I am doing a lab and there is one question I can't get. We have the enthalpy of fusion of crystalline polyeythlene, mass, onset temperature and energy required for a phase change of both low density polyethylene and high density polyethylene. They as to calculate the percent crystallinity of both by calculating the fraction of crystalline polymer in the samples. I really have no clue how to go about this I'm stumped. Any help would be greatly appreciated. Thanks.

Question

I am doing a lab and there is one question I can't get. We have the enthalpy of fusion of crystalline polyeythlene, mass, onset temperature and energy required for a phase change of both low density polyethylene and high density polyethylene. They as to calculate the percent crystallinity of both by calculating the fraction of crystalline polymer in the samples. I really have no clue how to go about this I'm stumped. Any help would be greatly appreciated. Thanks.

Answer 1

To calculate the percent crystallinity of the samples, you need to use the enthalpy of fusion and the energy required for a phase change. Here's a step-by-step guide to help you:

1. Understand the concept: Crystallinity refers to the extent of crystalline regions in a polymer sample. The enthalpy of fusion represents the energy required to convert a certain mass of polymer from the crystalline to the amorphous state or vice versa.

2. Determine the mass of the samples: You mentioned that you have the mass of both low density polyethylene (LDPE) and high density polyethylene (HDPE) samples. Make sure you have the mass in the same unit, such as grams.

3. Calculate the energy required for the phase change: Multiply the mass of each sample by the energy required for the phase change. This will give you the energy in the same unit as the enthalpy of fusion.

4. Calculate the fraction of crystalline polymer: Divide the energy required for the phase change by the enthalpy of fusion for the crystalline polyethylene. This will give you the fraction of the sample that is crystalline.

5. Calculate the percent crystallinity: Multiply the fraction of crystalline polymer by 100 to obtain the percentage.

Here's the formula to calculate the percent crystallinity:

Percent Crystallinity = (Energy for phase change / Enthalpy of fusion) * 100

Repeat steps 3-5 for both the LDPE and HDPE samples using their respective masses and energy values.

By following these steps, you should be able to calculate the percent crystallinity for both the low density and high-density polyethylene samples. Good luck with your lab!