Realtime monitoring of internal morphology of gel samples during drying process by X-ray computing tomography image...

This study was conducted to evaluate the change in the internal morphology of a wheat-based gel sample subjected to a drying process using X-ray computed tomography (CT) imaging with synchrotron radiation. To monitor the process in real time, the instrument was equipped with a developed drying system. The water contents of the sample decreased from around 0.42 to 0.1 g-water/g-dry solid and the falling rate drying was observed in the 0-180 min of drying period. The mechanical properties of the gel sample, represented by the Young's modulus, increased exponentially during the drying period. Thus, when subjected to low-water-content conditions, the hardness of the gel progressed sufficiently. In the X-ray CT images, small voids were generated uniformly in the sample during the early drying process, and the total number of voids and their volume also increased. Finally, they formed a band-like structure at the center of the sample. The total number of voids decreased at a rate of increase with the confluence of voids, and eventually reached a plateau. These results suggest that voids may be connected and cracked during drying. It was found that the drying process of a gel sample in this study proceeds in two phases: a void growth phase up to 60-80 min and thereafter, a crack generation phase. Consequently, the internal morphology of the gel was visualized using synchrotron-based X-ray CT imaging in real time, and it was demonstrated that the method is very effective for monitoring a gel during the drying process.