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Calormetric and Gravimetric Analysis of Polymers
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: