A lab developed a new biodegradable polymer. The polymer sample was tested with

Question

A lab developed a new biodegradable polymer. The polymer sample was tested with Differential scanning calorimetry (DSC). It was found that the heats of melting DHm and crystallization DHc of the polymer are 61 J/g and 5 J/g respectively. X-ray diffraction was used to measure the crystallinity( Xc) of the polymer sample. Xc was determined to be 55%. The polymer was then mixed with drug molecules to fabricate drug-encapsulated thin film. DSC analysis of the film showed that the heats of melting DHm and crystallization DHc of the polymer became 60 J/g and 11 J/g. What is the polymer crystallinity in the film?

Explanation / Answer

According to the given data:

DHm - DHc = 61 - 5 = 56 J/g

The above value indicates that part of the polymer sample which was already in the crystalline state before we heated the polymer above the Tc

Therefore, the above fraction divided by DHm = 56/61 = 0.918

But the fraction of crystallization of drug = 0.55

i.e. The uncrystallized fraction = 0.918 - 0.55 = 0.368

After mixing the above polymer with drug, DHm - DHc = 60 - 11 = 49 J/g

Now, (49 J/g) / (60 J/g) = 0.817

Therefore, the actual fraction crystallized = 0.817 - 0.368 = 0.449

Therefore, the polymer crystallinity in the film = 44.9% ~ 45%

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