Charge and fixation

摘要

The rate of fixation between the collagen structure and pre tanning/tanning/retanning agents, dyes, and many polymeric resins and fatliquors is determined by the charge of the collagen and the charge of the product. An increase in alkalinity causes an increase in negative charge within the skin, due to losses of amino~((+)) groups. Under these conditions, if a chemical with a strong positive charge is offered—such as chrome or aluminium salts—there is a very rapid reaction with the surface carboxyl~((-)) groups and no penetration. Under the same conditions, a product with a negative charge—such as a syntan—will combine slowly and penetrate deep into the structure as there is a reduced number of available amino~((+)) groups for fixation.