Microstructures - PowerPoint PPT Presentation

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Microstructures

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End the test when the time indicator sounds. Measure the extruded sample ... Thermal Properties. Recognized Transition Temperatures. Glass Transition Temperature ... – PowerPoint PPT presentation

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Title: Microstructures


1
Microstructures
  • MFG 355

2
Molecular Structure
  • Chain Length

3
Molecular Structure
  • Backbone

4
Molecular Structure
  • Pendant Groups

5
Molecular Structure
  • Branching

6
Molecular Weight
  • Molecular weight is a statistical measurement
  • Molecular weight has a large impact on processing
    parameters
  • Two important molecular weight parameters are
    Average Molecular Weight and Molecular Weight
    Distribution

7
Average molecular weight (Statistical Measure)
  • Broad Distribution
  • Narrow Distribution
  • Skewed Distribution
  • Bimodal Distribution

8
Degree of polymerization
  • DP n (number of repeat units in the chain)
  • (How much monomer has been polymerized)
  • n Mn/Mo where
  • Mn Ave Molecular weight
  • Mo Weight of a repeat unit

9
Melt Index testing machines
10
Melt Index
  • Ensure that the calibrated orifice is in place at
    the bottom of the heating chamber
  • Place sample material into the heating chamber
  • Position the calibrated weight with the push rod
  • Begin timing upon the release of the calibrated
    weight
  • End the test when the time indicator sounds
  • Measure the extruded sample
  • Compare with other samples

11
Molecular Weight and Melt Index
  • Molecular Weight
  • High Molecular Weight Low Melt Index
  • Low Molecular Weight High Melt Index
  • Melt Index (typical values)
  • HDPE 0.1 - 33 g/10 min
  • LDPE 0.2 - 70 g/10 min
  • LLDPE 0.2 - 20 g/10 min
  • PP 2.0 36 g/10 min

12
Thermal Properties
  • Recognized Transition Temperatures
  • Glass Transition Temperature
  • Temperature where the plastic becomes pliable and
    leathery
  • Heat Deflection Temperature
  • Temperature where plastic will deform a certain
    distance within a specified amount of time while
    still maintaining its basic shape and geometry
  • Melting Temperature
  • Temperature where the polymer chains can move
    freely past one another
  • Decomposition Temperature
  • Temperature at which polymer chains begin to
    break
  • Transition points are different for the different
    classifications of plastics

13
Heat Distortion (Deflection) Temperature
14
Thermal Properties
  • Transition points

15
Thermal Effects
  • Aging
  • Oxidation
  • Thermal protective additives
  • Thermal conductivity
  • Thermal expansion
  • Thermal stresses
  • Rates of reaction (Arrhenius equation)
  • Rate Ae-E/RT

16
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