6.3

• Polymers

  • Generally organic compounds based on carbon, hydrogen, and other non-metallic elements
  • Have large molecular structures
  • Typically have low densities and may be extremely flexible
• Polymers

  • Plastics
  • Rubbers
• Polymer applications


  • PVC pipes
  • Rubber tires
  • Polyurethane coated polyester raincoat
  • Kevlar helmet
• Polyethylene

  Easily formed into thin, airtight film
• Kevlar

  High tensile strength
• Plastics

  Materials that have some structural rigidity under load, and are used in general-purpose applications
• Classification of Plastics


  • Polyethylene
  • Polypropylene
  • Poly(vinyl chloride)
  • Polystyrene
  • Fluorocarbons, epoxies, phenolics
  • Polyesters
• Plastics


  • Some are very rigid and brittle
  • Others are flexible and experience considerable deformation before fracture
  • Either thermoplastic or thermosetting
• Plastics applications

  • Polystyrene and poly(methyl methacrylate) are used when optical transparency is critical
  • Fluorocarbons is used for coatings on nonstick cookware, bearings and bushings, and high temperature electronic components
• Trade Names, Characteristics, and Typical Applications for a Number of Plastic Materials

  • See table

  
• Elastomers

  • Properties depends on the degree of vulcanization and on whether any reinforcement is used
  • Mechanical properties, even vulcanized rubbers, are not satisfactory and may be improved by additives such as carbon black
• Natural rubber


  Still utilized to a large degree because it has an outstanding combination of desirable properties
• SBR


  The most important synthetic elastomer (Automobile tires, reinforced with carbon black)
• NBR


  Used when highly resistant to degradation and swelling is required
• Silicone elastomers


  • Posses a high degree of flexibility at low temperatures (to -90°C) and yet are stable to temperatures as high as 250°C
  • Used in automobile engine compartment
• Biocompatibility


  Property of silicone elastomers
• Fibers


  • Polymers that are capable of being drawn into long filaments having at least a 100:1 length-to-diameter ratio
  • Used in textile industry, being woven or knit into cloth or fabric
  • Aramid fibers are employed in composite materials
  • Convenience in washing and maintaining clothing depends primarily on the thermal properties of the fiber polymer
  • Must exhibits chemical stability to a rather extensive variety of environments, including acids, bases, bleaches, dry cleaning solvents, and sunlight
  • Must be Relatively nonflammable and amenable to drying
• Coatings


  • Applied to the surface of materials to protect the item from the environment that may produce corrosive or deteriorative reactions, to improve the items appearance, or to provide electrical insulation
  • Mostly organic polymers
• Coatings


  • Paint
  • Varnish
  • Enamel
  • Lacquer
  • Shellac
• Latex


  A stable suspension of small insoluble polymer particles dispersed in water, most common coatig
• Adhesives


  • Substance used to bond together the surfaces of two solid materials (termed "adherends")
  • Mechanical bonding - There is an actual penetration of the adhesive into surface pores and crevices
  • Chemical bonding - Involves intermolecular forces between the adhesive and adherend
• Adhesives

  • Natural adhesives (animal glue, casein, starch, and rosin)
  • Synthetic polymers (Polyurethanes, Polysiloxanes (silicones), Epoxies, Polyimides, Acrylics, Rubber material)
• Films

  • Polymeric materials fabricated and used extensively as bags for packaging food products and textile products
  • Characteristics are low density, high degree of flexibility, high tensile and tear strength, resistance to attack by moisture and other chemicals, and low permeability to some gases
  • Having thicknesses between 0.025 and 0.125 mm (0.001 and 0.005 in.)
• Foams

  • Plastic materials that contain a relatively high volume percentage of small pores and trapped gas bubbles
  • Both thermoplastic and thermosetting materials are used as foams (Polyurethane, rubber, polystyrene, poly(vinyl chloride))
  • Commonly used as cushions in automobiles and furniture as well as in packaging and thermal insulation
• Composites

  • Consists of more than one material type
  • Designed to display a combination of the best characteristics of each of the component material
• Composites

  • Fiberglass (Glass fibers embedded within a polymeric material, acquires strength from the glass and flexibility from the polymer)
  • Plywood
  • Fiberglass automotive spoiler
  • Carbon fiber bicycle frame
• Composites

  Most are made of 2 phases: Matrix phase (continuous phase present throughout the material) and Dispersed phase (surrounds and binds by matrix phase)
• Composites

  • Properties varies depending on the concentration, size, shape, distribution, and orientation of the dispersed phase
• Composites applications

  • Aerospace
  • Underwater
  • Transportation
• Classifications of Composites

  • Particle Reinforced Composites
  • Fiber Reinforced Composites
  • Structural Composites
• Particle Reinforced Composites


  • Uses tiny particles as its dispersed phase
  • Classified based on reinforcement - Large Particle Composites and Dispersion Strengthened Composites
• Large Particle Composites


  • The filler material replaces some volume of the material and modifies its properties
  • Examples are Concrete (cement - matrix, sand and gravel - particles) and Cermets (metal Cobalt or Nickel - matrix, ceramic Tungsten carbide or Titanium cabide - particles)
• Dispersed Strengthened Composites


  • Phase interaction takes place at atomic or molecular level
  • Matrix phase - Metal / Metal Alloys,
  • Dispersed phase - Metal / Non-metal
  • Example is Thoria Dispersed Nickel -Type of Nickel Alloy with 3 % Thoria
• Fiber Reinforced Composites

  • Fibers are characterized to their length to diameter ratio
  • Have high strength, stiffness, and greater elastic modulus
  • Classified as Continuously Arranged Fiber Reinforced Composites and Discontinuously Arranged Fiber Reinforced Composites
• Continuously Arranged Fiber Reinforced Composites

  Have orderly aligned fibers
• Discontinuously Arranged Fiber Reinforced Composites

  Discontinuous and/or Randomly arranged
• Structural Composites


  • Made of Homogenous and composite materials
  • Classified as Laminar Composites and Sandwich composites
• Laminar Composites


  • Composed of two-dimensional sheets or panels that have a preferred high-strength direction such as is found in wood and continuous and aligned fiber-reinforced plastics
  • Example is Plywood
• Sandwich Composites


  • Designed to be light-weight beams or panels having relatively high stiffnesses and strengths
  • Consists of two outer sheets, or faces, that are separated by and adhesively bonded to a thicker core
  • Used in roof, floors, walls
• Biomaterials

  • Components planted into the human body for replacement of diseased or damaged parts
  • Must not produce toxic substances (inert) and must be compatible with body tissues
  • All material types may be used