A mixture of CMCNa and HEC was first dissolved in
distilled water by stirring at room temperature until a clear
solution was obtained. First, HEC was easily dispersed, after
which CMCNa was added. CMCNa dissolution was slow at
the concentration adopted, requiring about 24 hours. Once
the cellulose solution was obtained, an aqueous solution of
citric acid (1% w/v) was added as a catalyst. The carbodiimide
was finally added and allowed to dissolve and distribute
homogeneously throughout the solution. The crosslinking
reaction occurred in a few hours at room temperature, leading
to the formation of a yellowish hydrogel. To remove the
unreacted chemicals, the partially swollen hydrogel samples
were then soaked in a large amount of distilled water until
equilibrium was attained. At this stage, the hydrogel samples
were perfectly clear and transparent. After the washing stage,
dry products were obtained by desiccating the hydrogel
samples by means of a thermal treatment in a convection
oven at 45∘
C. Powder-like samples were finally obtained by
grinding. The final powder size distribution was in the range
0.1–1 mm.