Polymer and Polymer Processing

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Polymer and Polymer Processing
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Polymer, Resin, and Plastics

• A polymer is any substance made up of many of
  repeating units, building blocks, called mers.
• When in form ready for further working, they are
  called resins.
• Polymers are seldom used in their neat form, most
  often compounded with various additives. The
  resulting material is usually referred to as a
  plastic.
• Frequently, polymers, resins, plastics are used
  interchangeably.

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Properties and Applications

• Low density, high corrosion resistance,
  electrical insulation.
• Ease of manufacturing into complex shapes.
• Widely used for consumer products.
• Emerging as structural polymers (Tlt150-250C).
• Sales of plastics, on a volume basis, has grown
  more than double the steel production in the U.S.

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Polymerization Reactions

• Chain polymerization, also called addition
  polymerization, with the aid of initiators, to
  form Paraffin or Benzene.
• Step reaction, also called condensation,
  dissimilar monomers joined into short groups that
  gradually grow with by-product released.

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Types of Polymers
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Basic Concepts

• Molecular weight (MW)
• Degree of polymerization (DP)
• Chain structures
• Crystalline and amorphous polymers
• Glass transition temperature (Tg) and melting
  temperature (Tm)
• Mechanical properties

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Source of Strength of Polymers

• Primary Bond - Covalent Bonding
• Secondary Bonds
• van der Waals
• Dipole Bonds
• Hydrogen Bonds

PE - mer
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Major Polymer Processes

• Extrusion
• Injection Molding
• Blow Molding
• Thermoforming
• Recycling

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Polymer Processes
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Extrusion
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Extrusion Product Examples
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Extrusion Characteristics

• The extrusion machine forms the basis of nearly
  all other polymer processes.
• Basically involves melting polymer pellets and
  extruding them out through a two dimensional die.
• Produces long, thin products
• Coating for electrical wire
• Fishing Line
• Tubes, etc.

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Injection Molding (See Video)
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Injection Molding Product Examples
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Injection Molding Machine Basics
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Injection Molding Process Control

• Very similar to die casting
• Must control heat transfer and fluid flow
• Do that by controlling temperature and pressure

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Gas Assist Injection Molding
Applicable to hollow parts without interior
control.
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Injection Compression Molding
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Injection Molding of Thermosets

• Plastics set when they cool
• Mold temperature will be set to allow full cavity
  fill, while increasing production rate
• Thermosets undergo a chemical crosslinking that
  produces the solid structure
• Mold temperature will be hotter usually set to
  allow full cavity fill, while accelerating the
  chemical reaction to cure.
• Often called Reaction Injection Molding (RIM)

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Blow Molding Example Products
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Blow Molding Processes (See Video)
Injection Blow Molding
Extrusion Blow Molding
Stretch Blow Molding
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Thermoforming
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Thermoforming Products
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Polymer Recycling

• 1998 Approximately 20 of plastic waste is
  recycled (optimistic estimate)
• 1998 Polymers account for approximately 18 by
  volume of material to landfills

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Needs vs. Challenges

• Needs for a viable program
• Stable supply of materials with reliable
  collection and sorting
• Economical, proven and environmentally sound
  recycling process
• End use applications for the recycled material

• Challenges
• 10-12 main polymer types
• Thousands of blends
• Additives
• Impurities in supply (labels, glass, dirt, etc)

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Recycling of Polymers

• PET (polyethylene terphthalate) beverage
  containers, boil-in food pouches, processed meat
  packages
• HDPE (high density polyethylene) milk bottles,
  detergent bottles, oil bottles, toys, plastic
  bags
• PVC (polyvinyl chloride) food wrap, vegetable
  oil bottles, blister packaging
• LDPE (low density polyethylene) shrink-wrap,
  plastic bags, garment bags

• PP (polypropylene) margarine and yogurt
  containers, caps for containers, wrapping to
  replace cellophane
• PS (polystyrene) egg cartons, fast food trays,
  disposable plastic silverware
• Other multi-resin containers

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Processing of Polymer Composites
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What are Composites

• Composites are often classified by the type of
  matrix polymer, metal or ceramic
• In addition, composites my be classified by the
  type of embedded material (a.k.a., reinforcement)
  fiber, particle, whisker, flake, etc.
• Rule of mixtures says that each constituent
  contributes to the properties of the composite in
  proportion to its volume fraction

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Fibers dominate composite properties
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Components of Polymer Composites

• Polymer Resin
• Usually a thermoset
• Epoxy
• Bismaleimide
• Polyimide
• Thermoplastics
• Polyester
• Vinylester
• Reinforcing fiber
• Fiberglass
• Graphite (Carbon)

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Fabrication of Composites (See Video)

• Fabrication of polymer-matrix composites
• Open-mold processes
• Pultrusion
• Closed-mold processes (Matched-die molding)
• Metal-matrix composites
• Ceramic-matrix composites

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Open-Mold Processes

• Shaping
• Male or female mold
• Hand lay-up
• Spry molding
• Tape laying
• Filament winding
• Curing
• Open air
• Vacuum bag
• High pressure bag
• Heated pressure vessel

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Filament Winding

• Control the orientation of the fiber using a
  relative motion of rotation and linear motion
• Example Products
• Pressure Vessels
• Fishing Poles
• Light Poles

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Pultrusion

• Fibers or cloth are pulled through a resin bath
• Heated in a die with a shaped profile
• Cured to shape
• Cut to length

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Closed Molding

• Can be done using Pre-preg or wet layup
• Process
• Resin impregnated fibers cut to proper geometry
• Heated Die sets close on part
• Part is cured at temperature
• Die opens and part is ejected from mold

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Resin Transfer Molding (RTM)
Male mold half
Female Mold Half
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Steps of RTM Process

• The Resin Transfer
• Molding Process
• Fiber reinforcement is placed in
• the mold
• The mold is closed and clamped
• Resin is injected into the mold
• cavity under pressure
• The resin cures
• The part is removed from the mold

Pressurized Resin
Air
Air
The RTM Process
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Open vs. Closed Molding

• Open Molding
• Only one sided mold
• Limited temperature control
• Lower capital cost for molds

• Closed molding or compression molding
• Two sided mold part is sandwiched between two
  mold halves
• Pressure applied
• Improved material properties (fewer voids)
• Higher Capital cost