Highly Stable Pickering Emulsions with Xylan Hydrate Nanocrystals

Abstract

Xylan is a highly abundant plant-based biopolymer. Original xylans in plants are in an amorphous state, but deacetylated and low-branched xylan can form a crystalline structure with water molecules. The utilizations of xylan have been limited to bulk applications either with inconsistency and uncertainty or with extensive chemical derivatization due to the insufficient studies on its crystallization. The applications of xylan could be greatly broadened in advanced green materials if xylan crystals are effectively utilized. In this paper, we show a completely green production of nano-sized xylan crystals and propose their application in forming Pickering emulsions. The branches of xylan were regulated during the separation step to controllably induce the formation of xylan hydrate crystals. Xylan hydrate nanocrystals (XNCs) with a uniform size were successfully produced solely by a mild ultrasonic treatment. XNCs can be adsorbed onto oil-water interfaces at a high density to form highly stable Pickering emulsions. The emulsifying properties of XNCs were comparable to some synthetic emulsifiers and better than some other common biopolymer nanocrystals, demonstrating that XNCs have great potential in industrial emulsification.

Keywords: Pickering emulsion; hemicellulose; nanocrystal; xylan.

Figure 1

(a) Molecular weight distribution and (b) XRD profiles of different xylan samples.

Figure 2

(a) Tyndall phenomenon, (b) AFM images, and (c) TEM images of xylan colloidal dispersions.

Figure 3

Particle size distribution and the average particle size of xylan colloidal dispersions.

Figure 4

Emulsifying activity (a–d) and emulsion cream index after centrifugation (e–h) at 0.5, 1, 2, and 4 wt% emulsifier concentrations.

Figure 5

Particle size distribution of emulsions with (a) 0.5 wt% and (b) 2 wt% emulsifiers.

Figure 6

Surface tension (a), rheological viscosity of xylan colloidal dispersions, and other emulsifiers at 4 wt% (b) and 2 wt% (c) concentrations.

Figure 7

(a) Laser confocal microscope images of UX1–UX4 adsorption on the oil droplet surface. FESEM images of the rigid polystyrene droplet (produced from in situ polymerization) surface: (b) no emulsifier, (c) UX3, and (d) UX4 as the emulsifier.