Triggering and acceleration of xylitol crystallization by seeding and shearing: Rheo-optical and rheological investigation

Abstract

The present study investigates the triggering and acceleration of xylitol crystallization for its use as a short-term TES. The combined effect of seeding and the action of shear on xylitol crystallization at a supercooled temperature has been investigated by direct observations under shear (rheo-optical approach) and by rheometry. The initial seed is an agglomerate of crystals of xylitol. In addition to the more classical erosion and rupture mechanisms leading to the dispersion of crystals, shear has shown to induce the detachment of crystalline dust adhered to the initial seed into the supercooled xylitol. These crystal fragments then serve as sites for secondary nucleation and subsequent crystallization. Rheo-optical observations have allowed the determination of shear conditions to control the size of crystals by dispersion. A second part has been dedicated to the effect of shear on crystallization of xylitol by seeding by means of rheology. The measurements, although not reproducible, clearly show that seeding in presence of shear (for the investigated conditions) is very efficient to trigger and accelerate the crystallization of xylitol. Post-mortem DSC and XRPD analyses of the final crystallized seeded and sheared samples have not shown any effect on the xylitol crystallinity degree.

Experimental Analysis of Nucleation Triggering in a Thermal Energy Storage Based on Xylitol Used in a Portable Solar Box Cooker

“…The main substrate for its production is xylan, which is usually extracted from birch, strawberry, raspberry, plum and wheat. It was discovered in 1891 [29,32] and is widely used as a food additive, especially in chewing gums and candies, and in pharmaceuticals. Its sweetening power is similar to that of sucrose, but it contains 40% less calories.…”

“…This behavior is probably caused by the fact that xylitol presents crystallization and supercooling issues, as discussed in Section 2.1. Numerous authors have therefore proposed different techniques to promote the nucleation and crystallization behavior of xylitol, such as seeding/shearing, bubbling or mechanical agitation [23,28,29].…”

“…In particular, due to its high energy density and high and stable supercooling, xylitol is considered a suitable substance for low to medium temperature applications, ensuring low heat losses due to only sensible heat that reduce insulation costs [25,26]. However, as shown by different experimental and theoretical studies [23,[26][27][28][29], the use of xylitol as a PCM for TES applications is hindered by its very difficult nucleation triggering and its slow crystal growth rate, resulting in a difficult energy discharge triggering and a low discharge power, respectively.…”

“…More recently, Delgado et al [29] experimentally investigated the nucleation triggering of xylitol and the acceleration of its crystallization rate for short-term TES applications. In particular, the authors studied the effect of seeding in presence of shear on the crystallization process of severely undercooled xylitol using both a rheo-optical approach and rheometry.…”

Xylitol Used as Phase Change Material: Nucleation Mechanisms of the Supercooling Rupture By Stirring

“…Moreover, as Beaupere et al [10] explained, the primary heterogeneous nucleation rate could be influenced by the agitation. On the other hand, Delgado et al [11] studied shearing and seeding in supercooled Xylitol to trigger its crystallization, emphasizing on the effect of secondary nucleation. The mechanisms behind nucleation in stirred Xylitol seem to be complex and not fully understood.…”