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Copyright - NWI, NC State University

Non-conventioanl Nonwovens

The Nonwovens InstituteNorth Carolina State University2401 Research DriveRaleigh, NC 27695-8301

Phone: 919-515-6551FAX: 919-515-4556URL: http://www.thenonwovensinstitute.comEMAIL: Nonwovens@ncsu.edu

Why We Need Nano Fibers For Mechanical Filtration

B Maze, HV Tafreshi, Q Wang, & B Pourdeyhimi, J. Aerosol Sci., 38, 550 (2007)

SVF=1.7%; 10 nm< dp<150 nm nanofibers do not significantly affect the air flow filed

How Do We Produce Micro & Nano Fibers?

Meltblowing

Reducing throughput Smaller capillary size &

compensating with higher hole density

Higher air attenuation Lower viscosity

polymers …

Spunbonding

Smaller capillary size Higher air attenuation … Bicomponent

Islands-in-the-sea Splittables

Other emerging technologies

Classical Bico Classification

Side-by-side

Sheath-core

Segmented-pie

Islands-in-the-sea

Tipped

Segmented-ribbon4

Card-splittable fiber after carding

Card-splittable fiber before splitting

Segment-Pie: Splitting by Carding

Ref: Middlebrooks, M. C.

Split Fiber Diameter -Segmented Pie

Number of Segments8 16 24 32 40 48 56 64

• 24 segments is probably the limit for this technology.

• The fibers form thin wedges and pack tightly when hydroentangled leading to low permeability

Bicomponent Fibers: Segmented Pie – Freudenberg’s Evolon

• High surface area (micro-denier fiber)

• Improved barrier properties• …

• Not good for an aerosol filter media… highly consolidated and low air permeability results in high pressure drops

Islands-in-the-Sea

• Consist of a sea component and an island component (many fine strands of polymer).

• With the sea component dissolved away in subsequent processing, one may obtain micro and nanofibers

300 Islands-in-the-sea As-spun Fiber

Islands: PLA

Sea: Co-PET

Island Fiber Diameter – I/S

50/50 Sea-Island Ratio

Number of Islands

7 37 240

0.340.220.15

• 7 islands yield similar diameter as 16 segmented pie

• Commercially proven technology in filament spinning

• NWI has successfully spun 360 islands with fibers down to 300 nm

N. Fedorova, , NCSU, 2005

Alternative to I/S – With Sacrificial Sea

Assumption: If sea can be fractured/fibrillated, several problems

are overcome. Process becomes GREENCost can be lowered – no weight loss

Two polymers will remain in the fabric. This can be problematic for dyeing and finishing…

Fibrillating I/S Fibers: The Process

Process will include mechanical shearing and hydroentangling in one step

Spunbond web is passed through a calender cold to cause mechanical shear

Web is then passed to hydroentangler and bonded sequentially and fractured simultaneously

The Mechanism…Nylon Core, Polyethylene Sheath

• The sheath or the sea is completely fragmented/fractured/fibrillated.

• The fibrillated/fractured elements wrap around the core or the islands providing better cover and higher strength

Note the onset of fibrillation

Fracturing Caused by Shear

The web was subjected to one manifold. Note the start of fibrillation Nylon/PLA 108 Islands

Onset of Fracturing by Hydroentangling

The fabric fully fibrillated on a 40 mesh hydroentangling belt. The “holes” are the result of the open mesh causing the open areas. Nylon/PLA 108 Islands

Fully Fractured Mechanically on a 40 Mesh Belt

The fabric fully fibrillated on a 100 mesh hydroentangling belt. There are no “holes”. The fabric was subsequently thermally bonded as well.

Nylon/PE 108 Islands

Fractured and Calendered

Mechanical Properties: Influence of Island Count

Number of Islands0 20 40 60 80 100 120

100 The I/S fibrillated

structures result in superior strength making them ideal for a number of critical applications.

Air Permeability

Mean Pore Size

Mechanical Properties: Influence of island count

Number of Islands0 20 40 60 80 100 120

Number of Islands0 20 40 60 80 100 120M

er (µ

Non-conventional Shaped Fibers

Applications: Filtration, wipes, artificial leather, …

Is it All About Surface Area… ??

Denier Per Filament0.0001 0.001 0.01 0.1 1 10 100 1000

, m2 /g

Diameter (Microns)0.1 1 10 100 1000

Surface area

4 11304000Specific Surface Area

where, is shape factor defined by, is total fiber length 9 10 cm ,

is fiber density 1.38 g / cm for PET , Denier is linear density

LDenier L

ned by 9000 A, is perimeter and is cross sectional area.P A

Photo courtesy of Fiber Innovation Technology

, m2 /g

What are the limits of Shaped Fibers by Extrusion?

Smallest 4DG ~ 6 dpf

What is Possible?

The shaped fibers available are Large > 6 dpf Are used in some filtration applications…

Can shaped fibers be formed < 6 dpf By bicopmonent spinning ….

New Shaped Fiber with Wings & Backbone

Sheath (Sacrificial)

PLAEastONECoPET

Core (Residual)

PPPETPA

Sheath-Core Configuration

, m2 /g

Winged

What Are the Limits of Shaped Fibers?

Photos courtesy of Allasso Industries. Inc.

B. Pourdeyhimi and Walter J. Chappas, High surface area fiber and textiles made from the same, 20080108265, May 8, 2008. 25

Polymers

Sheath: Sacrificial PLA

Core: PA, PET, PP, PLA

Sheath/Core Ratio: 50:50, 60:40

No. of Wings: 8, 16, 32

Basis Weight: 50, 100, 200 gsm

The Process

NaOH bath Water bath Neutralization bath

Drum dryer

TreatedWingedMedia

UntreatedWingedMedia

Spunbond Bico

Hydroentangling 5 manifolds – 250 bar

Post-process 6 – 10 % Caustic solution 90 °C, 2 – 4 min

Typical nylon Winged Fibers

Aspect Ratio = 0.54

Typical PP Winged Fibers

Aspect Ratio = 0.34

Core-Modified Trilobal Micro Fibers & Fabrics

Modified Tipped Trilobal

Tipped tri-lobalBoth the core and the tips are exposed on surface. Spinning can be difficult for incompatible polymers.

Modified tipped tri-lobalThe core is wrapped by the tips.Spinning is easy.

This can also be done by a trilobal sheath-core structure but splitting is harder.

Modified tipped tri-lobalThe core is wrapped by the tips

The fibers can be fractured to produce 4 separate fibers. This SEM micrograph shows the process of fracturing the tips or the sheath by hydroentangling.

Thermally bonded only

Hydroentangled and fractured.Note the curl and crimp – this leads to better “hand”

Modified Tipped Tri-lobal – PLA/PA6

Challenges with Modified Tipped Trilobal

The Core has to solidify quickly to allow fiber morphology development If using a removable/dissolvable polymer,

low ratios are not possible It is not possible to use high tip ratios High tip ratio is desirable – to reduce core

component

Conclusions for Modified Tipped Tri-lobal

Spinning can be problematic for exotic polymers, elastomers, etc.

High percentage of tip polymer not easily achieved

Fabric is similar to I/S Fibrillated

New Proposed System

Place a core in the tipped trilobal with the same composition as the tips.

This way, we can control the ratios and be able to produce ratios below 25 % easily. Higher ratios are also possible. The lowest threshold is believed to be about 5%. This may require modifications to the pump and metering systems.

Cored Trilobal Examples

Polymer B

Hollow Cored Trilobal

Polymer B

Cored Trilobal – Core is non-round

Polymer BPolymer B

New Pack Designed

Critical features: Tips (A) wrap the core The core (A) can be:

Hollow Contain another fiber

configuration of the same polymer as tips

The separator polymer (B) can be a very small percentage (< 50% and > 5%) of the overall fiber

Copyright - NWI, NC State University 40

PP/PP (with pigment) 80/20 RatioResults: July 14, 2007

PLA/PA6 80/20 RatioResults: July 14, 2007

PLA/PA6 70/30 RatioResults: July 14, 2007

Nylon/PLA

Some Results – 100 gsm fabric

Core/Tip Polymer Ratio25/75 50/50 75/25

30MD CD

Copyright - NWI, NC State University 44

Conclusions for Core Modified TT –Fibrillated

Properties Applications

• Extremely flexible, • Strong • High MVTR• High Absorbency• Excellent hand• High Pilling Resistance

• Intimate Apparel• Various Forms of Apparel• Outdoor Fabrics• Hunting/Sports• Wipes• Bedding• Automotive• …

The Nonwovens Institute North Carolina State University .../media/ITR2014/2014/... ·...

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