ASTM D6188-97(2003)
(Test Method)Standard Test Method for Viscosity of Cellulose by Cuprammonium Ball Fall
Standard Test Method for Viscosity of Cellulose by Cuprammonium Ball Fall
SIGNIFICANCE AND USE
This test method is suitable for use as a rapid control test for pulp manufacture or for careful determination of the viscometric molecular weight of purified cotton or wood derived pulps.
This test method is applicable over a very large range of cellulose molecular weights because seven sample sizes are defined. (Sample weights are reduced as cellulose molecular weight increases.)
Cotton and high molecular weight pulps may be difficult to dissolve. (Warning—This test method is only valid if the sample dissolves completely without gels.)
SCOPE
1.1 This test method describes the procedure for estimating the molecular weight of cellulose by determining the viscosity of cuprammonium (CuAm) solutions of cellulosic materials, such as wood pulp, cotton, and cotton linters. This test method is suitable for rapid, routine testing of large numbers of samples with high accuracy and precision. This test method updates and extends the procedure reported by the American Chemical Society (ACS).
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
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:D6188–97(Reapproved2003)
Standard Test Method for
Viscosity of Cellulose by Cuprammonium Ball Fall
This standard is issued under the fixed designation D 6188; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope ized water. Samples are either squeezed or pressed to 20 to
40 % consistency as necessary, then passed through a picker.
1.1 This test method describes the procedure for estimating
4.2 The wet pulp sample is dried with air whose maximum
the molecular weight of cellulose by determining the viscosity
temperature is 120°C and weighed under conditions that cause
of cuprammonium (CuAm) solutions of cellulosic materials,
the specified quantity of sample to be obtained. The weighed
such as wood pulp, cotton, and cotton linters. This test method
sample is placed in a glass 120-mL (4-oz) bottle, steel shot are
is suitable for rapid, routine testing of large numbers of
added, a vacuum is pulled on the bottle, and 97 mL of
samples with high accuracy and precision. This test method
cuprammonium solution are added to the bottle. The bottle is
updates and extends the procedure reported by the American
placed on a shaker to mix and dissolve the pulp sample in the
Chemical Society (ACS) .
CuAm solution.
1.2 The values stated in SI units are to be regarded as the
4.3 The dissolved sample is transferred to a glass viscosity
standard. The values given in parentheses are for information
tube. The tube is mounted vertically with a bright light behind
only.
the tube. A special glass bead (see 7.13) is dropped into the
1.3 This standard does not purport to address all of the
center of the solution in the tube. The time is measured in
safety concerns, if any, associated with its use. It is the
seconds(s)fortheglassbeadtopassbetweentwomarksonthe
responsibility of the user of this standard to establish appro-
tube which are 20 cm apart.This time (s) is the uncorrected “as
priate safety and health practices and determine the applica-
is” cuprammonium ball fall viscosity. The temperature of the
bility of regulatory limitations prior to use.
solution is determined, and the correction factor for this
2. Referenced Documents
temperature is multiplied by the uncorrected viscosity of the
sample. This gives the “as is” cuprammonium ball fall viscos-
2.1 ASTM Standards:
ity value.
D 1193 Specification for Reagent Water
4.4 The “as is” viscosity value for the sample size used is
D 1695 Terminology of Cellulose and Cellulose Deriva-
converted to the 2.50-g ACS viscosity by the equations
tives
provided in 14.4. The viscosity is reported in “ACS seconds”.
E 438 Specification for Glasses in Laboratory Apparatus
5. Significance and Use
3. Terminology
5.1 Thistestmethodissuitableforuseasarapidcontroltest
3.1 This standard terminology of cellulose and cellulose
for pulp manufacture or for careful determination of the
derivatives, see Terminology D 1695.
viscometric molecular weight of purified cotton or wood
4. Summary of Test Method
derived pulps.
5.2 This test method is applicable over a very large range of
4.1 An in-process or finished product sample is taken. All
cellulose molecular weights because seven sample sizes are
cooking and bleaching chemicals must be washed out of
defined. (Sample weights are reduced as cellulose molecular
in-process samples. Dry samples are wetted with demineral-
weight increases.)
5.3 Cotton and high molecular weight pulps may be difficult
This test method is under the jurisdiction of ASTM Committee D01 on Paint
to dissolve. (Warning—This test method is only valid if the
and Related Coatings, Materials, andApplications and is the direct responsibility of
sample dissolves completely without gels.)
Subcommittee D01.36 on Cellulose and Cellulose Derivatives.
Current edition approved May 10, 2003. Published June 2003. Originally
6. Interferences
approved in 1997. Last previous edition approved in 1997 as D 6188 - 97.
Carver et al., “A Standard Method for Determining the Viscosity of Cellulose
6.1 High temperature drying of pulp causes a reduction in
in Cuprammonium Hydroxide,” Industrial and Engineering Chemistry, Analytical
viscosity. Therefore, limit the maximum temperature of the air
Edition, Vol 1, No 1, 1929, pp. 49-51.
3 used to dry the sample to 120°C and the maximum drying time
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 6.03. to 20 min to keep viscosity loss to a minimum. All in-process
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6188–97 (2003)
TABLE 2 Effect of Volume Errors on Viscosity Error
samples must be washed to remove cooking and bleaching
chemicals,becausethepresenceofchemicalswhiledryingwill Volume Percent Viscosity Error
increase viscosity loss.
Error, (mL) Low Volume High Volume
6.2 The weight of sample used with this test method is
1 4.0 3.9
critical. The effect of incorrect sample weight on viscosity is 2 8.2 7.6
5 21.8 17.9
shown in Table 1.
10 48.3 32.6
6.2.1 If the pulp sample is properly weighed but a small
amount fails to dissolve, the viscosity will be incorrect by at
least the percentage of the sample that failed to dissolve.
TABLE 3 Temperature Correction Factors
6.3 The volume of cuprammonium solution used is also
Temperature Correction Factor
critical.The effect of incorrect volume on viscosity is shown in
Error, °C Low Temperature High Temperature
Table 2.
1 0.971 1.030
6.4 Use the temperature correction factors given in Table 3
2 0.943 1.061
to correct the cuprammonium viscosities to 25°C, assuming
3 0.915 1.093
4 0.888 1.126
that a 1°C increase causes a 3 % decrease in the measured
5 0.863 1.159
viscosity of the solution. Correction for temperatures off by
more than 5°C is not recommended. Samples should be
retested, ensuring than the CuAm solution is within tempera-
ture limits.
7. Apparatus
7.1 Testing Laboratory, maintained at 25 6 2°C.
7.2 Picker, suitable for shredding pulp without damaging it.
The picker must have provisions that permit sample remaining
afterpickingiscompletedtobeblownoutwithcompressedair.
7.3 Drier, suitable for pulp sample that dries the pulp with
hot air whose temperature is never permitted to get higher that
120°C.
7.4 Analytical Balance, capable of weighing to 60.001 g.
7.5 Bottles, wide mouth, glass, for use with an approxi-
mately No. 5 rubber stopper, and with a capacity of at least 120
mL (4 oz). The type of bottle must be selected such that it is
suitable for dissolving pulps in cuprammonium solution as
specified in this test method.
7.6 Steel Balls, chrome alloy, Grade 25, 3.2-mm ( ⁄8-in.)
diameter.
7.7 Automatic Pipet, special made, capable of delivering 97
61mLofCuAmsolution,whichispartofthecuprammonium
solution filling system (see Fig. 1).
7.8 Rubber Stopper Assembly (see Fig. 2).
7.9 VacuumSource, capable of pulling a vacuum of 686 mm
FIG. 1 Solution Filling System
Hg.
7.10 Shaker, capable of shaking bottles of cuprammonium
7.12 Viscosity Tube, specially made (see Fig. 4).
solution containing pulp. The shaker is to hold the bottles in a
7.13 Glass Viscosity Beads, for ACS cuprammonium vis-
horizontalposition,anditsdesignandoperationshouldbesuch
cosity determination. These beads are to be ground to a
that in-process pulps will be completely dissolved after 20 min
diameter that causes the viscosity of each second of bead fall
of shaking.
time in cuprammonium-cellulose solution to equal 22 cP. (This
7.11 Transfer Assembly, for transferring the
will mean that a sample that has a bead fall time of 10 s will
cuprammonium-cellulose solution from the bottle to the vis-
have a viscosity of 220 cP, and a sample that has a bead fall
cosity tube (see Fig. 3).
time of 50 s will have a viscosity of 1100 cP). Since the density
of various shipments of glass beads will vary somewhat, the
TABLE 1 Effect of Weight Errors on Viscosity Error
diameter of the beads will have to be varied to compensate for
Pulp Weight Percent Viscosity Error
the variation in the density of the glass. Generally the beads
Error, % Underweight Overweight
will be about 3.3 mm in diameter, and they will weigh about
1 3.8 3.9 0.046 g.
2 7.4 8.0
7.14 Moisture Balance—Apparatus to determine the dry
5 17.4 21.1
weight of cellulose.
10 31.8 45.6
7.15 pH Meter.
D6188–97 (2003)
10.2 If the sample is an in-process pulp sample, thoroughly
wash out any process chemicals (acids, bases, or bleach),
which may be present. Drain the excess water out of the wet
pulp sample (see 10.3).
10.3 If any sample is above 40 % consistency, wet it with
demineralized water. If the sample is below 20 % consistency,
hand squeeze it or press it until the consistency is between 20
to 40 %.
10.4 Seven sample sizes are authorized by this test method.
These sizes, in g, are 0.85, 1.00, 1.25, 1.50, 2.20, 2.40, and
3.50. Select the sample size which will be used for the test.
Generally, select a sample size which will give a CuAm
viscosity between 15 and 60 s. Never use a sample size that
gives a CuAm viscosity of less than 10 or more than 100 s. (If
a test result is not within these limits, a new sample size should
be selected.)
10.5 In order to ensure that traces of the last sample passed
through the picker will not contaminate the new sample, pick
enough of the present sample that an amount equal to at least
1 g of dry pulp has passed through the picker. Discard all of
FIG. 2 Rubber Stopper Assembly In Bottle
this portion of the sample. Then, pick enough of the sample to
carry out the viscosity test. Immediately after each sample has
been passed through the picker, turn on the compressed air
7.16 Viscosity Tube Holder/Lighting Assembly—This de- going into the picker for at least 2 s. (This is to blow out as
vice holds the viscosity tube vertically with a bright light much as possible of the sample before it has time to dry and
behind the tube so that the bead falling through the cupram- stick to the surfaces of the picker.)
monium solution can be easily seen. 10.6 Dry the picked sample with air as follows:
7.17 Bead Centering Apparatus—This consists of a small 10.6.1 Temperature does not exceed 120°C, and
corrosion resistant funnel topped tube having an internal
10.6.2 Time does not exceed 20 min.
diameter just sufficient to permit the beads to fall through 10.7 Weigh the sample in a manner that will consistently
freely.
give weighed samples which contain dry pulp weights within
7.18 Timer, accuracy/precision:630sover1h. the specifications of Table 4.
7.19 PlasticSieve,with0.250mmopenings,thesameasUS
10.8 More accurate and precise results will be obtained if
Alternate No. 70, Tyler 60 mesh sieve. the pulp sample is conditioned to an equilibrium moisture
7.20 Plastic Container, 2500 to 3500 mL graduated poly- content and the consistency of the sample determined by
ethylene beaker with handle. moisture balance. This modification provides better weight
control, but is not suited for rapid turn-around process control.
8. Reagents and Materials
11. Calibration and Standardization
8.1 Cuprammonium Solution, containing 20 6 1 g/L of
11.1 Select control pulp samples for which a relatively large
copper (expressed as copper) and 200 6 2 g/L of ammonium
supply is available. Ensure that the cuprammonium viscosities
hydroxide (expressed as ammonium).
of these samples are sufficiently different so that different
8.2 Water, potable.
sample weights are required. Determine the cuprammonium
8.3 Water, reagent (in accordance with Specification
viscosity of each sample using exactly the same procedure that
D 1193) with an electrical resistance of at least 1 000 000
would be used for testing unknown samples. Record the
V-cm. This water is used to determine the pH of the film left
cuprammonium viscosity in a log book. Keep a separate
after acid washing.
control chart of the cuprammonium viscosity values (or loga-
rithm of the values) for each of the samples. Measure these
9. Hazards
control samples at a convenient frequency.
9.1 CuAmsolutioniscorrosive,andthusharmfultotheskin
and eyes. Wear safety glasses or goggles while working with 12. Conditioning/Preparation
this solution. Gloves and laboratory coat or chemical apron are
12.1 Conditioning of dry samples to an equilibrium mois-
recommended.
ture content will give more accurate and precise results.
12.2 It is usually necessary to treat bottles, stopper assem-
10. Sampling
blies, and viscosity tubes with a solution of sulfuric acid to
10.1 The sample for this test may consist of a wet pulp or a coagulate the CuAm-cellulose solution before this apparatus
dry, finished product sample. Take a representative portion of can be cleaned. (Warning—It is very important that this
the pulp sample that contains at least 10 and not more than 25 apparatus be thoroughly washed to remove all of the sulfuric
g of dry pulp. acidbeforeitisdried.Ifthereisasmallamountofsulfuricacid
D6188–97 (2003)
FIG. 3 Solution Transfer Assembly In Bottle
remaining on the surface of any apparatus when it dries, a thin 13.5 Place a hose clamp on the rubber hose on the stopper
film of sulfuric acid will remain on the surface of the assembly to prevent air from entering the bottle (see Fig. 2),
apparatus.) and disconnect the hose on the stopper assembly from the
filling assembly. Place the bottle in the shaker so that the bottle
13. Procedure
is in a horizontal position, and shake for 25 6 3 min. Stop the
13.1 Carry out the following operations in a room main- shaker and remove the bottle. Observe the bottle to see if there
tained at 25 6 2°C (77 6 3.6°F). is any indication of undissolved material in the solution. If
13.2 This test method defines clean, dry bottles; clean, dry there is any indication of undissolved material, discard solu-
stopper assemblies; and clean, dry viscosity tubes as ones that tion, and report that the sample did not dissolve. If there is no
appear to be clean, do not have water or water droplets in or on indication of undissolved material, point the open end of the
them, and that will deliver water with a pH not lower than 5.0 rubber hose on the stopper assembly away from you and
or higher than 7.0 when their surfaces are washed with remove the hose clamp. (Sometimes, some of the
demineralized water. cuprammonium/ cellulose solution is sprayed out of the rubber
13.3 In carrying out this part of this test, note that CuAm hose when the hose clamp is remove
...
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