Plastics Flashcards
What are a couple of advantages of using plastics vs. using metals/castings etc. (5)
- Virtually unlimited variety of part geometry
- Plastics usually is a net shape process, and does not require machining or anything after
- Less energy $$ vs. metals
- Product handling during production is easier b/c lower temperatures and lighter weight $$
- Painting/plating not required $$
What are advantages of using plastic materials? (9)
- Corrosion and chemical resistance
- thermal and electrical insulating properties
- isotropic or anisotropic
- has good strength-weight ratio
- light weight babaaayyyy
- Thermoplastics are easy to process/reprocess
- can be rigid or flexible (ex. PVC)
- can be crystalline or amorphous (transparent, translucent, opaque)
What are some disadvantages of plastics? (8)
- Dimensional Instability (coeff. of thermal expansion)
- limited useful thermal range
- fragile (scratch, crack, break easy)
- flammable (smoke, flame)
- some are Hygroscopic (absorb moisture)
- can ruin with some chemicals
- can cost a lot
- some of the components (stabilizers, additives) can have health risks
What are 4 types of Plastic Products (types)
- Molded Parts
- Extruded
- Coatings (like electrical wires)
- Fibers (textiles)
Name some types of plastics used very commonly in the world (13)
- PE - polyethylene
- HDPE - High density polyethylene
- LDPE - Low density polyethylene
- PP - Polypropylene
- PVC - polyvinyl chloride
- PS - Polystytrene
- PU - Polyurethane
- PET - Polyethylene terephthalate
- PA - polyamides (nylon)
- ABS - Acrylonitrile-butadiene-styrene
- PC - Polycarbonate
- PMMA - poly(methyl methacrylate) (acrylic)
- PLA - polylactic acid (a bioplastic)
What is a monomer vs. polymer?
- CH2=CH2 (ethylene)
2. CH2-CH2-CH2-CH2-CH2-CH2 (polyethylene)
What are the two categories of plastics? Describe them a lil with regards also to their polymer chains.
- thermoplastics - their molecular structure doesn’t change upon heating, and therefore can be heated and reheated
- Thermosets - “set” after heating, which causes a cross linking in the molecular structure, and becomes permanent. (Crosslinking)
- TIP: polymers can be either or.
What are the visual differences due to molecular structure?
Crystalline - not clear, which is due to close packed chains of polymers. (ex. milk jug)
Amorphous - the polymer chains are twisted and not tight tight tight, which allows for light to go through. (ex. PET or acrylic)
What are 2 forms of raw plastic used for manufacturing?
Pellets and powder (ground pellets or bead)
Are polymers high or low viscosity? Why?
- high (therefore slow flow rates)
- due to its high molecular weight
- This is why polymers must be subjected to 20-30ksi when forced into molds
How is viscosity of polymers measured? what are the units? what scale is used? (hint: machine in the back of the plastics classroom)
-they are measured in grams per 10 minutes. the scale used is considered the “Melt Index” (MI)
When it comes to Melt Index, how many MI (9g/10min) is needed in extrusion vs injection?
extrusion = 1-5 MI injection = 10-120 MI
How much color is added to a batch when wanting to change the color of the plastic?
1-5%, depending on the viscosity of the plastic
What are some other additives used for plastics? (to improve some qualities of the final product)
- antifogging
- foaming
- wood flour (plastic lumber)
- sort fibers (molded car parts like the intake manifold)
- impact modifiers
- UV inhibitors
- perfumes and animal repellent smells
- antistatic (blast hole liners)
What is the difference between Primary and Secondary Processes/Products?
Primary: products and processes that use powder or pellets, or molding compound (eg. the injection molder in lab)
Secondary: products made using pre-made products such as sheets and films (ex. thermoforming in lab using a pre-made sheet of high impact polystyrene)
