ISO 5351:2004

INTERNATIONAL ISO
STANDARD 5351
First edition
2004-06-15
Pulps — Determination of limiting
viscosity number in cupri-
ethylenediamine (CED) solution
Pâtes — Détermination de l'indice de viscosité limite en utilisant une
solution de cupri-éthylènediamine (CED)

Reference number
©
ISO 2004
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©  ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle . 2
5 Reagents and materials. 2
6 Apparatus and materials . 3
7 Calibration of viscometers. 5
8 Sampling and preparation of sample. 6
9 Procedure. 6
10 Calculation. 7
11 Precision . 8
12 Test report. 9
Annex A (normative) Preparation and analysis of the cupri-ethylenediamine solution . 10
Annex B (normative) Values of [η] × c corresponding to different values of the viscosity ratio,
η (η/η ) . 14
ratio 0
Annex C (informative) Calculation of degree of polymerization. 16
Bibliography . 17

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 5351 was prepared by Technical Committee ISO/TC 6, Paper, board and pulps, Subcommittee SC 5,
Test methods and quality specifications for pulps.
It cancels and replaces ISO 5351-1:1981, which has been technically revised.
iv © ISO 2004 – All rights reserved

Introduction
The viscosity (or dynamic viscosity), symbol η, of a fluid is defined by the Newtonian equation
 (1)
τ=ηγ
where
τ is the shear stress;
η is the viscosity;

γ is the velocity gradient dv/dz (v being the velocity of one plane relative to the other and z the co-
ordinate perpendicular to the two planes).
In non-Newtonian behaviour, normally the case with high molecular mass polymer solutions such as cellulose,
the ratio of the shear stress to the velocity gradient varies with the shear stress.
The data required for evaluation of the limiting viscosity number of pulp in dilute solutions (for terms and
definitions, see Clause 3) are derived by means of a capillary-tube viscometer. The results of these
measurements are seriously affected by the shear rate.
The concentration c of the pulp is therefore chosen so that, if multiplied by the limiting viscosity number [η], it
gives a product [η] × c equal to 3,0 ± 0,4, corresponding to a viscosity ratio η/η equal to 6 to 10. The
−1
determination is then carried out at a reproducible shear rate G of (200 ± 30) s ; this involves the
employment of two viscometers, one for calibration and one for the measurement of the viscosity of the pulp.
The viscosity of a pulp in CED solution gives an indication of the average degree of polymerization (DP) of the
cellulose (see Annex C). Such a measurement therefore gives a relative indication of the degree of
degradation (decrease in cellulose molecular mass) resulting from the pulping and/or bleaching process.
Caution should be taken in drawing conclusions regarding strength properties of the pulp strictly from viscosity
measurements unless previous investigation has identified the relationship. A direct relationship between pulp
strength and viscosity has not been found.

INTERNATIONAL STANDARD ISO 5351:2004(E)

Pulps — Determination of limiting viscosity number in cupri-
ethylenediamine (CED) solution
1 Scope
This International Standard specifies a method which yields a number that is an estimate of the limiting
viscosity number of pulp in a dilute cupri-ethylenediamine (CED) solution.
This method is primarily applicable to CED-soluble samples of bleached chemical pulps but can also be
applied to any kind of pulp that dissolves completely in CED solution.
NOTE 1 The results can be used to estimate the extent of cellulose degradation caused by cooking or bleaching.
Results obtained with samples containing appreciable amounts of substances other than cellulose must be interpreted
with caution, however.
NOTE 2 In the strictest sense, viscosity measurement procedures are applicable only to the polysaccharide fraction of
the sample. This notwithstanding, viscosity measurement can usually be used to obtain a result on unbleached pulps
having lignin contents of up to 4 %, because most of these pulps can be successfully dissolved in CED. However, the
simple fact that an unbleached pulp can be dissolved in CED does not mean the results are valid. In summary, viscosity
results for pulps containing more than 0,5 % of lignin are not acceptable for technical specification purposes.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 638, Pulps — Determination of dry matter content
ISO 7213, Pulps — Sampling for testing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
shear rate
G
velocity gradient of a fluid layer, parallel to the direction of flow, at the periphery of the capillary, defined by the
equation
4V
G= (2)
πrt
f
where
V is the volume between two arbitrary calibration marks on the viscometer, in millilitres;
r is the radius of the capillary tube, in centimetres;
t is the efflux time of the fluid, in seconds.
f
3.2
viscosity ratio
(formerly called relative viscosity)
η
ratio
ratio of the viscosities η and η of a polymer solution of stated concentration and of the solvent, respectively,
at the same temperature, given by
η
η = (3)
ratio
η
NOTE It is dimensionless.
3.3
viscosity relative increment
viscosity ratio (3.2) minus one:
η−η
η
−=1 (4)
ηη
NOTE It is dimensionless.
3.4
viscosity number
VN
ratio of the viscosity relative increment (3.3) to the polymer concentration c, expressed in grams per millilitre,
in the solution:
η−η
VN= (5)
η ×c
NOTE It is measured in millilitres per gram.
3.5
limiting viscosity number
[η]
limiting value of the viscosity number (3.4) at infinite dilution:

ηη−
η = lim (6)


η ×c
c→0
0
NOTE 1 It is measured in millilitres per gram.
NOTE 2 In the literature, the term intrinsic viscosity is often used and is equal to the limiting viscosity number. There is
no general conversion factor between the limiting viscosity number in ml/g and other viscosities, determined by other
methods and expressed in mPa⋅s (see [7]).
4 Principle
Measurement of the times of efflux of the diluted solvent and the pulp solution through a capillary-tube
viscometer at a specified concentration at 25 °C. Calculation by Martin’s formula (see [9]) of the limiting
viscosity number from these measurements, and from the known concentration of the solution.
5 Reagents and materials
Use only chemicals of recognized analytical grade and only distilled or deionized water.
2 © ISO 2004 – All rights reserved

5.1 Cupri-ethylenediamine (CED) solution, c(CED) = (1,00 ± 0,02) mol/l, saturated with copper(ll)
hydroxide, for convenience referred to as CED solution.
The solution contains 1,0 mol of copper and 2,0 mol of ethylenediamine per litre. It is commercially available,
or may be prepared and analysed as described in Annex A.
NOTE By reason of allergens, avoid contact of skin with CED and ethylenediamine solutions. Ethylenediamine is
volatile, and repeated exposure may lead to severe respiratory allergic reactions with subsequent sensitization. Cupri-
ethylenediamine solutions should not be pipetted by mouth. CED solution is also environmentally harmful, and it is
recommended that a suitable destruction procedure be used before disposal.
5.2 Glycerol, solution in water, c(C H O ) = 65 % (by mass), having a viscosity of about 10 mPa⋅s.
3 8 3
5.3 Nitric acid (HNO ), dilute solution for cleaning the pieces of copper wire (6.4).
5.4 Reagents for calibrating capillary-tube viscometers equipped with an automatic time-recording
device.
As specified in the manufacturer's instructions.
6 Apparatus and materials
Ordinary laboratory apparatus and the following:
6.1 Capillary-tube viscometers (6.1.1 and 6.1.2), each with a water jacket connected to a constant-
temperature bath (6.3). Two different viscometers are required because of the great difference between the
viscosities of the test solution and the solvent. Suitable viscometers are shown in Figure 1.
NOTE Viscometers without a water jacket may be used if measurement is made while the viscometer is immersed in
the constant-temperature bath.
Capillary-tube viscometers equipped with an automatic time-recording device may be used provided they
comply with this International Standard and give similar results.
Clean the viscometers by rinsing with water and acetone. If any residual material remains after cleaning, clean
again with a sulfuric acid based cleaning solution designed for use with laboratory glassware. Soak
particularly dirty tubes overnight or longer in this cleaning solution to remove all traces of contaminants. After
cleaning, drain all cleaning solution from the tube, rinse well with water and acetone and dry.
6.1.1 Capillary-tube viscometer for calibration purposes, with an efflux time of about 40 s for the
0,5 mol/l CED solution used for calibration.
NOTE The efflux time of the viscometer for distilled or deionized water will be about 60 s.
6.1.2 Capillary-tube viscometer for determination of limiting viscosity number at constant shear rate,
−1
with an efflux time of about 100 s for a solution of η/η = 8,4 at a shear rate (see 3.1) of (200 ± 30) s .
NOTE Solutions of polymers of high relative molecular mass are usually non-Newtonian. Their viscosity decreases
as the shear rate (or in the present case the flow rate) increases. To avoid this complication, this International Standard
−1
specifies that the viscosity be determined at a shear rate of (200 ± 30) s . The dimensions of the viscometer (see
Figure 1b) are such that, for a solution of viscosity 10 mPa⋅s, the efflux time is about 90 s and the maximum shear rate
−1
(see 3.1) is then within the range (200 ± 30) s .
Dimensions in millimetres
a)  Viscometer for calibration b)  Viscometer for determining viscosities of
test solutions
Key
1 volume 1,0 ml or 2,0 ml
2 volume 1,0 ml
Figure 1 — Capillary-tube viscometers
6.2 Dissolving bottles, capacity approximately 52 ml, designed so that, when the bottle is filled with 50 ml
of test solution, the remaining air can be expelled by squeezing the bottle.
A polyethylene bottle with screw cap and rubber sealing ring can be used. Some practice will enable the
analyst to expel the air and close the bottle with the screw cap in one operation. The air may also be expelled
by a current of nitrogen.
If the pulp does not dissolve readily, use a flat-sided bottle.
6.3 Constant-temperature bath, capable of being maintained at (25 ± 0,1) °C, capable of accommodating
the dissolving bottles (6.2) and provided with a pump for circulating the water through the jackets of the
viscometers (6.1.1 and 6.1.2).
6.4 Pieces of copper wire, approximately 3 mm in diameter and between 10 mm and 20 mm long.
Clean the pieces of copper wire regularly with dilute nitric acid, rinsing them thoroughly afterwards with
distilled or deionized water and letting them dry.
4 © ISO 2004 – All rights reserved

6.5 Balance, accurate to ± 0,1 mg.
6.6 Timing device, capable of being read to the nearest 0,1 s.
6.7 Shaker or magnetic stirrer, for dissolving the test portion.
7 Calibration of viscometers
7.1 Bring the temperature of the various calibration liquids (see below) to 25 °C and the viscometers (6.1.1
and 6.1.2) to (25,0 ± 0,1) °C.
7.2 Use the viscometer specified in 6.1.1 (see Figure 1a) as the calibration viscometer to measure the
efflux times, in seconds, as described in 9.4, for
a) distilled or deionized water, t ;
w
b) glycerol solution (5.2), t ;
c
c) 0,5 mol/l CED solution, prepared by mixing equal volumes of distilled or deionized water and 1 mol/l CED
solution (5.1), t .
s
In each case, make at least two measurements and calculate the mean.
The ratio of the efflux time for the CED solution to that of distilled water, t /t , shall lie between 1,27 and 1,29.
s w
7.3 In the same way, measure the efflux time of the glycerol solution (5.2) in the viscometer to be calibrated
(6.1.2) (see Figure 1b). Calculate the viscometer factor f and the viscometer constant h using the equations
t
c
f = (7)
t
v
f
h= (8)
t
s
where
t is the efflux time, in seconds, of the glycerol solution in the calibration viscometer (6.1.1) (see
c
Figure 1a);
t is the efflux time, in seconds, of the glycerol solution in the viscometer to be calibrated (6.1.2) (see
v
Figure 1b);
t is the efflux time, in seconds, of 0,5 mol/l CED solution in the calibration viscometer (6.1.1) (see
s
Figure 1a).
The viscometer factor f is an apparatus constant and the viscometer constant h is dependent upon the solvent
(CED solution) used. Consequently, h shall be determined each time a fresh CED solution is used.
7.4 If viscometers with an automatic timing device are used, carry out the calibration in accordance with the
manufacturer's instructions.
8 Sampling and preparation of sample
If the test is being made to evaluate a pulp lot, sampling shall be carried out in accordance with ISO 7213. If it
is not, report the source of the sample and, if possible, the sampling procedure used.
Take a sample corresponding to approximately 10 g of oven-dry mass. Examine the pulp sample. If shives are
present, remove them by hand using a pair of tweezers or suspend the sample in water and remove the
shives by screening. If shives have been removed from the sample, this shall be stated in the test report. If it
is expected that the pulp will not disintegrate easily when the test solution is prepared (see 9.3), disintegrate
the sample in water in a suitable apparatus and form thin sheets in a Büchner funnel. Allow the pulp sample or
the prepared sheets to dry at room temperature overnight (drying can also be performed at an elevated
temperature, but not above 60 °C as over-drying can lower the viscosity). Tear the dry sample into small
pieces by hand, wearing gloves, and using a pair of tweezers if convenient. Do not cut the dry sample or use a
mechanical shredder because the viscosity is likely to be lowered as a result of this process of disintegration.
9 Procedure
9.1 Choice of concentration of solution
If the approximate value of the limiting viscosity number of the sample is not known, use a solution of
concentration between 125 mg/50 ml and 150 mg/50 ml. If the limiting viscosity number obtained is not within
the range prescribed by Table 1 for that concentration, adjust the concentration accordingly.
Table 1 — Concentration c to be used, as a function of the limiting viscosity number [η]
which will be measured
Limiting viscosity Quantity of
Concentration, c
number, [η] sample
g/ml
ml/g mg/50 ml
< 400 250 0,005
400 to 650 250 0,005
651 to 850 200 0,004
851 to 1 100 150 0,003
1 101 to 1 400 120 0,002 4
For samples of very high limiting viscosity number, the viscosity ratio is markedly dependent upon the shear
−1
rate. If a shear rate of 200 s is to be obtained in the viscometer, it is necessary to use pulp concentrations
selected in such a way that the measurements are made at exactly the same viscosity ratio. For pulps with a
−1
limiting viscosity number of less than 1 100 ml/g, shear rates of (200 ± 30) s and values for [η] × c of
3,0 ± 0,4 are allowable as the error in the result will not exceed 2 %. For pulps with a limiting viscosity number
of more than 1 100 ml/g, the error will be considerably larger if these tolerances are allowed. Accordingly, for
accurate determinations at these high viscosities, it is necessary to select pulp concentrations such that the
product [η] × c is as close to 3,0 as possible and in no case outside the range 3,0 ± 0,1. If the approximate
viscosity of the sample is unknown, an exploratory determination shall first be made to enable the correct
concentration to be selected.
9.2 Weighing of test portion
Weigh the chosen amount of sample, to an accuracy of ± 0,5 mg into a dissolving bottle (6.2). At the same
time, weigh out a separate test portion for the determination of the dry-matter content in accordance with
ISO 638 or any other method for determination of dry-matter content giving similar results.
Make sure that the test portions taken are representative of the sample received.
Carry out the determination in duplicate.
6 © ISO 2004 – All rights reserved

9.3 Preparation of test solution
Using a pipette, add 25,0 ml of distilled or deionized water to the test portion, together with 5 to 10 pieces of
copper wire (6.4) if using a shaker (see 6.7) or a stirrer bar if using a magnetic stirrer. Close the bottle, and
shake or mix until the test portion has completely disintegrated.
Add 25,0 ml of CED solution (5.1) and expel all of the remaining air by squeezing the bottle. Re-close the
bottle, and shake or stir again in the shaker or magnetic stirrer until the test portion is completely dissolved.
Cold-alkali-treated pulps, and unbleached pulps of high viscosity, may sometimes be difficult to dissolve. In
such cases, dissolution is facilitated if swelling is prevented by first dissolving the pulp in a solution of lower
CED concentration. Consequently, prepare a slurry of th
...