Cellulose (2018) 25:1353–1364
1361
23 C and 50% RH are shown in Fig. 7. There, for all samples containing silver, an average drop of around 20% in the L* values was observed in comparison with the reference paper sample P. An important observa- tion is that there was almost no difference between paper samples with silver NPs (PAg 0 ) and our final material (PZAg ? _EDTA). Colour stability (lightfastness) over time was also measured by spot light ageing tests performed with a micro fading tester. The results are expressed by D E values in Fig. 8. Again, the highest colour change values were noted for the samples containing silver, reaching 35 units for the PAg ? sample. The lightfast- ness of paper Ag NPs and the final sample PZAg ? _- EDTA is very much alike, with only three D E units difference.
2,5x10 3
2,0x10 3
1,5x10 3
1,0x10 3
5,0x10 2
0,0
the samples containing zeolites, PZAg ? and the final PZAg ? _EDTA, and slightly less so for the PAg ? sample. This indicates that in fact the active silver species in the mechanism of biocidal activity are silver cations and not silver zero valent NPs (PAg 0 ), which respond comparably to the paper reference sample P, indicating no biocidal activity and a low concentration of Ag ? . To illustrate the action of materials against E.coli strain, the inhibition zone is presented (Fig. 10). A halo, proving the antimicrobial behaviour of manu- factured material, can be seen around the paper disc. Fig. 9 Antibacterial effects expressed as ATP/AFM ratio by RLU counts for reference and modified paper materials against E. coli strain
Antimicrobial properties
The antimicrobial properties of the obtained final material and the reference samples are presented in Fig. 9. The tests were performed with respect to E. coli strains used typically as a representative to assess the biocidal properties of materials. The highest and comparable activity can be noted for both paper samples containing zeolites, as can be judged from the comparison of the ATP/ADP/AMP content in the samples (expressed as counts) in Fig. 9. The content of adenosine phosphates can be used as a direct measure of the bioactivity of the living organisms, especially if the bacterial strain is of the same identity (as discussed by Kwiatkowska et al. (2016) and references therein). The greatest drop in the values was observed for both
50
40
30
20
10
0
Fig. 8 Total colour change ( D E) obtained in micro fading tests for paper samples
Fig. 10 The image of the inhibition zone of prepared paper material
123
Made with FlippingBook Ebook Creator