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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: [email protected]
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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
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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
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Classical Bico Classification
Side-by-side
Sheath-core
Segmented-pie
Islands-in-the-sea
Tipped
Segmented-ribbon4
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Card-splittable fiber after carding
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Card-splittable fiber before splitting
Segment-Pie: Splitting by Carding
Ref: Middlebrooks, M. C.
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Split Fiber Diameter -Segmented Pie
Number of Segments8 16 24 32 40 48 56 64
Dia
met
er (M
icro
n)
0
1
2
3
4
5
6
• 24 segments is probably the limit for this technology.
• The fibers form thin wedges and pack tightly when hydroentangled leading to low permeability
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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
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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 nano- fibers
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300 Islands-in-the-sea As-spun Fiber
Islands: PLA
Sea: Co-PET
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Island Fiber Diameter – I/S
50/50 Sea-Island Ratio
Number of Islands
7 37 240
600
1200
Dia
mte
r (m
)
7.00
2.00
0.87
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
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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…
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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
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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
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Note the onset of fibrillation
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Fracturing Caused by Shear
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The web was subjected to one manifold. Note the start of fibrillation Nylon/PLA 108 Islands
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Onset of Fracturing by Hydroentangling
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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
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Fully Fractured Mechanically on a 40 Mesh Belt
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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
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Fractured and Calendered
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Mechanical Properties: Influence of Island Count
Number of Islands0 20 40 60 80 100 120
Burs
t Str
engt
h (k
gf)
0
20
40
60
80
100 The I/S fibrillated
structures result in superior strength making them ideal for a number of critical applications.
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Air Permeability
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Mean Pore Size
Mechanical Properties: Influence of island count
Number of Islands0 20 40 60 80 100 120
Air
Flo
w (C
FM)
0
10
20
30
40
50
60
Number of Islands0 20 40 60 80 100 120M
ean
Pore
Dia
met
er (µ
m)0
10
20
30
40
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Non-conventional Shaped Fibers
Applications: Filtration, wipes, artificial leather, …
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Is it All About Surface Area… ??
Denier Per Filament0.0001 0.001 0.01 0.1 1 10 100 1000
Spec
ific
Sur
face
, m2 /g
0.01
0.1
1
10
100
Diameter (Microns)0.1 1 10 100 1000
5
3
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
defi
Pαm
LDenier L
L
ned by 9000 A, is perimeter and is cross sectional area.P A
Photo courtesy of Fiber Innovation Technology
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Denier Per Filament0.0001 0.001 0.01 0.1 1 10 100 1000
Spec
ific
Sur
face
, m2 /g
0.01
0.1
1
10
100
Round
4DG
Diameter (Microns)0.1 1 10 100 1000
What are the limits of Shaped Fibers by Extrusion?
Photo courtesy of Fiber Innovation Technology
Smallest 4DG ~ 6 dpf
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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 ….
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New Shaped Fiber with Wings & Backbone
Sheath (Sacrificial)
PLAEastONECoPET
Core (Residual)
PPPETPA
PLA
Sheath-Core Configuration
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Denier Per Filament0.0001 0.001 0.01 0.1 1 10 100 1000
Spec
ific
Sur
face
, m2 /g
0.01
0.1
1
10
100
Round
4DG
Winged
Diameter (Microns)0.1 1 10 100 1000
What Are the Limits of Shaped Fibers?
Photos courtesy of Allasso Industries. Inc.
Photo courtesy of Fiber Innovation Technology
B. Pourdeyhimi and Walter J. Chappas, High surface area fiber and textiles made from the same, 20080108265, May 8, 2008. 25
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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
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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
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Typical nylon Winged Fibers
Aspect Ratio = 0.54
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Typical PP Winged Fibers
Aspect Ratio = 0.34
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Core-Modified Trilobal Micro Fibers & Fabrics
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Modified Tipped Trilobal
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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.
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Thermally bonded only
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Hydroentangled and fractured.Note the curl and crimp – this leads to better “hand”
Modified Tipped Tri-lobal – PLA/PA6
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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
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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
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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.
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Cored Trilobal Examples
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Polymer B
Polymer B
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Hollow Cored Trilobal
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Polymer B
Polymer B
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Cored Trilobal – Core is non-round
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Polymer BPolymer B
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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
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PP/PP (with pigment) 80/20 RatioResults: July 14, 2007
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PLA/PA6 80/20 RatioResults: July 14, 2007
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PLA/PA6 70/30 RatioResults: July 14, 2007
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Nylon/PLA
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Some Results – 100 gsm fabric
Core/Tip Polymer Ratio25/75 50/50 75/25
Tens
ile s
tren
gth
(kgf
)
0
5
10
15
20
25
30MD CD
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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• …