ISO 62:2008 download.Plastics-Determination of water absorption.
Plastics exposed to water are subject to several different effects:
a) dimensional changes (e.g. swelling) caused by absorption of water;
b) extraction of water-soluble components;
c) changes in other properties.
However, exposure to humidity, immersion and exposure to boiling water can result in distinctly different material responses. The equilibrium moisture content can be used to compare the amount of water absorbed by different types of plastics when they are exposed to moisture. Moisture content determined under nonequilibrium conditions can be used to compare different batches of the same material and to determine the diffusion constant of the material when determined under carefully controlled non-equilibrium conditions of exposure to moisture and when using plastic specimens of defined dimensions.
1.1 ISO 62 describes a procedure for determinmg the moisture absorption properties in the wough-lhe-thickness” direction of fiat or curved-form solid plastics. The International Standard also describes procedures for determining the amount of water absorbed by plastic specimens of defined dimensions, when immersed in water or when subjected to humid al under controlled conditions. The hrough-tha-thickness’ moisture diffusion coefficient can be determined for single-phase material by assuming Fickian ddkis4on behaviour with constant moisture absorption properties through the thickness of the test specimen. This model is valid for homogeneous materials and for reinforced polymer-matrix composites tested below their glass transition temperature. However, some two-phase matrices such as hardened epoxies may reqare a multi-phase absorption model which is not covered by this International Standard.
1.2 Ideally, the best comparison of the water absorption properties and/or diffusion coefficients of materials should be carried out onty using the equilibrium moisture content of plastics exposed to identical conditions The comparison of materials using properties at moisture equilibrium does not assume, and is therefore not trilled to, single-phase Fickien diffusion behaviour
13 Alternatively, waler absorption of plastic specimens of defined dimensions exposed to rmersion or humidity under controlled conditions but for an arbitrary time period can be used to compare different batches of the same material or far quality control tests of a given material. For this type of comparison, it is essential that all test specimens be of Idenuicat dimensions and, as nearly as possible, have the same physical attributes. e.g. surface smoothness, internal stresses. etc. However, moisture equiibriuni is not reached under these conditions. Therefore, results from this type of test cannot be used to compare the waler absorption properties of different types of plastics. For more reliable results, simultaneous tests are recommended.
1.4 The results obtained using the methods described lii ISO 62 are applicable to most plastics but are not applicable to cellular plastics, granulates or powders, which can show additional absorption and capillary effects. Plastics exposed to moisture under controlled conditions for defined periods of time provide relative comparisons between them. The tests described for the determination of the diffusion coefficient may riot be applicable to al plastics. Plastics that do not retain thelr shape when immersed in boding water should not be compared using method 2 (see 6.4).
2 Normative references
The folloietng 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 175:1999, Ptasbcs — Methods of test for the determination of the effects of unrnerslon in liquid chemicals
ISO 294-3, Plastics — Injection moulding of test specimens of the,mop1astic materials — Part 3: Small plates
ISO 2818. Plastics — Preparation of test specimens by machining
Test specimens are immersed io distiled water at 23 ‘C or in boding disliled waler, or exposed to 50 % relative humidity at given temperatures, for prescribed periods. Th. amount of water absorbed by each test specimen is determined by measuring its change in mass. Ic. the difference between its initial mass and that after exposure to water, the change being expressed as a percentage of the initial mass If required, the amount of water lost after drying the test specimens can also be determined.
In some applications, 70% to 90% relative humidity and temperatures of 70 ‘C to 90 ‘C may be necessary. Relative humidities and temperatures gher than those recommended in ISO 62 may be used by agreement between the interested parties When relative humidity and temperature conditions other than those recommended are used, a complete description of these conditions (with appropriate tolerances) shal be included wi the test repofl
4.1 Balance, with an accuracy of ± 0.1 mg (see also 6.1,3).
4.2 Oven, with forced-air convection or vacuum, maintained at (50.0 ± 2.0) ‘C or at any other agreed
temperature (see also 61.2).
4.3 ContaIners, containing disNied water or water of equivalent purity, equipped with a means of heating capable of maintaining the temperature specified.
4.4 Desiccator. with a desiccant (e.g. P205).
4.5 Means of measuring the dimensIons of the test specimens loan accuracy of ± 0,1 mm, if required.
5 Test specimens
For each material evaluated, test at least three test specimens. Test specimens of the required dimensions may be prepared by moiiding or extrusion. The methods used for preparation of all test specimens shall be Included In the test report
NOTE The risits of this method may be infkienced by surface effects For some materials, dd?er.nt resMs can be obtained between ma..ided spenens and specariens cii from a larger eheet
Any contaminant on the test specimen surface which could influence water absorption shall be removed by a cleaning agent which does not attack the plastic, the degree of attack being determined In accordance with ISO 175 — (or example, the notation ‘none’ (no change in appearance) in ISO 175:1999, Table 1. Allow specimens to &y at 23 C and 50% relative humidity for at (east 2 h after cleaning and before beginning the test. Wear clean gloves when handling test specimens to prevent contamination.
The cleaning agent shall have no effect on the the water absorption. When determining the moisture equllrium content in accordance with 6.3 (method 1) and 6.6 (method 4), the effects of the cleaning agent can be ignored.
5.2 Square-shaped test specimens for homogeneous plastics
Unless otherwise specified or agreed by all interested parties, the dimensions and dimensional tolerances of the square-shaped specimens shall be the same as those given in ISO 294-3, with a thickness of (1.0 ± 0.1) mm. They can be prepared by moulding In accordance with ISO 294.3. using conditions given In standards applicable to the material being tested (or using conditions recommended by the matenal suppber). For some materials, such as polyamides. potycarbonates and some reinforced plastics. use of a 1 mm thick specimen may not give meaningful result5 Furthermore, some prockict specifications require the use of thicker lest specimens tot the determination of waler absorption. In these cases. test speem’iens of (2.06 ± 0,05) mm thickness may be used. If specimens of thickness other than 1 mm are used, the specimen thickness shall be indicated in the test report. There are no requwements for the radii of the edges and corners. However, they shall be smooth arid clean to prevent material from the edges and cornei’s from being lost during the lest
Some materials may exhibit mould strinkage. If specimens of these materials are prepared using a mould with dimensions at the lower limits specified in ISO 294-3, the final dimensions of the specimens may be beyond the loleranoes given in this International Standard, in which case they shall be noted in the lest report.
5.3 Test specimens of reinforced plastics affected by anisotropic diffusion effects
For some reinforced plastic malerlals, such as carbon-fibre-reinforced epoxies, anesotropoc diffusion effects caused by the reinforcing malarial may produce erroneous results when small specimens are used. Where this Is of concern, test specimens that meet one of the following types of specimen shall be used and the specific dimensions and methods of test specimen preparation shall be induded in the test report:
a) A nominally square-shaped plale or curved panel with dimensions that satisfy the relation:
w is the nominal length of one side, in millimetres:
d ia the nominal thickness, In millimetres.
b) A 100 mm x 100mm square-shaped plate with stainless steel or akimiiium toll bonded to the edges so that moisture absorption through the edges is minimized When this specimen Is prepared, care shall be taken to weigh the specimen before and after bonding of the foil in order to obtain the mass increase duo to the toll and the adhesive. Use only pooiiy absorbing adhesive which will not affect the results.
5.4 Tubular test specimens
Unless speddlcally required by other International Standards, tubular test specimens shall have the following dimensions:
a) For tubes having an Internal diameter of 76mm or less, cut sections of tube that are (25 t 1) mm in length from a longer tube of the mateflal being evaluated. The cut shall be made perpendicular to the longitudinal axis of the tube. The cut can be made by machining, sawing or shearing and shall produce smooth edges free from cracks.
b) For tubes having an internal diameter larger than 76mm. cut out rectangular specimens (76±1) mm in length (measured along the outside surface of the tube) by (25±1) mm in width. The cut edges shall be smooth and free from cracks.
5.5 Rod-shaped test specimens
Rod-shaped test specwnens shall have the foltowing dimensions:
a) Forrods26mm indiameterorless, cutoffa seciionof(25±1)mmlnlength. Thecutahall bemade perpendicular to the longitudinal axis of the rod The diameter 01 the test specimen shall be the diameter of the rod.
b) For rods larger than 26mm in diameter. cutoff a sectIon 01(13± 1)mm in length. The cut shall be made perpendicular to the longitudinal axis of the rod. The diameter of the test specimen shall be the diameter of the rod.
5.8 Specimens cut from finished products, extrusion compounds, sheets or laminates
Unless required by another International Standard, cut a piece from the product that
— meets the requirements for the square-shaped test speczmeri
— has a length and width of (81 ± 1) mm and has the same shape (thickness and curvature) as the material being tested,
The machining conditions used to prepare the test specimens shall be agreed by all iiterested parties. They shal also be in accordance with ISO 2818 and shall be included in the test report.
If the nominal thickness te greater than 1.1 mm and in the absence of special provisions concerning the relevant application, the thickness of the test specimens shall be reduced to 1,0 mm to 1,1 mm by machining on one surface only.
When the surface of a laminate Is machined, the water absorption properties will be Inikienced to such an extent that the test results wit not be valid. Therefore, the specimens shall be tested at their original thickness and the dimensions shall be indicated In the test report,
6 Test conditions and procedures
6.1.1 Certain materials may require that the test specimens be weighed in a weighing vessel
6.1.2 Drying procedures other than those described in 6.3 to 66 may be used by agreement between the interested parties.
6.1.3 When the waler absorption of the material Is greater than or equal to 1 %, specimens which have been weighed accurately to ± 1 mg and whose mass is constant to t i mg are acceptable.
6.2 General conditions
6.2.1 Specimens shall be carefully dried prior to testing. At 50 C. for instance, a drying period of between
one and ten days will be necessary, the exact duration depending on the thickness of the specimens.
6.2.2 Use at least 8 ml of distilled water per square centimetre of the total surface of the test specimen but not less than 300 ml per test sPecimen. This will prevent any extraction product from becoming excessively concentrated in the water during the test.
6.2.3 Place each set of three test specimens In a separate container (43) and completely Immerse them in water or expose them to 50 % RH (method 4).
When several samples of the same composition are to be tested, the test specimens may be placed together m the same container with at least 300 ml of water per test specimen. However, in this case, significant surface contact between test specimens or with the walls of the container Is unacceptable arid shall be prevented.
NOTE Grids made of stainless steel may he to ensure an acoeptable detance between the lest specanens.
For specimens having a density lower than that of water, immerse the specimens by placing them in a stainless-steel wire basket connected to an anchor-weight by a stainless-steel wire Avoid surface contact of the anchor-weight with the specimens.
6.2.4 Tine Intervals for water immersn are given in 6.3 and 6.4. However, longer Immersion peflocts may be used by agreement between the interested parties. In such cases, the following precautions shall be taken:
— for tests performed in water at 23 C. agitate the water at least once daily, for example by swirling the contents of the container;
— for tests performed In bodIng water, add boding water as requwed in order to manben the volume,
6.2.5 During weighing operations, the specimens shall not absorb or release any water. They shall therefore be weighed immediately after being taken from the exposure environment (and, If necessary, removing any surface water). Special care shall be taken in the case of thin specimens and materials with a high coefficient of diffusion for water.
6.2.6 In the case of 1 mm thick specimens and materials with a high coefficient of diffusion for water, the first weighings shall be camed out after 2 hand 6 h.
6.3 Method 1: Determination of amount of water absorbed after immersion In water at 23 C
Dry all replicate test specimens in an oven (4.2) maintained at (50 ± 2) °C for at least 24 h (see 6.2.1) and allow them to cool to room temperature In the desiccator (4.4) before we.ghing them to the nearest 01 mg. Repeat this process until the mass of the specimens is constant (mass w) to within ± 0.1 mg
Then place the test specimens In a container (4.3) filled with distilled water maintained at 23,0 C ± 1,0 C cr± 2,0 C, depending on the relevant specification. In the absence of a specification, the tolerance shall be ±1,0 C.
After immersion for (24 t 1) h, take the test specimens from the water and remove all surface water with a dean. &y cloth or with filter paper. Reweegh the lest specimens to the nearest 0.1 mg within I min of removing them from the water (mass “2),
Th. water oonterit at saturation Is measured by re-Immersing th. test specimens and reweighing them at given time intervals. A typical immersion time scale is 24 h, 48 h, 96 h. 192 h. etc. At each of these intervals (± 1 h), remove the test specimens from the water, remove all surface water and rewelgh each test specimen to the neerest 0,1 mg within 1 min of removing them from the water (e.g. m4 h)
6.4 Method 2: DeterminatIon of amount of water absorbed after immersion in boiling water
Dry all replicate test specimens in an oven (4.2) maintained at (50.0 ± 2.0) C for at leest 24 h (see 6.2.1) and allow them to cool to room temperature in the desiccator (4.4) before we.ghing them to the nearest 0.1 mg. Repeat thto process until the mass o the specimens Is constant (mass m1)to within * 0.1 mg.
Then place the test specimens in a container (4.3) of boiling dIstilled water so that they are supported on one edge and entirely immersed. After (30±2) mm, remove the test specimens from the boiling water arid cool them In distilled water maintained at room temperature, After cooling the test specimens for (15 1) mm. remove them from the water one at a time. Remove all surface water with a dry cloth, then immediately weigh them to the nearest 0.1 mg (mass ). If the thickness of the test specimens Is less than approximately 1.5 mm. a small but measurable amount of water desorplion may occur during the weighing procedure. In this case, it is preferable to weigh the specimens in a weighmg bottle.
The water content at saturation is measured by re-immersang the lest specimens and rewei1ing them at (30±2) rein intervals. Alter eact of these intervals, the test specimens shall be removed from the water. cooled m distilled water, dried and weighed as desaibed above,
Cracks may form after repeated immersion and drØng. If so, the number of cycles at which the cracks are first observed shall be noted in the lest report
6.5 Method 3: DetermInation of water-soluble matter lost during immersion
When materials are known or suspected to contas’i appreciable amounts of waler-soluble ingredients. it Is necessary to correct for the water-soluble matter lost dunng the immersion test. For this purpose, after immersion In accordance with 63oi6.4, recondition the test specimens Ic constant mass (mass m3) in the same way as I, the original drying period In 6.3 and 6.4. If this reconditioned mass is less than the conditioned mass i, the difference shall be considered as the water-soluble matter lost during the Immersion test. For such materials, the water absorption vakie shall be taken as the sum of the increase In mass following immersion and the mass of the water-soluble matter.
6.6 Method 4: Determination of amount of water absorbed after exposure to 50 % relative humidity
Dry al replicate test specimens In an oven (4.2) maintained at (50.0 ± 2.0) C for at least 24 h (see 6.2,1) and allow them to cool to room temperature in a desiccator (4.4) before weighing them to the nearest 0.1 mg. Repeat this process until the mass of the specimens Is constant (mass m1) to within ± 0.1 mg
Then place the test specimens in enclosure or room containing air with a relative humidity of (50 ± 5) %
maintained at 23.0 C ±1,0 C or ±2,0 C. depending on the relevant specification. In the absence of a
specification, the tolerance shall be ± 1.0 ‘C. After exposing the test specimens for (24 ± 1) h. reweigh them to
the nearest 0.1 reg (mass m2) wIthin 1 min after the removal from the enclosure or room containing the air with
a relative humidity of (50±5) %.
The equilibrium moisture content is measured by repeating the exposure of the test specanens to 50 % relative humidity, following the same weighing procedure and Lising the same time intervals as given in method 1 (see 6.3).
7 Expression of results
7.1 Percentage by mass of water absorbed
For each test specimen, caicLiale the percentage change In mass c relative to the initial mass by using the appropriate formula:
a,1 is the mass of the test specimen, in milligrams (mg), after initial drng and before immersion;
m2 is the mass of the test specimen, in milligrams (mg), after immersion;
m3 as the mass of the test specimen, in milligrams (mg), after immersion and final &ying.
Express the result as the arithmebc mean of the three values obtained at the same exposure duration.
NOTE We certain Instances. It may be required to express the enount of waler absorbed as a percentage by mass
with respect 10 the iwa speonen mass after r.ai drying. using C-ie following formula:
7.2 Determination of the water content at saturation and th. water diffusion co.ffici.nt using FIck’s laws
At temperatures well below the glass transition temperature of the wet p0(yer, the water absorption of most polymers (determined by methods 1. 3 end 4) correlates wel with Fiolts laws (see Annex A). and a water diffusion coefficient independent of time and concentration (U can b calculated as described in the example below
However, In this case, the water content at saturation as well as (he diffusion coefficient D. expressed in millimetres squared per second (mmls), can be determined by fitting the expenmerital data to Fick’s law for sheets 12. without waiting for constant mass to be reached (see Clause A,2)
The waler content at saturation is expressed as when the test specimens are immersed ii water in accordance with method 1, 2 or 3 and as (50 %) when (he test specimens are exposed to air at 50% relative humidity (method 4). Graphical methods may be used to verify the Ficician diffusion behaviour of the test specimens, substituting the calculaled Dvalue. e.g. by a log plot which is then titled to the theoretical data or by using a commercially available software package. In order to verify that the water absorption of a polymer folows Ficluan diffusion behaviour, the experimental data have to be taken for a longer period L4) to the equilibrium concentration c4.
Figure A.1 shows a fairly exact solution of Ficks laws for shee(s A slope 0(0,5 has been found for
For precision data , see Annex B
9 Test report
The test report shall include the following:
a) a reference to this International Standard;
b) all details necessary for complete identification of the material or product tested:
c) the type of test specimen used and the method of preparation, stating whether the specimens have been cut or not, their dimensions, their initial mass and, if applicable, their initial surface area and their surface condition (for example whether they are machined or not);
d) the method (1, 2, 3 or 4) used and the immersion period(s);
e) the water absorption, calculated by one or more of the ways of expressing the results given in Clause 7, reporting the mean and the standard deviation of the results (if the calculations described in 7.1 and 7.2 give a negative value for the water absorption, this fact shall be stated clearly in the test report);
f) the water absorption at saturation c or c5(50 %) at 23 °C, calculated in accordance with 7.2;
g) the diffusion coefficient at 23 °C, calculated in accordance with 7.2;
h) any incidents likely to have affected the results;
i) the date(s) of testing.