Abstract

Microencapsulation processes based on complex coacervation developed in the 1950’s remain an active area of study today, because they can be used to produce a range of micro- and nano-capsules of interest to the food and agricultural industries. Accordingly, this article briefly discusses several aspects of complex coacervation phenomena that affect encapsulation procedures based on complex coacervation. The effect of polymer structure on formation of coacervates suitable for use in encapsulation procedures is noted. Steadily improving capsule production technology is attributed in part to a better understanding of how biopolymer structure affects complex coacervate formation. The cost and quality of some biopolymers has become an issue due to rapid demand growth. This is driving efforts to develop alternate shell materials able to produce capsules with acceptable properties. The author suspects they will be based on cellulose and starch, since abundant supplies of both biopolymers exist globally.

INTRODUCTION

This article is a brief discussion of various factors that affect micro- and nano-capsule formation by complex coacervation, a unique liquid/liquid phase separation phenomenon caused by polyelectrolyte complex formation in aqueous media. It complements a recent book chapter by the author (1) and is derived primarily from his experience working with complex coacervation encapsulation procedures. The focus is on biopolymer mixtures that can be used to form capsules for food and agricultural products. For simplicity purposes, micro- and nano-capsules are simply called capsules throughout this article.

Complex coacervation frequently occurs when two or more oppositely charged biopolymers are mixed in aqueous media under suitable conditions. It also occurs with many biopolymer/synthetic polymer mixtures. In all cases, two liquid phases are formed. One is polymer-rich (the coacervate phase) while the other is polymer-poor (the supernatant phase). Complex coacervate formation is favored by dilution and suppressed by salts.
At least one of the polymers involved is essentially a weak polyelectrolyte with a low or relatively low densit ...