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Polymer Processing

Polymer Processing. Polymer materials. Primary Bond - Covalent Bonding Secondary Bonds – van der Waals Dipole Bonds Hydrogen Bonds. PE - mer. Polymer Properties. T g Glass Transition Temperature MW Molecular Weight

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Polymer Processing

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  1. Polymer Processing

  2. Polymer materials • Primary Bond - Covalent Bonding • Secondary Bonds – • van der Waals • Dipole Bonds • Hydrogen Bonds PE - mer

  3. Polymer Properties • Tg • Glass Transition Temperature • MW • Molecular Weight • The combination of these two properties will be a great starting point for identifying any polymer material

  4. Major Processes • Extrusion • Injection Molding • Blow Molding • Thermoforming • Rotomolding

  5. Polymer Processes

  6. Extrusion

  7. Extrusion Product Examples

  8. Extrusion • The extrusion machine forms the basis of nearly all other polymer processes. • Basically involves melting polymer pellets and extruding them out through a two dimensional die. • Produces long, thin products • Coating for electrical wire • Fishing Line • Tubes, etc.

  9. Injection Molding

  10. Injection Molding Product Examples Nylon sheaves

  11. Injection Molding Machine Basics

  12. Injection Molding Machine Operating Sequence • Mold closes and screw begins moving forward for injection • The cavity fills as the screw moves forward as a plunger • The cavity is packed as the screw continues to move forward as part solidifies

  13. Injection Molding Machine Operating Sequence, ctd • The cavity cools as the gate freezes off and the screw begins to retract to plasticize material for the next shot • The mold opens for part ejection • The mold closes and the next cycle begins

  14. Injection Molding Process Control • Very similar to die casting • Must control heat transfer and fluid flow • Do that by controlling temperature and pressure

  15. Co-injection Molding 1. Inject Skin 2.a. Inject Core 2.b. Continue injecting core until cavity is filled 3. Inject Skin again to purge sprue.

  16. Injecting hollow parts with complex interior geometry

  17. Gas Assist Injection Molding – Hollow parts without interior control

  18. Injection – Compression Molding • Very similar to squeeze casting

  19. Injection Molding of Thermosets • Thermoplastics “set” when they cool • Mold temperature will be set to allow full cavity fill, while increasing production rate • Thermosets undergo a chemical crosslinking that produces the solid structure • Mold temperature will be hotter usually – set to allow full cavity fill, while accelerating the chemical reaction to cure. • Often called “Reaction Injection Molding” (RIM)

  20. Blow Molding

  21. Blow Molding Extrusion Blow Molding Injection Blow Molding Stretch (Parasin) Blow Molding

  22. Blow Molding Cost Analysis

  23. Thermoforming

  24. Thermoforming Products

  25. Thermoforming

  26. Thermoforming Video

  27. Rotomolding

  28. Rotomolding • Used for relatively dimensionally inaccurate items, usually with a hollow interior • Can be very large • Garbage Cans • Kayaks • Interior dimensions can not be critical • Relatively primitive and therefore inexpensive process

  29. Polymer Recycling • 1998 – Approximately 20% of plastic waste is recycled (optimistic estimate) • 1998 – Polymers account for approximately 18% by volume of material to landfills

  30. Needs for a viable program: Stable supply of materials with reliable collection and sorting Economical, proven and environmentally sound recycling process End use applications for the recycled material Challenges 10-12 main polymer types Thousands of blends Additives Impurities in supply (labels, glass, dirt, etc) Needs vs Challenges

  31. Recycling of Polymers • PET (polyethylene terphthalate) beverage containers, boil-in food pouches, processed meat packages • HDPE (high density polyethylene) milk bottles, detergent bottles, oil bottles, toys, plastic bags • PVC (polyvinyl chloride) food wrap, vegetable oil bottles, blister packaging • LDPE (low density polyethylene) shrink-wrap, plastic bags, garment bags • PP (polypropylene) margarine and yogurt containers, caps for containers, wrapping to replace cellophane • PS (polystyrene) egg cartons, fast food trays, disposable plastic silverware • Other multi-resin containers

  32. Basic recycling steps • Sorting • Size Reduction • Densification • Pulverization • Melt Filtration

  33. Sorting • Manual – very common • Density based sorter • Centrifugal • Float/Sink methods • Optical – same as peas, potato chips, etc • Spectroscopy – Infrared – automation possible

  34. Size Reduction • Shredders • Rotary Knife

  35. Densification • Basic purpose is to reduce to volume taken up by bulk material • Reduce from only 20 kg/m3 to almost 400 kg/m3 • Agglomeration – heat it up and compact it

  36. Pulverization • Convert clean plastic waste into powder • After this process, some of the product can actually be used if low purity requirements • Recycled plastic lumber for example

  37. Melt Filtration • Improve purity of pulverized polymer • Needed for extrusion, injection or blow molding processes • Basic process concept: • Melt it • Shove it through a screen • Additional chemical processing may be needed if additional purity requirement

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