2.5.4. Diffusion Coefficient

The moisture loss in term of diffusion through the coatings was determined by using Fick's law of diffusion, written as:

$$MR = \frac{M\_{\rm f} - M\_{\rm c}}{M\_{\rm o} - M\_{\rm c}} = \frac{8}{\pi^2} \exp\left(\frac{-\pi^2 Dt}{4L^2}\right) \tag{3}$$

Here, *MR*, *D*, *t* and *L* are the moisture ratio, effective diffusion coefficient (m2/s), time (s) and thickness (m) of the sample layer distributed in the drying chamber, respectively. Moreover, *Mt*, *Me*, *Mo* represents moisture levels at time interval of *t*, initial and equilibrium, respectively. The diffusion coefficient can be calculated from the slope of line (*α*) drawn between ln(*MR*) and time as:

$$
\kappa = \left(\frac{\pi^2 Dt}{4L^2}\right) \tag{4}
$$
