Moisture Sorption in Polymer Films

Many different commercial products can be formed from polymer films, which are thin unbroken plastics consisting of nylons, bioplastics, polyethylene or other components. This wide range of possible materials means that these polymers can be used for a variety of applications. For example, for storing medical drugs or food, for creating eco-friendly plastic bags or for creating a movie film. Each application requires different plastic properties and so these polymer films must be accurately defined to allow suitable uses in industry.

One of the most important properties for these polymer films is moisture and vapor sorption. Both the strength and stability are vital characteristics for polymer films which will be used to carry weight or form volumetric barriers. Photographic film strips also require polymer film which is transparent. These properties, however, are all defined by the moisture sorption of the polymer. Low moisture, for example, can lead to lower stability and increased brittleness, whereas high moisture can lead to chemical instability and mold formation.

Using gravimetric analysis techniques, the moisture sorption of these plastics can be characterized, bypassing these problems. These techniques usually employ dynamic flow methods to estimate a polymer’s moisture equilibrium as a product of humidity. Other methods also calculate the moisture diffusion coefficients of polymer films, to ensure both reliability and quality.

Moisture Sorption Measurements of Polymer Films

One method for calculating the moisture sorption of a polymer film is moisture diffusion (otherwise known as hygroscopic swelling). This method analyses the sorption, which results from mass changes under altering environmental conditions, through dynamic vapor sorption (DVS) analysis.

This approach analyses the changes in mass following environmental changes (such as altering humidity, flow rate, and temperature), which reveals a polymer’s moisture sorption qualities.

Another method used to characterize moisture sorption kinetics is the response test. This test monitors these kinetics whilst the humidity is increased, which also increases the concentration of moisture within the specimen. However, the moisture sorption of polymers can be influenced by many factors, and so this method is very complex for plastic applications. For example, moisture sorption could result in uneven swelling, resulting in water to polymer chain bonds, which can dramatically alter the diffusion rate.

Nonetheless, a DVS analyzer has been developed by IGAsorp to ascertain accurate equilibrium curves and diffusion coefficients for thin polymer films. A hypersensitive microbalance is utilized to monitor changes as small as 0.1 µg. This balance is additionally thermostatted to prevent inaccuracy and ensure stability. The humidity can be set at 0-98%, whilst the temperature of the specimen can range from 5-85 °C. Furthermore, the specimen can be dried at higher temperatures of ≤ 350 °C.

In conclusion, this device can be used to characterize polymer films for many different applications and to inform the user of potential suitable roles of new plastics.

This information has been sourced, reviewed and adapted from materials provided by Hiden Isochema.

For more information on this source, please visit Hiden Isochema.


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