Objective:
The objective of this lab is to become familiar with calorimetric and gravimetric analysis of polymers. The two major thermal transitions observed in polymers, glass transition and melting point will be determined. The experiment will use a modulated DSC in order to separate reversible from irreversible thermal events.

Instruments to be used:
Differential Scanning Calorimeter (DSC)
Thermal Gravimetric Analyzer

Materials:
PET water or soda bottle. Tire rubber for TGA.
If time permits other polymers will be investigated: polycarbonate, polystyrene, high impact polystyrene, polyethylene of several types (HDPE, LLDPE, LDPE) and nylon. Samples should be ground to a powder or cut from a sheet into small disks using a hole punch.

Procedure:
1) Calibrate the DSC and TGA using standards available with the instrument. This will require at least 2 standards such as indium and naphthalene. Follow instrument procedures.
2) Do several thermal scans on the DSC for each sample in heating and cooling at different rates, 5 deg/min, 10deg/min and 20deg/min on new samples. Run the samples through 2 cycles and observe the degradation temperature on a third heating run to 300 deg C.
3) Perform thermal gravimetric scans from room temperature to well beyond the degradation temperature.
4) For the PET sample, after determining the glass transition and melting points melt the sample and anneal at a series of temperatures between Tg and Tm (at least 5 temperatures) followed by a quench below Tg.
5) Measure a heating scan at 20°C per minute and determine Tm and the degree of crystallinity. Make sure to subtract the cold crystallization fraction in determining the degree of crystallization.
6) Perform a modulated DSC run at an amplitude of 0.5°K and a frequency of 1 minute with a heating rate of 5°C per minute.   First heating only.   If there is time repeat this with a new sample for the same heating rate and a modulated frequency of 10 seconds and 1 second.
7) Perform TGA on a piece of tire rubbert.

Analysis:
1) Determine the glass transition and melting points for all samples where these features occur.
2) Determine the degradation temperature and temperatures of maximum evolution of gasses for all samples. Make a guess as the low molecular weight materials present.
3) Estimate the degree of crystallinity for the samples.
4) Make a plot of degree of crystallinity versus crystallization temperature for the PET sample.
5) Make a plot of Tm versus Tc for PET. Include a line of Tm = Tc and extrapolate to the limiting melting point.
6) Comment on the features observed in the reversible and irreversible heating curves from the modulated DSC curve.  Comment on the variability in these results with modulation rate if these were run.
7) Determine the butadiene, SBR, oil and carbon content for the tire sample from the DTA trace.

Questions:

1. How does the heating rate effect the thermal transitions and the observability of these transitions. Why does this occur?
2. Why might glass transition be effected by heating rate?
3. What is cold crystallization and where is it observed in these measurements?
4. How do the measured values for Tg and Tm compare with literature values?
5. The values for degree of crystallinity from DSC are usually significantly higher that those from XRD. Why is this the case?
6. What is the difference between DSC and a DTA instruments? Which is preferred for polymer analysis?
7. What is the advantage of a modulated DSC over a non-modulated DSC scan?
   
8. Explain the degree of crystallinity versus crystallization curve you measured. Why does it have the shape observed? Why were measurements performed between Tg and Tm?
9. What is the meaning of the limiting melting point you obtained from the plot of Tm versus Tc? Where might this temperature be of use?
10. What is a Thermal Mechanical Analyzer (TMA)? What is the difference between a TMA and a DSC?