Microencapsulation is a coating technology by which active substances are encapsulated in a polymeric shell, leading to core-shell particles called microcapsules.
Microencapsulation is an effective method to prevent reactive, sensitive or volatile chemicals from reacting with moisture, light and oxygen. Besides, this technology not only enhances stability against external factors, but also allows a controlled release of the active substance. Indeed, microcapsules, when anchored to a material such as leather, can add new smart functionalities without affecting its look and feeling at touch.
Therefore, this technology holds great promise for the future of tanneries and leather end-user industries, such as footwear. It can transform a traditional leather-made item into an active one by incorporating microencapsulated products with active properties.
The selection of the most convenient microencapsulation methodology depends on the substance to be encapsulated, intended use and polymeric shell.
Among them, complex coacervation process is based on the phase separation that takes place spontaneously when in an aqueous medium, two or more colloids of opposite charges (a polycation and a polyanion) are mixed in the presence of a dispersion of an active substance. The scheme summarises the complex coacervation process.
Gelatine is an amphoteric macromolecule, which is positively charged at pH below its isoelectric point (pI). Thus, it is suitable to be used as polycation in complex coacervation reactions. As polyanion, LIFE microTAN project proposes the use of sodium carboxymethylcellulose, since it is negatively charged at low pH values. Glutaraldehyde is proposed to be used as microcapsules hardener.
The complex coacervation procedure had to be optimised, so that gelatine solutions can directly be used as produced in the demonstration plant. This way, the gelatine drying step can be avoided and a substantial reduction in water consumption is possible.
R-(+)-limonene, rosemary, violet and jasmine oils, among others, were successfully microencapsulated, using the gelatine produced at microTAN demonstration plant. Microencapsulation was performed both at laboratory and pilot scale.
Morphology, thermal properties, thermal stability and composition of the different microcapsules have been assessed. In addition, microcapsules have been incorporated into different materials.
The microcapsules were anchored to leather used in footwear upper components, using to different methods: direct application (spraying and/or brushing) and by incorporating them in laboratory drums during the retanning process of leather.
Microcapsules were also applied as a spray on tissue paper used to cover shoes during box storage, as well as in the textile component of roject folders prepared as merchandising material.