Polymers: Structure/Performance and Applications

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Polymers Structure/Performance and Applications

• Cathy Wedelstaedt
• Sr. Intellectual Capital Leader
• Performance Plastics and Chemicals
• The Dow Chemical Company
• Midland, MI

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Outline

• Polymers
• Definition
• Types of polymer
• Fabrication techniques
• Structure/property relationships
• Material selection exercise
• Careers associated with polymers

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Polymers

• Large molecules consisting of repeating
  structural units or monomers.
• Derived from the Greek poly (many) and meros
  (parts).
• Monomers are connected to each other via covalent
  bonds in a process called polymerization.
• Usually a collection of molecules of different
  lengths (distribution of molecular weights)-
  modified through polymerization conditions.

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Types of Polymers

• Homopolymer A-A-A-A-A-A
• Copolymers
• Random A-B-B-B-B-A-A-A-A-A-A-B-B-A-A-
• Block A-A-A-A-B-B-B-B-B-A-A-A-A-
• Graft A-B-B-B-A-A-A-A
• B-B-B-B-B-B-B-B

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Polymers in Everyday Life

• Clothing
• Oil recovery
• Food and flavors
• Agriculture
• Packaging
• Consumer items clothing, toys, skin care
• Automotive parts
• Industrial (pipes, parts, additives, etc)
• Electronics
• Medicines (proteins, antibodies, coatings for
  tablets, gel caps)
• Just about everywhere!

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Fabrication Methods

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More Fabrication Methods

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Structure/Property Relationships

• Additives
• Processing aids
• Stability enhancement

• Processing conditions
• Injection, cast, extrusion
• Time/temperature profiles

Polymer Performance

• Chemical composition
• New monomers in the backbone (type, quantity)

• Molecular architecture
• Blends
• Grafts, branching
• Molecular weight

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Materials Selection Exercise

• Congratulations- you are all now material
  scientists!
• You have been approached by a compact disc
  manufacturer for assistance in material
  selection.
• They are the exclusive producers of compact discs
  for the group, Red Hot Chili Peppers and want to
  make sure they choose the right polymer for an
  upcoming new release.
• There will be a lot of unhappy fans if they spend
  15 on a compact disc and is does not hold up to
  a variety of polymer performance factors.

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Performance Features - Compact Disc

• Strength
• Does not break if you drop it.
• Dimensional stability
• Does not change shape when exposed to heat.
• Withstands exposure to other materials (diet
  coke, water, your lunch, etc).
• Flexible
• Able to withstand some bending without breaking.
• Rigid
• Withstand fast spinning inside the player.
• Mass produce
• Easy to fabricate.

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Compact Discs

• A compact disc (or CD) is an optical disc used
  for storing digital data. It was originally
  invented for digital audio in 1979.
• Compact discs are made from a 1.2 mm thick disc
  of plastic coated with a much thinner aluminum
  layer.
• Aluminum layer is protected by a film of lacquer,
  which can be printed with a label.
• Injection molding is used to manufacture compact
  discs.

Plastic
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Candidate 1- Polyethylene

• Produced from petroleum product (ethylene), most
  commonly used polymer in consumer applications.
• Provide toughness, rigidity and strength for blow
  molding applications, extruded products, films,
  and injection molded items.
• Excellent combination of stiffness and resistance
  to chemicals/liquids.
• Key applications
• Containers- shampoo, detergent, milk, solvents
  and oils
• Bays, garbage can liners
• Toys, tote bins

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More About Polyethylene

• Polyethylene is classified into several different
  categories based branching and molecular weight.
• Linear polyethylene is much stronger than
  branched polyethylene, but branched polyethylene
  is cheaper and easier to make.

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Candidate 2- Polystyrene

• First produced in 1938 by The Dow Chemical
  Company.
• Made from monomer styrene, another petroleum
  based product.
• Protects products against moisture, maintains
  strength and shape over long periods of time
  (sturdy).
• Key applications
• Foam- egg cartons, insulation, packing
  materials,
• Food trays, cups
• Boxes for small objects, plastic utensils, cups
• Large and portable appliances

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More About Polystyrene

• ABS (acrylonitrile/butadiene/styrene)
• Addition of polar groups and rubber- better
  impact strength, more flexible.
• Key applications - sporting goods, helmets, toys,
  electronic and appliance housing, automotive body
  parts.
• HIPS (high impact polystyrene- addition of
  butadiene)
• Key applications - toys, household appliances,
  cases, boxes, and calculators, computer housings.

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Candidate 3- Polycarbonate

• Polymers with carbonate functional groups in the
  backbone.
• Very durable, transparent material, high heat and
  scratch resistance, resistance to
  chemicals/liquids.
• Key applications
• Bullet proof glass, safety wear (shields,
  glasses)
• Automotive headlamp lenses
• Bottles, high end tableware, computer housing
• Medical equipment

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More About Polycarbonate

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Tensile Properties

Stress/strain curve

• Continuous force exerted on a material as it is
  elongated.
• Stress force applied to produce deformation in
  a unit area of a test specimen (expressed in
  pounds per square inch).
• Strain ratio of elongation to the gauge length
  of a test specimen (no units).

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Tensile Properties- Results

• Tensile strength at yield - the stress a material
  can withstand without permanent deformation.
• Tensile strength at break - the maximum stress a
  material can withstand.
• Tensile elongation at break - the strain
  coordinate at rupture.
• Modulus - ratio of the stress to strain below
  yield point (slope of stress/strain curve)

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Flexural Properties

flexural stress
F is the load at a particular moment L is the
length of the support span B is the width of the
sample D is the thickness of the sample

• Ability of a material to withstand bending
  forces.
• Many polymers do not break under flex even under
  large degrees of bending.
• Usually more relevant for design purposes.

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Flexural Properties- Results

• Flexural modulus is a measure of stiffness during
  the bending process.
• Slope of the initial straight line portion of the
  flexural stress/strain curve.

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Thermal Properties

• Tg (glass transition temperature) temperature
  at which a material goes from a rigid, glass like
  state to a rubbery state.
• Tm (melting point) temperature at which a
  material changes from solid to liquid state.
• Critical parameter in determining
  fabrication/molding conditions, end use
  application opportunities.

Differential scanning calorimetry (DSC) measures
the energy necessary to establish a zero
temperature difference between the sample and an
inert substance
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Summary of Our Experiments
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The material of choice is..
Polycarbonate

• Rigid
• Strong
• Easy to fabricate
• Dimensional stability

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Careers Associated with Polymers

• Creating new materials (chemistry, chemical
  engineering, mechanical engineering, material
  sciences)
• Design of new molecules (chemistry, chemical
  engineering)
• Characterization of the chemical structure of
  materials
• Characterization of the material attributes
• Regulatory and environmental concerns
• Management of intellectual capital (protecting
  your innovations)
• Producing quantities of materials (chemistry,
  chemical or mechanical engineering)
• Scale up from lab experiments to production
• Consistency and quality of materials
• Fabrication
• Introduction of materials into the market place
  (chemistry, engineering, marketing, finance)
• Working with customers- what are their needs for
  performance
• Marketing and selling materials

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Thank you!