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Microstructures

Microstructures. MFG 355. Molecular Structure. Chain Length. Molecular Structure. Backbone. Molecular Structure. Pendant Groups. Molecular Structure. Branching. Molecular Weight. Molecular weight is a statistical measurement Molecular weight has a large impact on processing parameters

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Microstructures

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  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. Pure Amorphous Thermoplastic Transitions Heat Deflection Glass Transition Decomposition Pure Crystalline Thermoplastic Transitions Heat Deflection Melt Decomposition Typical Thermoset Transitions Heat Deflection Glass Transition Melt Decomposition 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. Thank You

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