Crystallization of polymer nanocomposites based on polypropylene

Dinzhos R.V.1, Fialko N.M.2, Sherenkovskiy Ju.V.2, Navrodska R.O.2, Meranova N.O.2 
1Mykolaiv V.O.Sukhomlynskyi National University, 24, Nikolska Str., Mykolaiv 54030, Ukraine. 
E-mail: dinzhosrv@gmail.com
2Institute of Engineering Thermophysics of NAS of Ukraine, 2a, Zhelyabova Str., Kyiv, 03057, Ukraine.

Non-isothermal crystallization of the neat isotactic polypropylene homopolymer (PP) and of the nanocomposite containing 4 wt. % (PP-4) of organosilica was studied in the standard DSC mode during constant-rate cooling from the melt state.
Analysis of the nucleation parameters derived from cooling rate dependencies of the temperatures for the onset of crystallization exotherms suggested a slight increase of the nucleation barrier for lamellar crystallization of PP within a confined space between neighboring nanoparticles of an infinite cluster of the nanocomposite, concomitant to stronger restrictions to transport of PP segments across the melt/lamellar crystal interface [1]. The overall crystallization rate data for PP-4 were consistent with the assumption of two separate contributions from the initial (unconstrained), and the subsequent (constrained) nucleation mechanisms, respectively [2].
The obtained results were considered as evidence for a coexistence in an undercooled PP melt of the nanocomposite of the initial nucleation sites characteristic for the neat PP, and the basically different nucleation sites (presumably, PP chains anchored by both ends to the surfaces of two adjacent nanoparticles). 

1.	V.P. Privalko, R.V. Dinzhos, N.A. Rekheta and F.J. Balta Calleja Structure-Diamagnetic Susceptibility Correlations in Regular Alternating Terpolymers of Ethene and Propene with Carbon Monoxide // J. Macromol Sci. Phys. — 2003. — Vol. B42, №5. — p. 929-938.
2.	Privalko, V.P. ; Kawai, T. ; Lipatov, Yu.S. Crystallization of filled nylon 6. III. Non-isothermal crystallization // Colloid & Polymer Sci. 1979, 257, 1042-1048.