Cellulose (2018) 25:1353–1364
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tester, a relatively novel device which can be used to obtain quick and non-destructive measurements of material colour change caused by incident light, was described in (Lerwill et al. 2008; Łojewski et al. 2011). The instrument was equipped with a high power xenon light source and VIS spectrometer, which allow induced colour changes to be monitored. Three lightfastness measurements were taken for each type of paper.
manufacturer’s instructions. The test gives relative content of ATP, ADP and AMP (RLU—relative luminescence units).
Results and discussion
Quantitative evaluation of material
The progress of ion exchange was monitored by XRF analysis, the results of which are shown in Fig. 1. It can be noted that the time necessary to achieve saturation in ion exchange was around 2 h. For the assumed half exchange, a time of 1 h was chosen. The degree of ion exchange was then measured by the XRF method, by digesting the samples in concentrated HNO 3 . In order to dispose of the external unattached silver moieties, complexation using EDTA sodium salt was employed. The progress of elution with the EDTA solution of a given concentration was monitored by XRF analysis of eluate solutions. To check the efficiency of EDTA washing, the AgFAU samples were also treated with the same quantities of water. After repeated treatment with the same portions of EDTA, the amount of silver in the eluent solution stabilises and reaches a low constant value, which is 0.15% of the initial value. This was assigned as the completion of the removal process. The state and amount of silver on the zeolite surface at different stages of elution were also analysed with XPS, which indicated the presence of silver NPs on the initial sample. Semi-quantitative results are shown in Table 2.
Degree of polymerisation
The weight-averaged degree of polymerisation (DP w ) of cellulose (cellulose triphenylcarbamate, CTC) was determined by size exclusion chromatography (SEC). The details concerning the analytical procedures used can be found elsewhere (Pawcenis et al. 2015). In brief, analysis of molecular mass distributions was carried out in tetrahydrofurane (THF) solvent used as a mobile phase, with double detection: (1) by multiple angle laser light scattering (MALLS, Waters), and (2) refractive index (RI). Both detectors worked at a light wavelength of 658 nm. In the measurements, a value of the specific increment of the refractive index equal to 0.162 cm 3 /g was used. The paper samples containing Ag 0 ,Ag ? and zeolite were first defibred in a beaker in 50 cm 3 of water (the process was aided by ultrasound waves). The standard procedure of preparing cellulose material was applied (Lauriol et al. 1987; Stol et al. 2002), using cellulose derivative CTC in THF solution. The AgFAU was removed from the CTC solutions by filtration through a Teflon syringe filter with pore diameter of 0.45 l m. The other additives were removed before derivatisa- tion by washing.
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Antimicrobial properties
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Escherichia coli from the culture collection of the laboratory of the Plant-Microbial Interaction Group of the Jagiellonian University (Krako´w, PL) were used in the laboratory tests. A detailed description of the sample preparation and analytical procedure can be found in our previous work (Łojewska et al. 2015). The efficiency of the biocidal process on the prepared paper samples was checked using the test LuciPac Pen equipped with a lumitester (Kikkoman lumitester PD- 20) (ATP ? AMP, Hygiene Monitoring test kit from Kikkoman Corp., code 60331), in accordance with the
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0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 20 30 40 50 60 70 80 90 100 0
time (h)
Fig. 1 Silver ion exchange isotherm
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