Amorphous Polymers
Amorphous Polymers
Polymer chains with branches or irregular pendant groups cannot pack together regularly enough to form crystals. These polymers are said to be amorphous. A two-dimensional schematic of an amorphous polymer is shown at the right.
Amorphous regions of a polymer are made up of a randomly coiled and entangled chains. They have been compared to a bucket containing a large number of entangled worms – each one 20-feet long and of 1/4-inch thickness. The worms are so tangled that an entire worm cannot slide past the others, but small portions of the worms can twist around within the mass.
Amorphous polymers are softer, have lower melting points, and are penetrated more by solvents than are their crystalline counterparts.
Pro’s
- Good Clarity
- High Impact
- Good Low Temperature Performance
- Good Surface Appearance
- High Stiffness
- Little Shrinkage
- No Warpage
- Wide Processing Window
Cons
- Poor Chemical Resistance
- Poor High Temperature Performance
- Flows Under its Own Weight Above Tg
- Poor Creep
- Little Memory (Not For Living Hinges)
- Solvent Bondable
- Easily Painted or Plated
- Good Cooling Needed
Specifications
| Polymer | Advantages | Drawbacks | Some Typical Applications |
|---|---|---|---|
| PAI | High heat, High wear | Very hard to process | Bearings, Aerospace |
| PEI | Impact, Heat, Sterilization, Microwave | Benzene, Gasoline | Engine internals |
| PSU | Alcohol, Salt, Hot water, Plumbing | Benzene, Gasoline | Hot water pipes |
| PUR | Gasoline, Acids, Oil, Plating | Boiling water | Fuel bowls |
| PPO | Hot water, Solvent bondable, Easy FR | Oil, Gasoline, Grease | Pump housings |
| PC | Impact, Stiffness, Optical | Oil, Gasoline, Grease, Chemicals | Safety glass lenses |
| ASA | Weatherable, Oil, Grease, Salt | Benzene, Alcohol | Auto trim, Signage |
| PMMA | Weatherable, Clarity, Lenses, Scratch resistance | Low temperature impact, Dishwater | Signs, Reflectors |
| COPOLYESTER | Some oil, Gas, Detergents, Scratch resistance | Temperatures, Inadequate cooling | Shampoo equipment |
| SMMA | Practical Toughness, Sterilization | High impact strength | Medical, Vacuum equipment |
| ABS | Impact, Stiffness, Economical | Oil, Gasoline, Grease, Esters | Housings, Auto interior |
| SAN | Clarity, Stiffness, Improved chemical resistance | Many chemicals, Impact | Tumblers, Cosmetics |
| PVC | Weatherability, Good impact, Water resistance | Environmental, Corrosion | Outdoor drains, Pools |
| PS/HIPS | Economical, Impact, Stiffness | Moderate Chemicals | Disposable housings |
