Exam 1 study guide Flashcards
What do you think is the greatest benefit of using polymers?
- polymers are organic materials with low density
- lots of versatility of synthesis-processing-property relationships
- raw materials and processing are cost effective
-recycling or disposal are practical
What are major industries that use polymers?
- packaging, clothing, electronic, medicine, oil recovery
What are the pros and cons of using polymers?
Pros: cheap, recyclable, easy processing, ductile
Cons: low melting point, negative environment effects
How does a polymer chain coil in solution or in the melt?
In a solution and a melt the chains are randomly intertwined forming a disordered and flexible structure
What are the theories we discussed on chain movement?
Rouse-Bueche-Zimm Theory
- works with non tangled chains
- chain motion in a solution
- move as spring like segments
Reptation Theory
- chains are entangled
- chain moves by snake-like motion within the constraints of the network: “tube”
How do we estimate chain length?
Mean Squared End to End Distance
- for solution or melt the chain is not fully extended and you use a random coil model
- equation with it
What do we mean by viscoelastic behavior?
Material experiences simultaneous existence of viscous and elastic properties
What is so important about molecular weight and polydispersity for polymers?
Molecular Weight
- affects the flow behavior of polymers
Polydispersity
- indicates molecular weight dispersity
- high PDI = more entanglements
- low PDI = more uniform
How is molecular weight measured with in polymers? order from most common to least…
- SEC
- Viscosity
- Osmotic pressure
- Light scattering
Can you calculate and define: Mn, Mw and D
- use equations
Define viscosity and be able to describe the role it plays in polymer processing.
- physical property characterizing the resistance of fluids to flow
- polymers are non-Newtonian fluids (change in viscosity from temp and shear rate)
- shear thinning means viscosity decreases as the applied shear rate increases
How do polymers crystallize?
- Nucleation
- Lamellar growth
Where do amorphous regions appear?
where the polymer chains do not pack into a regular, ordered crystalline structure
What are the pros and cons of the types of domains (crystalline vs amorphous)?
Pros for crystalline:
- higher melting temperature
- higher strength and stiffness
Cons for crystalline:
- brittleness
- harder for processing
Pros for amorphous:
- lower processing temperatures
Cons for amorphous
- low strength and stiffness
What role do the crystalline and amorphous regions play in polymer properties?
Crystalline regions:
- act as reinforcement points in polymer so they increase tensile strength and E modulus
- higher crystallinity = higher melting point
Amorphous regions:
-increase flow and viscosity
Define a thermoplastic.
They soften when heated and harden when cooled
Define a thermoset.
Irreversibly harden when heated and cannot be reshaped or remelted
Draw viscoelastic behavior of a polymer?
on graph
What is Tg and why is it so important of a design parameter?
Temperature where a polymer transitions from hard, glassy state to a rubbery state
Below Tg = rigid and brittle
Above Tg = soft and flexible
What does TGA measure and how is the data presented?
- Measures weight change as function of time and temperature
- Temperature vs. Weight (%)
What is DSC and how does it work?
- It is a thermal analysis technique that takes the heat flow difference between a sample and reference pan
What does DSC measure in polymers?
Heat flow
