Hydrogels from polysaccharides. II. Beads with cellulose derivatives

Abstract

The generation of hydrogels from solutions of cellulose ester derivatives of various types using an atomization device, in which the solution travels through air before phase inversion occurs in a nonsolvent, was unable to produce beads in spherical shape. Instead, irregularly shaped particles were formed. The cellulose derivatives included a series of cellulose esters with a high and low degree of substitution (DS) and with acyl substituents ranging in size from C3 to C12 (laurate). Starch was tested as a noncellulosic polysaccharide, and the list of cellulose derivatives included a fluorine containing ester. The formation of spherical hydrogel beads by this method became possible only when cellulose derivatives or starch were blended in solution with unmodified cellulose. The resulting beads had dynamic flow characteristics, for instance, linear velocity vs. pressure drop relationships, that closely followed the rule of mixing. An exception was cellulose laurate, which retained most of the strength of unblended cellulose even at 60% derivative content. The results suggest (a) that cellulose is needed for the formation of droplets with sufficiently high surface tension capable of withstanding the collision with the nonsolvent surface; (b) that cellulose derivatives require the presence of unmodified cellulose to attain sufficient gel strength; and (c) that waxy ester substituents provide the basis for hydrophobic interactions which contribute to gel strength retention. © 1996 John Wiley & Sons, Inc.