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Ref. No. : ISO/R 692-1968 (E)
IS0
I N T E R N AT I O N A L O R G A N I Z AT1 O N FOR STAND AR D I Z AT1 O N
IS0 RECOMMENDATION
R 692
PU LPS
DETERMINATION OF ALKALI SOLUBILITY
1st EDITION
March 1968
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 692, Aslps - Determinution of alkali solubility, was drawn up by
Technical Committee ISOlTC 6, Paper, board und pulps, the Secretariat of which is held by the
Association Française de Normalisation (AFNOR).
Work on this question by the Technical Committee began in 1962 and led, in 1964, to the
adoption of a Draft IS0 Recommendation.
In December 1965, this Draft IS0 Recommendation (No. 886) was circulated to all the IS0
Member Bodies for enquiry. It was approved, subject to a few modifications of an editorial nature,
by the following Member Bodies :
Argentina Germany Romania
Australia
India South Africa,
Belgium Iran
Rep. of
Brazil
Ireland Spain
Canada Israel
Sweden
Chile Italy
Switzerland
Colombia
Japan Turkey
Czechoslovakia
New Zealand U.A.R.
Denmark
Norway United Kingdom
Finland
Poland U.S.A.
France Portugal Yugoslavia
One Member Body opposed the approval of the Draft :
Netherlands
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council
which decided, in March 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 692-1968 (E
IS0 Recommendation R 692 March 1968
PU LPS
DETERMINATION OF ALKALI SOLUBILITY
FOREWORD
The object of both this IS0 Recommendation and of IS0 Recommendation R 699, hlps - Defer-
mination of alkali resisfance, is to permit the study of the behaviour of pulps in the presence of
alkali solutions, but their fields of application are different : while this IS0 Recommendation de-
scribes the volumetric determination of the alkali soluble constituents of the pulp and is applied
preferably to the control of bleached pulps, IS0 Recommendation R 699 describes the gravimetric
determination of the alkali insoluble constituents and applies to all categories of pulp.
1. SCOPE
This 1SO Recommendation describes a method for determining the solubility of pulp in cold sodium
hydroxide solutions of various and fixed concentrations. The concentrations of sodium hydroxide
solutions most frequently used are 18 and 10
(m/m).
2. FIELD OF APPLICATION
This method is mainly intended for investigation of bleached pulps, but may, however, also be used
with unbleached pulps, for example in the different stages of manufacture of bleached pulp.
3. PRINCIPLE OF THE METHOD
Pulp is treated with sodium hydroxide solution and the. dissolved organic matter is oxidized with
potassium dichromate. Excess potassium- dichromate is determined volumetrically and the cellulose
amount equivalent to the potassium dichromate consumed is calculated.
4. DEFINITION OF TERMS
S - value. Alkali solubility : the soluble fraction expressed as a percentage of the oven-dry pulp
4.1
mass.
or Sc. S-values in which the indices 18, 10 or c refer to the ohosen concentration ex-
4.2
SI 8, S,
pressed in grammes of sodium hydroxide per 100 g of solution.
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ISO/R 692-1968 (E)
5. REAGENTS
All reagents should be of analytical grade.
Sodium hydroxide solution, of known concentration, containing less than 1 g per litre of
5.1
sodium carbonate (see Note below), for example :
0.1 g of sodium hydroxide
sodium hydroxide solution, 5.39 t 0.03 M. containing 18.0
1 .O g of sodium
(NaOH) per 100 g of solution (pz0 = 1 .I972 g/cm3), equivalent to 215.5
hydroxide (NaOH) per litre.
sodium hydroxide solution, 2.77 ? 0.03 M, containing 10.0 f 0.1 g of sodium hydroxide
(NaOH) per 100 g of solution 1.0 g of sodium
= 1.1089 g/cm3) equivalent to 110.9
hydroxide (NaOH) per litre.
I'ollous :
NOTE. The sodium hydroxide solution is conveniently prepared as
Dissolve a quantity of solid sodiuni hydroxide in an equal mass of distillcd water and allow the suspended
sodium carbonate to settle. Decant the supernatant liquid and dilute with carbon dioxide-free distilled water
to the appropriate concentration. Check by titration with standard acid solution.
5.2 Sulphuric acid, concentrated. not less than 94 'Io sulphuric acid (H,SO,), (pz0= 1.84 g/cm3).
NOTE. If the concentrated sulphuric acid is of lower concentration than 94 %, the temperaturewillnot
reach the 125 to 130 OC required during the oxidation.
Potassium dichromate solution, about 0.067 M ( = 0.4 N), in 2.7 M sulphuric acid. 70 g of
5.3
potassium dichromate (K,Cr,O,) and 150 ml of sulphuric acid (H,SO,) (P,~= 1.84 g/cm3)
per litre of solution.
5.4 Ammonium iron (II) sulphate solution, approximately O. 1 N. (Normality known with an accu-
racy of ? 0.000 2) : 40 to 41 g of ammonium iron (II) sulphate (FeSO, (",) ,SO, . 6H20)
and 10 ml of sulphuric acid (H,SO,) = 1.84 g/cm3) per litre. This solution is not stable
and its normality should be checked every day.
NOTI.:. In order to restore the original normality of the ammonium iron (II) sulphate solution, a reducing
agent can be placed between the supply bottle and the burette.
Preparation of the reducing agent : metallic cadmium (which passes a sieve of 8 to 12 mesh per centimetre) is
from fine particles by washing u.ith water. The metal is treated for about 5 minutes with a 2 solution
freed
of mercuric nitrate (Hg (NO,),. H,O) or mercuric chloride (HgCI,) containing 5 ml of concentrated nitric
(II) sulphate solution may be
acid per litre. and then the amalgamated metal is washed. The ammonium iron
standardized against potassium dichromate as a primary standard.
The normality of the ammonium iron (II) sulphate solution stays constant \\hen, to a 10 litre bottle, are
5 g of aluminium shavings of more than 99.99 yo.
added
5.5 Phosphoric acid, 85 'Io (P20= 1.70 g/cm3).
5.6 Ferroin indicator solution, 15 g per litre of 1 : 10 -- phenanthroline monohydrate (C, ,H,N,.
H20) or 16 g per litre of 1 : IO ~ phenanthroline hydrochloride (C,,H,N,.HCl . H,O) and
7 g of iron sulphate (FeSO, . 7H,O) per litre of solution, or
5.1 Sodium diphenylaminosulphonate indicator solution, O. 1 g sodium diphenylaminosulplionate
(Cl ,Hl ,NSO,Na) per 100 ml of water.
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ISOlR 692-1968 (E
6. APPARATUS
6.1 Stirring equipment, with a propeller-type agitator made of stainless steel or other corrosion-
resisting material. The angle of the blades should be adjusted so that air is not introduced into
the pulp suspension during stirring.
NOTE. ~ Suitable equipment is shown in the Figure below. A satisfactory motor is one of 1/50 horse-
power, running between about 1700 and 1450 revolutions per minute.
0.2 "C.
6.2 Consrunr temperature bath, capable of maintaining a temperature of 20
6.3 Filtering crucibles or junnels, 50 ml, made of alkali-resistant material, with a sintered glass disc
having diameter of pores between 15 X 10-4 cm and 40 X cm (G 3).
Suction flasks, for the crucibles or funnels.
6.4
Balance. accurate to 1 mg.
6.5
6.6
Reaction vessel, of 200 ml capacity and tall in shape.
Dimensions in millimetres
A-A
I l
I I I 1
7. PREPARATION OF SAMPLE
If the pulp is in sheet form tear into pieces approximately 5 mm X 5 mna. If in sltsh form, remove
water by suction, press between blotters and dry at a'maximum temperature of 60 C. Before weigh-
ing the test pieces, condition them for not less than 20 minutes in the atmosphere near the balance.
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ISO/R 692-1968 (E
8. PROCEDURE
Weigh, to the nearest 0.005 g , the equivalent amount of approximately 1.5 g of oven-dry pulp. Then
immediately weigh out two test portions for dry matter content determination according to IS0
Recommendation R 638, Pulps - Determination of dry matter content.
With
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