THERMOPLASTICS

Question 0

Examples of addition polymers?

Answer 0

Polyolefins (PE, PP), PVC and PS

Question 1

What are thermoplastic materials?

Answer 1

Chemical compounds based on carbon atoms, often complex compounds

Question 2

Examples of condensation polymers?

Answer 2

PA, PET, PC

Question 3

Homopolymers?

Answer 3

Polymer formed from a single monomer:

-A-A-A-A-A-

Question 4

Copolymers?

Answer 4

Two types of monomers joined in a single polymer chain:

-A-B-A-B-A-B-

Question 5

Block copolymers?

Answer 5

When the two monomers cluster together and form blocks of repeating units inside the polymer chain:
-A-A-A-B-B-B-A-A-A-B-B-B-

Question 6

Terpolymers?

Answer 6

Polymer from three monomers

Question 7

Polymer blends?

Answer 7

Class of material analogous to metal alloys, at least two polymers are blended together to create a new material with different physical properties.

Question 8

General properties of amorphous materials?

Answer 8

1. BRITTLE (apart from PC or by the addition of rubber e.g. PVC and ABS)
2. MORE STABLE (low creep) under sustained load
3. EASIER TO MANUFACTURE at temps above Tg
4. TRANSPARENT to light
5. LESS RESISTANT TO SOLVENTS

Question 9

General properties of semi-crystalline materials?

Answer 9

1. LESS BRITTLE (except in low temps)
2. Wide range of strength and stiffness
3. Suitable for fibre reinforcement
4. LESS STABLE (more creep) under sustained load
5. More difficult to manufacture (increased molecular weight due to crystal structure, so more viscous)
6. Less transparent to light
7. More resistant to solvents

Question 10

What is the equivalent to metal grain structure in plastics?

Answer 10

SPHERULITE

Question 11

What does creep do to stiffness?

Answer 11

Creep decreases stiffness

Question 12

What is impact resistance dependent on?

Answer 12

Temperature (more so than metals) and dry or wet conditions

Question 13

How is heat deflection temperature tested and what does it test?

Answer 13

Place sample in hot oil and measure deflection. Tests ability to resist elevated temperature

Question 14

What is underwriters laboratory (UL) thermal index?

Answer 14

Test for various plastics : at what temp will strength be halved?

Question 15

How do plastic coefficient of thermal expansions compare to that for metals?

Answer 15

Much larger than for metals, expand significantly under elevated temperature (dimensional accuracy is a concern)

Question 16

What is Environmental Stress Cracking (ESC)?

Answer 16

Plastics degrade in same way as metals - (SCC) oxidation between grain boundaries weakens the metal - occurs in SPHERULITE structure in plastics.

Question 17

How can you judge ESC?

Answer 17

water absorption (lower the better), permeability (lower the better), solvent resistance (higher the better, semicrystalline), ultraviolet radiation degradation (low) and strength (high)

Question 18

What is volume resistivity?

Answer 18

Ratio of DC voltage per unit thickness to amount of current per unit area passing through the material :
Conductive > 4
Insulative 12-20
Static dissipative 4-11 ( a measure for antistatic or electrostatic discharge - A SAFETY PROPERTY!!)

Question 19

What is electrostatic discharge (ESD)?

Answer 19

A sudden and momentary electric current that flows when excess electric charge stored on an electrically insulated object finds a path to an object at a different potential

Question 20

What are the food and drug administration (FDA) and United States pharmacopeia (USP) classes?

Answer 20

VII (best, lowest biological risk), VI, V, IV (worst, highest biological risk)

Question 21

What is toxicology?

Answer 21

The biological effects cause by plastics. There are seven classes based on animals testing (either by extraction, implantation or both). Mice and rabbits are mostly used for a specific period of time. The animal’s response is observed.

Question 22

What are flammability UL ratings?

Answer 22

HB (High burning), V2, V1, V0 (lowest flame spread)

Question 23

What is the limiting oxygen index?

Answer 23

The minimum oxygen content that has to be present in order to sustain a fire (e.g. PVC requires 50% oxygen rating to continue burning) - the higher the better.

Question 24

What are processing temps related to?

Answer 24

Tg and Tm

Question 25

What is recrystallisation?

Answer 25

Very important to semi-crystalline materials, cool the plastic slowly and keep at it's recrystallisation temp so that crystals can form themselves - if this isn't done right the plastic will be very amorphous. The higher the recrystallisation temp the worse.

Question 26

How does drying time effect processing properties?

Answer 26

The longer the drying time the lower the economy (hours/degC)

Question 27

How to judge fluidity of melt?

Answer 27

Melt index - starts with 10 (PE) to 0 - higher the better. Can also judge by Tm

Question 28

Are semicrystalline materials generally easy to bond?

Answer 28

No

Question 29

What are the recycling symbol numbers and what do they mean for recyclability?

Answer 29

``` 1 - PET 2 - HDPE 3 - PVC 4 - LDPE 5 - PP 6 - PS 7 - others The lower the recycling number the better. ```

Question 30

What is the CO2 footprint?

Answer 30

The mass of carbon dioxide resulting directly from the production of a kg of the material. This includes emission due to: processing, the manufacture of feedstock, and the transport associated with the primary production process.

Question 31

What are reinforcements?

Answer 31

Typically high strength, high modulus, fibrous materials that form a good bond with the polymer.

Question 32

Why is short fibre used?

Answer 32

To improve strength, stiffness and dimensional and thermal stability

Question 33

How much reinforcement can be used?

Answer 33

Up to 50% by weight! but the higher the content of fibre the more difficult the moulding process.

Question 34

What type of plastic can be reinforced?

Answer 34

Semicrystalline

Question 35

What is the rile of mixtures used to calculate the resultant composite properties?

Answer 35

Pc = 0.4Pf*Vf + Pp*(1-Vf) Pc is composite property Pf is fibre property Vf is volume fraction of fibre Pp is plastic property

Question 36

How may the volume fraction of the fibre Vf be calculated?

Answer 36

Vf = (m(f)/rho(f))/((m(f)/rho(f)) + (m(p)/rho(p))