Powder Essay

1808 words - 8 pages

Crystallization Outcome
Antisolvent crystallization is a technique by which a nonsolvent is added to a concentrated solution to induce crystallization the solute. The addition of xylitol solutions to acetone decreased the solubility of the xylitol solute and thus rapidly generated a supersaturation state. The mixing process between the xylitol solvent and acetone antisolvent is likely to bring about an increase in the molar volume of the xylitol solution, and hence the solubility power towards the xylitol decreases, thus allowing the xylitol solute to precipitate.
In comparison to other crystallization media, when xylitol was crystallized in the presence of PVA16000, the crystallization medium exhibited a high viscosity (nearly solidified). Thus, additional distilled water was added to allow more xylitol to be dissolved and thus liquefy the solution. Therefore, the final concentration of PVA16000 (0.03%, w/v) was lower than other additives used (from 0.06% to 1.2%, w/v). Concentrations higher than 0.03% (w/v) generated extremely viscous solutions and thus were not investigated.
Characterization of Particle Size and Shape
It has been previously reported that the micrometric properties of engineered crystals (e.g. size and shape) could differ significantly by using a small amount of an ‘effective additive’ (Davey, 1982). Particle size distribution (PSD) for commercial xylitol and crystallized xylitol in the presence or the absence of different additives varied considerably (Fig. 2). Indeed, different additives could induce dissimilar viscous effect on the crystallization medium leading to different crystal growth rates.
Crystallized xylitol crystals demonstrated distinctly smaller size distribution than commercial xylitol (Fig. 2a). Commercial xylitol showed a heterogeneous size distribution with a span value of 2.5 ± 0.6, whereas crystallized xylitol crystals demonstrated a homogeneous size distribution with a span value of 0.4 ± 0.0 (Fig. 2e).
The influence of the concentration of the additive on the size of crystallized xylitol was dependent on the type of additive (Fig. 2). By increasing the concentration of PEG from 0.06 to 0.3%, crystallized xylitol crystals became smaller (Fig. 1b) and relatively less homogeneous in size (Fig. 1e). Xylitol particles crystallized from low concentrations of PVP demonstrated smaller size (Fig. 2c) and relatively more–heterogeneous (higher span) (Fig. 2e) size distribution in comparison to than xylitol crystallized from higher concentrations of PVP. Indeed, the MD increased with the concentration of PVP within the crystallization media (SM–1). This suggested that PVP could inhibit the growth rate of xylitol crystals due to a possible increase in the width of the Ostwald metastable zone during crystallization. The concentration of PVA22000 had no significant (P > 0.05) influence on the size of crystallized xylitol (Fig. 2d). However, in comparison to xylitol crystallized using PVA22000, xylitol crystallized...

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