New insights into physicochemical aspects involved in the formation of chitosan@alginate biobased polyelectrolyte complexes on natural montmorillonite clay surface

Abstract

The use of alginate@chitosan-based polyelectrolyte complexes (PEC) in encapsulation process is common due to the electrostatic interactions between the two oppositely charged biopolymers. However, the incorporation of montmorillonite (Mt) particles in the complex formation for improving the encapsulation efficiency as well as the physicochemical properties of PEC remains a challenge due to the competitive polymer–polymer and polymer-nanoparticle interactions. This study aimed to investigate the binding mechanism of alginate and chitosan through layer-by-layer approach in the presence of montmorillonite nanoparticles as a function of pH and the addition order of the components. Various techniques were employed to examine the formation of the alginate@chitosan PEC on the surface of Mt, such as zeta potential, conductivity and turbidity measurements. The characterization of the different PEC systems was performed using Fourier Transformed Infrared spectroscopy (FTIR), X-Ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The results indicate that the formation of the complex is pH-dependent. The highest intercalation of the complex was observed when chitosan was added first at a lower pH, while the intercalation was reduced at neutral pH. Additionally, the thermal stability of PEC was enhanced in the presence of montmorillonite, and was dependent on both pH and the order of addition of the biopolymers. This study provides a new understanding of the complex formation mechanism between alginate and chitosan in the presence of montmorillonite nanoparticles, showing that the combination of biopolymer-based PEC with clay particles can potentially provide a low-cost, more stable and effective nanocomposite for encapsulation and delivery of active agents.