L14 Polymers Flashcards
What is the word plastic in Greek and its meaning?
The word is Plastikos meaning ‘it can be molded and shaped’
Name characteristics of Plastic
- Low density
- Low strength
- Low stiffness
- Electrical and Thermal insulating properties
- Good chemical resistance
What were early polymers made from?
Natural organic materials such as celloluse and the earliest synthetic polymer was phenol formaldehyde (aka Bakelife lol its Bakelite pussy) in 1906
Side note, he seemed to mention bakelite a lot in class
When did modern polymer technology begin and what was plastic produced from?
- 1920s
- Plastics began to be produced from petroleum products (ethylene)
“Mono” is single in monomer what is the word for part?
Part: Meros
What kind of bonds and atoms do polymers usually consist of?
Covalently bonded carbon and hydrogen atoms
How are monomers joined together to form polymers?
Through a polymerization process
Thermoplastics consist of these two types of polymers and thermosets consist of the other two type of polymers (ie four all together)
- Thermoplastics
- Linear polymers
- Branched polymers
- Thermosets
- Crosslinking polymers
- Networked polymers
Define Linear polymers
Linear bonding structure but are not linear or straight in shape
Define Branched polymers
Side branched structures attached to the main chain during synthesis resulting in higher strength but lower density
Define Crosslinked polymers
Individual chains are linked by adjacent chains via covalent bonds which provide strength and dimensional stability (as Balinh does for all of us)
Define Networked polymers
Have three active covalent bonds for improved strength
Polymers have the ability to obtain both “_____” and “_____” structures
- “Crystalline”
- “Amorphous”
As crystallinity increases, polymers become…
- Stiffer
- Harder
- Less Ductile
Can 100% cyrstalline polymers be achieved
No… (insert Balinhs voice) like what
Pure amorphous structures can be “______”, (relating to optics) but what happens as crystallinity increases?
- “Transparent”
- Opaqueness increases
What is the glass transition temperature?
- As temperature increases, amorphous polymers undergo a distinct change in mechanical properties
- Low temp: hard, glassy, brittle material to high temp: rubbery, leathery material
What happens to the density as you heat beyond the glass transistion temp?
Density decreases (spec. volume increases)
What happens to the glass transition temp as crosslinking increases?
The point of glass transition becomes less well defined
What kind of bonds determine the strength of thermoplastics?
Secondary bonds, such as VDW, hydrogen bonds, ionic bonds
What happens as you heat a thermoplastic?
Secondary bonds are broken due to thermal induced vibrations which allow adjacent chains to move easily and be shaped
For thermoplastics, once you heat and stuff, upon cooling, do you get the orignal hardness and strength back?
Yes, you do get it back; the process is reversible but thermal aging can occur which causes degradation
What other name can be catorgorized as thermoplastic?
Viscoelastic materials
For thermoplastics, what happens when you stretch it at a high strain rate with a constant load?
It continues to elongate over time: Creep
