Continuous production of cellulose acetate microspheres for textile impregnation using a mesostructured reactor

In this work, the emulsion step of a previously reported batch formulation, for production of cellulose acetate (CA) microspheres, is transposed to continuous mode using the NETmix technology. NETmix is a static mixer and reactor that consists of a network of cylindrical chambers operating as mixing zones and interconnected by prismatic channels behaving as plug flow. The quality of the mixture is set by the Reynolds number, and above a critical value (Re > 150) the system evolves to a self-sustained oscillatory laminar flow regime inducing local strong laminar mixing. This patented technology has been used for many applications, such as production of nanocrystalline hydroxyapatite, production of melamine–formaldehyde microcapsules, photocatalysis processes, and Pickering emulsions. Cellulose acetate microspheres containing eugenol as a strong antimicrobial activity component were produced through a solvent evaporation method. Emulsions were produced at different Reynolds number (Re) ranging from 200 to 1200 to evaluate its effect on the size of the resulting microspheres, all of which characterized by a well-defined spherical shape with a rough and a porous shell. The mean diameter decreases from 31 ± 3 µm to 6.5 ± 0.6 µm ongoing from Re = 200 to Re = 500, and a roughly constant value of ca. 6.2 ± 0.9 µm is reached for Re > 500. CA microspheres loaded with eugenol show core contents of 34 ± 4% (w/w) and encapsulation efficiencies of 37 ± 5% and a yield of 54.2 ± 3.5%. The thermogravimetric analysis shows that the CA matrix is thermally stable up to 260 °C and that the eugenol-loaded CA microspheres retain their content up to ca. 100 °C. Scanning Electron Microscopy shows the good adhesion and integrity of selected microspheres on cotton textiles. Release studies of eugenol from treated textiles show that after 84 days, ca. 30% of eugenol was released. This work showed that the NETmix reactor enables controlling the diameter of microspheres by changing Re, leading to the required diameter for the textile application.