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M144 Ch03 Spec
 

M144 Ch03 Spec

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    M144 Ch03 Spec M144 Ch03 Spec Presentation Transcript

    • Classes of Polymeric Materials Chapter 3: Specialty Polymeric Products Professor Joe Greene CSU, CHICO
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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)
    • 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
    • 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
    • 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.
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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.
    • 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
    • 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