Water solubility index and water absorption index
were determined using the method described in Ref.
12. A small sample of dry powders (2.5 g) was added
to 30 ml of water at 30 °C in a 50 ml centrifuge tube,
stirred intermittently for 30 min, and then centrifuged
for 10 min at (5100g). The supernatant was carefully
poured off into a Petri dish and oven-dried overnight.
The amount of solid in the dried supernatant as a
percentage of the total dry solids in original 2.5 g
sample gave an indication of the WSI. Wet solid
remaining after centrifugation was dried in an oven
overnight. WAI was calculated as the weight of dry
solid divided by the amount of dry sample.