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O. Nadtoka et al.
linked by the radiation method are poly(vinyl alcohol), poly(ethylene glycol), and
poly(acrylic acid) [2–4].
It is shown that the radiation cross-linking of polymers upon irradiation in
aqueous solutions is achieved at lower doses than when the polymer is irradiated
in a solid or molten state, due to the participation in the cross-linking of free OH
radicals formed as a result of radiolysis of water [5].
Hydrogels, particularly highly swollen ones, usually possess poor mechanical
properties. So, the aim of our research focuses on cross-linked PVA to obtain
hydrogels with improved mechanical properties that will be further used as wound
dressing materials. We investigate mechanical and thermal properties of crosslinked hydrogels depending on the PVA’s concentration.
12.2 Experimental
12.2.1 Hydrogel Synthesis
Polyvinyl alcohol from Fluka with M w = 4 × 10 5 g/mol was used for hydrogel
synthesis. Polymer was dissolved in distilled water (T = 70 ◦ C); solution was
cooled and kept at room temperature. PVA solutions with concentrations 0.04, 0.06,
and 0.08 g/ml were used for gel preparation. All these concentrations were above
the critical crossover concentration (C*) for PVA sample chosen for this study.
Value of C* was determined by viscometry method [6] and was equal to 0.03 g/ml.
Homogeneous solutions were hermetically placed in PE ziplock packages, and the
thickness of solution in each pack was about 3 mm. Then, samples were irradiated
under electron beam by pulsed electron accelerators of “ARGUS” (the electron
energy E e = 1 MeV) and “Electronic” (E e = 4 MeV) models with dose 50 kGy
to become cross-linked [7]. The electron flux intensity was varied within an interval
from 0.1 to 2.5 μA/cm 2 . The control of the current density in the electron beam
and the integral dose of the irradiation were carried out by the Faraday cylinder
method. Measurement of sample temperature during electron irradiation was carried
out using a differential thermocouple “alumel-chromel.” The required temperature
(25 ◦ C) was supported by the balance of heating by the electron beam of the
incandescent lamp and cooling by the air fan. The hydrogels in the final form were
transparent sheets of few millimeters.
12.2.2 Experimental Methods
12.2.2.1 Morphological Analysis
The sample morphology was examined by using a scanning electron microscope
mod, Stereoscan 440 (LEO), Cambridge, UK instrument. This analysis aimed to
O. Nadtoka et al.
linked by the radiation method are poly(vinyl alcohol), poly(ethylene glycol), and
poly(acrylic acid) [2–4].
It is shown that the radiation cross-linking of polymers upon irradiation in
aqueous solutions is achieved at lower doses than when the polymer is irradiated
in a solid or molten state, due to the participation in the cross-linking of free OH
radicals formed as a result of radiolysis of water [5].
Hydrogels, particularly highly swollen ones, usually possess poor mechanical
properties. So, the aim of our research focuses on cross-linked PVA to obtain
hydrogels with improved mechanical properties that will be further used as wound
dressing materials. We investigate mechanical and thermal properties of crosslinked hydrogels depending on the PVA’s concentration.
12.2 Experimental
12.2.1 Hydrogel Synthesis
Polyvinyl alcohol from Fluka with M w = 4 × 10 5 g/mol was used for hydrogel
synthesis. Polymer was dissolved in distilled water (T = 70 ◦ C); solution was
cooled and kept at room temperature. PVA solutions with concentrations 0.04, 0.06,
and 0.08 g/ml were used for gel preparation. All these concentrations were above
the critical crossover concentration (C*) for PVA sample chosen for this study.
Value of C* was determined by viscometry method [6] and was equal to 0.03 g/ml.
Homogeneous solutions were hermetically placed in PE ziplock packages, and the
thickness of solution in each pack was about 3 mm. Then, samples were irradiated
under electron beam by pulsed electron accelerators of “ARGUS” (the electron
energy E e = 1 MeV) and “Electronic” (E e = 4 MeV) models with dose 50 kGy
to become cross-linked [7]. The electron flux intensity was varied within an interval
from 0.1 to 2.5 μA/cm 2 . The control of the current density in the electron beam
and the integral dose of the irradiation were carried out by the Faraday cylinder
method. Measurement of sample temperature during electron irradiation was carried
out using a differential thermocouple “alumel-chromel.” The required temperature
(25 ◦ C) was supported by the balance of heating by the electron beam of the
incandescent lamp and cooling by the air fan. The hydrogels in the final form were
transparent sheets of few millimeters.
12.2.2 Experimental Methods
12.2.2.1 Morphological Analysis
The sample morphology was examined by using a scanning electron microscope
mod, Stereoscan 440 (LEO), Cambridge, UK instrument. This analysis aimed to