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: guna_textile@yahoo.co.in

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.

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