025 ml

Relative Error

33.25 ml/g

33.68 ml/g

0.51 ml/g

Constant Error

0.00 ml

-0.014 ml

0.010 ml

Rubber

33.25 ml/g

33.21 ml/g

0.07 ml/g

0.00 ml

-0.011 ml

0.006 ml

24
NBS TECHNICAL PUBLICATIONS

PERIODICALS NONPERIODICALS

JOURNAL OF RESEARCH reports National

Bureau of Standards research and development in physics, mathematics, chemistry, and engineering.

Comprehensive scientific papers give complete details of the work, including laboratory data, experimental

procedures, and theoretical and mathematical analyses. Illustrated with photographs, drawings, and

charts. Published in three sections, available separately: • Physics and Chemistry

Papers of interest primarily to scientists working in these fields. This section covers a broad range of physical and chemical research, with major emphasis on standards of physical measurement, fundamental

constants, and properties of matter. Issued six times

a vear. Annual subscription: Domestic, $9.50; for- eign, $11.75*. • Mathematical Sciences

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment; design,

numerical analysis, theoretical physics and chemistry, logical design and programming of computers

and computer systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic,

$5.00; foreign, $6.25*. • Engineering and Instrumentation

Reporting results of interest chiefly to the engineer

and the applied scientist. This section includes many

of the new developments in instrumentation resulting

from the Bureau's work in physical measurement,

data processing, and development of test methods.

It will also cover some of the work in acoustics,

applied mechanics, building research, and cryogenic

engineering. Issued quarterly. Annual subscription:

Domestic, $5.00; foreign, $6.25*.

TECHNICAL NEWS BULLETIN

The best single source of information concerning the Bureau's research, developmental, cooperative and

publication activities, this monthly publication is designed for the industry-oriented individual whose

daily work involves intimate contact with science and

technology

for engineers, chemists, physicists, re- search managers, product-development managers, and

company executives. Annual subscription: Domestic,

$3.00; foreign, $4.00*.

• Difference in price is due to extra cost of foreign mailing.

Applied Mathematics Series. Mathematical tables, manuals, and studies. Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) de- veloped in cooperation with interested industries,

professional organizations, and regulatory bodies. Special Publications. Proceedings of NBS conferences, bibliographies, annual reports, wall charts,

pamphlets, etc. Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities. National Standard Reference Data Series.

NSRDS provides quantitive data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality and methods for testing various industrial products. These standards are developed cooperatively with interested Government and industry groups

and provide the basis for common understanding of product characteristics for both buyers and sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other agency and

NBS-sponsored work) of limited or transitory interest. Federal Information Processing Standards Publications. This series is the official publication within

the Federal Government for information on standards

adopted and promulgated under the Public Law

89-306, and Bureau of the Budget Circular A-86

entitled, Standardization of Data Elements and Codes

in Data Systems.

CLEARINGHOUSE

The Clearinghouse for Federal Scientific and

Technical Information, operated by NBS, supplies

unclassified information related to Government-generated science and technology in defense, space, atomic energy, and other national programs. For

further information on Clearinghouse services, write: Clearinghouse

U.S. Department of Commerce

Springfield, Virginia 22151

Order NBS publications from: Superintendent of Documents

Government Printing Office

Washington, D.C. 20402
U.S. DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20230

OFFICIAL BUSINESS POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COM MERC




REYNOLDS

BINDERY, INC. HTjl1**11