Plastic Material: Moisture Absorption

What is "Moisture Absorption"?

Also known as "Water Absorption",  the increase in weight (%) after immersion of a plastic specimen in distilled water for 24 hrs at 23℃，please see below for the formula:

Factors Influence Water Absorption

Water absorption of plastic material varies because of the different property of each kind of plastic material, relative humidity and temperature in the environment, or Chemical Additives used for modified the property of plastic material. Water absorption may result in better chance of molding defeat such as silver streaks or brittleness,  tensile strength and impact strength of finished plastic article may be influenced as well, thus before the production, it's important and necessary to dry the material properly to prevent molding defect, for suitable drying time and temperature, please check the material data with supplier, if there's no relative information, please check out our article Plastic Material: Drying Temperature & Processing Time, we've sorted out a summary of different kinds of polymers.

How to measure Water Absorption?

ASTM D570 - Standard Test Method for Water Absorption of Plastics
1.1 This test method covers the determination of the relative rate of absorption of water by plastics when immersed. This test method is intended to apply to the testing of all types of plastics, including cast, hot-molded, and cold-molded resinous products, and both homogeneous and laminated plastics in rod and tube form and in sheets 0.13 mm (0.005 in.) or greater in thickness.

1.2 The values given in SI units are to be regarded as the standard. The values stated in parentheses are for information only.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Remarks: ISO 62 is technically equivalent to this test method.

Source: ASTM International

ISO 62: 2008 - Determination of Water Absorption
ISO 62 describes a procedure for determining the moisture absorption properties in the “through-the-thickness” direction of flat or curved-form solid plastics. It 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 air under controlled conditions. The “through-the-thickness” moisture diffusion coefficient can be determined for single-phase material by assuming Fickian diffusion behavior 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 require a multi-phase absorption model which is not covered by this International Standard.

The results obtained using the methods described in this International Standard 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.

Source:  ISO official website

Plastic Material-Water Absorption Value

Blow table has sorted out the minimum water absorption value and maximum water absorption value of different kinds of plastic material:
(Mobile phone user, please swipe to the right for viewing all the data)

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