Antifungal activity and humidity sensitivity of quaternized cellulose synthesized in NaOH/urea aqueous solution

In this work we report the fabrication of cellulose-based humidity responsive material with antifungal activity. The quaternized cellulose (QC) derivatives with low degree of substitution (DS) values of 0.08-0.37 were synthesized in NaOH/urea aqueous solution. Water insoluble QC membranes (c-QCM) were prepared by casting from QC aqueous solutions, followed by crosslinking with glutaraldehyde. The c-QCMs were disintegrated in acid solutions, but were able to keep membrane shape in neutral and mild basic solutions with pH value of 7.2 and 9.7. The equilibrium water adsorption ratios of c-QCMs were in the range of 66-98%, depending on the DS values of quaternary ammonium groups and the pH value of the aqueous solutions. The antifungal activity of QC was evaluated and found that QC could effectively inhibit the reproduction of Rhizopus stolonifer, Aspergillus flavus and Penicillium digitatum, with minimum inhibitory concentration of 5, 10, and 7.5 mg/mL, respectively. The resistivity of the c-QCM changed for about 65-134 times corresponding to the change of environmental relative humidity from 20 to 99%; and the performance of c-QCM as a resistive-type humidity responsive material was consistent in the cycling of relative humidity.