Leather vacuum and conventional processing
Diffusion of leather tissue chemical agents is a natural process of concentration migration. Diffusion in solids is very slow, and the present example is analyzed using the first law of Fick's diffusion J=-Ddcdx and the Arrhenius formula D=D0e-EDRT. The J diffusion flow in the formula indicates the mass per unit area diffused per unit time; the D diffusion coefficient indicates the diffusion flow per unit concentration gradient (dcdx=1): the D0 frequency factor indicates the ratio of the temperature to the diffusion coefficient. The constant, the diffusion material and the diffusion medium are constant for a certain time; the diffusion activation energy of ED means the barrier encountered when the diffusion material diffuses in the diffusion medium; R and T are the gas constant and the diffusion temperature, respectively.
ED is the diffusion resistance, and its value is affected by the atomic bonding form of the diffusion media and the mode of movement (intrusion or replacement) of the diffusion material. The spread of chemical agents in the tissues of leather collagen fiber bundles is based on crowding gaps. When the ambient pressure is lower than 9332 Pa, the leather fiber tissue is affected by the difference between the internal pressure and the ambient pressure, and the phenomenon of swell is observed. The higher the degree of vacuum is, the more obvious this phenomenon is. The loosening of the internal binding of the leather tissue, and the migration of chemical agents in it, the barrier to overcome is the diffusion activation energy ED decreases, and the diffusion coefficient D increases.
In the vacuum and conventional processing, the same working temperature range, the same concentration of the operating liquid, and the similar degree of mechanical force are used, so that the amount of chemical substances contained in the tissue after soaking is equal (in fact, the unit of taring The former is higher than the latter in terms of drug dose. Depending on the time the leather is fully soaked in each processing step, it can be easily calculated that different chemical agents are used at a vacuum of 4000 Pa, a temperature of 28-30 e, and a rotation speed of 9 r/min. In the case of diffusion in leather tissue, the diffusion coefficient D is higher than that at atmospheric pressure N. The formula D=D0e-EDRT is the same as the frequency factor D0 at vacuum and atmospheric pressure: ED=-RTlnD0D0=De-EDRTED atmospheric pressure ED Vacuum = -RTlnD Atmospheric Pressure D0-RTlnD Vacuum D0 (1) Substituting D0 = D Atmospheric Pressure e-ED Atmospheric Pressure RT (1) In the formula, available ED Atmospheric Pressure - ED Vacuum = RTlnN Formula Representing 4000 Pa Vacuum Degree Next, when the chemical agent diffuses in the skin tissue, the relationship between the diffusion activation energy ED (diffusion resistance) and the reduction value at normal pressure (ED normal pressure-ED vacuum) and the diffusion coefficient increase magnification value N are obtained. The comparison between vacuum and atmospheric diffusion shows that, from the analysis of the diffusion mode, the vacuum conditions provide favorable conditions for replacing the chrome tanning agent with a macromolecular tanning agent that is less harmful to the environment.
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