Films with different compositions and crosslinking agent contents
were dried sufficiently at 105 ◦C and weighed. Then the films
were wrapped in a stainless steel net (150 mesh) and extracted with
Soxhlet extractor at 90 ◦C for 12 h where water was used as solvent.
Afterward, the stainless steel net encapsulated residue was taken
out, then dried and weighed.