218

■Bio-mathematics, Statistics and Nano-Technologies: Mosquito Control Strategies

Figure 12.1: Complex coacervation process (Madene et al. 2006).

have to be washed out with a solvent to reach a biologically acceptable level, restricting

its use in many applications; such cross-linkers include aldehydes i.e. glutaraldehyde and

formaldehyde (Butstraen and Salaün, 2014; Yang, et al. 2014; Zhang et al. 2012). Sodium

tripolyphosphate (TPP) is non-toxic cross-linker that has been proposed as an alternative

to aldehyde crosslinkers (Butstraen and Salaün 2014).

Complex coacervation is a promising technique for the production of mi-

cro/nanoparticles or microcapsules within industry. It is simple without the use of sol-

vent, allowing high payloads, good controlled release, heat resistant properties and high

efficiency (Lv et al. 2014; Nakagawa and Nagao 2012; Yang J. et al. 2015). In a microen-

capsulation process based on coacervation, the pH is a key parameter. Aziz et al (2014)

evaluated the effects of core material (krill oil) to wall material (gelatin-gum Arabic) ratio,

stirring speed and pH on the encapsulation efficiency. It was found that pH had the most

significant effects on the encapsulation efficiency (EE). Stable microcapsules, with 92%

EE were synthesized using optimal conditions of pH 3.8, stirring speed 3, and a ratio (of

core material to wall material) of 1.75:1 (Aziz et al. 2014). Stirring speed is important be-

cause the microcapsules can be significantly affected by the homogenization rate during

the process of emulsification. When a lower rate is used during preparation, the microcap-

sules release the core material more rapidly than those prepared with a higher rate during

the process (Zhang et al. 2012).

Microcapsules produced by complex coacervation are also affected by the polymer

properties including molecular mass, ionic charge density and concentration in the for-

mulation (Nakagawa and Nagao 2012). Microencapsulation of Melaleuca alternifolia (tea

tree) EO by complex coacervation led to an increase in the evaporation temperature of tea

tree EO from 140 °C to 230 - 260 °C because of the core protection provided by the poly-

mers gelatine (G) and sodium carboxymethyl-cellulose (C). The ratio of these polymers

(G/C), affected the formation of the coacervate during synthesis and the EE of tea tree

EO. The increase in G/C ratio lead to an increase in EE (63.3 ± 1.4%) up to G/C = 10,

because of the amount of coacervate formed, and above this value, the amount of oil in the