1

Technical Seminar about Nano Fiber Technology

by aeolus filter3 corp 111 C Creek Ridge Rd Greensboro NC 27406

Phone 336 - 272 1268

Frank Recker

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Nanotechnology – A novel and promising

approach to nonwoven fabrics

NAFA Technical Seminar 2007

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Introduction Particle Deposition Mechanisms Established Manufacturing Techniques for Nanofibers Development of a new Production Process Comparison of Manufacturing Techniques Conclusion

Overview

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Ant (~ 5 mm)

Dust Mite (~ 200 μm)

Human hair (~ 60-120 μm wide)

DNA (~ 1-1/2 nm)

5 Atoms of silicon (~ 1nm)

Head of a pin (~ 1-2 mm)

Micro Electro Mechanical Devices (~ 10-100 μm wide)

Red blood cells

Pollen grain

Stacks of clay mineral pletelets, each platelet with

~ 1 nm thickness

Carbon Nanotube (~ 2 nm diameter)

Polymer nanofibers (~ 20-200 nm)

10-2

10-3

10-4

10-5

10-6

10-7

10-8

10-9

10-10

1 cm 10 mm

1 mm

1 nm

0,1 mm 100 μm

0,01 mm 10 μm

10 μm 100 nm

0,01 μm 10 nm

0,1 nm

Visible Spectrum

Mill

iscal

e M

icro

scal

e N

anos

cale

Red blood cell with white cell (~ 2-5 μm)

Introduction - What is Nanotechnology?

Nanotechnology is the creation of functional materials, devices, and systems through control

of matter on the nanometer (1 to 100+ nm) length scale and the exploitation of novel properties

and phenomena developed at that scale.

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Potential Applications for Polymer Nanofibers

Polymer Nanofibers

Tissue engineering scaffold Adjustable biodegradation rate

Better cell attachment

Contraollable cell directional growth

Wound dressing Prevents scar

Bacterial shielding

Medical prosthesis Lower stress concentration

Higher fracture strength

Heamostatic devices Higher efficiency in fluid adsorption

Sensor devices Higher sensitivity

For celd, arteries and veins

Electrical conductors Ultra small devices

Optical applications Liquid crystal optical shutters

Material reinforcement Higher fracture toughness

Higher delamination resistance

Protective clothing Breathable fabric that blocks chemicals

Filter media Higher filter efficiency

Cosmetics High utilization

Higher transfer rate

Drug delivery Increased dissolution rate

Drug-nanofiber interlace

6

0

2

4

6

8

10

12co

mpo

und

grow

th ra

te [%

]

1995-2002 2000-2005 2005-2010Period

nonwoven total

nonwoven for filtration

Source: Nonwoven End Use Products; World Market Forecast to 2010 David Rigby Associates Limited, January 2003

Growth Rates for Nonwovens for Filtration

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Some Facts:

Indoor air contaminants: Volatile organic compounds, allergens, microorganisms …

Health and productivity related threats

90 % of particles are < 1 μm

Particles adsorb chemicals, including carcinogens and mutangens

Particles contain many irritants, toxic chemicals and nitrogen oxides

Negative environmental impact

Constant enhancement of filtration media is of great importance

Some Facts

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Introduction Particle Deposition Mechanisms Established Manufacturing Techniques for Nanofibers Development of a new Production Process Comparison of Manufacturing Techniques Conclusion

Overview

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Particle Deposition Mechanisms - Overview

Particle Deposition

Screening Inertial impaction Interception Diffusion

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Particle Deposition Mechanisms - Slip Flow Effect I

For nanofibers another effect has to be taken into account:

Slip flow effect

Air velocity is zero at the fiber surface

Air velocity is not zero at the fiber surface

Slip flow Non-slip flow

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Particle Deposition Mechanisms - Slip Flow Effect II

Knudsen number:

fr

Kn l= With: λ = gas mean free path (for air: λ = 0.006 μm)

rf = radius of the fiber

Kn < 0.1 non-slip flow

Kn > 0.1 slip flow starts

Kn ≈ 0.25 definit slip flow!

For fibers with diameters smaller than 0.5 μm the slip flow effect has to be taken into consideration!

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Particle Deposition Mechanisms - Slip Flow Effect III

( )2

f

0

dftUp ahD =

Impacts of the slip flow effect:

Decreasing pressure drop

Increasing collection efficiency

η = viscosity

df = diameter of the fiber

t = thickness of filter

U0 = face velocity of filter

α = Volume fraction of fibers in a filter

porosity1volumetotalvolumefiber

-==a( ) ( )35.1 56164f aaa += for 0.006 < α < 0.3

where

With:

For example, a filter having a df of 0.1 μm and α of 0.05 has a Δp that is 70 % of that predicted

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Introduction Particle Deposition Mechanisms Established Manufacturing Techniques for Nanofibers Development of a new Production Process Comparison of Manufacturing Techniques Conclusion

Overview

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Manufacturing Techniques

Electrospinning

Meltblown Process

Island-In-The-Sea

Manufacturing

Techniques

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Manufacturing Techniques - Electrospinning

Advantages Disadvantages

ü Fiber diameters as low as 50 nm

ü Various polymers applicable

ü Homogeneous fiberdiameters

Low production rate

Use of environmentally critical solvents

Two-step-process

Fibers only in layers

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Manufacturing Techniques – Island-In-The-Sea

Spinning of bicomponent fibers

Island-in-the-sea structure

Different geometries

Dissolving sea-polymer

Advantages Disadvantages

ü Standard spinning processes for bico-fibers

ü Narrow diameter range

Nano-range not easy achievable

Solvent use

Two-step-process

Source: Kuraray

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Manufacturing Techniques – Meltblown

Advantages Disadvantages

ü High productivity

ü Solvent free

ü Single step process

normal operation: fiber diameters of only 1-2 microns

Recently increasing R&D activities

New improvements for finer fiber diameters

polymer

hot air hot air polymer

fibers

air air

spinneret

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Introduction Particle Deposition Mechanisms Established Manufacturing Techniques for Nanofibers Development of a new Production Process

(Filter Material with Integrated Nanofibers) Comparison of Manufacturing Techniques Conclusion

Overview

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New Production Process – Characteristics

ü Integration of polymer nanofibers into nonwoven material

ü Inline Process

ü Solvent free fabrication of fibers with different diameters

ü Task specific fiber diameters for filtration

ü Gradient control of nanofiber distribution

Enhanced filtration performance

One-layer pleatable filter material

Unmixed Material

Patented Technology

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Integrated Nanofibers - Performance

Why do we need integrated nanofibers ?

Nanofibers increase filtration efficiency

Integrated nanofibers increase deep bed filtration

Microfibers

Nanofibers

air flow

filter media

increasing nanofiber density

cross section

Result: Longer lifetime

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Introduction Particle Deposition Mechanisms Established Manufacturing Techniques for Nanofibers Development of a new Production Process Comparison of Manufacturing Techniques

(Electrospinning vs. Modified Meltblown Process) Conclusion

Overview

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Electrospinning

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Nanocoated Filter Media via Electrospinning I

100 μm

100 μm

Nanofibers like a grid on top of structure of single fibers and bundles of standard medium No Nanofibers in the middle of standard medium

Fiber diameters: Standard medium: approx. 21 μm

Nanofibers: approx. 250 nm

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100 μm

100 μm

10 μm

10 μm

After treatment with NaCl

NaCl-particles mainly on Nanofibers Only few particles on „common“ thick fibers

Nanocoated Filter Media via Electrospinning II

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0

1

2

3

4

0 1 2 3 4 5 6 7 8 9 10 11 12Normalized Pressure Drop [Pa]

Nor

mal

ized

Col

lect

ion

Effic

ienc

y

standard media

electrospinning nanocoated media

Nanocoated Filter Media via Electrospinning III

Enhancement of collection efficiency of more than 10 %!

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Nanocoated Filter Media via Electrospinning IV

Characteristics

Nanofiber size: mainly 100 – 300 nm

Microfiber size: 1 – 20 microns

Costs

Solvent Disposal

Surface filtration

Coverage of big holes not sufficient

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Modified Meltblown Process

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100 μm

Nanofibers Generated by the Modified Meltblown Process I

Fiber diameters: Standard medium: approx. 20 μm

Nanofibers: approx. 250 nm

Nanofibers are integrated into 3-dimensional structure Integration of Nanofibers into the Meltblown-process

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10 μm

10 μm

5 μm

5 μm

Particle concentrated on Nanofibers in the Middle of the Media

Only few particles are captured by „common“ thick fibers

Nanofibers Generated by the Modified Meltblown Process II

After treatment with NaCl

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0

1

2

3

4

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Normalized Pressure Drop

Nor

mal

ized

Col

lect

ion

Effic

ienc

y

integrated nanofiber media

standard media

Nanofibers Generated by the Modified Meltblown Process III

Enhancement of collection efficiency with consistent pressure drop

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Characteristics

Nanofiber size: mainly 100 – 300 nm

Microfiber size: 1 – 20 microns

Quality assurance by microscopy and filtration performance tests

High process stability and safety

High productivity of nanofibers (solvent free)

Nanofibers Generated by the Modified Meltblown Process IV

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Introduction Particle Deposition Mechanisms Established Manufacturing Techniques for Nanofibers Development of a new Production Process Comparison of Manufacturing Techniques Conclusion

Overview

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Conclusion

How can we achieve optimal filtration performance?

understanding scientific

correlations

competitive process

development

enhanced product

characteristics ( ) ...d

ftUp2

f

0ahD =

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Thank you for your kind attention!

Feel free to ask questions

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[1] eSpin Technologies, Inc.: Nanofibers: A novel Approach to Filtration, http://es.epa.gov/ncer/sbir/success/pdf/nanofibers.pdf

[2] HS-Luftfilterbau V. GmbH: Grundlagen der Filtertechnik, http://www.hs- luftfilterbau.de/upload/produkte/Grundlagen/PDF/Filtertechnik_0I00.pdf

[3] Hills Inc.: Polymeric Nanofiners, http://www.hillsinc.net/Polymeric.shtml

[4] Donaldson Co.: Polymeric Nanofibers and Nanofiber Webs: A New Class of Nonwovens, http://www.donaldson.com/en/filtermedia/support/datalibrary/052025.pdf

[5] R. R. Hegde, A. Dahiya, M. G. Kamath: Nanofiber Nonwovens, http://web.utk.edu/~mse/pages/Textiles/Nanofiber%20Nonwovens.htm

[6] Polymer Nanofibers – an Overview of Applications and Current Research into Procesing Techniques, http://www.azonano.com/details.asp?ArticleID=1280

[7] T. Subbiah, G. S. Bhat, R. W. Tock, S. Parameswaran, S. S. Ramkumar: Electrospinning of Nanofibers, Journal of Applied Polymer Science, Vol. 6, 557-569 (2005). (http://www3.interscience.wiley.com/cgi-bin/fulltext/109925432/PDFSTART)

[8] K. Graham, M. Ouyang, T. Reather, T. Grafe, B. McDonald, P. Knauf: Polymeric Nanofibers in Air Filtration Applications, Donaldson Co., Inc., Presented at the Fifteenth Annual Technical Conference & Expo of the American Filtration & Separation Society, Galveston, Texas, April 9-12, 2002. (http://www.donaldson.com/en/filtermedia/support/datalibrary/052022.pdf)

[9] W. C. Hinds: Aerosol Tecchnology, John Wiley & Sons, Inc., 1999. (Buch)

Literature