  Two types of high-strength composite hydrogels possessing the structure of
interpenetrating polymer networks were synthesized via free-radical
polymerization of acrylamide carried out straight within the matrix of plant or
bacterial cellulose swollen in the reactive solution. The mechanical behavior
of synthesized hydrogels subjected to the action of compressive deformations
with different amplitude values was studied. The analysis of the stress-strain
curves of compression tests of the hydrogels of both types obtained in
different test conditions demonstrates the substantial difference in their
mechanical behavior. Both the plant cellulose-based and bacterial
cellulose-based hydrogels withstand successfully the compression with the
amplitude up to 80 %, but the bacterial cellulose-based compositions
demonstrate in the multiple compression tests the substantial decrease of the
mechanical stiffness caused by the action of compressions. This effect takes
place straightly during the multiple cyclic compression tests or in the course
of relaxation of previously compressed samples in water in unloaded state
during 2-3 days after the first compressive tests. Being subjected to the
action of the extremely sever compression (up to 80 %) the bacterial
cellulose-based hydrogel varies greatly its mechanical behavior: during the
subsequent compressions the stiffness of the material keeps extremely small (as
compared to that registered in the first compression) up to the deformations as
high as 50-60 % with the dramatic increase of the stiffness during the further
loading. Submicron- and micron-scale specific features of structures of
composite hydrogels of both types were studied by cryo-scanning electron
microscopy to explain the peculiarities of observed mechanical effects.
