Biomedical Engineering Reference
In-Depth Information
For water permeation, the measurements were carried out by using a pervaporation
method. This differential permeation method allow to obtain the diffusion and perme-
ability coefficients by taking into account the exposed area of the film and the vapor
pressure difference across the two sides of the film.
The permeation flux through the film is measured as a function of time. The per-
meation cell consisted of two compartments separated by the polymer film. Both com-
partments were flushed by dry nitrogen gas in order to dry the polymer film. There-
after, a stream of water was introduced into the upstream compartment. The water
concentration was measured in the downstream compartment by using a hygrometric
sensor (a chilled mirror hygrometer) coupled to a data acquisition system.
Figure 7.
Apparatus based on a differential permeation method (Alexandre, 2009; Marais, 1999).
Both Water Sorption and Permeation
Different approaches were studied for obtaining both water sorption coefficient and
water permeability coefficient. For that, some authors cut rectangular specimens of
polymer films which are dried in vacuum oven at 50°C and their weight was measured
until reaching no weight loss change. The films were immersed in a deionized water
bath at 37°C. All specimens were weighed as a function of immersion time until the
sorption process was complete. Then, the mass uptake at time t, and water solubility
were calculated and thereafter water diffusivity, sorption and permeability coefficients.
Vacuum Quartz Microbalance
The water diffusion and permeability coefficients can be measured from a two-com-
partment cell by using a vacuum quartz spring microbalance techniques at controlled
temperature. Iordanskii and co-workers have described the water resistance-PHB con-
centration dependence with this technique for PHB/LDPE blends made by melting in
a single-screw extruder (Iordanskii, 1999). The effect of hydrophilic groups on water
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