DSC I and II

Question 1

differential scanning calorimetry

Answer 1

• standard test method for characterizing temperature-dependent behavior of polymers and metals
• measures the difference in the amount of heat required to increase the temperature of a specimen and reference material

Question 2

Polymers and medical devices

Answer 2

• widely used due to their low cost, controllable material properties, and degradability
• common examples include PLA, PEEK, and PE
• biodegradable stents

Question 3

Temp-dependent mechanical behavior

Answer 3

• mechanical characteristics of polymers depend on temperature
• increase temperature leads to a decrease in elastic modulus, less tensile strength, and more ductility

Question 4

using DSC analytically

Answer 4

• thermo-analytical technique, can identify the amount of energy absorbed (endothermic) or released (exothermic) by a material as it is cooled and heated
• outputs a heat flow rate as a function of temperature
• use curve tangents to identify start/finish/peak temperatures of different material phases

Question 5

specific heat capacity

Answer 5

• quantity of heat/energy required to raise the temperature in 1g of a material by 1 degree K (or C)
• heat capacity CHANGES with temperature and material phase, so a small Cp denotes SPECIFIC heat capacity

Question 6

heat of fusion

Answer 6

• heat (enthalpy) of fusion, delta Hf, is the amount of heat/energy absorbed or released when a material undergoes a phase transition

Question 7

how does DSC work?

Answer 7

• sample material and reference crucible are heat, and the heat flow into each pan is monitored by a thermocouple
• both materials are maintained at an equal temperature… the required heat flow is monitored
• use a purge gas (e.g. nitrogen) to ensure smooth heat distribution and eliminate hot spots

Question 8

glass transition temperature (Tg)

Answer 8

• polymer changes from its brittle/glassy state to a flexible, rubbery state
• DSC thermogram exhibits a “step change” in heat capacity
• second order/continuous phase endothermic transition
• delta Q: jump in heat flow during the glass transition
• hatched area ‘A’ is the endothermic heat flow associated with the enthalpy relaxation

Question 9

crystallinity and polymers

Answer 9

• polymers can be amorphous or crystalline, depending on factors such as the shape of their repeat unit and their molecular weight
• in some areas, long chains align and pack together to form crystals… while other areas have disordered chains that can’t pack together
• can have semi-crystalline polymers

Question 10

effects of increased crystallinity

Answer 10

• crystalline polymers have greater density
• crystallinity will increase a polymer’s strength (more intramolecular bonds)
• with increasing crystallinity, the intensity of the glass transition (step height) decreases
• higher molecular weight also increases the glass transition temp/melting temperature

Question 11

melting temperature (Tm)

Answer 11

• polymer changes from solid to liquid state
• endothermic peak on the DSC thermograph
• first order transformation

Question 12

heat of fusion from DSC curve

Answer 12

• heat/energy involved in a phase transition
• calculated from area under the DSC curve
• then divide by heating rate and normalize by specimen mass