A. PAVELKOVA et al.: ELECTROSPINNING OF BIODEGRADABLE POLYESTER URETHANE: ...
195–197
ELECTROSPINNING OF BIODEGRADABLE POLYESTER
URETHANE: EFFECT OF POLYMER-SOLUTION CONDUCTIVITY
ELEKTROPREDENJE BIORAZGRADLJIVEGA POLIESTER-
URETANA: VPLIV PREVODNOSTI RAZTOPINE POLIMERA
Alena Pavelkova, Pavel Kucharczyk, Vladimir Sedlarik
Centre of Polymer Systems, University Institute, Tomas Bata University, Tr. Tomase Bati 5678, 76001 Zlín, Czech Republic
apavelkova@cps.utb.cz
Prejem rokopisa – received: 2015-06-29; sprejem za objavo – accepted for publication: 2016-02-10
doi:10.17222/mit.2015.139
This work deals with an investigation of fabrications of nanofibres based on biodegradable polylactic-acid/polyethylene-glycol-
chain-linked copolymers, using the electrospinning technique. Crucial attention is paid to describing the effect of
polymer-solution conductivity on the morphology of the resulting nanofibres. Nanofibre systems were studied with scanning
electron microscopy and the subsequent image analysis of nanofibre diameters. Hydrolytical degradability of the investigated
copolymers was studied using gel permeation chromatography. The results show a significant effect of polymer-solution
conductivity on the quality of nanofibres.
Keywords: electrospinning, nanofibres, polylactide polyethylene glycol copolymer
To delo obravnava preiskavo izdelave nanovlaken na osnovi biorazgradljive, v verigo povezanih kopolimerov polimle~ne
kisline/polietilen glikola, z uporabo tehnike elektropredenja. Najve~ja pozornost je usmerjena v opis vpliva prevodnosti razto-
pine polimera na morfologijo izdelanih nanovlaken. Sistem nanovlaken je bil prou~evan z vrsti~no elektronsko mikroskopijo in
analizo slik premerov nanovlaken. Hidroliti~na degradacija preiskovanih polimerov je bila prou~evana z gelsko permeacijsko
kromatografijo. Rezultati ka`ejo mo~an vpliv prevodnosti raztopine polimera na kvaliteto nanovlaken.
Klju~ne besede: elektropredenje, nanovlakna, polilaktid polietilen glikol kopolimer
1 INTRODUCTION
Electrospinning products based on biodegradable
polymers have been suitable materials for innovative
tissue-engineering applications.1
Polylactic acid (PLA) is a biodegradable thermo-
plastic polymer with good properties and processability.
Nevertheless, its properties can also be limiting in some
of the applications.2 An effective way of how to improve
the PLA properties can be a modification of synthesis
using a chain-linking reaction.3 In this two-step process,
a functionalized low-molecular-weight prepolymer is
prepared first and then, in the second step, the chain
linking through the reactive chain ends with a chain-link-
ing agent (usually diisocyanate) is carried out.4
The research presented here focuses on the electro-
spinning of polyester urethane (PEU) based on
PLA/polyethylene glycol (PEG) copolymer chain linked
with diisocyanates. The morphology and characteristics
of the prepared nanofibres are correlated with the con-
ductivity of the polymer solution. Degradability of the
studied PEU was studied under abiotic conditions in a
phosphate-buffer medium.
2 EXPERIMENTAL PART
2.1 Materials
L-lactic acid, poly(ethylene glycol) (PEG, MW = 400),
hexamethylene diisocyanate (HMDI) and Tin(II)2-
Materiali in tehnologije / Materials and technology 51 (2017) 2, 195–197 195
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 620.1:620.3:67.014 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(2)195(2017)
Figure 1: Scheme of the synthesis route: 1) preparation of prepolymer, 2) poly (lactic acid)-poly (ethylene glycol) chain-linking reaction
Slika 1: Shema poti sinteze: 1) priprava predpolimera, 2) poli (mle~na kislina)-poli - (etilen glikol) reakcija veri`nega povezovanja
ethylhexanoate Sn(Oct)2 (92.5–100.0 %) were purchased
from Sigma-Aldrich; phosphate buffer (PB, 0.1 mol.L–1,
pH = 7, NaH2PO4 adjusted with NaOH) and tetrahydro-
furan (HPLC-grade) were sourced from Chromspec,
Brno, Czech Republic.
The synthesis of copolymers was conducted through
a polycondensation reaction and, in the second step, a
chain-linking reaction with hexamethylene diisocyanate
(HMDI) was performed (Figure 1). In this study, a co-
polymer with a molar ratio of NCO and OH groups equal
to 3.2 was used. The preparation of the studied PEU is
described in detail in our previous work.5
2.2 Method
The molecular weight of PEU was examined with gel
permeation chromatography under the conditions de-
scribed in reference.5 A hydrolysis test was performed on
round-shaped samples (a diameter of 3.4 mm and a
thickness of 1.5 mm) fully immersed in a liquid-buffer
medium (pH = 7) at 37 °C and 55 °C.
The electrospinning process was carried out on an
in-house constructed apparatus consisting of a jet and a
target with a separation distance of 18 cm at 23 °C. The
PEU solution (12 % of the mass fraction in DMF) was
charged with DC 75 kV. The flow rate of the polymer
solution was 0.086 mL min–1. The conductivity of the
polymer solution was adjusted with citric acid and
sodium tetraborate (3:1, w/w) to 59.5, 107.9 and 150.9
μS cm–1.
The morphology of the electrospun nanofibres was
studied with scanning electron microscopy (Tescan Vega
II LMU, Czech Republic). The morphology analysis of
the nanofibres was carried out with an image analysis of
SEM micrographs using the ImageJ software.
3 RESULTS
The values of the average molecular weight (Mw) of
the studied PEU and their reduction during the degrada-
tion process at 37 °C and 55 °C are presented in Table 1.
While Mw of PEU at the beginning of the degradation ex-
periment was 300 kg.mol–1, the samples showed a 99 %
Mw reduction after 25 d.
Table 1: Molecular-weight loss of PLA-PEG copolymers during the
degradation experiment
Tabela 1: Zmanj{anje molekulske mase PLA-PEG kopolimera, med
preizkusom degradacije
Degrada-
tion time
(days)
55 °C 37 °C
Mw
(kg mol–1) \
Mw
(kg mol–1) \
0 300 9.2 300 9.2
4 42 5.6 143 7.3
11 8.0 5.1 84 6.8
25 2.3 3.2 3.0 2.5
32 2.0 2.8 1.9 1.9
52 not detected not detected 1.0 1.5
Diameter distributions of the nanofibre systems
prepared from the PEU solutions with various conduc-
tivity values, together with inserted SEM micrographs,
can be seen in Figure 2. Table 2 presents the number
(Dn), the weight average (Dw) and the polydispersity
(Dw/Dn) of nanofibre diameters.
Table 2: Effect of PEU-solution conductivity on the fibre diameter
Tabela 2: Vpliv prevodnosti raztopine PEU na premer vlaken
Conductivity
(μS cm–1) Dn (μm) Dw (μm) PDI
59.5 0.24 0.36 1.50
107.9 0.18 0.28 1.55
150.9 0.29 0.42 1.42
A. PAVELKOVA et al.: ELECTROSPINNING OF BIODEGRADABLE POLYESTER URETHANE: ...
196 Materiali in tehnologije / Materials and technology 51 (2017) 2, 195–197
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 2: Histogram of PEU fibre-diameter distribution and corres-
ponding SEM micrographs (inserted). The conductivity of PEU
solutions was adjusted to: a) 59.5 μS cm–1, b) 107.9 μS cm–1 and c)
150.9 μS cm–1
Slika 2: Histogram razporeditve premera REU-vlaken in njihov
SEM-posnetek. Prevodnost PEU raztopine je bila uravnana na:
a) 59.5 μS cm–1, b) 107.9 μS cm–1 in c) 150.9 μS cm–1
4 DISCUSSION
The degradation behaviour of PEU is in accordance
with the already published results.5 The kinetics of the
Mw reduction is interesting as it is strongly dependent on
the temperature. A significantly faster degradation of
PEU occurs at a temperature (55 °C) that is close to the
glass-transition temperature. On the other hand, the
degradation rate observed at 37 °C provides results com-
parable with the PLA-based polymers. The homogeneity
of the electrospun PEU nanofibres was enhanced by
increasing the conductivity of the polymer solution, un-
like in the case of low-conductivity PEU solutions where
an occurrence of the inhomogeneity of the electrospun
products was observed. A combination of nano- and
sub-microfibres was obtained for the PEU solutions with
the lowest (59.5 μS cm–1) and the highest conductivity
(150.9 μS cm–1) while a relatively narrow distribution of
nanofibre diameters was found for the PEU solution with
a medium conductivity (107.9 μS cm–1). The non-unifor-
mity of fibre diameters could have been caused by a
broad molecular-weight distribution, whose relation to
the fibre distribution was reported in the work of J.
Lyons et al.,6 though for a different type of material.
5 CONCLUSIONS
Biodegradable PEU nanofibres based on PLA/PEG
chain-linked copolymers can be easily fabricated using
the electrospinning process. The morphology of the
resulting nanofibres can be significantly influenced by
adjusting the polymer solution before the electrospinning
process. PEU can provide a product with a mixture of
nano- and sub-microfibres that can be potentially useful
for specific filtration applications.
Acknowledgements
This work was financially supported by the Czech
Science Foundation (grant No. 15-08287Y), the Ministry
of Education, Youth and Sports of the Czech Republic
(grant No. LO1504) and the Internal Grant Agency of
TBU in Zlin (grant No. IGA/CPS/2015/003).
6 REFERENCES
1 W. Jiang, B. Y. S. Kim, J. T. Rutka, W. C. W. Chan, Nano-
particle-mediated cellular response is size-dependent, Nature
Nanotechnology, 3 (2008) 145–150
2 A. P. Gupta, New emerging trends in synthetic biodegradable
polymers – Polylactide: A critique, European Polymer Journal, 43
(2007), 4053–4074
3 S. I. Moon, C. W. Lee, I. Taniguchi, M. Miyamoto, Y. Kimura,
Melt/solid polycondensation of L-lactic acid: an alternative route
to poly (L-lactic acid) with high molecular weight, Polymer, 42
(2001), 5059–5062
4 J. Kylmä, J. Tuominen, A. Helminen, J. Seppälä, Chain extending of
lactic acid oligomers. Effect of 2, 2?-bis (2-oxazoline) on 1,
6-hexamethylene diisocyanate linking reaction, Polymer, 42
(2001), 3333–3343
5 A. Pavelkova, P. Kucharczyk, P. Stloukal, M. Koutny, V. Sedlarik,
Novel poly (lactic acid)-poly (ethylene oxide) chain-linked
copolymer and its application in nano-encapsulation, Polymers
for Advanced Technologies, 25 (2014), 595–604
6 J. Lyons, Ch. Li, F. Ko, Melt-electrospinning part I: processing
parameters and geometric properties, Polymer, 45 (2004),
7597–7603
Materiali in tehnologije / Materials and technology 51 (2017) 2, 195–197 197
A. PAVELKOVA et al.: ELECTROSPINNING OF BIODEGRADABLE POLYESTER URETHANE: ...
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS