I will assume your crystallisation is by cooling from the melt in a DSC instrument. The filler will bind polymer at the interface reducing polymer mobility and the filler surface may nucleate crystallisation. If nucleation occurs the onset of crystallisation will occur at a higher temperature. There will likely be more nuclei formed due to the filler, and nuclei should form at the same time giving smaller crystals with narrower size distribution. However the radial growth rate of crystals should be slower giving a broader exotherm, since mobility of polymer will be reduced by interaction with filler. Thus the filler will inhibit polymer molecules from migrating to the growing crystal faces.

A further complexity could be secondary crystallisation as inter-crystalline amorphous polymer crystallises late in the process, creating an added broadening or shoulder on the exotherm.

The argument will be similar for isothermal crystallisation except that time replaces decreasing temperature. Cold crystallisation, by heating from an amorphous state below glass transition, is similar except that mobility is increasing with increase in temperature.

The filler being used is crystalline, you are getting overlapping crystal diffraction for the instrument you are using.

Thanks alot , i am using DSC

i think only polymer have to be crystallize ?

I will assume your crystallisation is by cooling from the melt in a DSC instrument. The filler will bind polymer at the interface reducing polymer mobility and the filler surface may nucleate crystallisation. If nucleation occurs the onset of crystallisation will occur at a higher temperature. There will likely be more nuclei formed due to the filler, and nuclei should form at the same time giving smaller crystals with narrower size distribution. However the radial growth rate of crystals should be slower giving a broader exotherm, since mobility of polymer will be reduced by interaction with filler. Thus the filler will inhibit polymer molecules from migrating to the growing crystal faces.

A further complexity could be secondary crystallisation as inter-crystalline amorphous polymer crystallises late in the process, creating an added broadening or shoulder on the exotherm.

The argument will be similar for isothermal crystallisation except that time replaces decreasing temperature. Cold crystallisation, by heating from an amorphous state below glass transition, is similar except that mobility is increasing with increase in temperature.

Thank you alot for kind and useful info

Also, my composites have a cold crystallization , Which is more broader than that of melt crystallization. Any reason for this behaviour please

I offer a speculative description of why cold crystallisation (on heating from below Tg) would be broader than crystallisation on cooling from the melt, assuming heating and cooling rate are the same. Near the melt, on cooling the molecules the molecules have high mobility, too rapid to crystallise. When mobility has slowed molecules can start to adsorb and nucleate on an added nucleating agent (or filler) and at lower temperature segments can spontaneous cluster into nuclei. Crystals can then grow as segments rapidly migrate and attach to the growing crystals. At a temperature typically mid-way between Tm and Tg mobility starts to decrease and crystallisation rate has reached a maximum at this mid-way temperature.

Picture the reverse cold crystallisation on heating. When above Tg molecular segments gain mobility but insufficient to migrate and form crystals. As temperature rises mobility is reached where segments can assemble on nuclei or spontaneously nucleate. Crystal growth is slow, though most of the polymer is amorphous. At this stage when crystallisation should be rapid, due to concentration of uncrystallised polymer, it is slow because mobility is low retarding migration. Further heating increases crystallisation rate until mid-way between Tg and Tm where the rate reaches a maximum. At higher temperatures mobility is too high and some segments trying to join crystals detach and diffuse away.

Overall, due to low mobility in the early stage of crystallisation, I would expect the exotherm to be broader for cold crystallisation.

Dear all;

I found the two contributions of Dr. Robert A. Shanks really perfect and covering the most outstanding facets of the question. Thanks Doctor for the extended explanation. Regards

That is really great information. in particluar , first part was clear for me

You are changing the kinetic of crystallization. Follow it carefully with microscopic studies.

Helena

Thanks Helena

WHat do you mean by kinetic of crystallization

Thanks

WHat broadening of crystall size distrubition ? can any one explain this ?

Kinetic of crystallization means kinetic of nucleation and growth of crystals. If you add something to polymer it is not the same proces as for clean polymer. You can change the number of nuclei and due to this  the size of the growing crystals. In consequence you can have more differentiated size of crystallizng aggregates.This influenes as well on DSC peaks broadening.

Helena

THanks Helena  , its clear

cheeerrs