Cellulose products modified with monomeric and gemini surfactants: antimicrobial aspects

The aim of this study was to examine the impact of microbiocides on the reduction of the microbial population on paper in order to protect it against biodeterioration. The cellulose products were modified with the cationic gemini surfactant hexamethylene-1,6-bis-(N,N-dimethyl-N-dodecylammonium bromide) C6 and its monomeric analog (didecyldimethylammonium chloride) DDAC. The microbiocides were introduced into the paper by coating and spraing. In the coating method the microbiocides were mixed with starch solution and applied to paper surface as a wet film with a thickness of 24 and 50 µm. In the spraying method the surfactants were applied at 3% concentration in water to get 0.005 ml/cm² of paper. Experiments were performed with moulds of the genera Aspergillus, Penicilllium, Chaetomium and Trichoderma and bacteria represented by the genera Bacilllus and Pseudomonas. The antimicrobial properties of the paper modified with surfactants were determined by qualitative and quantitative methods. The zones of inhibition were measured using the parallel streak method. Macroscopic assessment of mould growth on the surface of the paper samples was performed over 21 days of incubation. In quantitative analysis, the survival rate of microorganisms on the modified paper samples was determined over 24 h. Aspergillus brasiliensis was the least sensitive mould, with no observable inhibition zones. No growth of this mould was observed either on or underneath the sample. Both of the surfactants applied as coatings or sprays protected the paper effectively against the growth of bacteria and mould. However, the spraying method is simpler to use. Over 24 h, the number of spores and bacteria in all the samples containing surfactants was reduced to below 1 log/10 cm² (reduction factor up to 99.9%). The compounds may therefore be applied as antimicrobial agents for the protection of paper.