Polymer Processing Flashcards
Condensation polymerization (step-growth)
Bonds are formed between individually reacting mers, polymer grows step-by-step until reactant is consumed
Addition polymerization (chain growth)
Mers bond simultaneously, accelerated reaction rate
As molecular weight increases, so does
chain length
tensile strength
impact strength
crack resistance
Degree of Polymerization (DP)
Ratio of polymer weight to repeating unit weight
Higher DP = higher viscosity
4 bond types
Covalent (primary)
Van Der Waals, hydrogen, and ionic (secondary)
As crystallinity increases, ___ and ___ increase and ___ decreases
stiffness; heat/solvent resistance; ductility
Thermoplastics
Can be heated, formed, and cooled while maintaining the same properties over and over
Thermosets
Once cured, can’t be reformed again
Generally have better mechanical, thermal, and chemical properties than thermoplastics
Extrusion (polymer)
Thermoplastic pellets/powder are heated, liquified, and forced through die
Injection molding
Essentially hot chamber die-casting
Thermoplastic melted and forced into split die chamber
Cold runner molds
Mold is not heated so plastic starts solidifying right when it leaves nozzle so scrap plastic must be removed
Insert molding
Metal components are placed into mold before injection of plastic
Blow molding
Mold cavity is expanded using hot air
Rotational molding
Creates hollow shapes with thin walls
Thermoforming
Sheet of thermoplastic draped over mold then vacuumed to mold
Characteristics of additive manufacturing
Allows rapid prototyping
Parts built up layer by layer
Support structures required
Stereolithography
Laser cures liquid photopolymer resin
Thin layer formed after each laser pass
Polyjet
Printheads deposit photopolymer onto build tray
UV bulbs cure layers
Use differ materials for support
Fused deposition modeling (FDM)
Extrude thermoplastic filament out heated nozzle onto build plate
Selective laser sintering and melting (SLS/SLM)
Powder melted into final shape w/ laser
Binder jet printing
Print head drops inorganic binder onto powder
Binder fuses powder
Evaporate binder solvent w/ heat lamp
Laser metal deposition
Laser creates weld pool
Metal powder shot into pool
Can combine w/ CNC milling for both add + subtractive process
