Dear Prajna Deepthi many thanks for posting this interesting technical question. As an inorganic chemist I'm certainly not a proven expert in the field of polymer chemistry. However, I would not be surprised when certain physical properties of PTFE polymer change in one or the other direction when you add non-metallic graphite on one hand and graphite coated with metallic and highly conductive copper on the other hand. For some more information about this please have a look at the following potentially useful articles:

Thermal property improvement of polytetrafluoroethylene nanocomposites with graphene nanoplatelets

https://pubs.rsc.org/en/content/articlepdf/2018/ra/c8ra01047a

This paper has been published Open Access and can be freely downloaded as pdf file from the internet (see attachment)

Tribological and Mechanical Behavior of Graphite Composites of Polytetrafluoroethylene (PTFE) Irradiated by the Electron Beam

(also attached as pdf file)

I hope this is useful. Good luck with your work and best wishes, Frank Edelmann

I guess you should check the interactions between the materials. In the case of copper coated graphite, the transition metal could make electrostatic interactions with electro negative fluorine and as the surface charge are negative for both they repelling each other so more energy and heat require for fusion and crystallization. But in the other composite, PTFE has fluorine branches on the carbon backbone that they have negative charge and graphite surface has positive charge hence they absorb each other then less energy and heat required for crystallization and fusion .