increasing

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increasing
molecular weight
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Chains have different molecular weights There is
a distribution
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Is it important?
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Is it important?
Very important in processing If viscosity too
high, polymer difficult to process
If too low, an extruded material won't hold
together until it solidifies
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Step 1 make preform by extrusion or injection
molding
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Step 1 make preform by extrusion or injection
molding
Step 2 use air pressure to inflate preform
inside closed, hollow mold. Polymer expands to
take shape of cooled mold solidifies under
pressure
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• Normal crystalline materials
• Either crystalline (100, neglecting defects) or
  amorphous at a particular temperature
• Melt at a sharp, well-defined temperature

• Crystallizable polymers
• Never 100 crystalline
• Melt over a range of temperatures

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Chain folding - polyethylene
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So crystalline region looks like this
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In many polymers, crystalline regions grow to
form spherulites
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Pull thin polymer rod in tension
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Polymer fibers have aligned crystalline regions
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Polymer fibers have aligned crystalline
regions - alignment gives greater strength to
fiber
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• Breaking strength of polymer fibers (tenacity)
• measure denier (wt. in grams of 9000 meters of
  fiber)
• run tensile test

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Tenacity also increases w/ chain length - fewer
crystal defects
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Glass transition temperature (Tg)
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Glass transition temperature (Tg)
Chemical structure
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Glass transition temperature (Tg)
Chain stiffness
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Glass transition temperature (Tg)
Chain stiffness
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Glass transition temperature (Tg)
Bulky side groups