Preparation and process optimization of encapsulating cellulose microspheres

Abstract: Microspheres are spherically shaped particles within the size range of 1-1000 μm in diameter. Due to the their small size and round shape, microspheres show many advantages in various applications such as pharmaceuticals, composites and coatings. The microspheres can be customized to fit a specific application and are manufactured in various forms such as solid, hollow and encapsulating. Encapsulating cellulose microspheres have been produced in this project by the emulsionsolvent evaporation technique. The purpose of this study was to further investigate the possibility of producing encapsulating microspheres with a size range of 10-50 μm that will have a high encapsulation. A second purpose of this study was optimizing the emulsifier system for the preparation of these spheres. This has been accomplished by varying several process parameters such as type of emulsifiers and solvents to study the effect on morphology and encapsulation efficiency. The analyses of the spheres were performed with optical microscopy, thermal gravimetric analyzer (TGA) and scanning electron microscopy (SEM). The emulsifier type and concentration affected the encapsulation and size distribution but had no direct effect on the internal and external structure, which was multi-cellular and porous, respectively. The highest encapsulation in relation to average size was obtained with 0.1 v/v- % of the emulsifier mixture Emulsifier 1 (E1)/Emulsifier 2 (E2) (70/30 %). The solvent used to dissolve the polymer had a direct effect on encapsulation, a combination of Solvent 2 (S2) and Solvent 1 (S1) proved best for the three tested cellulose derivatives with low, medium and high number average molecular weight. The solvent also had an effect on the internal structure of the microspheres, becoming more core-shell when using the S1/S2 combination.