M144 Ch03 Spec


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M144 Ch03 Spec

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