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Indian Journal of Fibre & Textile Research
Vol. 37, September 2012, pp. 211-216
Characterization of nanomembrane using nylon-6 and nylon-6/poly
(e-caprolactine) blend
P Gunavathi1,a
, T Ramachandran
2 & K P Chellamani
1
1The South India Textile Research Association, Coimbatore 641 014, India
2Karpagam Institute of Technology, Coimbatore 641 105, India
Received 3 May 2011; revised received and accepted 5 August 2011
This study is mainly focused on characterization of nanomembrane using nylon-6 and its blend with poly
(e- caprolactine) (PCL). Nylon-6 nanomembrane has been developed using formic acid at four different viscosity levels of
158.4, 420.8, 920.8 and 1417 cPs. Another nanomembrane of nylon-6/PCL (80:20) blend has also been developed using
nylon-6 polymer solution viscosity of 1417 cPs at three different polymer concentrations (8, 10 and 12%) of PCL. The
characterization of nanomebrane is done using scanning electron microscope and Fourier transformed infrared. It is
observed that the nanomebrane of 80:20 blend ratio of nylon-6/PCL at 1417 cPs nylon-6 viscosity and 12 % concentration
of PCL produces uniform fibre structure.
Keywords: Fourier transformed infrared, Nylon-6, Nanomembrane, Poly (e-caprolactine)
1 Introduction
Electrospinning is a technique that utilises electric
force alone to drive the spinning process and to
produce polymer fibres from solution (or melts)1. The
basic mechanism of electrospinning involves applying
an electric force between a suspended droplet solution
or melt at a capillary tip and collector2. When the
intensity of the electric field overcomes the surface
tension of the polymer solution or melt, a charged jet
is ejected and travels to the grounded target,
generating fibres typically in the form of nonwoven
mat. The major advantage of electrospinning is that
nanofibres can be spun directly from polymer
solutions, hence this method forms one of the central
research interests associated with nanofibre
technology and has been applied to many kinds of
synthetic polymers as well as the natural biogenic
structural proteins and polysaccharides3.
Electrospinning process and the characteristics of the
fibres depend on the various parameters, such as
solution concentration, applied electric field strength,
tip-to-collector distance and fluid flow rate.
Specifically, applied voltage, solution surface tension
and conductivity can influence the formation of
beaded fibres4. The fibres that can be produced using
electrospun fibres have different characteristics such
as very large surface area to volume ratio, flexibility
in surface functionalities, and superior mechanical
performance (e.g. stiffness and tensile strength)
compared with any other known form of that
material5. The use of electrospun nanofibrous mats
has also attracted a great deal of attention in
biomedical applications such as tissue engineering,
scaffolding, wound dressing, artificial blood vessels,
drug delivery carriers, cosmetic and skin masks6.
Nylon-6 is widely used as engineering polymer for
fibre and film manufacturing7. Attempt was also made
to produce a nonwoven fabric of intimately
co-mingled nylon-6 and polyethylene oxide (PEO)
electrospun fibres for controlling pore size
distribution independently from fibre formation8.
Nylon-6 fibres with average diameter ranging from
120nm to about 700 nm could be electrospun from
nylon-6 solutions in 88% formic acid. The fibre size
and size distribution was mainly affected by solution
concentration9.
The morphology and
mechanical
properties of nylon-6 nanofibres were investigated as a
function of molecular weight (30,000, 50,000,
and
63,000 g/mol) and electro spinning process conditions
(solution concentration, voltage, tip-to-collector
distance, and flow rate)
10. The filtration characteristics
of a nylon-6 nanofilter made by electrospun nanofibres
are tested as a function of the fibre diameter. Nanofilter
media with diameter in the range of 100-730 nm can be
produced in optimized conditions11
.
_______________ a To whom all the correspondence should be addressed.
E- mail: [email protected]
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2012
212
Poly (e-caprolactine) (PCL) is a semi-crystalline
polymer and has been widely used in tissue
engineering scaffolding, due to its properties such as
non-immunogenicity, slow biodegradability and good
drug permeability12
. PCL is a biocompatible,
biodegradable polymer that has been successfully
electrospun. It is capable of supporting a wide variety
of cell types, including marrow stromal cells
(MSCs)13
. PCL has various advantages, including
mechanical flexibility, low antigenicity, easy
processability, and low degree of chronic
persistence14
. A fibrous scaffold comprising chitosan
and poly(e-caprolactone) (PCL) was electrospun from
a novel solvent mixture consisting of formic acid and
acetone15
. PCL/gelatin (70:30) nanofibrous scaffolds
proved to be a promising biomaterial suitable for
nerve regeneration16
.
It is found that there is not
enough information available on the effect of adding
PCL into the nylon-6 polymer solution for the
production of nanofibre nanomembrane.
In the present work, investigation on the
characteristics of nylon-6 nanomembrane produced
using four different polymer solution viscosities has
been undertaken. Nylon-6 blends with PCL
nanomembrane have been successfully produced
using different process and solution parameters, and
characterised.
2 Materials and Methods
2.1 Materials
Nylon-6 polymer pellets with molecular weight
about 30000 – 40000 g/mol were procured. The
solvent system used was formic acid.
Polycaprolactone with molecular weight 45000 g/mol
was procured, and toluene and methanol were used as
solvent.
2.2 Solution Preparation
Nylon-6 solutions of the concentration 10, 12, 15
and 16 wt% were prepared by dissolving nylon-6
pellets in 85% formic acid. The solutions were
prepared in a room temperature for 2 h. The
viscosities of solutions were measured using
Brookfield viscometer model DV – II + Pro. The
viscosity values are found to be 158.4 cPs for 10 wt%
solution, 420.8 cPs for 12 wt% solution, 920.8 cPs for
15 wt% solution and 1417 cPs for 16 wt% solution.
The poly(e-caprolactone) (PCL) polymer solutions
of concentrations 8, 10, and 12wt% respectively were
blended with 16 wt% concentration of nylon-6
polymer solutions for electrospinning. The blend ratio
of nylon-6/PCL was selected as 80/20. The blended
nylon6/PCL solutions were stirred with magnetic
stirrer for an hour.
2.3 Development of Nanomembrane
Schematic diagram of an electrospinning set-up
used for the experiment is shown in Fig.1. Two
mililitre solution was poured into a 2 mL disposable
plastic syringe (A). The positive electrode from the
positive power supply was connected to a syringe
metal tip, while the other was connected to a rotating
drum collector (M) wrapped by a piece of aluminum
foil being used as ground. The applied voltage, the
distance between the tip and the collector, flow rate
for the production of electrospun nylon-6
nanomembrane were fixed at 20 kV, 10 cm and
0.2 mL/h respectively. The selected process
parameters for the production of nylon-6/PCL blend
nanofibres are given in Table 1.
2.4 Characterization
The morphologies of nylon-6 and its blend with
PCL nanomembrane were investigated by using JEOL
JSM – 6390 scanning electron microscope (SEM).
Fourier transformed – Infrared spectroscopy (FTIR)
was used to analyse the functional groups of nylon-6
and nylon-6/PCL electrospun blend nanomembrane.
Fig. 1 Schematic diagram of electrospinning set-up
Table 1 Influence of nylon - 6 polymer solution viscosity on
average fibre diameter
Polymer solution
viscosity, cPs
Avg fibre
diameter, nm
% increase in average
fibre diameter
158.4 67.26 -
420.8 83.28 23
920.8 105.60 57
1417 130.90 94
GUNAVATHI et al.: CHARACTERIZATION OF NANOMEMBRANE USING NYLON-6 & NYLON-6/PCL BLEND
213
3 Results and Discussion In this research work, nylon-6 nanomembrane
and its blend with PCL have been successfully
produced with electrospinning technique. The
influence of polymer solution parameters and
different process parameters on nylon-6 and its
blend are analysed.
3.1 Morphological Structure of Nylon-6 Nanomembrane
The morphology of electrospun ultra-fine fibres is
influenced by various parameters such as the applied
voltage, solution flow rate, distance between capillary
and collector, and especially the properties of the
polymer solutions including concentration, surface
tension and nature of the solvents. Amongst these
parameters, the viscosity of the solution is one of the
biggest factors which has the maximum effect on the
process of fibre formation and the resulting fibre
diameter.
Figure 2 shows that at low nylon-6 polymer
solution viscosity (158.4 and 420.8 cPs), defects in
the form of beads and breaking fibres have been
observed in the structure of nylon-6 nanomebrane. As
the nylon-6 polymer solution viscosity increases, the
beads and breaking fibres disappear, because of the
cohesive nature of the high viscosity solution. Table 2
shows that when nylon-6 polymer solution viscosity
increases from 158.4 cPs to1417 cPs, the average
fibre diameter also increases proportionately from
67.26 nm to 130.90 nm, i.e. 94% increase in fibre
diameter from the lowest viscosity level of 158.4 cPs.
Fifty five fibres were tested to calculate the average
fibre diameter.
Table 2Electrospinning process and solution parameters for
the production of electrospun nylon - 6/PCL (80:20)
nanomembrane
[Collector distance 12 cm]
Sample
code
Nylon – 6/PCL
concentration
wt%
Flow
rate
mL/h
Applied
voltage
kV
Avg fibre
diameter
nm
S1 16/8 0.02 18 70
S2 16/8 0.05 15 74
S3 16/10 0.02 18 71
S4 16/10 0.05 15 75
S5 16/12 0.02 18 73
S6 16/12 0.05 15 76
Fig. 2 Influence of nylon − 6 polymer solution viscosity on morphological structure of nanomembrane [(a) 158.4 cPs, (b) 420.8 cPs,
(c) 920.8 cPs and (d) 1417 cPs]
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2012
214
At a lower viscosity, the higher amount of solvent
molecules and fewer chain entanglements will mean
that surface tension has a dominant influence along
the electrospinning jet, causing beads to form along
the fibre. When the viscosity is increased which
means that there is a higher amount of polymer
chains entanglement in the solution, the charges on
the electrospinning jet will be able to fully stretch
the solution with the solvent molecules distributed
among the polymer chains. The electrospun fibres
cannot be formed at low viscosity and the fibre
formation ability and fibre diameter increase with
increasing solution viscosity. At low viscosity,
droplets and breaking fibres are formed, which
coalesced so as to constitute an electrospray, but as
the solution viscosity increases, fibres begin to form,
and the formation of beads is suppressed. Hence, the
fibre formation ability and its morphology are
closely related to viscosity of the solution.
3.2 FTIR Spectroscopy
The FTIR spectra of nylon-6 shows the presence of
amide groups (CO-NH) separated by linear chains of
the methylene units (- (CH2)5 -). All amide groups are
oriented approximately perpendicular to the polymer
chain axis and form intermolecular hydrogen bonds.
As expected, two strong bands at 1645 cm-1
and 1538
cm-1
are due to the presence of amide I and amide II
functional groups. This confirms the presence of
nylon-6 present in the nanomembrane.
3.3 Influence of Electrospinning Process Parameters on
Morphological Structure of Nylon-6/PCL Nanomembrane
Based on the analysis of the SEM images (Fig. 3) it
is observed that at low voltages (15 kV), the structure
Fig. 3 Influence of electrospinning process parameters on the morphological structure of nylon-6/PCL nanomembrane [ (a) S1, (b) S2,
(c) S3, (d) S4, (e) S5 and (f) S6]
GUNAVATHI et al.: CHARACTERIZATION OF NANOMEMBRANE USING NYLON-6 & NYLON-6/PCL BLEND
215
consists predominantly of beads, but as the voltage is
increased from 15 kV, the fibrous structure is
stabilized. From the all combinations, sample
S5 (nylon-6/PCL nanomebrane with concentration of
16%/12%) is produced without any bead and uniform
nanofibre. From Table 3 it is understood that in all the
cases, the average diameter of the fibre decreases with
increasing voltage from 15kV to 18 kV and also the
uniformity of the fibre diameter is increased. It is also
observed that the average nano fibre diameter of
nylon- 6/PCL nanomembrane is lesser than that of
average diameter of nylon-6 nanomembrane produced
with 16 wt% concentration.
Figure 4 shows the frequency (%) of fibre diameter
of the nylon- 6/PCL nanomembrane samples. It can
be observed from the figure that the nylon-6/PCL
fibre diamater is in the range of 40-120 nm. Major
frequency % of uniform fibre diameter is in the range
of 60 - 80 nm and amongst all the samples, S5 sample
shows higher % of uniform fibre diameter. On the
contrary, S2 sample shows lower frequency % of fibre
diameter in the range 60 - 80 nm. Hence, the sample
S5 is produced with less variation in fibre diameter
compared with all other samples.
3.4 Influence of Electrospinning Process Parameters on
Functional Groups of Nanomembrane
To determine if the blended nylon-6/PCL
electrospun fibres are successfully fabricated, we
analyzed the FTIR spectrum of Nylon-6/PCL at
different process parameters. The FTIR spectrum of
nylon-6/PCL blended mats shows that their structure
contains all the peaks corresponding to PCL and
nylon-6. In PCL the band around 3300 cm-1
represents
the characteristic of carbon hydrogen stretching
absorption. The CH3 asymmetric stretching vibration
occurs at 2975- 2950 cm-1
, while CH2 absorption
occurs at about 2930 cm-1
. The CH3 symmetric
stretching vibration occurs at 2885- 2865 cm-1
, while
CH2 absorption occurs at about 2870-2840 cm-1
. The
CH3 asymmetric deformation vibration occurs at
1470-1440 cm-1
. This band is overlapped with the
CH2 scissor vibration occurred at 1490-1440 cm
-1. The
symmetric CH3 deformation vibration occurs at
1390-1370 cm-1
. The presence of t-butyl group can be
conformed by the presence of bands at around
1255 and 1210 cm-1
, while the isopropyl group
shows bands near 1170 and 1145 cm-1
. When there
are four or more CH2 in a row, a rocking absorption
is found centered at 720 cm-1
. This absorption splits
into two bands when the number of adjacent
methylene groups reaches about ten methylene
groups. In nylon-6, the peaks at 1650 cm-1
represent
the primary amide while C=O stretch occurs at
1680 cm-1
, secondary amide at 1550 cm-1
and
C=O stretch at 1650 cm-1
. From all these results, it is
clear that the combined electrospun scaffold contains
both nylon-6 and PCL.
4 Conclusion The characterization of nylon-6 nanomembrane
shows that higher polymer solution viscosity of
1417 cPs gives uniform fibre structure of 130.90 nm
average fibre diameter. It is observed that the increase
in polymer solution viscosity of nylon-6 increases the
fibre diameter proportionately. It is also observed that
electrospinnabiliy of nylon-6/PCL nanomembrane of
concentration 16%/12% with 18 kV applied voltage
shows uniform fibre structure. The blending of PCL
with nylon-6 polymer solution results in reduction of
nanofibre diameter still further to 40%.
Acknowledgement The authors are thankful to The South India Textile
Research Association (SITRA) for conducting trials.
Thanks are also due to Ms Indra Doraiswamy,
Research Advisor, (SITRA) for her valuable
suggestions which have helped the authors
consolidating the ideas put forth in this paper.
References 1 Liu Y, He, J H & Yu J Y, Fibres Text East Eur , 15 (4)
(2007) 31.
2 Lee S & Kay Obendorf S, Text Res J, 77(9) (2007) 696.
3 Ohkawa K, Hayashi S, Nishida A & Yamamoo H,
Text Res J, 79(15) (2009) 1396.
Fig. 4 Influence of procees parameters and polymer
concentration on frequency% of average nanofibre diameter
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2012
216
4 Dhanalakshmi M & Jog J P, Express Polym Lett, 2(8) (2008)
540.
5 Kilic A, Oruc F & Demir A, Text Res J, 78(6) (2008) 532.
6 Liu W & Adanur S, Text Res J, 80(2) (2010) 124.
7 Lee K H, Kwan Kim K W, Pesapane A, Kim H Y &
Rabolt J F, Macromolecules, 41 (2008) 1494.
8 Frey M W & Li L, J Eng Fibre Fabrics, 2 (1) (2007) 31.
9 Lei Li, Margaret W Frey & Thomas B Green, J Eng Fibre
Fabrics, 1 (1) (2006) 1.
10 Satyajeet S Ojha, Mehdi Afshari, Richard Kotek &
Russell E Gorga, J Appl Polym Sci, 108 (2008)
308–319.
11 Gil Tae Kim, Young Chull Ahn & Jae Keun Lee,
Korean J Chem Eng, 25(2) (2008) 368-372
12 Luong-Van E, Grondahl L, Chua K N, Leong K W,
Nurcombe V & Cool S M, Biomaterials, 27 (2006) 2042.
13 Pham Q P, Sharma U & Mikos A G, Biomacromolecules, 7
(2006) 2796.
14 Glowacki J & Mizuno, Biopolymers, 89 (2008) 338.
15 Shalumon K T, Anulekha K H, Girish C M, Prasanth R,
Nair S V & Jayakumar R, Carbohyd Polym, 80 (2010) 413.
16 Laleh Ghasemi-Mobarakeh Molamma, Prabhakaran P,
Mohammad Morshed, Mohammad-Hossein Nasr-Esfahani,
Seeram Ramakrishna, Biomaterials, 29 (2008) 4532.