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Transcript of Nonwoven Textiles Basic Course
8/6/2019 Nonwoven Textiles Basic Course
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Nonwoven Textiles
Basic course
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Contents
• Definition of nonwovens
• Production, position and end-uses of
nonwovens
• Clasification of nonwovens
• Fibers for nonwovens, special fibers
•
Binder for nonwovens• Nonwovens technologies
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Nonwoven definition (Europe)
• A sheet, web or batt – directionally orrandomly oriented fibers
• Bonded by FRICTION and/or
COHESION and/or
ADHESION
Excluded: paper, knitted, woven,…
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Nonwoven definition (USA)
• A sheet, web or batt – natural or man-made
fibers or filaments
• That have not been converted into YARNS
•
Bonded to each other by any of several means
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Production principles of nonwovens
• Web forming
• Web bonding
•
Fabric finishing
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Web forming methods
- Dry Laid ( of staple fibers )
Carded, Air Laid, Combined Carded – Air Laid
- Wet Laid ( of staple fibres)- Spun Laid
Spunbond, Melt Blown, Electrostatic spun
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Web bonding methods
- Mechanical bonding
Needled, Stitch bonded, Spunlaced, Felts
- Chemical bondingDispersion bonded by saturation, spraying,
screen printing, foam
Polymer solutions bonded- Thermal bonding by calender, thru-air,
ultasound, infrared
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Finishing methods
• Coated
• Laminated
•
Crimped• Printed
• Special finished
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Nonwovens Growth in Regions 2006
0
2
4
6
8
10
12
14 Japan
North America
W-Europe
Rest of theWorld
Asia
Middle East
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Nonwovens
• Geotextiles, Agrotextiles
• Automotive
•
Hygiene (wet wipes, napkin, diaper)• Filtration
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Fibers for nonwovens
• Polypropylene
• Polyester ( poly ethylene terephthalate)
•
Rayon ( Viscose)• Polyamide 6 ( Nylon 6), Polyamide 6,6
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Basic parameters of staple fibers
• Linear density ( weight of 1000 m of fiber ingrams) 1,3-20 dtex
- Lenght of staple fibers
- For mechanical technologies 38-85 mm
- 2-30 mm for wet-forming
• Stress – strain behavior
• Fiber crimp
• Fiber finishings
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Special fibers
• Fiber with modified cross-section
• Bi-component fibers
a) Sheath/core b) Side by side c) Island in the
sea d) Orange
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Special fibers
• In bulk modified fibers- modify the fibre
properties
Non-flammable, UV-stable, antistatic and semi
conductive, antimicrobial, pigment
- Surface modified fibers
Metallized fibers, Silanized fibers
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Special fibers
• Glass fibers
• Basalt fibers
•
Carbon fibers• Metal fibers
• Aramide fies
• Novoloid fibers• Extremely strong polyethylene fibers
• Superabsorbent fibers
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Binders for nonwovens
• Polymer solution
• Polymer dispersion ( latexes )
•
Foamed polymer dispersions• Polymer pastes
• Solid polymers: Thermoplastic fibers
Thermoplastic powder, foil, meltblowns orspunbond sheet, netting
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Polymer dispersion ( latexes )
• An aqueous polymer dispersion is a two-
phases system consisting of homogeneus
phase ( water ) and particles of a polymer.
• A surfactant is an important part of dispersion.
• The surfactant prevents the particles from
unit.
• Surfactants are chamicals which reduce
surface tension on the surfaces between two
immiscible materials.19
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Coagulation of dispersion
• Removing water, by evaporation for instance
• Increasing the kinetic energy of particles so
they are able to overcome electrostatic
repulsive powers and join together.
• Inhibition of surfatant dissociation which
results into loss of charge on the surfaces of
particles – by freezing of dispersion, by
dramatic change in acidity, by adding water
soluble salts, adding thermosensibilizers
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Example of dispersion binders
The most important properties of binder are:
- Adhesion to the fibers
- Mechanical properties (stress-strain behavior)- Swelling and solubility in water and organic
solvent
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Example of dispersion binders
• Styrene-butadiene copolymers
• Acrylic copolymers
•
Butadiene- acrylonitrile copolymers• Poly vinyl acetate and its co-polymers
• Polyurethane dispersions
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Nonwoven Technologies
From staple fibers From polymer
Preparation of fiber materials Melting of polymer
Forming fiber layer Forming fibers and fiber layer
Bonding fiber layer
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Web forming methos
Dry-laid methods :
Formation and layering carded web (mehanical
methods)
Aerodynamic web formation ( air-lay)
Combined mechanical-aerodynamic methods
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Mechanical methods
• Carding – In the carding process, individual
staple fibers are separated from clumps of
fibers and more or les uni-directionally
oriented
• Nonwovens- roller card
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Layering of carded web
• Longitudinal layering
•
Cross layering
• Perpendicular layering
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Longitudinal layering
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Cross layering-horizontal cross-
lapper
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f
ba
c
d
e
a) Web b) Feed belt c) Upper conveyor belt d) Lower conveyor belt
e) Delivery belt
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Perpendicular laying
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5
1) Carded web 2) reciorocating comb3) conveyor belt 4) wire grid 5) compresing bar
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Perpendicular laying
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Aerodynamic web forming
• Advantages are:
- Isotropic stucture of the web
- Voluminous webs can be produced- Wide variety of fibres processable as natural,
synthetic, glass, steel, carbon, etc.
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Aerodynamic web forming
• The main disadvantages are as follows:
- Low level of opening fiber material by lickerin
- Various stuctures of web in width of layer due
to irregular air flow close to walls of duct
- Possible entangling of fibers in air strem
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Aerodynamic forming device
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1) Condenser screen2) Lickering3) Condenser screen4) Fan
6) Duct
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Combined mechanical-
aerodynamic methods
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The random card 1) Random roller 3)Condensing rollers2) Two doffer
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Combined mechanical-
aerodynamic methods
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Three-cylinder principle
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Combined mechanical-
aerodynamic methods
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1
Web former Fehrer K-21
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Wet-laid methods
• Wet laid methods were developed as a
modification of the papermaking process.
• When compared with dry-laid methods, the
wet process are distinguished by:
- large, expensive and high-performance
devices, outpu speeds up to 1000 m/min.
- High demand on energy
- Lightweight, non-voluminous products,
usually below 100 /m2.38
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Process
• Wet-laid process comprises the following
steps:
- Wetting and dispersing fibers in water
- Transport of fiber dispersion towards web-
forming device
- Forming fiber web on the moving endless wire
screen or perforated drum
- Removing water by suction, pressure and
drying39
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Process ( Bonding)
• Hydrogen bonds when using self-bonding
cellulosic fibers or wood-pulp.
• Bonding dispersions applied before drying
process by spraying, printing,etc.
• Thermoplastic bonding fibers are admixed to
fiber material
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Fiber
• The wood pulp, short cellulosic fiber, is a
typical raw material used in papermaking.
• Rayon, polyester, polyolefin and polyamid,
glass fibre
• Good wettability of fibers is necessary to
easily form water dispersion
• The tendency of fibers in the water dispersion
to cluster, entangle or flocculate is main
problem with the wet-laid process41
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Fiber
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• Length of staple 2-30 mm
• Concentration of fiber dispersion
• 0,005-0,05 mass percent of fibers are common
• Increasing the dispersion viscosity prevents
flocculation
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Wet forming device
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5
3
1) Dispersion inlet 2) Inclined wire screen 3) Dewatering pipes
4) Suction box 5) Formed sheet
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Wet forming device
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8
4
7
1) Dispersion inlet 2) Stirrer 3) Forming perforated cylinder
4) Formed sheet 5) Adjustable over- flow dam 6)Dewatering pipes7) Free dewatering 8) Suction dewatering
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Polymer- laid method
• Spun bond
• Melt blown
• Electrostatic spinning
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Spunbonding process
• Operations:
- Polymer melting, transport and filtration of
polymer melt
- Filament extrusion
- Filament drawing
- Filament deposion- Bonding
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Spunbond
• Any fiber-forming polymer such as
polypropylene, polyester, polyamide, can be
processed by spunbonding.
• The polymer pellets or granules are fed into
the extruder hopper. As the polymer moves
through the extruder, it melts due to the heat
and friction. Polymer melt is filtred .
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Spunbond
• Filament extrusion- Spinneret is one of he
components of the die assembly. It is a single
block of metal having several thousands
drilled orifices or holes. Polymer melt is forcedtrough the holes and formed into filaments.
The fillaments are cooled by a stream of air
under the spineret.
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Spunbond
• Drawing of the filaments follows spinning.
• The route e employes two blow ducts
49
C
Babcde
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Spunbond
• The primary blow duct, located below the
spinneret, cools filaments. In the secondary
blow duct, located over the entire working
width of the producton line, a ventilatorgenerated under-pressure sucks filament and
air down from the spinnerets and cooling
duct.
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Spunbond
• The filaments are sucked trough a venturi
( high-velocity low pressure) zone to
distributing chamber, which serves to more
randomly move the filament around and to
some extent case then entangle.
- He filament deposition follows the drawing.
The filaments are deposited on the wirescreen conveyor belt usually in layers of
overlapping circular loops of filaments.
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ab
c
d
h
a) Polymer meltb) Screen packc) Hole of spinneretd) Drawing jete) Drawing conduit
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Spunbond
• Bonding:
- Autoadhesion
- Thermal bonding-calander
- Chemical bonding
- Needle punching
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Spunbond
• Properties:
- Area weights between 5-800 g/m2
- Filaments diameters 15-50 micrometers
End-uses
- Geotextiles, portective medical, agriculturalapparel, top sheet for diapers, sanitary
napkins
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Melt-blowing process
The melt blowing process consists of the
following integrated operations:
• Polymer melting, transport and filtration of
polymer melt
• Polymer extrusion and filament forming using
hot air
• Forming web on the surface of wire screen
collector belt-bonding
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a
e
f
a) Extruder b) Gear pump c) Die d) Air manifolde) Collector drum f) Winder
Schematic of melt-blowing process
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Polymers for melt-blowing procces
• Polypropylene
• Polyethylene
• Polyester
• Polyamide
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Schematic of melt blown die
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a) Inlet of hot air b) Inlet of polymer melt c) Cooling aird) Collector drum e) Fiber stream f) air knife g) Air angleh) Air gap
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Bonding
• Self-bonding due to fiber entanglement and
cohesive sticking ensures sufficient cohesion
of the melt-blown web in many applications.
• Additional calander bonding is required in
some cases
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Process variables
• The most important on-line variables of the
melt-blowing process and examples of their
typical values are as follows:
Temperature of polymer melt: 200-400 C
Temperature of air: 250-400 C
Air throughput rate: 100-500 m/s
Mass ratio air:polymer 100
Die-to-collector distance: 0,2-0,5 m
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End-uses of melt-blown webs
The main applications of melt-blown webs are
- Filtration - thermal insulation
- Oil absorption - sanitary napkins
- Industrial wipes - respirators
- Adhesives - protective apparel
- Batery separtors - diapers cover stock- Surgical face masks, and many others
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Web bonding methods
• Mechanical bonding methods
• Chemical bonding
• Thermal bonding
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Mechanical bonding methods
• Needle-punching
• Stich-bonding
• Spunlaced
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Chemical bonding
• In chemical bonding, bonding adhesives are
used in the form of polymer dispersion ( latex)
or polymer solution
• Steps:
Forming fiber layer Apllication of binder,
Coagulation of binder Drying Curing
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Methods of binder application
• The following methods of binder application
are used:
Saturation
Spraying
Printing
Froth bonding
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Saturation
66
3
1) Fiber layer 2) Tank with circulation binder 3) squeeze rolls
Saturation applicator for pre-strengthened layers
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Saturation
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Saturation applicator for non-solidified fiber layers
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Spraying
• The spraying process is employed mainly to
produce voluminous fabrics.
• It consists of spraying the binder on one or
both surfaces of the fiber layer
• A vacuum systém is usually employed to help
the binder particles to penetrate through the
thickness of the layer.
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Spraying
• The binders are atomized in spray guns using
high pressure air or in spray jets using
hydraulic pressure.
• In the spray guns , latex and air are fed underthe pressure of 0,2-0,5 Mpa.
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Pneumatic spraying gun
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2
1
2
2
2
1) Input of binder 2) Input of air
Spraying device with a spraying