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1National Institute for Laser, Plasma and Radiation Physics - INFLPR, Bucharest-Magurele, Romania 2 University of Bucharest, Faculty of Chemisty, 4-12 Regina Elisabeta Street, Bucharest, Romania
3 University of Bucharest, Faculty of Physics, Atomistilor Street, no. 405, Magurele, Romania
*Correspondent author: [email protected]
Radiation synthesis and characterization of the
network structure of PVP- collagen
superabsorbent hydrogels
A. Scarisoreanu1, M. Demeter1,2*, I. Calina1,3, C. Vancea1,3, E. Stancu1,3, E. Badita1
Fourth International Conference on Radiation and Applications in Various Fields of Research
May 23 – 27, 2016, Nĭs, Serbia
Outline
1. Introduction
2. Experimental section
2.1. Synthesis of PVP-collagen superabsorbent hydrogels
2.2. Experimental setup
2.2. Characterization
3. Results and discussions: 3.1. Gel fraction
3.2. Swelling degree
3.3. Hydrogel compositions
3.4. Rheological analysis (G’ and G’’ determination)
3.5. Network parameters
4. Conclusions
1. Introduction – Superabsorbent polymers
Definiton: moderately crosslinked, 3-D, hydrophilic network polymers that
can absorb and conserve considerable amounts of aqueous fluids even under
certain heat or pressure [1].
Applications:
• diaper industry
• agriculture
• medicine, pharmacy
• tissue engineering
• wound dressings
Fig. 1. Example of PVPCOL hydrogels:
A - swollen COLPVP (70 :30)
B - dried COLPVP hydrogels;
C - swollen COLPVP hydrogel (50 :50)
SD =10 000 %
The purpose of study
• to develop new PVPCOL superabsorbent hydrogel
with better swelling, network parameters and
mechanical properties through electron beam
radiation synthesis in the presence of sodium
salts of acrylic acid and a water soluble crosslinking
agent, N’N methylene-bis-acrylamide to be use in
medical field as wound dressings.
Collagen Type I (1%, w/w) Mw = 300 000 g/mol
Polyvinylpirrolidone (10%, w/w) Mw = 360 000 g/mol
2.1. Synthesis of PVP-collagen superabsorbent hydrogels
Mixtures of PVP-collagen
30:70, 50:50 and 70:30
0.075; 0.05; 0.02 moles of Acrylic Acid (99%, anhydrous)
0.07; 0.04; 0.013 moles of NaOH
2 %, 1%; 0.5 % of N’N-Methylenebis(acrylamide) 99%
Fig. 2. Plastic syringes
with PVP-collagen
blends before EB
irradiation
2.2. Experimental setup – electron beam (EB) irradiation
• Linear electron accelerator ALIN 10
(6. 23 MeV, INFLPR, Magurele -
Romania)
• Absorbed doses:
• 5; 7.5; 10; 12.5; 25; and 40 kGy
• Average dose rate: 1.88 kGy/min.
• Dosimetry:
- graphite calorimeter (built by our
group according to ISO/ASTM 51631
[5] and calibrated at the Institute of
Nuclear Chemistry and Technology,
Poland). Fig. 3. PVP-collagen hydrogels after
EB irradiation
3.1. Gel fraction
The sol fraction was removed by
immersing the cylindrical hydrogel
samples with the thickness of 4-5
mm in deionised water for 48 h at
constant room temperature (25ºC),
in accordance with the method
described by Nagasawa et al. [6].
After 48 h, the swollen gels were
dried again in a vacuum oven at a
constant temperature to constant
weight.
The gel fraction (G) was calculated
from the initial dry gel weight (Wi)
and the dried insoluble part of the
sample after water extraction
(Wd):
Fig. 3. Gel fraction of PVPCOL hydrogels with
0.02 moles AAc and 0.5 % NMBAm
% *1 00 d
i
WG
W
3.2. Swelling degree (1)
Hydrogel dried samples with a 0.1-0.2
g mass were placed in silk bags,
weighed and then immersed in
deionised water. At the established
reading time, the silk bags were moved
out, carefully blotted with filter paper
and then weighed again.
After swelling, based on dry (Wd) and
swollen (Ws) gel weights, the swelling
degree (SD) was calculated as:
Fig. 4 . Swelling degree of PVPCOL hydrogels
A - with 0.075 moli AAc and 2% NMBAm
B - with 0.05 moli AAc and 1% NMBAm
A
B
100
s d
d
W WSD x
W
3.2. Swelling degree (2)
Fig. 5. Swelling degree of PVPCOL hydrogels
- with 0.02 moles AAc and 0.5 % NMBAm
3.3. Hydrogel compositions – FTIR investigations
Fig. 6. FTIR spectra of PVPCOL dried hydrogels
with 0.075 moli AAc and 2% NMBAm
The ATR-FTIR spectra are
presented only in the 4000 - 2500
cm-1 range, this area is the most
specific for hydrogels structure.
Hydrogels present a large band
between 3550 and 3000 cm−1
linked to the stretching O–H from
the intermolecular and intra-
molecular hydrogen bonds.
The vibrational band observed
between 2800 and 3000 cm−1
refers to the stretching C–H from
alkyl groups [7].
The shifting of the FTIR band
position towards the lower
wavenumbers or increase of
intensity can be related to the
crosslinking reactions.
0.02 moles AAc
0.5 % NMBAm
0.05 moles Aac
1% NMBAm
In the FTIR spectra of PVP-collagen
hydrogels, the large band specific to
stretching vibration of νO–H was found
at 3330, 3367 and 3390 cm-1.
This band shifted toward the higher
wavenumbers function of hydrogel
composition.
The stretching vibrations of alkyl groups
were found at 2920 cm-1 and 2855 cm-1.
In the case of PVP-collagen 50:50 and
70:30, the increase of band intensity of
O–H function of radiation dose was
observed
At higher absorbed dose the position of
absorption band is shifted to lower wave
numbers.
3.4. Rheological analysis - (G’ and G’’ determination)
• In order to determine the elastic moduli of the gels (G’-elastic
modulus and G”-viscous modulus), oscillatory rheological
measurements were performed.
• All measurements were performed at 25oC in the linear viscous
elastic region, at the rate of deformation γ = 0.1-1% and the
frequency range of ω0 = 0.01-1 Hz, using a Thermo MARS II
Rheometer equipped with a 20 mm diameter plate (plate geometry).
The gap size was settled at 0.139 mm.
• This measurements were performed to determine the strengthen of
PVPCOL hydrogels and for calculation of molecular weight between
crosslinks (Mc)
3.5. Network parameters
n2,x polymer volume fraction in the swollen state and
after irradiation
Mc molecular weight of the polymer chain between two
crosslinks
x mesh size
1
21/ (1 / ( 1)x w wn
1/ 32 / 3'
2 2MG A RT
c r m
1/ 22
1/ 3 2
McC
s nl
Mr
x n
Tabel 1. Network parameters of PVP-collagen hydrogel
Dose
(kGy)
G’
(Pa)
(g/mol)
(mol/cm3)
ξ
(nm)
5 6344 7174 1.39E-04 56
7.5 4950 9293 1.08E-04 60
10 4595 9891 1.01E-04 63
12.5 3923 11745 8.51E-05 69
25 3574 15517 6.44E-05 72
40 3601 13498 7.41E-05 77
The elastic modulus (G’) decreased with radiation dose
According to rheological tests, the stronger gel was obtained at 5 kGy for
PVPCOL hydrogel with 70:30 in composition
The Mc increase as function of absorbed dose up to 25 kGy
The crosslinking density decreased with the absorbed dose, as a direct
consequence of the increase of the mesh size
4. Conclusions
• PVP-COL superabsorbent hydrogels with a
swelling degree over 10 000% were obtained
• Gels with excellent mechanical properties (6 kPa)
can be obtained from a COLPVP 70:30 blend
• The addition of 0.02 moles of AAc and
0.5 % NMBAm and irradiating at 5 kGy, has given
the best results for the PVP-collagen hydrogel
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Thank you!
Acknowledgement: This work was supported by the National Authority for Scientific Research and Innovation, Romania (Nucleus Program PN0939/0402) and INFLPR.