Obtaining and characterising Cu-infused antimicrobial films formed from regenerated cellulose-CaCO3 composite

Abstract

Cellulose and cellulose-CaCO3 dopes were prepared by ultrasound dispersion of CaCO3 (0, 0.26, or 0.65 w/w%) and dissolution of cellulose (13 w/w%) in ionic liquid 1-ethyl-3- methylimidazolium acetate at 90 °C. Thereafter, the films were obtained by rode casting over a pre-heated glass plate, together with methanol used as a regeneration agent. Subsequently, the films were washed in hot water (80 °C) to remove the residual ionic liquid solvent - a process that can be extended to recover ionic liquid for re-use. To impart antimicrobial properties to the cellulose-CaCO3 composite films, selected samples of the wet films were treated with 10 mM CuSO4 solution for different times (30, 60, and 120 min). Furthermore, half of these CuSO4 treated films were subsequently treated with ascorbic acid to synthesise in situ Cu-based nanoparticles on the film surface. After drying whilst held under tension at room temperature, the films were characterised in respect to their mechanical properties as well as antimicrobial activity. The results revealed that, in the case of films treated for 30 min with CuSO4 solution, the incorporation of 0.26 w/w% CaCO3 correlated with an increase in the film hardness, while in the case where the treatment with CuSO4 solution was performed for longer (60 min) this hardness trend was reversed. The elastic modulus decreased with increasing content of CaCO3. Only the films treated with CuSO4, and those with Cu-based nanoparticles, possessed excellent antimicrobial activity against the bacteria E. coli, S. aureus, and the fungus C. albicans. However, the results in the case of C. albicans, showed an additional dependence, in that films treated with CuSO4 solution for 60 min demonstrated increasing antimicrobial activity against the fungus specifically with increasing CaCO3 content.