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Open AccessArticle

Estimating the Nucleation Ability of Various Surfaces Towards Isotactic Polypropylene via Light Intensity Induction Time Measurements

1
Dipartimento di Chimica e Chimica Industriale, Università degli studi di Genova, via Dodecaneso 31, 16146 Genova, Italy
2
Borealis Polyolefine GmbH, Innovation Headquarters, St. Peterstrasse 25, 4021 Linz, Austria
*
Author to whom correspondence should be addressed.
Entropy 2019, 21(11), 1068; https://doi.org/10.3390/e21111068
Received: 23 September 2019 / Revised: 21 October 2019 / Accepted: 28 October 2019 / Published: 31 October 2019
(This article belongs to the Special Issue Crystallization Thermodynamics)
Crystallization of isotactic polypropylene (iPP) at the interface with crystalline films of two commercially employed nucleating agents (sodium benzoate (NaBz) and sodium 2,2’-methylene bis-(4,6-di-tert-butylphenyl)phosphate (NA-11)) and with a glass fiber (GF) was investigated using a polarized optical microscope. The analysis of the light intensity evolution during the crystallization process enabled the successful estimation of the time at which the crystal growth began, i.e., the induction time (ti), at various crystallization temperatures. Meaningful differences in the ti values were observed between the investigated systems. Moreover, the ti data have been analyzed according to different nucleation models proposed in the literature, which consider either the time to form the first crystalline layer in contact with the substrate or the time required to grow a cluster of critical size. It has been found that the two models are applicable in different temperature ranges depending on the efficiency of the given substrate. Therefore, in order to obtain the value of the surface free energy difference function, Δσ, which is directly related to the nucleation energy barrier and useful for the definition of a universal nucleating efficiency scale, a model that considers both the above-mentioned times was fitted to the overall data. The values of Δσ for the nucleation of iPP on the surface of the different substrates are thus obtained and discussed in the framework of the literature results. View Full-Text
Keywords: crystal nucleation; polypropylene; nucleating agents; induction time; heterogeneous nucleation crystal nucleation; polypropylene; nucleating agents; induction time; heterogeneous nucleation
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MDPI and ACS Style

Carmeli, E.; Wang, B.; Moretti, P.; Tranchida, D.; Cavallo, D. Estimating the Nucleation Ability of Various Surfaces Towards Isotactic Polypropylene via Light Intensity Induction Time Measurements. Entropy 2019, 21, 1068.

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