Flow induced crystallisation of polymers

Abstract

This tutorial review describes the state of current research and findings on the phenomena of polymer crystallisation under processing conditions, with particular emphasis on the effects of fluid flow. Preliminarily, it is stated why the crystallisation processes are relevant in polymer science, then the motivation of the study is briefly outlined. The remaining of the paper is divided in two parts. In the first part of the review, the basics of polymer crystallisation are summarized; the main factors acting on the process are identified; and the methods to investigate and to quantify the crystallization are described. A brief summary of the modelling approaches is also proposed. In the second part of the review, a similar path was followed in order to analyse the complex framework of phenomena collectively known as flow induced crystallisation. Therefore, the experimental techniques used are listed and the main findings are reported. A reference to the modelling approaches proposed in the literature is also summarized. Throughout the review, a selection of the literature in the field is of course cited.

Modeling Flow-Induced Crystallization

“…Because timescales for flow and crystallization are separated, this protocol isolates flow-induced structure formation. Using this protocol, flow-induced point-like nucleation (appearing for low to mild flow rates) has been thoroughly characterized, using a shear cell combined with optical microscopy, for iPP [19][20][21][22][23][24][25][26][27][28], isotactic poly(1-butene) [29][30][31], and poly(lactic acid) [32]. Alternatively, a rheometer can be used to apply flow and monitor subsequent crystallization in terms of rheology [32][33][34][35][36][37][38].…”

Tuning Crystalline Morphology of High‐Density Polyethylene by Tailoring its Molecular Weight Distribution for Coupling with a Secondary Flow Field

“…Then, the change in chain conformation was sensitive to flow and the chains to orient or to stretch was more likely to happen. [8,9,30] Meanwhile, the oriented or stretched chains could further develop into oriented lamellae or shish-kebab structures. Whereas, as a result of a narrow MWD with a small amount HMW chains, much less possibility of the oriented or stretched crystals formed in N-PE parts.…”

“…The effect of the flow on crystal growth is expected to depend on the extent of flow imposed on the polymer melt and the orientation relaxation time of the chains, that is, the value of De. [7,8,30] The narrow MWD with less HMW chains for the N-PE had low degree of chain entanglements and low melt viscosity, resulting in melt rapid propulsion and an intense flow in the cavity during the secondary gas penetrating melt stage. Although an intense flow was imposed on the melt, a relative short relaxation time of chains was determined due to less HWM chains and lower degree of chain entanglements.…”

Enhancement of stereocomplex formation in poly(l-lactide)/poly(d-lactide) mixture by shear

“…Shear-induced crystallization has been extensively studied in polymers such as polyethylene (PE) [23,24] and polypropylene (PP) [25,26]. A general observation is the enhanced nucleation due to the entropy depression by shear [27]. Also a number of studies have been carried out on shear-induced crystallization of PLLA [28e36].…”