Classes of Polymeric Materials
Chapter 3: Specialty Polymeric
Products
Professor Joe Greene
CSU, CHICO
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Polymeric Fibers
– Many naturally occurring polymeric fibers; protein or cellulose based
• Animal origin- wool, mohair, angora, fur, silk, cashmere, alpaca, llama, etc.
• Vegetable origin- cotton, flax, linen, sisal, etc..
– Polymeric fibers are referred to as man-made, synthetic, or
artificial fibers
• Used in a variety of applications, including filters, cords, cables, and fabrics
• Fabrics require the fibers undergo a process which gives them a texture.
• Figure 3.112- Fiber Texture for
– continuous filaments, staple filaments, or spun staple filaments
• Continuous monofilament tows or yarns are cut into staples which are
subjected to a process often referred to as yarn spinning.
• Yarn spinning separates the monofilaments and tangles with a twist or spin
into a spun yarn consisting of
– relatively short filaments whose mechanical interlocking give a reasonable
strength,
– while loose ends afford a bulkier, less silky feel and appearance
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Polymeric Fibers
– Manufacture of fabrics consists of
• Weaving, knitting and other mills
• Many types of fabrics
– Woven fabrics or clothes are either
» Plain, patterned (dobby or jacquard), loop-type (terry or cut loop pile)
– Knitted fabrics are either circular (weft knit) or flat (warp knit)
– Tufted fabrics are produced as cut or uncut pile
– Stitch-bonded fabrics rely on a secondary fiber to hold the primary yarns in a
given pattern.
– Non-woven fabrics are subdivided into
» Bonded webs that make use of a polymeric binder to hold continuous or
staple yarn together
» Needle punch felts which involve a mechanical-type interaction.
• Fiber-forming polymers are normally crystallizing, uncross-linked type that
have a high degree of orientation
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Characterization
– Long-established textile industry developed specific methods and
an associated jargon to characterize fibers and associated units
– Fiber dimensions
• Reported as titer in denier (mass in g of 9000 m of monofilament or
multifilament yarn)
– Monofilaments range from 3 to 15 denier
» For a specific gravity of 1.3, a titer of 10 denier corresponds to a diameter
of 0.030 mm (0.001 in)
» Hosiery usually involves filaments of 15-denier titer
» Apparel may involve 12-filament twisted yarn with a global 50-denier titer
» Tire cord may involve 2448-filament untwisted yarn with a global 15,000
denier titer
– Fiber strength is often reported as tenacity in force (gf) per unit titer (denier)
» For a specific gravity of 1.3, a tenacity of 6 gf/denier corresponds to a
tensile strength of 100 kpsi (700 MPa)
» Tenacity of common fibers is in the range of 3-9 gf/denier (30 to 150kpsi)
» Fiber moduli range from 30-50 gf/denier, corresponding to .3-1 Mpsi
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Processing
– Formation of monofilaments involves two basic steps (Fig 3.113)
• Step 1: Filament spinning- formation of the filament or “as-spun
monofilament”, which is semi-crystalline, but nonoriented
• Step 2- “cold drawing” or “drawing”, confers most of the orientation
through a stretching, yielding, and drawing process that takes place in the
solid state, but above the Tg of the crystallizing polymer
• Monofilament in final form is “drawn filament”
– Filament spinning, achieved in several ways
• Chemical reaction during the fiber-forming stage, or
• Transformation are only physical, involving heat and mass transfer
– Wet spinning (Fig 3.114) involves the extrusion of a liquid-like
fluid through small holes (orifices) of a spinneret in a bath
containing another fluid with which the extruded strand interacts,
either chemically or through molecular exchange
• After sufficient interaction and residence time, the strand becomes solid and
as-spun monofilament
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Processing
– Dry spinning (Fig 3.115) involves the extrusion of a concentrated
polymer solution through small spinneret holes.
• Emerging strands are then dried (solvent is evaporated by cross-flow if air)
• Difficulty is in handling the solvents
– Melt spinning (Fig 3.116) involves extrusion of a molten polymer
through relatively large spinneret holes and its cooling and
solidification in a cross-flow of air.
• Difficulty is in the thermal stability of the melt and its high viscosity
– Strands are rapidly pulled (elongated) as they emerge from
spinneret holes, primarily in order to reduce the diameter.
– Acrylic and acetate fibers are wet- or dry spun
– Polyamides, polyolefins, and polyesters are commonly melt spun
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Commercial Types
– Seven major types of polymeric fibers
• Rayon- viscose rayon fibers are sold as regular, cross-linked, or high wet
modulus types
• Acetate- or triacetate fibers are based upon cellulose acetate
• Olefinics- include polyethylene and polypropylene
• Vinylinics- based on PVC, but also with copolymerization with vinyl acetate
or vinylidenechloride
• Acrylics- based on PAN, but can involve copolymerization with PVC
• Polyamides- or nylons involve aliphatic polyamides
• Polyesters- involve PET
• Special Purpose or high performance fibers
– Polyurethanes, aramids, extended chain, PBI, and PEEK
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Polymeric Films
– Widely used in the form of wide products of uniform thickness
(gauge)
– Film is associated with a thickness of less than 0.25mm (thickness
between 0.040 mm (0.001 in or 1 mil) and 0.4mm (10 mils)
• Dry cleaning garment bags are made from LDPE at a thickness of 0.013 mm
or 0.5 mils thick.
– Sheet is thicker than 0.25mm.
– Plastic film is manufactured in flat extrusion on chin rolls (film
casting or calendering) and tubular (bubble) extrusion blowing
– Uni-axial or bi-axial molecular orientation can be obtained using a
flat stretching device or through the bubble process, improves
properties
– Subjected to several standard tests
• Burst resistance, tear resistance, puncture resistance, folding endurance, slip,
curl, and resealability
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Polymeric Film Materials
– Regenerated cellulose, CLE, (Cellophane)- used for many years.
and can be coated with a thermoplastic for heat sealing.
– Cellulose Nitrate, CN, and Cellulose Acetate, CA- were the earliest
films.
– LDPE and HDPE- most common film materials.
– PP is generally used as oriented PP, OPP.
– Ionomers (IO) or Surlyn are olefin related film materials.
– PVC- is used in plasticized form.
– PVDC, or Saran Wrap- is used in copolymer form with 10-15%
acrylonitrile, AN, or with ethylene-vinyl acetate, EVA, or ethylynevinyl alcohol, EVOH.
– PET is used in film form for mylar sheet.
– PS is used as biaxially oriented film of for thermoforming sheet
– PC, polysulphone (PSU), Polyimides (PI), polyetherimides (PEI)
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Polymeric Film Materials
– Composite films can be defined as parallel layers of
different materials designed to offer a set of properties
not possessed by either material
• Coating or lamination of materials, e.g., paper or foil.
• Multilayer films are made by coextrusion with each layer:
– Mechanical strength: PET
– Sealing: PE
– Barrier : PVDC, EVOH
– Adhesives are needed to form bonds between layers
– Complex coextrusion dies can handle over 10 layers are
are used for tubular or flat extrusion
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Copyright Joseph Greene 2001
Specialty Polymeric Products
• Polymeric Film Applications
– Mechanical packaging: applications that require mechanical
resistance of the film
– Barrier packaging: displacing traditional packaging in glass or
metal containers.
• Some are flexible, e.g., bags or pouches for food items
• Some are rigid, e.g., yogurt containers, margarine tubs, etc.
– Packaging is essential for
• Sanitary and conservation reasons and should retard the
deterioration (spoilage) of foods, e.g., decay, discoloration of
meats, staleness of breads, etc.
– Barrier packaging involves control of
• Oxygen, carbon dioxide, and water.
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• Food characteristics
or aroma,
odor,
Copyright
Joseph Greene
2001 scent of food oils and fats
Specialty Polymeric Products
• Food containers
– Heat resistant packaging for boil-in, cook-in, and bake-in
• Requires sterilization of 120°C (250°F) and control of oxygen,
nitrogen , and carbon dioxide.
– Liquid food stuffs includes soups, beverages, wine, soda,
water, liquor can be packaged with plastics and are
replacing glass containers.
• Carbonated beverages can develop up to 100 psi pressure and
require resistance to carbon dioxide permeation.
– Semi-fluid food stuffs include dressing, mayonnaise,
relishes, and tomato ketchup, sauces (BBQ, pasta), and
jelly, jam, or preserves.
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Copyright Joseph Greene 2001
Polymeric
• FoodSpecialty
containers (continued)
Products
– Most solid foods are candidates for all plastic packaging,
but there are large differences in requirements that are
associated with the food and the intended use
• Animal products require odor control, water barrier, and
controlled oxygen permeation (PVC)
• Frozen poultry is shrink wrapped
• Dairy products including milk (HDPE) and cheese wraps
• Bakery products (bread, cakes, pies) must be wrapped with
suitable water barriers to prevent premature drying.
• Dry foods include cereals, biscuits, coffee, snack foods, chips
require moisture and oxygen to be kept out and aroma to be
kept in.
• Confectionery includes chocolate products whose high oil
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content requires oil resistant acrylonitrile based film
Copyright Joseph Greene 2001
Specialty Polymeric Products
• Mechanical film packaging applications include
– LDPE and HDPE
•
•
•
•
Thick-gauged sacks for powdered or granular products
Garbage and trash bags, general merchandise and tee-shirt bags
Thin gauge dry-cleaning garment covers and florist wraps
Heat shrinkable (biaxially stretched) can be made with LDPE,
PVC, PP, etc.
– Shrinking is achieved with hot water, hot air convection or radiation
• Stretch wrapping by winding a thin plastic tape under some
controlled tension
• Construction and public works uses for polymer film
– Construction coverings, roof liners, industrial liners
– Agricultural for silo covers, water reservoir liners 14
Copyright Joseph Greene 2001
Cellular Polymers
• Polymers can be combined with a gas
– Forms voids or cells in the polymer causing the polymer
to be very light
– Referred to as cellular, blown, expanded polymer, foam
• Elastomeric foam- matrix (polymer) is an elastomer or rubber
• Flexible foam- soft plastic matrix, e.g., plasticized PVC (PPVC), LDPE, PU
• Rigid foams- PS, unsaturated polyesters, phenolics, urethanes (PU)
– Type of polymer matrix, thermoplastic or thermoset can form basis
for classification
– Amount of gas added reflects the resulting density
• Light foams: density = 0.01 to 0.10 g/cc (1 to 6 lb/ft3)
• Dense foams: density = 0.4 to 0.6 g/cc (25 to 40 lb/ft3)
– Note: water = 1g/cc or 62.3 lb/ft3
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Copyright Joseph Greene 2001
Cellular Polymers
Closed cell
Matrix Gas
• Arrangement and distribution of gas in the cellular polymer
corresponds to the structure of the foam system.
• Two types (Figure 3.117)
Open cell
Matrix Gas
Closed cell
Interconnection
– Closed cell: spherical or roughly spherical voids (cells) are fully separated by
matrix material.
– Open cell: spherical or roughly spherical voids (cells) are interconnection occurs
between the cells.
• Degree of interconnection can be assessed if a sample is subjected to a moderate
vacuum and liquid is allowed to flow into the interconnections and causes the weight
to increase.
• Cell size is important for heat and mass transfer
– Cell density (number of cells per unit cross-section area or volume)
• Characterizes the courseness or fineness of a foam
– Structural foam: foamed core is sandwiched between solid skins
• Structured foam between integral skins
– Foaming can give an inhomogeneous structure
Copyright Joseph Greene 2001
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Cellular Polymers
• Closed-cellular polymers
– Nature of entrapped gas may have an effect on certain properties or
suitability for specific applications
• Air, nitrogen, water, pentane, methylene chloride, fluorohydrocarbon vapors
can be used as blowing agent
• Amount of gas changes with time as the gas moves through the material and
exits to the atmosphere leaving a cellular structure
• Mechanism for the formation of cellular structure
– Aeration or frothing: mechanical agitation is used to incorporate air
into liquid resin system (latex, reactive urethane)
– Physical blowing agent:
• Add N2 gas into solution or to liquid melt which comes out of solution when
pressure is released and forms cells.
• Add liquids at room temperature and have low boiling point. The liquids
vaporize upon heating or by chemical reaction heat.
– Aliphatic hydrocarbons (pentane), methylene chloride, trichloro-fluoromethane,
or freon 11
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Copyright Joseph Greene 2001
Cellular Polymers
• Mechanism for the formation of cellular structure (continued)
– Chemical blowing agents are compounds that decompose under
heat and liberate large amounts of and inert gas,
• N2, CO2, CO, water, ammonia, H2, etc.
• Activators can sometimes be added to allow lower decomposition
temperature and release more gas at a lower temperature.
• Early blowing agents were
– Sodium bicarbonate, which liberates CO2
– Other carbonates and nitrates liberate hydrogen or nitrogen.
– Hydrogen can be generated in large quantities, but diffuses away quickly
• Organic compounds can be used for some high temperature thermoplastics
–
–
–
–
–
Toluene sulfonyl hydrazine
Oxybis benzene sulfonyl hydrazide
Toluene Sofonyl semicarbazide
Trihydrazinatrizine
Phenyl tetrazole
• Can be in finely divided solid form to create cellular structure
• Nucleating agents and surfactants are used to control cellular structure
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Copyright Joseph Greene 2001
• Examples
Cellular Polymers
– Polystyrene: PS or expanded polystyrene foam (EPS)
• Made from expandable polystyrene beads which are small spheres of
polystyrene (diameter of 0.3 – 2.3 mm) containing 3-7% pentane as physical
blowing agent
– Bulk density of beads (with air spaces) is 0.7 g/cc.
• Manufacturing (Figure 3.118)
– Beads are pre-expanded with the use of a steam chamber to a bulk density of
0.02-0.05 g/cc.
– Beads are cooled and reached equilibrium with air penetrating the cells.
– Placed back in steam chamber and molded into final foamed shape.
» Forms basic cellular structure is closed cell type
– Large blocks are molded which are cut into insulating boards or molded into
custom products
» Cups, insulating containers, protective elements
– Extrusion process can be used with blowing agent
» Meat trays, egg cartons
Void
Expandable bead
Pre-Expanded bead
Copyright
2001
Initial Joseph
Stage Greene
Preexpansion
Mold Filling
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Cellular Polymer
Final Expansion
• Examples
Cellular Polymers
– Polyurethane can be made in cellular form
• Stiffness can vary widely from that of a soft elastomer to a rigid plastic.
• Density can vary widely from 0.03 g/cc (rigid foam) to 0.08 g/cc (flexible)
• Cell structure varies from open cell structure for flexible and closed cell
structure for rigid foam which traps the blowing agent (Freon 11)
• Produced with a water-blown Carbon dioxide blowing agent
– Manufacturing
• Continuous formation of rigid or flexible foam of large block (log, bun, loaf)
• Uses a suitable mold using a mixing head on a boom that is placed on top of
a carrousel with several molds. The resin is injected in one mold while
others are curing.
• Typical cross section is 2m x 1m and a typical linear speed of production is
4m/min
• Called foamstock
– Subsequent products are cut from foamstock using hot wires
Copyright Joseph Greene 2001
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Cellular Polymers
• Manufacturing (continued)
– Another method involves permanently placing the foam in a cavity
of a product, called in-situ (In-place) foaming
• For insulation, buoyancy, structural or combined purposes.
• Requires good adhesion to the cavity walls and may require treatment
(degreasing, carona discharge, etc..)
– Spray-on method
• Liquid or frothed resin is projected against a surface (substrate) but rises
freely on the opposite side.
• External insulation of tanks, vessels, roofs, truck boxes
– Molding method with molds
• Parts are to a specific complex shape. (Steering wheel covers, foam seats)
• Demolding will require the use of a external spray and internal release agent
– Usually soap based zinc stearate
• Pressure generated during molding requires adequate control, otherwise
– Dimensions may vary significantly and poor formation of integral skin 21
and cells
Copyright Joseph Greene 2001
Cellular Polymers
• Manufacturing (continued)
– Frothing method corresponds to 2-stage expansion.
• Suitable low boiling point blowing agent is incorporated to the
resin under pressure (4-5 atmospheres) (1 atmosphere = 14.69
psi) to prevent expansion
• Pressure release at the exit of the dispensing nozzle causes the
immediate formation of a froth (foamed cream) corresponding
to a pre-expansion ratio of 10X. Subsequent expansion is
associated with the curing reaction which causes the
vaporization of the other blowing agent with expansion of 3X.
• Pressure developed in a cavity and temperature variations are
lower than in the case of direct liquid feeding and mush larger
than by successive layer build-ups.
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Copyright Joseph Greene 2001
Cellular Polymers
• Structural Foam
– Feature cellular core and solid skins
– Based upon thermoplastic or thermosets
– Produced in a variety of methods
• Low pressure (Union Carbide) process Fig 3.119
– Forms the foam in an accumulator from which it is transferred into mold
cavity under moderate pressure (35 atm or 500 psi)
– Tooling is inexpensive, Surface finish is not very good
• High pressure process (United Shoe Machinery). Fig 3.120
– Conventional injection of the melt containing a blowing agent
– High pressures (15kpsi to 20 kpsi) prevents foaming and allows for
better surface finish
– Tooling is expensive, Surface finish is very good
– Mold cavity is enlarged (expansion mold) to allow molten core to foam
– Reaction Injection Molding Process can produce urethane structural
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foam parts
Copyright Joseph Greene 2001
• Applications
Cellular Polymers
– Mechanical properties are very good on per weight basis
• Core materials in conjunction with composites
– Composite floor pans
• Thermal insulation properties are outstanding
– Closed cell are used as insulation board and for packaging of frozen or
perishable foods, e.g., ice cream, fish, poultry.
• Floatation devices for closed cell
• Shock absorption and vibration resistant applications
– Automotive occupant protection
– Automotive bumper impact, urethane foam and expanded PP beam foam
• Acoustic insulation or dampening materials
• Open cellular structures used in filtering and humidifying applications
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Copyright Joseph Greene 2001