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Polymer Process Engineering

Polymer Process Engineering

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Polymer Process Engineering

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  1. Polymer Process Engineering Chapter 1. Primer Chapter 1. Primer/introduction

  2. Fundamental concepts + language Nomenclature Chemical bonding, chemical interactions, entanglements Molecular weight Thermal transitions PRIMER Chapter 1. Primer/introduction

  3. Berzelius (1883) – Poly (many) + mer (unit) Polystyrene polymerized in 1938; polyethylene glycol made in 1860s Early polymer products were based on cellulose- gun cotton = nitrated cellulose WHAT IS A POLYMER? Chapter 1. Primer/introduction

  4. A polymer is… • Long chain molecule, often based on organic chemical building blocks (monomers) • Long molecules (Mw ~100,000 Da) have solid-like properties • The chain may be amorphous (no regular structure), crystalline (a regular repeating structure), crosslinked,… • Dendrimers and oligomers have different properties Chapter 1. Primer/introduction

  5. Chemical structure Chain morphology – constitution, configuration, conformation Degree of polymerization = number of repeating units Building block sources – hydrocarbons, renewable materials HOW DO YOU BUILD A MOLECULE? Chapter 1. Primer/introduction

  6. Building blocks • 5% of petroleum goes into polymers • Sustainable use is possible • Energy recovery is possible if solid polymers are combusted Chapter 1. Primer/introduction

  7. ‘Building’ methods Chain (addition) Step (condensation) Example – poly(ethylene terephthalate) (PET) from terephthalic acid and ethylene glycol Endgroups react to build the chain; long reaction times needed to achieve high polymer • Example – polyethylene (PE) from ethylene • Small number of reacting chains at any one time, which can grow into long molecules prior to termination • Long reaction times needed to achieve high conversions Chapter 1. Primer/introduction

  8. Multiple building blocks • Copolymers, terpolymers, … • Using multiple building blocks leads to polymers with intermediate properties or unique properties compared to the homopolymers Chapter 1. Primer/introduction

  9. Several copolymer configurations Chapter 1. Primer/introduction

  10. Chain configurations • Linear – repeating units are aligned sequentially • Branched – large segments ‘branch’ off the main chain/carbon backbone • Crosslinked/network – chemical crosslinks between chains add mechanical strength • EXAMPLES? Chapter 1. Primer/introduction

  11. Multiphase systems • Composites • Structural • Random • Other • Nanocomposites • Blends • Dispersed lamellae, cylinders, spheres Chapter 1. Primer/introduction

  12. Structure – chemical, configuration solid performance (mechanical + thermal properties) other HOW DO WE CLASSIFY POLYMERS? Chapter 1. Primer/introduction

  13. Mechanical + Thermal • Thermoplastic – solidified by cooling and reheated by melting • Thermosets – retain their structure when reheated after polymerization (usually crosslinked) • Elastomers – rubbers, deform readily with applied force • Thermoplastic elastomers • other Chapter 1. Primer/introduction

  14. Very few commercial products are ‘pure’ MWD – molecular weight distribution additives WHAT IS IN A COMMERCIAL PRODUCT? Chapter 1. Primer/introduction

  15. Polymers vs. metals Why do we use polymers? Chapter 1. Primer/introduction

  16. Polymeric materials • Compete well on a strength/weight basis • Easy to form into 3D shapes • Creep under load is usually poor; this behavior is usually corrected by adding fillers or fibers • Low corrosion in the environment compared to metals • Generally good solvent resistance Chapter 1. Primer/introduction

  17. Thermoplastics • Commodities: 75% of the polymer volume used is with 4 polymer families, polyethylene, polystyrene, polypropylene and poly(vinyl chloride) [low cost] • Intermediate: higher heat deflection temperatures • Engineering plastics: can be used in boiling water • Advanced thermoplastics: extreme properties Chapter 1. Primer/introduction

  18. Thermosets • High moduli, high flex strengths, high heat deflection temperatures • Shape is retained during thermal cycling • Often made with step/condensation polymerization systems • Crosslinking is usually used Chapter 1. Primer/introduction

  19. Chapter 1. Primer/introduction

  20. Polymerization Formulation Fabrication HOW DO WE MAKE A PART? Chapter 1. Primer/introduction

  21. Formulation • Additives are used to modify properties and/or lower costs • Additives: heat stabilizer, light stabilizer, lubricant, colorant, flame retardant, foaming agent, plasticizer • Reinforcement: particulate minerals, glass spheres, activated carbon, fibers • Blends, alloys, laminates Chapter 1. Primer/introduction

  22. Additives can change: • Processing properties • Performance properties • Composites: polymers with fiber fillers • Packaging: multiple layers often used Chapter 1. Primer/introduction

  23. Formulation operations • Thermoplastics: melting or solvent processing • Thermosets: additive addition to monomers or to prepregs Chapter 1. Primer/introduction

  24. Fabrication • Varies by industry sector • Adhesive • Coating • Elastomer • Plastic • fiber Chapter 1. Primer/introduction

  25. Overview of the polymer industry Chapter 1. Primer/introduction

  26. Commodity plastics Chapter 1. Primer/introduction

  27. Film blowing High strength films are achieved by orienting the crystallites. The film is biaxially oriented; the wind-up rolls stretch the film in the machine direction and the expansion of the film radially provides a hoop stress force. Chapter 1. Primer/introduction

  28. Wire coating Wire coating speeds can be high, and process start-up is challenging. Metal wires may need sizing, or wetting agents in the polymer melt for good adhesion. Chapter 1. Primer/introduction

  29. Calendaring Thin and thick section calendaring is used to make wide sheets (8-12 ft). Chapter 1. Primer/introduction

  30. Bottle blowing The parison is inflated, developing biaxially orientation similar to that of blown film. The sides of the mold provide cooling, quickly ‘freezing’ in the orientation developed during the blowing process. When this process is used to make soda bottles of PET, the orientation is critical to achieving low carbon dioxide permeation rates (and long bottle shelf life). Chapter 1. Primer/introduction

  31. Compression molding Chapter 1. Primer/introduction

  32. Thermoset applications Chapter 1. Primer/introduction

  33. Elastomers • The polymers used for elastomers usually have very low heat deflection and melt temperatures • Solids with good mechanical properties are made by crosslinking polymer chains together • The “molecular weight” of elastomer parts is the size of the object • Vulcanization of rubber uses sulfur to provide crosslinks between the C=C bonds of natural rubber. Chapter 1. Primer/introduction

  34. Fibers • Fibers are based on highly crystalline polymers that can be oriented axially to have great strength. Orientation (cold drawing) develops crystal structure in the solid. • Most natural fibers from biomass are based on cellulose; spider silk has different compositions and is based on a set of copolymers Chapter 1. Primer/introduction

  35. Elastomer polymers Chapter 1. Primer/introduction

  36. Synthetic fibers Chapter 1. Primer/introduction

  37. Coatings • Coatings. Major area for expansion; solar cells, windows, … Supplier base is highly fragmented. • Paints. Major area for expansion; vehicles,… Materials supplier base is clustered; painting systems base is clustered; user base is fragmented Chapter 1. Primer/introduction

  38. Adhesives • Highly fragmented market. Chapter 1. Primer/introduction

  39. Foams • Major area: insulation for housing, sound control,… • Materials: polystyrene, polyurethanes, … • Reaction injection molding example Chapter 1. Primer/introduction

  40. Composites • Thermosets and thermoplastics • Sheet molding compounds • Filament winding Chapter 1. Primer/introduction

  41. Polymer nomenclature is widely varied. Trademarks and common names may be industry-sector specific. Nomenclature: Polymer Handbook. Chapter 1. HOW DO WE NAME POLYMERS? Chapter 1. Primer/introduction

  42. Source-based names • Source-based name when the polymer is derived from a single (original or hypothetical) monomer; or random co-/ter-polymers • Poly(vinyl alcohola) • Poly(styrene-co-butadiene) • Polyformaldehyde (not polyoxymethylene)b • Poly(ethylene oxide) (not poly(ethylene glycol)b a – when the name is long, parentheses are used to separate the name from ‘poly’ b - actually the second name is quite common Chapter 1. Primer/introduction

  43. Structure-based names • Structure-based name when the constitutional repeating unit (CRU) has several components • The CRU is independent of the monomers and polymerization methods • Poly(hexamethylene adipamide) • Poly(ethylene terephthalate) Chapter 1. Primer/introduction

  44. copolymers Chapter 1. Primer/introduction

  45. Chapter 1. Primer/introduction

  46. Polymers with other backbones Chapter 1. Primer/introduction

  47. Bonding along the backbone is not extraordinary. With long chains, secondary valence forces, integrated over the entire chain, provide considerable ‘bonding’ forces. Chain entanglements provide physical linkages. WHY ARE LONG CHAIN MOLECULES SOLIDS? Chapter 1. Primer/introduction

  48. Chemical bonding in polymers • Most primary bonds along the backbone are covalent • Secondary valence bonds • Much smaller forces than the covalent bonds, but become significant when integrated over the entire chain • Consider the forces acting on this macromolecule as it is ‘pulled’ through the tube surrounding its structure in three dimensional space • As each chain segment moves, it must overcome the local interactions at the tube surface • Longer chains will have more resistance to motion Chapter 1. Primer/introduction

  49. Secondary valence forces • Secondary valence forces affect the glass transition, the melting temperature, crystallinity, melt flow,… • They include: nonpolar dispersion, polar dipoles, polar induction, and hydrogen bonds Chapter 1. Primer/introduction

  50. Few synthetic polymers are monodisperse, i.e., have one chain length. Many biological polymers do have specific molecular weights, e.g., proteins, DNA, … The molecular weight distribution has critical effects on polymer properties in the melt and solid states. WHAT ARE TYPICAL CHAIN LENGTH DISTRIBUTIONS? Chapter 1. Primer/introduction