Leather dyeing using a new liposome-based process assisted by dense gas technology

Liposomes are spherical vesicles characterized by a double lipidic layer surrounding an inner aqueous core; they have been employed in several fields, such as pharmaceutical, cosmetic and nutraceutical. In this work another possible application is explored: the deposition of dyes on sheep leather is attempted, using liposomes as dye vehicles to obtain a better adhesion of dye on leather surface. A supercritical assisted method called SuperLip is proposed to load red aniline into liposomes, for leather coloration. Process parameters have been optimized such as dye and lipid concentration in the system, water flow rate for vesicles inner core production and Gas to Liquid Ratio of the Expanded Liquid to control size and particles distributions. Nanometric liposomes of about 150 nm diameter have been obtained, with a red aniline Encapsulation Efficiency (EE) of about 75%; micrometric vesicles of about 2 μm were also produced with EE up to 82%, in order to provide large dimensions for covering macroscopic surfaces. A conventional dyeing method and the new liposomal method were compared in terms of deposition time, and color resistance. Liposomes, produced in this work, speeded up dye deposition from 60 min to 30 min, and resulted in a higher resistance to heat exposure; indeed, a discoloration down to 2.3% was observed using the proposed method and 25.1% using conventional method.