The development of
fully natural wheat gluten foams showing rapid
and high uptake of water, sheep blood, and saline solution, while
maintaining high mechanical stability in the swollen state, is presented.
Genipin was added as a natural and polar cross-linker to increase
the polarity of the protein chains, whereas cellulose nanofibers (CNFs)
were added as a reinforcement/stiffener of the foams, alone or in
combination with the genipin. The presence of only genipin resulted
in a foam that absorbed up to 25 g of water per gram of foam and a
more than 15 g uptake in only 8 min. In contrast, with CNF alone,
it was not possible to maintain the mechanical stability of the foam
during the water uptake and the protein foam disintegrated. The combination
of CNF and genipin yielded a material with the best mechanical stability
of the tested samples. In the latter case, the foam could be compressed
repeatedly more than 80% without displaying any structural damage.
The results revealed that a strong network had formed between the
wheat gluten matrix, genipin, and cellulose in the foam structure.
A unique feature of the absorbent/foam, in contrast to commercial
superabsorbents, was that it was able to rapidly absorb nonpolar liquids
(here, n-heptane) due to the open-cell structure.
The capillary-driven absorption due to the open-cell structure, the
high liquid absorption in the cell walls, and the mechanical properties
(both in dry and swollen states) of these natural foams make them
interesting as a sustainable replacement for a range of petroleum-based
foam materials, including absorbent hygiene products such as sanitary
pads.