Week 8 Polymers II

Question 1

What are the 6 external factors that impact mechanical properties of polymers?

Answer 1

1. temperature (melting and glass transition)
2. testing parameters
3. stress and strain amplitude
4. type of deformation (shear, tensile, etc.)
5. heat treatments or thermal history
6. manufacturing process

Question 2

Melt temperature - Tm

Answer 2

transformation of a solid material having an ordered structure of aligned molecular chains to a viscous liquid in which the structure becomes highly random

Question 3

The presence of what 2 things increase the melt temperature?

Answer 3

1. double bonds and aromatic groups in the polymer backbone lowers chain flexibility and increase Tm
2. polar groups (Cl, OH, and CN) leads to significant intermolecular bonding forces and relatively high Tm

Question 4

Glass transition temperature - Tg

Answer 4

the temperature at which the polymer experiences the transition from rubbery to rigid state

Question 5

What factors affect Tm and Tg?

Answer 5

1. chain stiffness increased by:
   a. bulky side groups
   b. polar groups or side groups
   c. chain double bonds and aromatic chain groups
2. increase with increasing chain stiffness
3. regularity of repeat units arrangements affect Tm ONLY

Question 6

side branches promote _________ into the polymers and __________ the Tg

Answer 6

flexibility and lower Tg

Question 7

Annealing polymers:

Answer 7

1. increases crystallinity
2. increases strength
3. decreases ductility
4. decreases vacancies in polymeric structure
5. increases the melt temperature

Question 8

How to measure viscosity

Answer 8

the behavior of a fluid in laminar flow between two parallel plates when the upper plate moves with a constant velocity

Question 9

When testing for viscosity there is 2 things:

Answer 9

shear stress and shear force

Question 10

pseudoplastic

Answer 10

shear thinning

Question 11

dilatant

Answer 11

shear thickening

Question 12

viscosity property

Answer 12

represents internal resistance of a fluid to motion or to the “fluidity”

Question 13

What are 3 properties of thermoplastics?

Answer 13

1. little cross-linking
2. ductile
3. soften with heating

Question 14

What are 4 examples of thermoplastics?

Answer 14

1. polyethylene
2. polypropylene
3. polycarbonate
4. polystyrene

Question 15

What are the 3 properties of Thermosets?

Answer 15

1. significant cross-linking
2. hard and brittle
3. does NOT soften with heating

Question 16

What are 4 examples of thermosets?

Answer 16

1. vulcanized rubber
2. epoxies
3. polyester resin
4. phenolic resin

Question 17

The effects of temperature on stress-strain behavior: increasing the temperature causes:

Answer 17

1. decrease in elastic modulus
2. reduction in tensile strength
3. enhances ductility

Question 18

Influence of strain rate on thermoplastics:

Answer 18

increasing the strain rate = same effects as if decreasing the temperature

Question 19

Results of drawing (3):

Answer 19

1. increases elastic modulus in the stretch direction
2. increases tensile strength in the stretching direction
3. decreases ductility

Question 20

Annealing after drawing: (3)

Answer 20

1. decreases chain alignment
2. decreases E and TS
3. enhances ductility

Question 21

Drawing a polymer results in (2):

Answer 21

1. stretches the polymer prior to use
2. aligns chains in the stretching direction

Question 22

Extrusion - thermoplastics

Answer 22

1. plastic pellets drop from hopper to turning screw
2. melt as turning screw pushes them forward by heaters
3. molten polymer forced under pressure through the shaping die to form final produce = extrudate

Question 23

What medical devices use single screw extrusion?

Answer 23

1. catheters
2. tubing
3. sutures
4. rings

Question 24

What medical devices use twin screw extrusion?

Answer 24

1. drug embedded sutures
2. tubing
3. colors

Question 25

What is blow molding?

Answer 25

air is blown into a molten balloon with a mold, thereby forcing the plastic into a desired shape

Question 26

Compression molding is used with _______________

Answer 26

thermosetting plastics

Question 27

What is compression molding?

Answer 27

the material is placed into a hot mold and the mold is closed by a hydraulic press - typical mold temp is 350 F - mold pressure is 100 psi - cures in 3 min - typically done 5-10 C above Tg

Question 28

What is an example that uses compression molding?

Answer 28

polymer and drug mixtures compressed into wafer

Question 29

What is injection molding?

Answer 29

molten plastic under pressure is forced through a nozzle into the mold

Question 30

Thermoforming

Answer 30

air or mechanical forces are applied to thermoplastic sheets until they take the shape of the mold

Question 31

What are the three steps in thermoforming?

Answer 31

1. heating sheet 2. forming 3. trimming

Question 32

How does 3D Printing/Additive Manufacturing occur?

Answer 32

1. design sent through an STL file to 3D printer 2. G-code used to translate design layer-by-layer 3. theory based on extrusion process but gravity is involved 4. material is heated in the barrel of extruder and excreted through the die 5. speed, temperature, in-fill rate, thickness of extreme importance for material properties

Question 33

Bioprinting

Answer 33

simultaneous writing of living cells and biomaterials with prescribed layer-by-layer stacking organization using a computer-aided transfer process for fabrication of bioengineered constructs

Question 34

Bioinks

Answer 34

aggregate emulsions containing cells suitable for printing or self-assembly - combine with drugs, growth factors, biomaterials

Question 35

Bioprinting techniques - Inkject bioprinting

Answer 35

1. hydrogel pre-polymer solution with encapsulated cells (bioink) is stored in the ink cartridge then connected to a printer head and acts as the bioink source during the electronically controlled printing process 3. during printing, the printer heads are deformed by a thermal or piezoelectric actuator and squeezed to generate droplets of a controllable size

Question 36

What are the advantages of Inkjet Printing (3)

Answer 36

1. low cost due to similar structure with commercial printers 2. high printing speed conferred by ability of printer heads to support parallel work mode 3. relatively high cell viability (80-90%) determined by many experimental results

Question 37

Bioprinting for the future (3)

Answer 37

1. emerging bioprinting market for tissue fabrication for drug testing and high-throughput assays 2. bioprinted tissue models have been used in drug screening 3. used in cancer research to investigate cancer pathology, growth, and metastasis

Question 38

electrospinning

Answer 38

technique used to develop nanofibers (3-5 micrometers)

Question 39

advantages of electrospinning (3)

Answer 39

1. simplicity 2. low cost 3. scalability

Question 40

Parameters that can alter the form of a nanofiber are:

Answer 40

1. solubility of polymer 2. concentration of polymer in the solution 3. number of channels in the spinneret die 4. shape of the needle tip 5. applied voltage - high will increase electrical field and reduce diameter of fibers 6. polymer flow rate 7. working distance - between tips of needle and collector

Question 41

What 2 medical devices use solvent casting/salt leaching?

Answer 41

1. drug delivery films 2. scaffolds (salt added)

Question 42

Salt leaching is used because it can control the ____________

Answer 42

pore size by the particulate size

Question 43

What is the advantage and disadvantage of salt leaching?

Answer 43

A - quick and easy method D - hard to control