ISO 2896:2001

INTERNATIONAL ISO
STANDARD 2896
Third edition
2001-07-01
Rigid cellular plastics — Determination
of water absorption
Plastiques alvéolaires rigides — Détermination de l'absorption d'eau
Reference number
©
ISO 2001
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ii © ISO 2001 – All rights reserved

Contents Page
Foreword.iv
1 Scope .1
2 Normative references .1
3 Principle.1
4 Materials .1
5 Apparatus .1
6 Specimens.4
7 Procedure .5
8 Corrections for swelling and cut surfaces.5
9 Expression of results .7
10 Precision and accuracy.8
11 Test report .9
Annex A (normative) Determination of average cell diameter (see 8.1.3.1) .10
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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 2896 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 10,
Cellular plastics.
This third edition cancels and replaces the second edition (ISO 2896:1987), which has been technically revised.
Annex A forms a normative part of this International Standard.
iv © ISO 2001 – All rights reserved

INTERNATIONAL STANDARD ISO 2896:2001(E)
Rigid cellular plastics — Determination of water absorption
1 Scope
This International Standard specifies a method for the determination of the water absorption of rigid cellular plastics
by measuring the buoyant force on a test specimen after immersion under a 50 mm head of water for 4 days.
Corrections are specified to take account of any change in volume of the specimen and also to correct for the
volume of water in the cut surface cells of the specimen. The water absorption is expressed as the average, for
several specimens, of the percentage increase in volume relative to the original volume.
The method described is intended for quality control and for use in product specifications.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 291:1997, Plastics — Standard atmospheres for conditioning and testing
ISO 1923:1981, Cellular plastics and rubbers — Determination of linear dimensions
3Principle
The water absorption of a material is determined by measurement of the buoyant force on a specimen immersed in
distilled water for a specified time.
4 Materials
4.1 Distilled water, de-aerated (by storage for at least 48 h after distillation), for use as the immersion liquid.
5 Apparatus
5.1 Balance, accurate to 0,1 g and capable of suspending the cage (5.2).
5.2 Underwater-weighing cage, made of a stainless material not attacked by distilled water and large enough
to contain a test specimen. A sinker heavy enough to compensate for the upthrust produced by the test specimen
shall be attached to the base of the cage. The cage shall be fitted with a means of suspending it from the balance.
See Figure 1 for an example.
5.3 Cylindrical vessel, at least 250 mm in diameter and 250 mm in height.
5.4 Low-permeability plastic film, for example polyethylene.
Key
1 Mesh cage
2 Specimen
3Sinker
Figure 1 — Test specimen in mesh underwater-weighing cage
5.5 Slicer: cutting-blade apparatus capable of preparing thin specimens (0,1 mm to 0,4 mm thick) for cell size
viewing. Figure 2 shows an acceptable apparatus.
5.6 Slide assembly, consisting of two pieces of slide glass hinged by tape along one edge, between which is
placed a calibrated scale (3 cm in length) printed on a thin plastic sheet (see Figure 3).
5.7 Projector: conventional 35 mm slide projector that accepts standard 50 mm � 50 mm slides, or a projection
microscope with a calibrated scale.
2 © ISO 2001 – All rights reserved

NOTE The spacer thickness is chosen to give the required viewing-specimen thickness.
Figure 2 — Razor-blade equipment for slicing cellular plastics for determination of average cell diameter
Dimensions in millimetres
Key
1 Calibrated glass slide
2 Flexible tape hinge
3 Blank cover glass
4 Cell-count scales
Figure 3 — Slide assembly
6 Specimens
6.1 Number of specimens
At least three specimens shall be tested.
6.2 Dimensions
Specimens shall be at least 500 cm in volume, with a nominal length of 150 mm and a nominal width of 150 mm.
For materials produced and sold with natural or laminated skin surfaces, the thickness shall be as produced. For
materials produced with a thickness greater than 75 mm and without skin surfaces, the material shall be trimmed to
75 mm in thickness for testing. The distance between two faces shall not vary by more than 1 % (tolerance of
parallelism).
6.3 Preparation and conditioning
Surfaces of specimens shall be smooth and free from dust. Dry the specimens in a desiccator at ambient
temperature until the results of two successive weighings, at intervals of at least 12 h, do not differ by more than
1 % of their mean.
4 © ISO 2001 – All rights reserved

7 Procedure
7.1 Operate in a room where the temperature is maintained in accordance with ISO 291. Unless otherwise
1�
specified , conditions shall be (23� 2) °C and (50� 5) % relative humidity.
7.2 Weigh a specimen to the nearest 0,1 g (mass m ).
7.3 Measure the dimensions of the specimen in accordance with ISO 1923 for the calculation of V .
7.4 Fill the cylindrical vessel (5.3) with de-aerated distilled water (4.1) at ambient temperature.
7.5 Immerse the assembled cage (5.2), remove any bubbles, attach it to the balance and determine the apparent
mass (m ) to the nearest 0,1 g.
7.6 Place the specimen in the cage. Re-immerse the cage so that the distance between the surface of the water
and the top surface of the specimen is approximately 50 mm. Remove obvious air bubbles from the specimen with
a brush or by agitation.
7.7 Cover the cylindrical vessel with low-permeability plastic film (5.4).
7.8 After (96� 1) h, or another agreed immersion period, remove the plastic film and determine the apparent
mass (m ), to the nearest 0,1 g, of the submerged cage containing the specimen.
7.9 Visually examine the specimen for evidence of swelling. To determine corrections for swelling and cut
surfaces, follow procedure A (8.1) for uniform swelling and procedure B (8.2) for non-uniform swelling.
7.10 Carry out the above procedure for each specimen individually.
8 Corrections for swelling and cut surfaces
8.1 Procedure A (uniform swelling)
8.1.1 Applicability
Use procedure A when there is no evidence of non-uniform deformation of the specimen.
8.1.2 Correction for uniform swelling
Remove the specimen from the water and re-measure its dimensions within 4 h of removal. The correction for
uniform swelling of the specimen S is
VV�
S �
V
where
V is the original volume, in cubic centimetres, of the specimen (see 9.1);
1) For tropical countries, test conditions will normally be (27 � 2) °Cand (65 � 5) % relative humidity.
dl��b
11 1
V �
d being the specimen thickness, in millimetres, after immersion;
l being the specimen length, in millimetres, after immersion;
b being the specimen width, in millimetres, after immersion.
8.1.3 Correction for the volume of water in the cut surface cells
8.1.3.1 Using the method described in annex A, determine the average cell diameter D of a specimen
obtained from the same sample of material as that from which the water absorption specimens were taken. Use
this average cell diameter D, expressed in millimetres, to calculate the volume V of the surface cells cut during
c
specimen preparation as follows:
8.1.3.1.1 For samples with natural or laminated skin surfaces:
0,54Dl(��d b�d )
V �
c
8.1.3.1.2 For samples having cut cells on all surfaces:
0,54D (l��dl�db� �d )
V �
c
8.1.3.2 For samples with an average cell diameter of less than 0,50 mm and a specimen volume of at least
500 cm , the correction for cut surface cells is relatively small (less than 3,0 %) and may be omitted.
8.2 Procedure B (non-uniform swelling)
8.2.1 Applicability
Use procedure B when there is evidence of non-uniform deformation of the specimen.
8.2.2 Combined correction for swelling and the volume of water in the cut surface cells
Obtain a cylindrical vessel similar to the one described in 5.3 but fitted with an overflow. Fill this vessel with water
until it runs from the overflow. When the water level has stabilized, place a graduated receptacle of capacity at
least 600 cm under the overflow. This receptacle shall be capable of allowing the volume of water deposited in it
to be measured to � 0,5 cm (this may be done by weighing). Remove the specimen and cage from the original
vessel. Allow them to drain until the surface water has run off (approximately 2 min). Carefully immerse the
specimen and cage in the water-filled vessel and determine the volume of water displaced V . Repeat this
procedure with the empty cage to determine its volume V .
The combined swelling and cut surface correction factor S is given by
VV��V
S �
V
where V is the original volume of the specimen (see 9.1).
6 © ISO 2001 – All rights reserved

9 Expression of results
9.1 Calculate the original volume of the specimen using the equation
dl��b
V �
where
V is the original volume, in cubic centimetres, of the specimen;
d is the original thickness, in millimetres, of the specimen;
l is the original length, in millimetres, of the specimen;
b is the original width, in millimetres, of the specimen.
9.2 Calculate the water absorption WA , expressed as a percentage by volume, as follows:
V
9.2.1 If procedure
...