Experimental study of leather wet processing under normal pressure or vacuum
Adsorption and desorption adsorption on the surface of leather and on the surface of internal fibers is a spontaneous process in which the concentration of the substance changes at the phase interface. The solid surface molecules have an unsaturated field of force and thus have a substance adsorbed on the interface to reduce the free surface of the surface. tendency.
Adsorption capacity and adhesion when reaching adsorption equilibrium are related to its surface tension and surface state, and also to the pressure (at the time of gas) or the concentration (at the time of liquid) of the adsorbed material and the temperature of the adsorption process. Obviously, the greater the value of (R solid gas R liquid gas), the stronger the adhesion of solid and liquid once they are in contact. The R solid gas and R liquid gas values ​​under vacuum are higher than those under normal pressure, so the amount of chemical adsorbed on the surface layer of the leather is not only higher than that at normal pressure, but also has strong mutual adhesion. Due to the acceleration of diffusion under vacuum in the interior of the skin tissue, the concentration of the agent that migrates to the interior within a unit of time is high, and thus the molecules of the adsorbed molecules on the internal fiber surface are also increased when compared with normal pressure. Physisorption and general chemisorption are exothermic reactions, and low temperatures favor the adsorption process.
The wet processing of leather is carried out under normal pressure or vacuum, and the temperature is generally relatively low, so the influence is not involved when comparing with each other. Desorption is the reverse process of adsorption. The easier the adsorption, the greater the amount, and the stronger the adhesion, the more difficult it is to desorption. Experimental studies have shown that processes such as deliming and pickling with a significant desorption process do not significantly shorten the processing time even if vacuum conditions are used, but rather prolong the time due to improper handling. Due to the acceleration of the diffusion process under vacuum, the amount of diffusion per unit time is significantly increased, the requirement for the concentration gradient is reduced, and the concentration of the working solution (the amount of chemical agent consumed) in some processes must be lowered in consideration of the desorption requirements of the subsequent process. Adjustment.
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