2019 (2) 4

Influence of nano-filler on the mechanism of crystallization of systems based on polypropylene and aerosil

R.V. Dinzhos1, E.A. Lysenkov1, N.M. Fialko2, V.V. Klepko3

1V.O. Sukhomlinskyi Mykolaiv National University

24, Nikolska str., Mykolayiv, 54030, Ukraine

2Institute of Technical Thermophysics, NAS of Ukraine

2a, Maria Kapnist (Zhelyabova) str., Kyiv, 03057, Ukraine

3Institute of Macromolecular Chemistry of NAS of Ukraine

48, Kharkivske shose, Kyiv, 02160, Ukraine

Polym. J., 2019, 41, no. 2: 116-122

Section: Physics of polymers.

Language: Ukrainian.

Abstract:

The dependence of crystallization of thermoplastic polymers on the conditions of introduction and the nature of the distribution of the filler in the production of nanocomposites is an extremely important characteristic. However, due to the low concentration of concentration series, some effects of the influence of the nanofiller on the mechanisms of crystallization remain unexplored. Therefore, the purpose of this work was to study the influence of the filler on the mechanisms of crystallization and the growth of crystals in the overcooled melt nanocomposite.

To study the kinetics of crystallization of nanocomposites, systems based on polypropylene (PP) and pyrogenic aerosil, which specific surface was 175 m2/g, and an outer diameter of <d> » 40 nm, were used. The samples were made by mixing in a melt at a temperature of 200 °C using an extruder. The content of the filler was (0,2 ¸ 1,0) wt. % The kinetics of nonisothermal crystallization was studied using crystallization exotherm, which was obtained by differential scanning calorimetry.

As a result of this work, the influence of the filler on the mechanisms of crystallization and the growth of crystals in the overcooled melt of nanocomposite polypropylene-aerosil was studied. The analysis of the parameters of crystallization obtained from the dependences of the rate of cooling of samples from the areas under the crystallization exotherms showed an increase in the barrier of crystallization of the lamellar crystallization of the PP in the volume between adjacent nanoparticles of an infinite nanocomposite cluster, which corresponds to a strong restriction to transport of PP segments across the melt/lamellar crystal interface.

The exotherm of crystallization for the non-filled PP was analyzed in the framework of the standard Kolmogorov-Avrami equation. From the kinetics of crystallization for a system containing 1% of the aerosil, the assumption, based on the superposition of the contributions of the initial (unimpeded) and the secondary (limited) mechanisms of crystallization, respectively, is confirmed. The obtained results confirm the coexistence in the overcooled melt PP of a nanocomposite of the initial mechanism of crystallization, characteristic of the unpolished PP, and of essentially other areas of crystallization. For composites based on PP filled with aerosil, at 0,2 % the mechanism of a strained matrix is   realized, at 1 % a three-dimensional mechanism is realized.

Keywords: crystallization kinetics, nanocomposites, Avrami exponent, aerosil, polypropylene.

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