Environmentally friendly calcium carbonate-polydopamine microcapsules with superior mechanical, barrier, and adhesive properties

Abstract

There is a rising need to deliver perfume molecules to fabric surfaces during washing cycles to enhance consumers' perception. With upcoming regulations phasing out intentionally produced microplastics by 2027, the focus is on sustainable alternatives to conventional non-biodegradable synthetic microcapsules (e.g. melamine-formaldehyde). Calcium carbonate (CaCO3) has shown promise to form the microcapsule shells due to its environmental benignity, inexpensiveness, and potential for liquid formulations, particularly detergents. Notwithstanding, its inherent porosity undermines the performance of the ensuing microcapsules. Bio-inspired by the adhesive properties of mussel proteins, dopamine is proposed for forming a protective organic coating on CaCO3-based microcapsules. This research aims towards developing primary microcapsules with CaCO3 shells encapsulating hexylsalicylate (HS) as a perfume oil, applying a polydopamine (PDA) coating via oxidative auto-polymerisation of dopamine-hydrochloride (pH 8.5), and conducting a comprehensive analysis of morphological, mechanical, barrier, and adhesive properties through advanced techniques, namely fluorescent-sensing/scanning electron microscopy (SEM), micromanipulation, UV–Vis spectrometry, and a microfluidic chamber fitted with polyethylene-terephthalate (PET) fabrics. The obtained microcapsules (D[3, 2]=31.2 ± 0.4 μm) exhibited a spherical core-shell structure with a smooth PDA-coated surface. Mechanical assessments reveal remarkable rupture stress (2.2 ± 0.3 MPa) comparable to that of commercial microcapsules. After one month in water, ∼40% of HS was released from PDA-coated microcapsules, while the primary ones released the entire amount within 4 h. When mimicking washing conditions (pH 9), the PDA-coated microcapsules demonstrated improved retention (∼60%) on the PET substrate at hydrodynamic shear stress of ∼1 Pa, whereas that of the primary microcapsules was below 10%. Overall, this study suggests the successful fabrication of eco-friendly microcapsules featuring a hybrid inorganic-organic shell, with enhanced mechanical strength, reduced leakage, and improved adhesion, showcasing their potential in applications within the fast-moving consumer goods industry.