ASTM D1926-00(2011)
(Test Method)Standard Test Methods for Carboxyl Content of Cellulose
Standard Test Methods for Carboxyl Content of Cellulose
SIGNIFICANCE AND USE
These test methods measure the amount of carboxyl groups present in wood or cotton linter pulp. Carboxyl groups are indicative of the surface charge of the pulp which is a very important quantity for use in the papermaking industry.
SCOPE
1.1 These test methods cover the determination of the carboxyl content, or ion-exchange capacity, of cellulose from any source. Two test methods are described, the sodium chloride-sodium bicarbonate method (1) and the methylene blue method (2). The test methods must be used within their limitations, and it must be recognized that there is no way of determining the accuracy of any method for the determination of carboxyl. The precision of the sodium chloride-sodium bicarbonate method is low in the lower range of carboxyl values. The methylene blue method can be used over the whole range of carboxyl values; it is especially useful in the low range. It is not applicable to the determination of carboxyl in soluble carbohydrate material. Although these test methods may be used to determine the ion-exchange capacity of unbleached pulps, the residual lignin will cause an undetermined error, especially the sulfonic acid groups in unbleached sulfite pulps (3).
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D1926 − 00 (Reapproved 2011)
Standard Test Methods for
Carboxyl Content of Cellulose
This standard is issued under the fixed designation D1926; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Significance and Use
3.1 These test methods measure the amount of carboxyl
1.1 These test methods cover the determination of the
groups present in wood or cotton linter pulp. Carboxyl groups
carboxyl content, or ion-exchange capacity, of cellulose from
are indicative of the surface charge of the pulp which is a very
any source. Two test methods are described, the sodium
important quantity for use in the papermaking industry.
chloride-sodium bicarbonate method (1) and the methylene
blue method (2). The test methods must be used within their
4. Purity of Reagents
limitations, and it must be recognized that there is no way of
4.1 Reagent-grade chemicals shall be used in all tests.
determining the accuracy of any method for the determination
Unless otherwise indicated, it is intended that all reagents shall
of carboxyl. The precision of the sodium chloride-sodium
conform to the specifications of the Committee on Analytical
bicarbonate method is low in the lower range of carboxyl
Reagents of the American Chemical Society, where such
values.Themethylenebluemethodcanbeusedoverthewhole
specifications are available. Other grades may be used, pro-
range of carboxyl values; it is especially useful in the low
vided it is first ascertained that the reagent is of sufficiently
range. It is not applicable to the determination of carboxyl in
high purity to permit its use without lessening the accuracy of
soluble carbohydrate material. Although these test methods
the determination.
may be used to determine the ion-exchange capacity of
unbleached pulps, the residual lignin will cause an undeter-
4.2 Unless otherwise indicated, references to water shall be
mined error, especially the sulfonic acid groups in unbleached understood to mean reagent water conforming to Specification
sulfite pulps (3).
D1193.
1.2 The values stated in SI units are to be regarded as
SODIUM CHLORIDE-SODIUM BICARBONATE
standard. No other units of measurement are included in this
METHOD
standard.
5. Summary of Test Method
1.3 This standard does not purport to address all of the
5.1 In the sodium chloride-sodium bicarbonate method the
safety concerns, if any, associated with its use. It is the
specimen is de-ashed with hydrochloric acid, washed, soaked
responsibility of the user of this standard to establish appro-
in sodium chloride-sodium bicarbonate solution, filtered, and
priate safety and health practices and determine the applica-
an aliquot of the filtrate titrated with 0.01 N hydrochloric acid
bility of regulatory limitations prior to use.
to a methyl red end point. The difference between the concen-
tration of the filtrate and of the sodium chloride-sodium
2. Referenced Documents
bicarbonate solution is a measure of the ion-exchange capacity
2.1 ASTM Standards:
of the cellulose.
D1193 Specification for Reagent Water
6. Reagents
6.1 Hydrochloric Acid, Standard (0.01 N)—Prepare and
standardize a 0.01 N solution of hydrochloric acid (HCl).
These test methods are under the jurisdiction of ASTM Committee D01 on
Paint and Related Coatings, Materials, and Applications and are the direct
6.2 Hydrochloric Acid (1 + 99)—Dilute 1 volume of con-
responsibility of Subcommittee D01.36 on Cellulose and Cellulose Derivatives.
centrated HCl (sp gr 1.19) with 99 volumes of water.
Current edition approved June 1, 2011. Published June 2011. Originally
approved in 1961. Last previous edition approved in 2006 as D1926 – 00 (2006).
DOI: 10.1520/D1926-00R11.
2 4
The boldface numbers in parentheses refer to the list of references at the end of Reagent Chemicals, American Chemical Society Specifications American
these test methods. Chemical Society, Washington, DC. For suggestions on the testing of reagents not
For referenced ASTM standards, visit the ASTM website, www.astm.org, or listed by the American Chemical Society, see Analar Standards for Laboratory
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Standards volume information, refer to the standard’s Document Summary page on and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
the ASTM website. MD.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1926 − 00 (2011)
6.3 Methyl Red Indicator Solution. carboxyl content. For pulps varying in carboxyl content from
5.75 to 0.40 mmol/100 g pulp, the repeatability (intralabora-
6.4 Sodium Chloride-Sodium Bicarbonate Solution—
tory) expressed as a percent coefficient of variance was 2.2 to
Dissolve 5.85 g of sodium chloride (NaCl) and 0.84 g of
8.1 %, respectively. Interlaboratory results based on different
sodium bicarbonate (NaHCO ) in water and dilute to 1 L.
materials and various test methods gave percent coefficient of
6.5 Sodium Hydroxide Solution (0.4 g/L)—Dissolve 0.4 g of
variance of 9.0 to 33 % for these same materials.
sodium hydroxide (NaOH) in water and dilute to 1 L.
10.2 No statement on bias can be made as no suitable
7. Procedure
reference material exists for determining bias.
7.1 Condition the specimen in the atmosphere near the
METHYLENE BLUE METHOD
balance for at least 20 min before weighing duplicate portions
of 2.5 6 0.01 g. At the same time, weigh specimens for the
11. Summary of Test Method
determination of moisture. Disintegrate the specimen in water,
11.1 In the methylene blue method the specimen is treated
filter through fritted glass, and disperse to about 1 % consis-
with 0.0002 M methylene blue solution buffered to a pH of 8
tencyinHCl(1 + 99)atroomtemperature.After2hcollectthe
with diethylbarbituric acid (barbital). The decrease in methyl-
specimen on a fritted-glass filter funnel and wash with water
eneblueconcentration,measuredphotometrically,isafunction
saturated with carbon dioxide (CO ). Continue the washing
of the ion-exchange capacity of the cellulose.
until the filtrate, after boiling, does not require more than 1 or
2dropsofNaOHsolutiontogiveanalkalinecolorwithmethyl
12. Apparatus
red.
12.1 Spectrophotometer or Filter Photometer, capable of
7.2 Weigh the wet pulp pad, transfer it immediately to a
measuring absorbance near 620 mm.
250-mL glass-stoppered Erlenmeyer flask, add 50 mL of the
12.2 Shaker or Mixer for agitating the specimens in the
NaCl-NaHCO solution with a pipet, and shake to obtain a
methylenebluesolution.Awheelorrod,towhichthespecimen
homogeneous slurry (Note 1).Allow the mixture to stand for 1
vials can be attached, that rotates at about 15 r/min, has proven
h at room temperature. Filter through a clean, dry, fritted glass
satisfactory.
funnel, pipet a 25-mLaliquot of the filtrate into an Erlenmeyer
flask, and titrate with 0.01 N HCl, using methyl red solution as
12.3 Centrifuge, capable of settling the cellulose from the
an indicator. When the first change in color occurs, boil the
methylene blue solution.
solution for about 1 min to expel the carbon dioxide and
continue the titration to a sharp end point.
13. Reagents
13.1 Buffer, Stock Solution—Dissolve 1.151 g of diethylbar-
NOTE 1—If the cation-exchange capacity is very low, use a solution
containing about 5.85 g of NaCl and 0.42 g of NaHCO per litre. It is
3 bituric acid (barbital) in water, add the equivalent of 0.16 g of
importantthattheexcessofNaHCO belargeenoughthatthepHdoesnot
sodium hydroxide using a standard solution and buret, and
fall below 7.0.
dilute with water to 1 L in a volumetric flask.
7.3 Pipet 25 mL of the NaCl-NaHCO solution into an
13.2 Hydrochloric Acid (1 + 99)—Dilute 1 volume of con-
Erlenmeyer flask and titrate as described in 7.2.
centrated hydrochloric acid (HCl, sp gr 1.19) with 99 volumes
8. Calculation of water.
13.3 Methylene Blue, Stock Solution (0.002 M)—Dissolve
8.1 Calculate the cation-exchange capacity, c, of the speci-
men in milliequivalents per 100 g as follows: 0.640 g of methylene blue in water, making allowance for
moisture, and dilute to 1 L in a volumetric flask.
av 2
c 5 b 2 a 2 (1)
S D
50 G
NOTE 2—Information on the determination of the purity of methylene
blue is given in the literature (5).
where:
13.4 Methylene Blue—Buffer Solution (0.0002 M)—Mix 1
G = weight of oven-dry specimen, g,
volume of methylene blue stock solution with 1 volume of
v = weight of water in the
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