Question

Percent crystallinity may also be determined using outputs from DSC. a. Explain how DSC works. b. Explain how you can determine percent crystallinity from DSC. c. Using this article: http://www.perkinelmer.com/Content/appicationnotes/app thermaicrystailinitythermo plastics.pdf and the information below. Determine the percent crystallinity in another PET sample: i. Delta H_m = 10J/g ii. Delta H_c =5J/g
Can you guys please help me with this

Answer 1

(a) The differential scanning calorimeter (DSC) is a fundamental tool in thermal analysis. It can be used in many industries – from pharmaceuticals and polymers, to nanomaterials and food products. The information these instruments generate is used to understand amorphous and crystalline behavior, polymorph and eutectic transitions, curing and degree of cure and many other material properties used to design, manufacture and test products.

The biggest advantage of DSC is the ease and speed with which it can be used to see transitions in materials. If we work with polymeric materials of any type, then the glass transition is important to understanding our material. In liquid crystals, metals, pharmaceuticals and pure organics, we can see phase changes or polymorphs & study the degree of purity in materials.

(b) Now, we just calculated the total heat given off when the polymer melted. We can get the total heat absorbed during the crystallization.

Then, we have

H_m,total - H_c,total = H'

where, H_m,total = total heat given off during melting

H_c,total = heat of the crystallization

Now with our magic number, H' we can figure up the "percent crystallinity".

H' / H*_m = m_c

Crystalline fraction = m_c / m_total

The percent crystallinity is given by -

percent crystallinity = (crystalline fraction) x 100%

percent crystallinity = (m_c / m_total) x 100%