2.4.4. Water absorption index (WAI) and water solubility index (WSI) measurement
Two centrifuge tubes were weighed separately with individual weights. 2.5 g of sample was then put in each tube.
30 mL of distilled water were added and stirred with sample to avoid lumps.
The tubes were closed and placed in the water bath with 25 °C for 20 min.
Those tubes were centrifuged at 5000 rpm for 10 min.
The water was then decanted from the tube without loss of solids. Finally, the tube and residues were weighed out.
The WAI was calculated as following equation 2.5 g of sample were placed into a centrifuge tube, and then 30 mL of distilled water were added.
The mixture was shaken for 5 min with intermittent agitation on a vortex mixer, and then centrifuged at 5000 rpm for 10 min. The supernatant was poured into a moisture dish of known weight.
The sample was dehydrated overnight in the oven set at 40 °C. The dish was removed from the oven, and put in the desiccators to equilibrate. Finally, the dish with dried sample and lid were weighed. The WSI was calculated as: