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. Evolution of solvents and monomers will be conducted with a nylon sample and degradation temperatures will be used to determine operating windows for processing. The relationship between degree of crystallinity and crystallization temperature will be determined. A plot of melting point versus crystallization temperture will be made and the limiting melting point will be determined.

Instruments to be used:
Dynamic thermal analyzer or DSC if available
Gravimetric analyzer

Materials:
PET water bottle. 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.

Procedure:
1) Calibrate the DTA (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 DTA (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 tempertures) 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.

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.

Questions:

1. How does 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 the DSC used in the lab? Would a modulated DSC be of use for the samples you studied?
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?