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M144 Ch03 Spec

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  • 1. Classes of Polymeric Materials Chapter 3: Specialty Polymeric Products Professor Joe Greene CSU, CHICO
  • 2. 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
  • 3. 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
  • 4. 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
  • 5. 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
  • 6. 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
  • 7. 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
  • 8. 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
  • 9. 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 ethylyne-vinyl 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)
  • 10. 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
  • 11. 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.
        • Food characteristics or aroma, odor, scent of food oils and fats
  • 12. 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.
  • 13. Specialty Polymeric Products
    • Food containers (continued)
      • 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 content requires oil resistant acrylonitrile based film
  • 14. 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
  • 15. 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/ft 3 )
        • Dense foams: density = 0.4 to 0.6 g/cc (25 to 40 lb/ft 3 )
          • Note: water = 1g/cc or 62.3 lb/ft 3
  • 16. Cellular Polymers
    • Arrangement and distribution of gas in the cellular polymer corresponds to the structure of the foam system.
    • Two types (Figure 3.117)
      • 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
    Matrix Closed cell Gas Matrix Open cell Gas Closed cell Interconnection
  • 17. 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 N 2 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
  • 18. 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,
        • N 2 , CO 2 , CO, water, ammonia, H 2 , 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 CO 2
          • 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
  • 19. Cellular Polymers
    • Examples
      • 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
    Expandable bead Initial Stage Void Cellular Polymer Preexpansion Mold Filling Final Expansion Pre-Expanded bead
  • 20. Cellular Polymers
    • Examples
      • 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
  • 21. 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 and cells
  • 22. 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.
  • 23. 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 foam parts
  • 24. Cellular Polymers
    • Applications
      • 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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