Polyphosphate, complex coacervation

Encapsulation of hydrophobic liquids and solids is a major co irimercial application which illustrates coacervation with polyphosphates. First described by Green and Schleicher, simple and complex coacervation can yield capsules for use in controlled drug delivery,carbonless paper,fragrance samplers and cosmetic ingredients." The choice of coacervation system is important, as this can affect the composition of the shell wall and hence capsule properties. 

Complex Coacervation Procedures. Gelatin/alginate (G/A), gelatin/ polyphosphate (G/P), and gelatin/gum arabic (G/GA) complex coacervate and supernatant phases were used in this study. G/A complex coacervate and supernatant phases were formed at pH 4.2 with a 3.7 1 (w/w) mixture of gelatin (227 bloom) and sodium alginate (total solids 1.8 wt. percent). G/P complex coacervate and supernatant phases were formed at pH 4.4 with a 9 1 (w/w) mixture of gelatin (283 bloom) and polyphosphate (total solids ... 

Complex Coacervation of Acid-Precursor Gelatin with a Polyphosphate... 

Brungenberg de Jong and coworkers carried out the first extensive studies of complex coacervation (1). They characterized the gelatin-gum arabic coacervation system, a system that later was developed into a process capable of producing microcapsules loaded with a variety of lyophobic materials (2). More recently, an encapsulation process based on the coacervation of gelatin with a polyphosphate has been reported (3). The present paper describes results of a study designed to characterize the gelatin-polyphosphate coacervation interaction and define how various experimental paramenters affect it. 

Figure 1 is a plot of total solids content versus pH for a 4.4 percent gelatin (275 bloom) - 0.48 percent polyphosphate mixture. The continous curve shown encloses the region in which complex coacervation occurs and two phases coexist. These two phases are a polymer-rich phase called the complex coacervate and a more dilute phase called the equilibrium liquid. The straight line that divides the curve into two parts is the total solids content of the mixture before coacervation (4.88 percent). Points that fall above this line (open circles) are total solids contents of the coacervate at various pH values. Points below this line (solid circles) are corresponding total solids contents for the equilibrium liquid. 

Many pairs of oppositely charged Polyelectrolytes (qv) are able to form a liquid complex coacervate suitable for microcapsule formation. Normally, gelatin is the positively charged polyion, because it is readily available and forms suitable complex coacervates with a wide range of polyanions. Polyanions typically used include gum arabic, polyphosphate, poly(acrylic acid), and alginate. 

Much has been published on ethanol and sodium sulfate for inducing simple coacervation in gelatin solutions, and on the gelatin-gum arabic complex coacer-vate system. Polyphosphates have been relatively little studied in the literature, but are examples of polyelectrolytes which can participate in both simple and complex coacervate formation. 

Essentially the same procedure is reported for encapsulation by gelatin-polyphosphate complex coacervation at pH 4-5 Compared with gum arabic, however, maximum coacervation is achieved at only 1 part of commercially available sodium hexametaphosphates to 10-20 parts of acid-extracted pigskin gelatin. This is due to the lower apparent (ionic) equivalent weight of polyphosphates." The gelatin-... 

---