Emulsifiers-free lubrication process using natural oils dispersions in non-aqueous solvents for leather

Abstract

The current practising method for the lubrication of leather uses emulsions of oils in water (fatliquors) that are prepared using emulsifiers. In particular, the fatliquoring process is a sum of three processes – surface wetting, oil emulsion spreading and coating of oil on the fibre bundles. This method suffers from drawbacks on account of high water consumption for oil diffusion and discharge of wastewater carrying emulsifiers. This paper reports a new approach of preparing emulsifier-free ready-to use oil–solvent dispersions, and their tuning to obtain required softness in leather. The oil and the solvent, both determine the size of the dispersions. The addition of non-aqueous solvent tunes the size of the dispersions, as seen for an e.g. in the case of castor oil in heptane (Hep) and ethyl acetate (EA) mixture at a volume ratio of 0.9 : 0.1, wherein, size is 4 nm as against 3060 nm in 0.1 : 0.9 mixtures. The kinematic viscosity (ν) of oil–solvent dispersions was comparable with that of commercial fatliquors. In all cases, the surface tension of oil progressively decreases up to a certain concentration and thereafter, remains almost invariant. This is suggestive of formation of aggregates of solvents. An interesting correlation between the size and lubrication performance was observed. Such of those dispersions with appropriate diameter (10 < size < 300 nm) and polydispersity index < 0.3 had a good diffusion, leading to softer leathers. It is to be noted that to form oil in water emulsions with size in this range, a very large amount of emulsifiers/surfactants, which is invariably equal to or more than that of weight of oil is required. Surface energy of leathers was significantly altered depending on type of oil dispersions, thus in turn influencing the dispersion-leather contact and hence oil spreading on leather surface.