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FUNCTIONALIZATION OF INDUSTRIALLY PRODUCED POLYMERIC NANOFIBROUS

MATERIALS AT PARDAM, LTD.

Miroslav TEJKL1, Jaroslava MORÁVKOVÁ1, Aneta KRAUSOVÁ1, Ladislav TORČÍK2, Tomáš

SYROVÝ3

1) Pardam s.r.o., Pardubice, Czech Republic, EU, info@pardam.cz,

2) NanoTrade s.r.o., Olomouc, Czech Republic, EU, info@nanotrade.cz,

3) University of Pardubice, Studentská 95, Pardubice, Czech Republic, EU

Abstract

Industrial production of polymeric nanofibers leads to new applications of well-known and broadly used

polymeric materials. Added value is created by formation of these materials into fibrous nanostructures.

Subsequent added value is achieved by functionalization. Generally, functionalization can be achieved by

adding functional components into the spinning solution or by post-treatment of the spun nanofibrous

material. Company Pardam primarily focusing on industrial nanofiber production has successfully tested

processes of functionalization of its nanofibrous products. As an example of adding functional components

into the spinning solution the incorporation of Ag nanoparticles with antibacterial effect into the polymeric

nanofibrous membranes for water filtration is presented. Antibacterial effect was experimentally confirmed in

cooperation with company NanoTrade that prepared suitable Ag nanoparticles solution. As an example of

functionalization by post-treatment the increasing of nanofibrous membrane conductivity by impregnation

with a conductive polymer (PEDOT:PSS) dispersion is presented. The electric resistance was decreased by

at least three orders of magnitude to values of hundreds of Ω. There is a wide range of ways to functionalize

nanofibrous materials and these examples are not meant to be an exhaustive list of successful modifications

that Pardam can achieve.

Keywords: Nanofibers, nanoparticles, functionalization, antibacterial treatment, nanosilver, conductive

treatment, PEDOT

1. INTRODUCTION

Production of nanofibers on industrial scale is a core business of Pardam, Ltd. The Forcespinning

technology when fibers are created in a top-to-down way from a polymeric solution was adopted for

economically feasible production. The production processes involving polymers and solvents with suitable

physicochemical properties were developed and optimized. Because of practical reasons the main focus is

on limited number of well known materials available on the market for reasonable price with properties

suitable for fiber production. The product portfolio is somehow limited to those materials. The way to broaden

such limited portfolio is a functionalization that is in general an introduction of functional chemical groups

giving new properties to the material. Generally, functionalization can be achieved by adding functional

components into the spinning solution or by post-treatment of the spun nanofibrous material. The examples

of both approaches are presented and effects of functionalization are confirmed by measurements reported

in this paper.

2. FUNCTIONALIZATION OF SPINNING SOLUTION

Addition of functional material into the spinning solution has certain limitations because the negative impact

of a presence of the functional additive on spinning process must be avoided. There are some requirements

on physicochemical properties and concentration of functional additives such as physical and chemical

compatibility with solution components (miscibility, inertness), long-term stability and low impact on polymeric

solution rheological properties affecting the spinning process. From this point of view the solid nanoparticles

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of chemically stable materials are suitable candidates as functional additive of spinning solution. In case of

Forcespinning technique involving thin nozzles the mandatory requirement is the relatively small size of such

introduced solid particles in orders of tens of nanometers and their stability in terms of particle

agglomeration. Functional components are distributed through whole volume of the fibers, but only those

exposed on the surface could be active. It must be experimentally tested that there is sufficient amount of

exposed particles on the surface to reach desired functional activity.

Pardam, Ltd. produces nanofibrous membranes under the brand NnF MBRANE® of various polymeric

materials (PA6 [1], PUR [2], etc.) using centrifugal spinning technology Forcespinning. These membranes

are deposited onto the various substrate layers, e.g. nonwoven textile, woven mesh etc. Nanofibrous

membranes consist of randomly oriented continuous nanofibers and certain small amount of defects like

micro-droplets or thicker insufficiently drawn fibers. Such membranes have open porous structure and large

free volume. These properties are advantageous for liquid or gas filtration applications.

The dispersion of Ag nanoparticles nanosilver® is produced by NanoTrade, Ltd. with proved antibacterial

activity. [3] Antibacterial activity of Ag nanoparticles in polymer composites was also examined elsewhere,

e.g. [4]. Nanofiber mesh with antibacterial activity was prepared by adding the nanosilver® dispersion into the

polymeric solution for NnF MBRANE® production.

2.1 Sample preparation and experimental methods

Polymer solutions for production of the NnF MBRANE® – PA6 and NnF MBRANE® – PUR were prepared

according standardized procedure. Dispersion of Ag nanoparticles nanosilver® supplied by manufacturer

NanoTrade, Ltd. was used as is. Polymer solution and Ag dispersion were mixed in desired ratio and

thoroughly homogenized. Nanofibrous polymeric membranes were manufactured according standardized

procedures using Ag doped spinning solutions.

Microscopic images of functionalized nanofibers with Ag nanoparticles were captured using scanning

electron microscope. Due to low conductivity of uncoated polymeric fiber samples the low vacuum electron

microscopy in water vapor and back-scattered electron detector were used.

Membrane samples containing the 0,04 g and 0,03 g of Ag doped PA6 and PUR nanofibers respectively

were submerged into nutrient solution with microorganisms of 103 CFU/ml and cultivated under physiological

conditions together with control sample without nanofibers. Tests were conducted with two types of

microorganisms: Staphylococcus aureus (CCM 4516) and Escherichia coli (CCM 3954). At moment of

sample submersion and after 1, 7 and 24 hours the total viable count was assessed. Sample incubation was

48 hours at 35 °C. All samples were doubled and results are reported as mean values.

2.2 Results and discussion

Polymer spinning solutions containing dispersed Ag nanoparticles were spun without any major

complications comparing to spinning of standard solutions. Doped Ag nanoparticles colored white fiber layer

into yellowish shade. There are visible Ag particle agglomerates protruding fiber surface on the SEM images

at ~8000x magnification (Fig. 1A). Elementary composition of such a agglomerate was assessed using EDS

detector of electron microscope (Fig. 2). At sufficiently high magnification (~80000x) SEM images there are

visible Ag nanoparticles with approximate size of 30 nm (Fig. 1B). Particle distribution on the fiber surface

appears random and uniform.

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A)

B)

Fig. 1 SEM images of NnF MBRANE® – PUR + nanosilver® nanofibers at A) 7 575x magnification and

B) 87 018x magnification.

Fig. 2 SEM image of NnF MBRANE® – PUR + nanosilver® nanofibers with marked spot of EDS analysis and

result graph confirming a presence of Ag.

Results of antibacterial activity tests are reported in Table 1. There is a considerable antibacterial effect of

the nanofibers containing Ag nanoparticles in comparison with control samples. Antibacterial activity is in

case of both polymers similar, which corresponds with the same addition of nanosilver® dispersion into the

spinning solution. It must be noted, that nutrient solution with bacteria was not mixed during exposition to

nanofibrous samples, which could delay a contact of bacteria with Ag nanoparticles and thus decrease the

antibacterial activity. When using such Ag doped nanofibrous filtration membranes in a practice, the filtrated

media flows through the pores promoting the contact of bacteria with doped nanofibers. Entrapped bacteria

in the filtration membrane are killed due to contact with present Ag nanoparticles preventing growing of

bacteria biofilm clogging the filter membrane.

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Fig. 3 Total viable counts through the time of exposition of bacteria to nanofibrous samples containing

Ag nanoparticles

3. FUNCTIONALIZATION BY POST-TREATMENT

Means of post-treatment involves wide range of processes including introducing of functional material on the

nanofiber surface (e.g. dip coating, lamination, sol-gel reaction, plasma treatment of coated functional

precursors) or modification of the nanofiber surface by chemical or plasma treatment (usually oxidation of the

polymer). Such a treatment is usually made in a way preserving an open porous structure. Usually good

adhesion to fiber surface and physicochemical stability of introduced material and long-term stability of

surface modifications are desired. Post-treatment as next processing step represents extra costs of

production process increasing resulting material price.

Functionalization of polymeric membranes NnF MBRANE® – PA6 by conductive polymer coating was tested.

The water-based dispersion of conductive polymer PEDOT:PSS was obtained from manufacturer COC Ltd.

as a sample. The main goals of this trial were to evaluate formation of polymeric film on the nanofiber

surface, preservation of open porous structure and increase of membrane conductivity.

3.1 Sample preparation and experimental methods

NnF MBRANE® – PA6 nanofiber membrane samples of size 20 x 20 cm were peeled of the substrate.

Certain amount of PEDOT:PSS dispersion was spread on the center part of the membrane samples with

micro spatula ensuring the wetting of membrane volume. Samples were dried in stretched shape. Three

samples of different optical density of impregnated nanofibers were prepared (A, B, C at Fig. 4).

SEM images of impregnated and non-impregnated membrane samples were captured using scanning

electron microscope Phenom G2 pure without metal coating. Electrical properties were characterized by

resistance measurement using the multimeter RIGOL DM-3068 with two-point round pin probe with electrode

distance 9 mm. The impregnated samples were mounted onto an insulating pad. Electric resistance was

measured on five randomly picked spots of the impregnated area of the samples.

A

B

C

Fig. 4 Appearance of nanofiber NnF MBRANE® – PA6 samples impregnated with PEDOT:PSS

3.2 Results and discussion

Comparing SEM images of non-impregnated and impregnated samples (Fig. 5) one can see somewhat less

open fibrous structure as result of impregnation. Images of higher magnification (Fig. 5) show that shapes of

fibers and their intersections were not qualitatively changed by presence of dried PEDOT:PSS film. The

interfiber distance and free volume of the nanofibrous layer were decreased considerably. Macroscopically,

flexible and soft to touch nanofibrous membrane turned to paper like, more brittle and less flexible layer. Still

fibrous open structure of the impregnated membranes was remained. White particles on the SEM images are

dust particles introduced during sample manipulation.

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A)

B)

Fig. 5 SEM images of NnF MBRANE® – PA6 A) non-impregnated at 2000x and 7900x magnification resp.

and B) impregnated with PEDOT:PSS dispersion at 2000x and 8000x resp

Results of electric resistance measurements are reported in the Tab. 1 as mean values. Sample electric

resistance inversely corresponds with the amount of impregnated polymer corresponding with the layer

optical density.

Table 1 Results of electric resistance measurement of NnF MBRANE® – PA6 samples non-impregnated and

impregnated with PEDOT:PSS

Sample Electric

resistance [KΩ] Relative error [%]

Non-impregnated > 100 MΩ -

A 200 7

B 500 10

C 350 8

It is known that resulting conductivity of PEDOT:PSS thin films is strongly dependent on a process of

orientation of the polymer chains occurring during polymer dispersion drying. Formation of continuous

polymer film depends on substrate surface wetting. These processes can be regulated e.g. by the presence

of secondary dopants affecting speed of drying and chain orientation and surfactants or substrate plasma

treatment affecting the film formation. [5]

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4. CONCLUSIONS

Production process of nanofibers was not affected dramatically by the presence of Ag nanoparticles. At least

part of the Ag nanoparticles added into the spinning solution remained protruding the surface of nanofibers

with preserved antibacterial activity. Antibacterial filtration membrane was prepared by adding the Ag

dispersion nanonilver® to the spinning solution of NnF MBRANE® – PA6 followed by standard production

process. Impregnation of NnF MBRANE® – PA6 nanofibers by the conductive polymer PEDOT:PSS

dispersion led to the decrease of electric resistance by at least three orders of magnitude. Open structure of

nanofibrous layer was preserved after impregnation. Functionalization of polymeric nanofibers either by

doping of spinning solution or by post-treatment of the spun nanofibers was successfully accomplished in

Pardam, Ltd.

ACKNOWLEDGEMENTS

These trials were conducted in cooperation with NanoTrade, Ltd. and Department of Graphic Arts

and Photophysics, University of Pardubice during trial runs in Pardam, Ltd. production facility

in Nové Město na Moravě which was founded with support of Ministry of Industry and Trade of

the Czech Republic within operational program Enterprise and Innovation 2007 – 2013, projects

4.1 IN04/689 and 4.2 PT03/386.

LITERATURE

[1] NnF MBRANE® – PA6 (Nylon 6): Product description. Pardam: We make nanofibers [online]. Pardam, 2013 [cit.

2013-09-13]. Available at: http://pardam.cz/products/?wpcproduct=nnf-mbrane-pa6

[2] NnF MBRANE® – PUR: Product description. Pardam: We make nanofibers [online]. Pardam, 2013 [cit. 2013-09-

13]. Available at: http://pardam.cz/products/?wpcproduct=nnf-mbrane-pur

[3] Certificates, Approvals, Tests and Analyses. Nanosilver: nanotechnology for ever [online]. Olomouc: NanoTrade

s.r.o., 2008 - 2012 [cit. 2013-09-13]. Available at: http://www.nanosilver.eu/Tema/Why-Nanosilver/Certificates-

Approvals-Tests-and-Analyses

[4] DALLAS, Panagiotis, Virender K. SHARMA a Radek ZBORIL. Silver polymeric nanocomposites as advanced

antimicrobial agents: Classification, synthetic paths, applications, and perspectives. Advances in Colloid and

Interface Science. 2011, Vol. 166, Issues 1–2, 119–135. Available at:

http://www.sciencedirect.com/science/article/pii/S0001868611001175

[5] ELSCHNER, Andreas. PEDOT: principles and applications of an intrinsically conductive polymer. Boca Raton, FL:

CRC Press, c2011, xxi, 355 p. ISBN 14-200-6911-2.