Chapter 8

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Chapter 8 Polymer Families

• Recall polymer categories
• Plastics
• Thermoplastics
• Engineered and commodity
• Thermosets
• Engineered and commodity
• Elastomers
• Thermosets and thermoplastics

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Most plastics are thermoplastics. Most
thermoplastics are commodity Most commodity
thermoplastics are PE, PP, PVC and PS This
accounts for 80 of all thermoplastics!!!
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Commodity vs. Engineered Thermoplastics

• Commodity thermoplastics lt 1.50/lb (06)
• Engineered thermoplastics 1.50 to 6.00 range
  but some can be north of 100 for special
  plastics. See http//www.curbellplastics.com/cat
  alog.asp1
• Engineered plastics used for durable goods, have
  better mechanical properties or special
  property.
• Commodity plastics are used for consumer goods
  (i.e. food storage), are more readily available
  and generally have lower mechanical properties.
• 80 - 85 of all thermoplastics are commodity,
  balance are engineered.

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Commodity Thermoplastics

• Polyethylene (PE) (includes LDPE, HDPE, UHMW,
  PETE)
• Polypropylene (PP)
• Polyvinyl Chloride (PVC or vinyl)
• Polystyrene (PS)
• These are broad families many variations exist
• Density, blends, additives, fillers, etc
• These are all ethenic polymers (based on the
  ethylene molecule)

Account for 80 of all thermoplastics!!
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More on Commodity Thermoplastics

• Most are linear in structure with minimal
  branching and cross-linking.
• Most are low strength to strength comparable to
  that of engineering plastics.
• Polyethylene (PE) and polypropylene (PP) both
  have a translucent, waxy texture, and are the
  only non-foam plastics that float in water (i.e.
  density lt 1.0 g/cm3)
• Can be amorphous (PS, PVC) or semi-crystalline
  (PE, PP)
• See chapter 8 summary for more!

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Ethenic Polymers (all based on the ethylene
molecule)

• A series of polymers can be created by modifying
  the ethylene monomer essentially replacing a
  hydrogen atom with something else

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These ethylene polymers (with polyethylene)
make up about 80 of the tonnage of polymers in
use.
8

• Arrangement Effects
• Chain Flexibility
• How easily the main chain of the polymer can
  move, is a key factor in determining the
  properties of the material.
• There are several factors that will determine the
  chain flexibility
• Temperature
• Types of bonds
• Side groups
• Branching
• Additives

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• Arrangement Effects
• Chain Flexibility Branching
• Although branching can increase the entanglement
• of the polymer chains, branching increases
• the chain flexibility.
• Larger branches hold the molecules further
• apart, increasing the free volume (and
  decreasing
• density, giving the molecules more room to
  move.
• Additives also greatly reduce chain flexibility
  (i.e. glass filled).

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Polyethylene (PE)

• Surpasses all plastics in quantity produced.
• Simplest of molecules CH2-CH2
• Qualities Stiffness, strength/toughness, low
  cost, ease of forming, resistance to chemicals,
  permeability to gas, ease of processing.

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Polyethylene (PE)

• Crystalline Yes only C-H bonds, flexible no
  side groups
• Hygroscopic No (not O or N)
• Glass Transition Low (-125 C)
• Flammability Yes only C-H bonds

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Polyethylene (PE)

• Uses
• LDPE Bread bags, frozen food bags, grocery bags.
• HDPE Milk, water and juice containers, grocery
  bags, toys, liquid detergent bottles.

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• Arrangement Effects
• Polyethylene is probably the most chemically and
  heat resistant thermoplastic material. It
  contains only carbon and hydrogen bonds.
• Polypropylene is also very chemically and heat
  resistant, it comes close to Polyethylene, but
  falls a little short.

Polyethylene
Polypropylene
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Polyethylene (PE)

• Many options available

Most Common
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Density Options
Low Density ( 0.91 - 0.925 g/cm3) Trash bags, grocery bags,etc
   
Medium Density ( 0.926 - 0.941 g/cm3) Bowls, lids, gaskets, containers
   
High Density ( 0.941 - 0.959 g/cm3) Bottles, piping
   
Very high Density ( 0.959 - higher g/cm3) Toys
   
UHMWPE ( 0.93 - 0.97 g/cm3) Toys, wear items, tough, low coefficient of friction, excellent abrasion resistance

• Density increases so does strength and
  toughness, also linearity of chain orientation
  increases. High density grades tend to be more
  crystalline.
• Low density grades have significant degree of
  branching and hence, lower melting point

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• 30 glass filled, high density, strength can
  approach 7 ksi
• UHWPE strength approx. 6 ksi
• Conclusion can approach strength of engineered
  polymers w/ special polyethylene options!!

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• Polyethylene Terephthalate (PET) (aka Polyester)

• Crystalline Yes, flexible enough
• Hygroscopic Yes (O)
• Glass Transition (69 C)
• Flammability Yes (only C-H and CO bonds)

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Polypropylene (PP)

• Monomer of PP contains methyl group (CH3) in
  place of one H

What is the chemical formula??
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Polypropylene (PP)

• Crystalline Yes only C-H bonds, flexible
  side groups every other C
• Hygroscopic No (not O or N)
• Glass Transition Low (- 20 C)
• Flammability Yes only C-H bonds

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Polypropylene (PP)

• Strengths similar to HDPE, but easier to
  injection mold.
• Good fatigue properties.
• Excellent chemical resistance no solvent for PP
  at room temperature!
• Low density (.9 to .915 g/cm3) means lighter than
  water (i.e. it floats).
• Qualities Strength/toughness, resistance to
  chemicals, resistance to heat, barrier to
  moisture, low cost, versatility, ease of
  processing, resistance to grease/oil.

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Polypropylene (PP)

• Uses
• Gasoline tanks, chemical tanks, luggage, battery
  cases, ropes, fibers or filaments.
• Consumer products Ketchup bottles, cups yogurt
  containers and margarine tubs, medicine bottles.

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Polypropylene (PP)
Options
Su 10 ksi
Su 5 ksi
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• Arrangement Effects
• Chain Flexibility Side Groups
• Side groups restrict chain movement. The larger
  the side group, the more rigid the molecule
• Having a Methyl (CH3) group attached to one side
• of the main chain will add some stiffness.
• Polypropylene is relatively flexible even at
• room temperature.
• Having one attached to both sides of the
  main chain will add a lot of stiffness. PMMA
  is very
• rigid.

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Polyvinyl Chloride (PVC aka Vinyl)

• Monomer of PVC contains one chlorine atom in
  place of one H

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Polyvinyl Chloride (PVC aka Vinyl)

• Crystalline No, rigid (Cl to big to allow)
• Hygroscopic No (not O or N)
• Glass Transition High (185 F)
• Flammability No (Cl puts out)

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Polyvinyl Chloride (PVC aka Vinyl)

• Two types
• Plasticized (vinyl) low strength mostly used
  for decorative coatings (wallpaper), wire
  coating, imitation leather, etc.
• Rigid (no plasticizer) much stronger!!!
• PVC has excellent transparency, chemical
  resistance, long-term stability, flammability
  resistance, good weatherability, flow and
  insulatory electrical properties.
• Qualities Versatility, ease of blending,
  strength/toughness, resistance to grease/oil,
  resistance to chemicals, clarity, low cost.
• Low fracture toughness (brittle)
• Glass Transition 81 C

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Polyvinyl Chloride (PVC aka Vinyl)

• Uses
• Plumbing products/ hardware, outdoor signs
• Clear food packaging, shampoo bottles

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Polyvinyl Chloride (PVC aka Vinyl)

• Can be copolymerized to get property
  modifications.

Options
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Polystyrene (PS)

• H atom substituted with a large benzene ring

Or, simplified
Recall chain stiffening
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Polystyrene (PS)

• Accounts for 20 of all thermoplastics in
  commercial use.
• Very versatile plastic that can be rigid or
  foamed.
• PS is brittle poor impact strength. Its
  mechanical properties can be improved by blending
  with polybutadiene.
• Qualities Versatility, insulation, ease of
  processing, low cost, clarity
• Horrible weatherability, does not have chemical
  resistance like PE and PP.
• Glass Transition 100 C

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Polystyrene (PS)

• Uses
• Foamed
• Insulation, beverage cups, fast-food sandwich
  containers
• Rigid
• Videocassette cases, compact disc jackets,
  knives, spoons and forks, cafeteria trays,
  grocery store meat trays

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Polystyrene (PS)

• Arrangement Effects
• Chain Flexibility Side Groups
• Having a Benzene ring attached to one side of the
  chain will greatly affect the stiffness.
  Polystyrene is very stiff to the point of being
  brittle (CD cases)

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Polystyrene (PS)

• Crystalline No (Benzene ring makes it too
  rigid)
• Hygroscopic No (not O or N)
• Glass Transition High (210 F)
• Flammability Yes only C-H bonds

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Polystyrene (PS)
Options
35
Approximate tensile strength note PP, PVC
approach engineered thermoplastics!!