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)
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
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