Crystallization-induced formation of rigid amorphous fraction

Abstract

Semicrystalline polymers contain amorphous fractions of different mobility that develop upon crystallization or ordering. The restraints created by the ordered phase, together with the entanglements present in the amorphous areas, set up a disordered nanophase called rigid amorphous fraction (RAF). The RAF is located at the crystal/amorphous boundary and mobilizes at temperatures higher than the glass transition of the mobile amorphous fraction. An updated three‐phase description of semicrystalline polymers is here depicted, with special attention given to the link between RAF vitrification and crystallization kinetics. The methods commonly used to quantify the RAF, and the influence of thermal history and crystal structure/morphology on the RAF, as well as the influence of RAF on materials properties, are presented and discussed in this review.

Polyamide 11/Poly(butylene succinate) Bio-Based Polymer Blends

“…The overall crystal fraction, as measured by a comparison of the experimentally observed enthalpy of fusion and the heat of fusion of 100% crystalline PBS of 220 J g −1 [45] indicates a crystal fraction w C = 0.28. The rigid amorphous fraction, w RA , as calculated by difference [46,47,48], amounts to w RA = 0.50. Small endotherms at temperatures close to 40 °C have been reported in the literature for PBS, and ascribed to the melting of small crystals that is caused by annealing at temperatures above T g [45].…”

Overview and critical survey of polyamide6 structural habits: Misconceptions and controversies

“…Essentially based on calorimetric and dynamic mechanical analyses, this model applies to a large number of semicrystalline polymers, more particularly to polyamides such as PA6 and PA66. [31,98,116,143,[191][192][193][194][195][196][197] The presence of two kinds of molecular dynamics in the amorphous phase of both polyamides was also given evidence by solid-state nuclear magnetic resonance, dielectric spectroscopy and neutron scattering, [198][199][200][201] SAXS studies of isothermally crystallized PA66 and PA11 samples via correlation function also confirmed the presence of an interphase or transition zone with electronic density gradient between the crystal and the amorphous phase. [202,203] The extent of the RAF or interphase thickness depends not only on the chemical nature and chain stiffness of the polymer (see introduction ref.…”

Amorphous rigidification and cooperativity drop in semi−crystalline plasticized polylactide

“…This could be the signature of the melting of very small defective crystals formed during the annealing, exhibiting smaller stability when formed at lower T c , but one may as well attribute this event to the RAF devitrification. In PLA different approaches have been proposed to follow the evolution of the RAF by MTÀ DSC, from isothermal and nonÀ isothermal crystallization conditions [72], but none has referred to this event. However, in several studies regarding oriented PLA [73,74], it has been suggested that the organization of RAF could lead to mesophase, which is observable from calorimetric techniques.…”

“…Thus, as shown by Del Rio et al [34], RAF is dedensified in PLA. This is related to the formation of a high number of new holes of smaller free volume during crystallization [34,72]. One may attribute the increase of f v , being the most spectacular in scÀ PLA_10, to the ability of the amorphous phase to accommodate plasticizer.…”