Micro-encapsulation of Essential Oils for AntimicrobialFunction and Mosquito Repellency

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clove, thyme and cinnamon (Shinde and Nagarsenker, 2011; Soliman et al., 2013). The

formulation of sodium alginate particles is achieved through cross-linking, such as ionic

cross-linking. A study on lemon balm-loaded sodium alginate beads cross-linked with cal-

cium chloride found that there was no interaction with the extract and its antioxidant activ-

ity was not affected by the encapsulation (Najafi-Soulari et al. 2016).

Due to the rise in antibiotic resistance, the ecological concern created by current syn-

thetic antimicrobials and the increased demand for eco-friendly antimicrobials and textile

products, the development of "green" formulations based on natural antimicrobials such as

EOs and natural formulation ingredients such as biopolymers should be explored for safe

and functional textiles.

12.2

MICROENCAPSULATION TECHNOLOGY

A microcapsule is comprised of a core (usually the active component needing pro-

tection) and wall materials (also referred to as the coating or shell) which are commonly

polymers, carbohydrates or proteins (Bakry et al. 2016; Haidong et al. 2012). The pro-

cess of microencapsulation involves the coating of droplets or particles of a substance (e.g.

drugs, hormones, proteins, fertilizers, cosmetics, oils) with a thin wall of natural or syn-

thetic polymers that acts as a protective barrier, to create individual particles (Butstraen and

Salaün 2014). There are various methods of microencapsulation including physical (e.g.

spray-drying and freeze-drying), chemical (e.g. solvent evaporation and in situ polymeriza-

tion) and physicochemical (e.g. ionic gelation, coacervation and emulsification) methods

(Tomaro-Duchesneau et al. 2013). Methods of encapsulating the active material to be used

are depending on the nature of the core material, the desired particle size, desired release

of the core and the intended application of the final product (Ghayempour and Montazer

2016; Haidong et al. 2012).

12.2.1

Complex coacervation

Complex coacervation technique for microencapsulation is based on the coacervation

of two or more types of polymers under specific conditions that are dependent on the charge

and charge density of the wall polymers used, the processing temperature and the process

itself, such as cooling and stirring (Piacentini et al. 2013). During complex coacervation a

spontaneous reaction occurs between two polymers of opposite charge, leading to a phase

separation in which an aqueous phase and a polymer phase are formed once the charges

are neutralized as illustrated in Figure 12.1 (Piacentini et al. 2013).

Butstraen and Salaün (2014) prepared the microencapsulation of oils using chitosan

and algination. In the microencapsulation process, the oil-in-water emulsion containing

an anionic emulsifier was added to an aqueous chitosan solution and subsequently con-

verted into microcapsules by the addition of a suitable electrolyte such as alginate. Mi-

croencapsulation requires the cross-linking of the wall polymers to increase the thermal

and mechanical properties of the capsules (Butstraen and Salaün 2014; Zhang et al. 2012).

Most of the cross-linking agents used to enhance microcapsules are toxic in nature and