Salix Viminalis as a Source of Nanomaterials and Bioactive Natural Substances - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 98

activity of the extracts. The 1 H NMR experiments were recorded on a Bruker Avance
spectrometer operating at 700 MHz.
Chromatographic separation of binary gas mixtures was performed using a gas
chromatograph Schimadzu GC-14B supplied with a TCD detector kept at constant
temperature of 110°C. Volume flow of carrier gas (helium) was set at 10, 15, 20, 25,
30, 40, and 50 cm 3 /min. The flow rate value was set regarding the results of van Dem-
ter optimization procedure preformed prior to the separation tests. A. glass chromato-
graphic loop was 2.5 m long and its inner diameter was 2.6 mm. The separation tests
were performed at several temperatures (70, 60, 50, 40, 30°C) and consisted in re-
cording of chromatograms for injected samples (pure gases, two component mixtures,
and three component mixtures). For better separation of gases two measures were
undertaken:
• Instead of bar carbon molecular sieves whose average surface area is placed
within the range 300-400 m 2 /g, activated carbon were obtained via conventional
zinc chloride method (final surface above 1,400 m 2 /g).
• Active carbon was grained, sieved and 0.02-0.25 mm fraction was collected for
filling of chromatographic loop.
The antioxidative effect of the obtained phenolics fractions on a selected diester
DBS (dibutyl sebacate) was carried out following the ASTM D 4871 standard. This
universal test allows the examination of oxidation stability of a liquid test sample. The
samples of uninhibited DBS and after addition of ca. 1,000 ppm of a selected antioxi-
dant agent (BHT, extract A, extract B) were prepared and examined. Commercial BHT
(2,6-ditertbutyl-4-methylphenol) was used as a standard antioxidant for comparison.
Investigated samples with a mass of 100 g were subsequently placed in the reaction
vessel and oxidized at 150°C by flowing air stream (100 cm 3 /min).
results
The Salix viminalis originated active carbons are in fact solids containing a network of
very tinny pores. Average calculated linear dimension (Horvath and Kawazoe, 1983)
was below 1 nm. In practice, these pores nearly exclusively contribute to the total pore
volume of the obtained carbons. Moreover PSD is very narrow suggesting that such
materials are potential molecular sieves providing molecular sieving abilities (Figure 2).
This property of the obtained carbons needed an experimental verification.
We assumed that molecular sieving effect over a porous solid should be more ef-
ficient if the gas molecules (to be separated) are of possibly different dimensions and
when the size of pores becomes comparable to dimensions of the molecules. In our
study, average pore size approaches sub-nanometer range which in general is only
few times bigger than average dimensions of some simple molecules. Dimensions of
simple molecules and atoms in gas phase (Table 1) are given in literature (Shirley and
Lemcoff, 2002). The dimensions were estimated basing on experimental results and
theoretical considerations.
Some studies (Corma, 1997; Ivanova et al., 2004) point out the importance of
geometric factor as the main reason of gas separation leading to differentiated adsorp-
tion rate of molecules from gas phase in static condition (determination of adsorption