Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Wasseraufnahme}} {{PSM_Infobox}} Water absorption FORCETOC ==Fundamentals== Several different effects occur in plastics that are subjected to medial stress by water, e.g: * dimensional changes (swelling) caused by water absorption, * extraction of water-soluble components and * changes in various properties. From a physical point of view, water absor..."

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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Wasseraufnahme}} {{PSM_Infobox}} Water absorption __FORCETOC__ ==Fundamentals== Several different effects occur in plastics that are subjected to medial stress by water, e.g: * dimensional changes (swelling) caused by water absorption, * extraction of water-soluble components and * changes in various properties. From a physical point of view, water absor..."

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{{Language_sel|LANG=ger|ARTIKEL=Wasseraufnahme}}
{{PSM_Infobox}}
Water absorption
__FORCETOC__

==Fundamentals==

Several different effects occur in [[Plastics | plastics]] that are subjected to medial [[Stress | stress]] by water, e.g:

* dimensional changes (swelling) caused by water absorption,
* extraction of water-soluble components and
* changes in various properties.

From a physical point of view, water absorption is a diffusion process.

==Experimental methods==

The methods for determining water absorption are described in ISO 62 [1]:

* Method 1: Determination of water absorption in water at 23 °C
* Method 2: Determination of water absorption in boiling water
* Method 3: Determination of water-soluble components
* Method 4: Determination of water absorption after storage at 50 % relative humidity (see: [[Standard Atmospheres| standard climate]])

According to the standard, exposure to humidity, immersion in water at 23 °C and boiling water can cause completely different [[Materials Testing | material behaviour]]. Immersion in water at 23 °C and storage at 100 % humidity are practically equivalent in terms of their effects [2]. The amount of water absorbed when the equilibrium state is reached can be used to compare different [[Plastics | plastics]]. The carefully controlled, non-equilibrium exposure of test [[Specimen | specimens]] made of plastics with precisely defined dimensions can be used to compare different charges of the same [[Material & Werkstoff | material]] and to determine the diffusion constant of the material to be tested [1].

==Physical-chemical processes==

The possibility of chain cleavage by reaction with water (hydrolysis) exists for [[Plastics | polymers]] that contain ester, amide or similar functional groups in the main chain. Acids and alkalis can act as catalysts here and favour chain cleavage, especially in hot water, which thus represents the reverse reaction of polymer synthesis. Due to their hydrophobic phenyl groups, aromatic polyesters only absorb very few aqueous solvents, so that hydrolysis is only observed at elevated temperatures and generally have good cold water resistance [3].

Physico-chemical processes in connection with hydrolysis can be, for example, the local change in [[Crystallinity | crystallinity]], the release of additives or softening when water is absorbed.

Typical mechanical processes are, for example, the formation of [[Tensile Test Residual Stresses Orientations | residual stresses]] as a result of locally different swelling processes or the abrasive damage of plastic surfaces in the presence of aqueous solutions with high flow rates, e.g. during the transport of liquids or natural weathering.

==Determination of characteristic values==

The principle of the quantitative description of water absorption consists of immersing [[Specimen | test specimens]] in distilled water at 23 °C or in boiling distilled water or exposing them to climates with 50 % relative humidity at specified temperatures and for a specified period of time [1]. The amount of water absorbed is calculated by determining changes in mass using commercially available weighing instruments ([[Error Limit|error limit]] ± 0.1 mg).

The [[Specimen|test specimens]] used are square or round panels, tubular or rod-shaped test specimens or test specimens made of prefabricated profiles, extruded parts, panels and laminates.

The water absorption ''c'' is described as the difference between the mass of the test specimen after immersion ''m''2 (swollen test specimen) and the mass of the test specimen after drying ''m''1 (extracted test specimen)

{|
|-
|width="20px"|
|width="500px" | <math>c\,=\,m_2-m_1 \ \left[mg\right]</math>
|}

or as a relative change in mass as a percentage (%)

{|
|-
|width="20px"|
|width="500px" | <math>c\,=\,\frac{m_2-m_1}{m_1}\cdot 100 \ \left[%\right]</math>
|}

or

{|
|-
|width="20px"|
|width="500px" | <math>c\,=\,\frac{m_2-m_3}{m_1}\cdot 100 \ \left[%\right]</math>
|}
where are:
{|
|-
|''m''1
|width="15px" |
|Mass of the test speciemen after the first drying and before immersion in mg
|-
|''m''2
|
|Mass of the test specimen after immersion in mg
|-
|''m''3
|
|Mass after immersion and final drying in mg

|}

{| border="1px" style="border-collapse:collapse"
|+ '''Tab. 1''': Water absorption of various plastics in cold water [2]
!! style="width:160px; background:#DCDCDC" | Material
!! style="width:220px; background:#DCDCDC" | Water absorption after 4 d (mg)
|-
|CA
|style="text-align:center" | 100–250
|-
|PA
|style="text-align:center" | 50–800
|-
|PC
|style="text-align:center" | 5–10
|-
|PE
|style="text-align:center" | ca. 0
|-
|PF , Typ 31
|style="text-align:center" | 100–180
|-
|PF, filler free
|style="text-align:center" | 10–20
|-
|PMMA
|style="text-align:center" | 30–40
|-
|POM
|style="text-align:center" | 20
|-
|PS
|style="text-align:center" | 2–5
|-
|PVC-copolymerisate
|style="text-align:center" | 5–20
|-
|UF, Typ 131
|style="text-align:center" | 200–300
|-
|Vulkanized fibre
|style="text-align:center" | 1500
|}

==See also==

* [[Ageing]]
* [[Standard Atmospheres|Standard atmospheres]]
* [[Test Climate|Test climate]]
* [[Plastography]]
* [[Moulding Compound Test|Moulding compound test]]

'''References'''

{|
|-valign="top"
|[1]
|ISO 62 (2008-02): Plastics – Determination of Water Absorption
|-valign="top"
|[2]
|Stoeckhert, K., Woebcken, W. (Eds.): Kunststoff-Lexikon. Carl Hanser Munich Vienna (1998), 9th Edition, p. 605, (ISBN 3-446-17969-0) (see [[AMK-Büchersammlung | AMK-Library]] under G 3)
|-valign="top"
|[3]
|Franck, A.: Kunststoff-Kompendium. Vogel Buchverlag, Würzburg (2000) 5th Edition, p. 258 (ISBN 3-8023-1855-2)
|}

[[Category:Specimen Preparation]]

Water Absorption - Revision history