Transcript Plastics and Composites

Plastics and Composites
Welding of Plastics
Polymers
• Polymer - a single building
block (mer) is repeated to
form a long chain molecule
– Thermoplastic polymers
soften when heated, harden
when cooled
• 2-liter bottles
– Thermosetting polymers
don’t soften when heated
• Car tires, caulking compound
(Poly)ethylene
H
H
C=C
H
H
add H2O2
HH
··· -C-C- ···
HH
Curing of Polymers
Types of Thermoset Polymers
• Anaerobic
Cyanoacrylates
• Epoxies
Urethanes
• Silicones
• Thermosets form long polymer chains by
chemical reaction (curing)
– Heat is the most common means of curing
– Ultraviolet light, oxygen - acrylics
– Moisture – Cyanoacrylates (superglue)
0.1.1.2.6.T26.95.12
Moffatt, Pearsall, & Wulff, “The Structure and Properties of Materials”, John Wiley & Sons.
Curing of Polymers
• Thermoplastics (hotmelts)
– Adhesive is heated until it softens, then hardens
on cooling -Polyethylene, PVC
0.1.1.2.6.T26.95.12
Materials, Scientific American Book, W.H. Freeman & Company
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B
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D
C
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Materials, Scientific American Book, W.H. Freeman & Company
Cautions
• Some older tests for plastic recognition suggested burning of
the polymer and noting its flame and smell. Some materials
can emit harmful vapors so this is not recommended for a class
exercise, and should be done only under controlled conditions.
•Any heat applied to a plastic should be done in a ventilating
hood.
Composite Materials
Wood Cross Section
Materials, Scientific American Book, W.H. Freeman & Company
Composite Fiber
Properties
Stiffness
Strength
Materials, Scientific American Book, W.H. Freeman & Company