Crystallization and melting behavior of iPP studied by DSC

Abstract

This article is a part of a study of model and bulk composites, based on isotactic polypropylene (i-PP) and glass (or carbon) fibers, produced from knitted textile preforms of hybrid yarns. First, we report the results on crystallization and fusion of textile-grade i-PP, used for the processing of hybrid yarns and the corresponding knitted fabrics. The kinetics of the crystallization process, in the dynamic and isothermal regime, was followed by DSC, and the results were analyzed by Avrami, Ozawa, and Harnisch-Muschik methods. Isothermal crystallization of i-PP was carried out at 388-400 K, and values for the Avrami exponent ranging from 1.93 to 4.39 were determined. The equilibrium melting temperature was determined by the Hoffman-Weeks method, and g Å 2.54 was found. Double melting peaks were observed both when the crystallization was performed at lower temperatures (isothermal regime) and at higher cooling rates (nonisothermal regime). A single melting peak appeared upon melting following isothermal crystallization at 400 K. The nonisothermal kinetics data showed that the peak crystallization temperature changes from 377 to 386 K as the cooling rate decreases from 20 to 3 K/min. Applying the Ozawa method, a value of the exponent n Å 2.33 was determined, which is in agreement with the results for isothermal crystallization at 391-400 K. The Harnisch-Muschik approach was also applied to compare the results for n, and a similar trend in the results of isothermal and nonisothermal crystallization was found, due to the predominant homogeneous mechanism of nucleation at lower cooling rates (lower isothermal T c ) in spite of being heterogeneous at higher cooling rates (higher isothermal T c ).

The influence of glass fibers on the morphology of β-nucleated isotactic polypropylene evaluated by differential scanning calorimetry

“…The trigonal β-form is metastable and can be obtained, or can become predominant, under specific crystallization conditions or in the presence of β-nucleating agents. [24][25][26][27][28] In a previous studies, the crystallization behavior and morphology of modified and unmodified iPP, used as a matrix in composites with differently sized/ /treated glass fibers, were thoroughly studied. The orthorhombic γ-form is the least frequently observed, and usually it can be obtained after crystallization at high pressures.…”

Crystallization of Polypropylene: Application of Differential Scanning Calorimetry Part Ii. Crystal Forms and Nucleation

“…5) [64]. The resulting crystal structure of PP in this type of fiber/PP composites exhibits lower lamellae thickness but is less disposed to recrystallization and is more stable [65][66][67] Recently, much attention has been paid to PP-nanocomposites, produced by different techniques and containing mainly carbon nanotubes/nanofibers or layered silicates [68][69][70][71][72][73][74][75][76][77][78][79]. Numerous reports describe the fabrication of a range of PP-nanocomposites, and, in particular, the impact of nanofillers on the crystallization of a matrix.…”

Crystallization of Polypropylene: Application of Differential Scanning Calorimetry Part I. Isothermal and Non-Isothermal Crystallization

“…At the same time, the value of low-temperature melting peak increases as T c increases from 430.7 K to 435.7 K and the melting peak becomes sharper. Besides the fact that the melting and crystallization behavior of iPP are comprehensively reviewed [53] some peculiarities are still a subject of debate [15]. The equilibrium melting temperature (T m o ) is an important thermodynamic parameter for determining the degree of undercooling, which signifies the kinetic driving force for crystallization of a crystallizable polymer.…”

“…Investigation of the crystallization behavior of polypropylene has become a subject of special interest also due to the increased development of some new technologies, where semi-crystalline thermoplastic polymers are used as matrices for long fiber-reinforced composite materials [15][16][17][18]. The morphology and the resulting crystallinity of the thermoplastic component in composite material may be significantly influenced by the condition (temperature regime, pressure, etc) applied during processing.…”