Synthesis and characterization of biobased capsules formed from interpenetrating networks of alginate and poly(ethylene glycol) for the encapsulation of blue dye

Abstract

Encapsulation technologies have been utilized in laundry detergents mainly as formaldehyde-based capsules which are commonly used to encapsulate active compounds like fragrances, bluing agents and fluorescent whitening agents. Nevertheless, formaldehyde derived materials are toxic, carcinogenic, and non-biodegradable leading to an increase in the microplastic pollution in oceans and consequently harming the marine life. Therefore, the researchers are currently tending towards the replacement of these components by biobased ones. In this work, we present the synthesis of capsules with more than one shell using biodegradable polymers to replace these materials. Moreover, the blue dye used in laundry detergent industry was successfully encapsulated in biodegradable capsules formed by an interpenetrating network of alginate and poly(ethylene glycol) diacrylate (PEGDA) prepared using different conditions. Besides, the capsules were characterized to study their chemical, morphological, thermal, and mechanical properties, to evaluate their water solubility, and to determine how the composition and the preparation methods can affect their properties. The novelty of this system lies in evaluating how modifying a previously reported system using poly(ethylene glycol) dimethacrylate (PEGDMA) and alginate as shells -achieved by replacing the PEGDMA diacrylic monomer with PEGDA- affects the morphology and properties of the resulting capsules. It has been shown that the capsules with PEGDA exhibited improved thermal and mechanical properties compared to the previously described system, which could make them more suitable for their intended applications.

Fig. 1

Chemical structure of: (a) α-L-guluronate (G) and β-D-mannuronate (M) residues present in sodium alginate; (b) Crosslinking of alginate chains by calcium ions; (c) Poly (ethylene glycol) (400) diacrylate (PEGDA); (d) Crosslinked PEGDA; and e) general scheme of the synthesized capsules with the encapsulated blue dye.

Fig. 2

Composition of the capsules and methodology followed in the dye encapsulation process of: (a) capsules which shell is only made of alginate; (b) Capsules which shell contains both alginate and PEGDA and were irradiated with UV light during 5 min before or after leaving them for 24 h under magnetic stirring.

Fig. 3

FTIR spectra of: a) PEGDA; b) Sodium alginate; c) A; d) A-PG-UV0h; and e) A-PG-UV24h.

Fig. 4

(a) Optical microscope images of capsules of the following samples: (i) A-PG-UV0h, (ii) A-PG-UV24h, (iii) A-PG-AVI0.8-UV0h and (iv) A-PG-AVI0.8-UV24h; (b) ESEM images of synthesized capsules showing the whole capsule (magnification x160), its surface (magnification x500) and its cross-section (magnification x200, x285, x235, and x245 for A-PG-UV0h, A-PG-UV24h, A-PG-AVI0.8-UV0h and A-PG-AVI0.8-UV24h, respectively): (i) A-PG-UV0h, (ii)A-PG-UV24h, (iii) A-PG-AVI0.8-UV0h and (iv) A-PG-AVI0.8-UV24h.

Fig. 5

(a) ESEM images of the capsules (magnification x100) and their surface during their preparation (magnification x500); and (b) Diameters of the different types of capsules investigated during their preparation.

Fig. 6

Optical microscope images of samples after compression tests of: (a) A-PG-AVI0.8-UV0h and (b) A-PG-AVI0.8-UV24h.