The water absorption of plastics influences application-determining properties with increasing water content as follows:


    • Increase of dielectric losses.
    • Decrease of stiffness and hardness.
    • Increase of toughness (impact strength; elongation at break).
    • Increased dimensional change due to swelling or drying.


The maximum water absorption of plastics up to saturation varies greatly. For non-polar plastics (e.g. polyolefins) it is often negligible, whereas for hydrophilic (polar) plastics (e.g. polyamides) water absorption must be taken into account for application-related purposes. In such cases, in order to achieve an application-specific required water concentration, post-treatment is carried out by conditioning of the plastic parts. Diffusion processes in solid materials proceed much more slowly compared to heat conduction processes.


Conditioning times also increase disproportionately (quadratically) with the cross-sectional thickness of the parts. In order to keep the post-treatment times as short as possible, conditioning is carried out in temperature-controlled hot water baths (40 °C to 90 °C) or in saturated steam systems (above 100 °C).


The conditioning temperatures must be matched to the thermal stability of the plastics. Depending on the type, amount and distribution of additives as well as on processing-affected material structures (e.g. degree of crystallinity), short-term conditioning processes may cause negative effects (discoloration, deposits, warpage, cracking). A countermeasure would be the less aggressive conditioning with warm humid climate in climate chambers.