Standard Test Method for Water Absorption of Plastics

ASTM D570 testing is now offered by Micom as part of its material testing and of its plastics and polymer testing services . ASTM D570—Water absorption of plastics—describes various procedures that evaluate the amount of water that is absorbed by the sample. Moreover, it also permits to assess the uniformity of the imbibed specimen.

Water Absorption of Plastics—Uses and Factors to Consider

The purpose of ASTM D570 is to determine the rate of absorption of water by immersing the specimen in water for a specific period of time. More specifically, this test protocol evaluates the percentage increase in weight of the sample following the experiment as a means to characterize this attribute. Furthermore, this standard details many procedures in order to properly address a wide range of materials through the adjustment of the period of immersion and of the temperature of water. As a matter of fact, the reason why there is a variety of methods is due to the fact that each material has a different rate of assimilation of water and it is necessary to alter the test conditions accordingly. Moreover, it is important to assess this attribute, because polymers have a tendency to soak up water and this propensity may lead to an alteration of the properties of the plastic. Indeed, attributes such as: electrical insulation resistance and mechanical strength are tightly associated with the moisture content of that kind of material. Lastly, it is important to keep in mind that the specimen does not necessarily assimilate water in a uniform manner, therefore it is essential to appraise that aspect with this test.

The main factors that are to be considered when running this test are: the time of immersion, the temperature of the water, the thickness of the sample and the type of material.

Typical Experimental Parameters for ASTM D570 Testing

The number of specimens required is three and their sizes are listed in table 1. The conditioning and the immersion specifications are detailed in table 2 and table 3 respectively.

Table I: Specimens sizes

Type of materialsSpecifications
Molded plasticsThe samples have to be in the form of disks of 50.8 mm (2 in) in diameter with a 3.2 mm (1/8 in) thickness.
Homogeneous plasticsThe dimensions of the samples are 60 mm by 60 mm by 1 mm.
SheetsThe samples have to be in the form of bars of 76.2 mm (3 in.) long by 25.4 mm (1 in.) wide

The thickness has to be specified, but a thickness of 3.2 mm (1/8 in) has to be used in order to compare with molded plastics.
RodsThe diameter of the sample is the same as the finished product.
If the diameter is 25.4 mm or less, the length is 25.4 mm (1 in.).
If the diameter is greater than 25.4 mm, the length is 12.7 mm (1/2 in.).
TubesIf the inside diameter is less than 76 mm (3 in.), the test specimens shall be the full section of the tube and 25.4 mm (1 in.) long.
If the inside diameter is greater than 76 mm (3 in.) a rectangular sample shall be cut 76 mm in length in the circumferential direction of the tube and 25.4 mm in width lengthwise of the tube.

Table II: Conditioning specifications

Type of specimensSpecifications
Materials whose water-absorption value would be significantly affected by temperatures similar to 110 °C (230 °F)Dried in an oven for 24 h at 50 ± 3 °C (122 ± 5.4 °F)
Cooled in a desiccator
Materials whose water-absorption value will be compared with other plastics
Materials whose water-absorption value has been shown not to be appreciably affected by temperatures up to 110 °C (230 °F)Dried in an oven for 1 h at 105 to 110 °C (221 to 230 °F).

Table III: Immersion specifications

Type of immersion protocolSpecifications
Twenty-four hours immersionImmerse the samples for 24h in distilled water maintained at 23 ± 1 °C (73.4 ± 1.8 °F).
Comparison of absorption values between plastics
Two hours immersionImmerse the samples for 2h in distilled water maintained at 23 ± 1 °C (73.4 ± 1.8 °F).

(For materials with a high rate of absorption)
Repeated immersionImmerse the samples for 2h in distilled water maintained at 23 ± 1 °C (73.4 ± 1.8 °F).
Immerse once again for 24h in distilled water maintained at 23 ± 1 °C (73.4 ± 1.8 °F).
Long term immersionImmerse the samples for 24h in distilled water maintained at 23 ± 1 °C (73.4 ± 1.8 °F).
Dry, weight and reimmerse in the container for a week
Dry, weight and immerse once again in the container
(After this step, the weighing is executed every two weeks until the mass increase between a two-week period does not differ more than 1% of the total weight or 5 mg; the ending criterion is the greater one of them).
One half hour boiling water immersionImmerse the samples for 30 minutes in boiling distilled water.
Cool in room temperature distilled water for 15 mins.
(For materials with a high rate of absorption)
Immersion at 50 °CImmerse the samples for 48h in distilled water maintained at 50 ± 1 °C (122.0 ± 1.8 °F).

Other Test Methods Related to ASTM D570

For additional related test methods, please see polymer testing.

If you have any questions about the ASTM D570 test, we invite you to contact our material testing lab today. It will be our pleasure to answer your questions and help you with your custom material testing requirements.