Nucleation in polymer crystallization: A physical or a chemical mechanism?

Abstract

Primary nucleation is in general heterogeneous in polymer crystallization. In unseeded polymers, the crystallization originates from a very small concentration (<0.1 percent) of unknown submicroscopic heterogeneous nuclei. Only in three cases have the nucleation mechanisms been identified with precision. The first example is self‐nucleation, which relates to the nucleation of a polymer melt by fragments of its own crystals previously present in the melt. Another example of heterogeneous nucleation is represented by epitaxial nucleation of polymers on inorganic and organic substrates recently established by Lotz and Wittmann. More recently, it was discovered that finely divided organic salts added to reactive polymers do not behave as inert heterogeneous substrates but rather dissolve and cut molten macromolecules producing ionic chain ends which precipitate into the melt and form organized aggregates which are the true nucleating species. It is clearly shown that mechanisms of physical and chemical origin are involved in heterogeneous primary nucleation of polymer crystallization.

Nucleation mechanism and crystallization behavior of poly(ethylene terephthalate) containing ionomers

“…[22][23][24][25][26] This reaction induces chain scissions and produces ionic chain ends, which subsequently precipitate from the melting and associate into ionic clusters. Eventually, the clusters initiate heterogeneous nucleation.…”

“…[19][20][21][22][23][24][25][26] Metal salts of organic polymers containing pendant carboxyl groups are also effective for the acceleration of the crystallization rate. [1,18,[27][28][29] In the present paper, the influence of an ionomer, AClyn, on the crystallization of PET is examined and compared with another ionomer, Surlyn.…”

Crystallization of tethered polyethylene in confined geometries

“…One well-known example is the addition of heterogeneous nucleation agents, usually micronsized crystalline particles, to induce crystallization at higher temperatures and rates. [1][2][3][4][5] Particle addition also creates a uniform dispersion of nucleation sites and affords some control of spherulite size. Another well-known technique for modifying crystallization is the addition of plasticizers, which reduce both the melting temperature (T m ) and the crystallization temperature (T c ).…”

Crystallization Behavior of Poly(ethylene terephthalate) Modified by Ionomers

“…Over the past decades, a great deal of efforts has been devoted to the discovery of nucleating agents or crystallization promoters, to accelerate the crystallization rate of PET, and a number of additives has been reported in the literature. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] For a few years, a detailed study of the effects of additives on crystallization behavior of PET was carried out in our laboratory. In our previous papers, [16 -19] the additives were divid into two kinds: one is nucleating agent, which can be used as a heterogeneous nuclei and effectively enhance nucleation rate of polymers in high temperature region; the other is nucleating promoters which are able to improve molecular motion of chains and promote primary nucleation of chains on the surface of nucleating agents and subsequently crystal growth.…”